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• Elasticity and failure behaviors of the resin-coated aramid paper are analysed. • A novel segmented equivalent mechanical model of the material is proposed. • Equivalent mechanical parameters of multi-layer structure are derived theoretically. • Proposed model performs well in ultrasonic cutting simulation of Nomex honeycomb. • Difficulty of modelling and CPU time of simulation are reduced significantly. Nomex honeycomb, as the core part of sandwich structure, has been widely used in the aviation and aerospace industries. Ultrasonic cutting, as a technology that can reduce machining defects, has been highlighted in recent years, but some problems in the cutting process still need to be investigated significantly. Finite element method (FEM) offers an alternative way of in-depth understanding of the problems. However, the multi-layer structure of the Nomex honeycomb cell wall, which is the resin-coated aramid paper, makes it difficult to establish a detailed multi-layered finite element (FE) model at a macro-scale level. Therefore, a novel segmented material mechanical model, which is applicable to the equivalent single-layer model, is proposed based on the analysis of the mechanical behaviour of the multi-layer structure of the resin-coated aramid paper. Moreover, the calculating method of equivalent mechanical parameters of the multi-layer structure are proposed theoretically. The proposed method is first verified by FE models at a micro-scale level in both single-layer and multi-layer approaches. Additionally, simulations and experiments are performed to verify that the proposed method performs well in the simulation of ultrasonic cutting for Nomex honeycomb, and the difficulty of modelling and CPU time of simulation are reduced significantly. [Display omitted] [ABSTRACT FROM AUTHOR]

Abstract: The rolling of a cylindrical drum on a stack of separate paper sheets is studied using the finite element method. A two-dimensional model under plane strain conditions is considered. The material of the sheets is modelled by a linearly elastic orthotropic constitutive law. The friction between the various contacting surfaces is modelled by the conventional Coulomb''s law. As a result of the FEM-calculations, the time development of the displacements, stresses and strains of the paper layers is obtained. The slip behaviour at the various contacting surfaces is presented. The micro-slip pattern of the contacting surfaces in the nip area and, particularly, at the trailing edge of the nip, seems to be the main reason for the tightening effect of the nip. The results are compared to the corresponding results for a solid elastic block under the rolling cylinder. [Copyright &y& Elsevier]

• Developed a theoretical model for the conformal analysis of circular islands and substrates. • Predicts conformal behavior on surfaces of any curvature and modulus. • Proposed a generic strategy for conformal electronics in various applications. This paper introduces a set of design criteria that aim to integrate flexible electronics onto three-dimensional surfaces in a mechanically adaptive manner. Previous studies have been limited to conformal integration on specific shapes (Such as spherical surfaces and corrugated surfaces) of rigid surfaces or soft substrates, there is a lack of a universal design strategy that takes into account the complexity of substrate shapes and varying hardness. To address this gap, the paper outlines a mechanical model that utilizes Hertzian contact theory to describe the interaction between the thin film and the substrate, and the conformal surface morphology and stress state were derived from minimizing the total energy of the island-substrate structure. The proposed formulations are verified through finite element methods and experiments, analyzing the effects of Young's modulus, in-plane size, and thickness of the "island" on its conformability. Therefore, this paper proposes a generic on-demand conformal design strategy that takes into account the complexity and hardness of the substrate. This study's findings will contribute to the development of conformal electronics that can be used in various fields, such as epidermal electronics, flexible robots, robot electronic skin, and aircraft smart skin. [Display omitted] [ABSTRACT FROM AUTHOR]

As the demand for low-frequency and ultra-low-frequency vibration isolation in aerospace inspection and ultra-precision manufacturing grows exponentially, traditional vibration isolation strategies have been unable to satisfy these escalating needs due to their drawbacks such as a loose appearance, substantial dead weight, and elevated mechanical friction. Metamaterials, as artificially constructed periodic materials, have provided a promising solution to these above issues. In this paper, a novel compact one-dimensional quasi-zero-stiffness metamaterial with a tunable bandgap is presented, composed of a single unit centered on a truncated conical shell with a unique quasi-zero-stiffness structure. The monolithic quasi-zero-stiffness configuration significantly reduces the weight and size compared to conventional vibration isolation structures, ensuring high reliability with a minimum number of units and a compact form factor. A combination of theoretical analysis, finite element method and experiment is employed to investigate the vibration isolation properties of metamaterials comprehensively. Notably, the metamaterials designed in this paper can achieve vibration isolation at a very low frequency. Through the strategic application of pre-displacement, the entire bandgap can be systematically shifted to lower frequency ranges, which results in a reduction of the starting frequency to 15.01 Hz, marking a remarkable decrease of 46.6%. The novel proposed metamaterial, as detailed in this paper, can provide a reference for researchers involved in this field. [Display omitted] • A generic method for the design of quasi-zero-stiffness truncated conical shells is established. • Quasi-zero stiffness can be achieved with only single unit. • A novel compact one-dimensional quasi-zero-stiffness metamaterial is obtained. • The band gap of the metamaterial can be shifted to 15 Hz by adjusting the initial displacement, a reduction of 46.6%. [ABSTRACT FROM AUTHOR]

Rotor unbalances failure due to various factors such as manufacturing defects, mounting errors, and material inhomogeneity is inevitable, and will be aggravated by bearing pulse displacement excitation caused by maneuvering flight. Therefore, the purpose of this paper is to study the vibration of the rotor system under disk unbalance forces and bearing pulse displacement excitation. Firstly, the differential equation of motion for four-disk flexible hollow shaft rotor system modeling with a simple finite element model(SFEM) is established by the Lagrangian method in non-inertial systems, and the shaft is modeled using Timoshenko beam theory. Then, the dynamic characteristics of the four-disk flexible hollow shaft rotor are analyzed and compared with the 3D finite element model(3D FEM) to verify the accuracy of the model. To analyze the effects of different disk unbalanced positions and pulse displacement excitation on the vibration characteristics of the rotor, the characteristic vector method and the Runge–Kutta method are used to obtain the steady-state solution and the transient solution, respectively. In addition, the simulation results show that suitable in-shaft damping has a stable effect on the rotor during the start-up. Disk 2 and Disk 3 are more sensitive to synchronous harmonic excitation and pulse displacement excitation than Disk 1 and Disk 4. The research of this paper provides an important basis for vibration monitoring and control, and vibration transmission analysis of aero-engine rotor system. [Display omitted] • The 3D FEM verifies SFEM of four-disk hollow shaft rotor with Timoshenko beam. • Natural frequency of rotor confirms proper inner diameter of hollow shaft id. • The vibration transmission law is studied with unbalanced or pulse excitation. • High-order whirling frequency is excited in transient response. • In-shaft damping has the stabilizing effect during rotor start-up. [ABSTRACT FROM AUTHOR]

Press forming is one of the most suitable paperboard converting techniques to produce deep trays. However, during the forming, severe deformations occur in the tray corners, which can cause cracks and other defects that deteriorate the tray. Formability can be enhanced with creases which assist the folding of the paperboard blank. In this paper, we study the press forming process with the aid of finite element simulations. We focus especially on the effect of creases on the formability. The effects of different materials are also compared. The finite element model consists of a male die, female die, blank holder and paperboard blank. The paperboard is modeled as an orthotropic elastoplastic material. Hill’s yield criterion with isotropic hardening is used to define the plastic behavior. Hinge connector elements are used to model the creases. The modeling is complemented by experimental studies. The results obtained from the finite element analysis show that high localized strains occur in paperboard tray corners during forming and that the intensity and areal size of the strains can be decreased with creases. It is concluded that the developed model can be used to compare different crease patterns which, in turn, enables better crease pattern design. [ABSTRACT FROM AUTHOR]

• A method is proposed for the first time to the parameters of the sound radiation of plates with arbitrary holes. • The model can be applied to arbitrary boundary conditions and a large number of elastic materials. • The effect of parameters on the sound radiation characteristics is investigated by parametric analysis. Vibroacoustics of plates with arbitrary holes is a common problem in engineering and it is essential to develop a fast and efficient model to calculate the relevant parameters of the sound radiation of plates with arbitrary holes. In this paper, a unified and fast computational method based on the spectral-geometry method (SGM) is proposed for the first time to investigate the sound radiation characteristics of elastically constrained plates with arbitrary holes, where the open part of the plate is considered as an extremely thin section and the displacement of the plate can be expanded to a modified Fourier series, which deals with the discontinuity of the original cosine function at the elastic constraint boundary by adding additional terms to the conventional Fourier cosine function. The unknown Fourier coefficients are considered as an independent set of generalised coordinates and solved by the Rayleigh-Ritz method. The Rayleigh integral equation for sound radiation is used to calculate the sound radiation of the plate structure. The accuracy of the method in this paper is verified by comparison with the finite element method (FEM). The effect of each parameter on the sound radiation characteristics of the plate with arbitrary holes is investigated by detailed parametric analysis. This paper provides a reference for the application of plates with arbitrary holes in engineering. [Display omitted] [ABSTRACT FROM AUTHOR]

• The heterogeneous aggregate expansion rooted from fast neutron was considered. • Radiation-induced damage yields significant stiffness degradation. • Combined effect of neutron radiation, lateral stress ratio and strain rate was investigated. • Failure mechanism of radiation-induced concrete under biaxial compression was revealed. • Formulas of biaxial compression strength for radiation-induced concretes were derived. As a good shielding material, heavyweight concrete is largely utilized for building the Concrete Biological Shielding (CBS) wall of the commercial nuclear power plant, and is often subjected to the biaxial loadings with a strain rate possibly varying from 10−5s−1 to 10−2s−1. This paper assesses the combined effects of the lateral stress and the strain rate on the compressive strength of radiation-induced heavyweight concrete on the example of serpentine concrete. For this goal, a 3-dimensional rectangular numerical concrete specimen containing special aggregates and ITZs was firstly established. Exposed to neutrons of different fluences, the initial damages caused by the fast neutron were assessed by a thermal-mechanical approach. Then, a series of static and dynamic biaxial compressive tests on the rectangular specimens having initial damages of different degrees were carried out by finite element analysis via ABAQUS. The failure modes, the crack patterns, and the ultimate compressive strengths of the pre-irradiated serpentine concrete were obtained numerically. Finally, based on the numerical results and the classical "Kupfer-Gerstle" ("K-G") criterion, this paper derives the biaxial strength criterion of the radiation-induced heavyweight concrete undergoing both lateral stress and strain rate. Through the formula, it was found that the fast neutron fluence of high level reduces significantly the biaxial compressive strength of the heavyweight concrete. Besides, if the heavyweight concrete undergoes additionally lateral stress and the strain rate, the biaxial compressive strength could be enhanced. The enhancement effect was maximized at the lateral stress ratio of 0.5 and the strain rate of 10−2s−1. The current numerical approach was developed with a potential application to the lifetime extension of the heavyweight concrete infrastructures used in commercial nuclear reactors. [Display omitted] [ABSTRACT FROM AUTHOR]

• A stress-based evolutionary topology optimization framework via XIGA is proposed. • Geometric boundaries of optimized design explicitly expressed as B-spline. • Satisfactory stress accuracy along the structural boundaries is guaranteed by XIGA. • No need for fine meshing to achieve clear strength design with smooth boundaries. • Structural boundary control points of the strength design can be directly edited to further improve strength performance. This paper presents a novel approach to stress-based topology optimization that employs NURBS representations of explicit geometric boundaries to address stress minimization and stress-constrained problems. The proposed methodology is compatible with CAD systems and utilizes Extended IsoGeometric Analysis (XIGA) to ensure an accurate representation of stress field in the evolving structure. A p -norm aggregation scheme is used to measure global stress levels, and the aggregated stress constraint is augmented to the objective (compliance) via a Lagrange multiplier in stress-constrained problems. The proposed approach introduces a novel and efficient Lagrange multiplier trail strategy aimed at reducing computational costs. Additionally, a normalization scheme and a partial differential equation filter are presented to stabilize the highly nonlinear stress-based optimization. Validation studies demonstrate the effectiveness and characteristics of the proposed approach. Moreover, control points of the structural design can be directly edited to further improve strength performance. Comparative studies show clear advantages of the proposed methodology in terms of computational efficiency compared to other Finite element analysis (FEA)-based optimization methods. Overall, this paper presents a practical and novel approach that addresses the limitations of existing FEA-based optimization methods in terms of accuracy, flexibility, and degree of freedom (DOF) cost, and makes a significant contribution to the field of stress-based topology optimization. Graphical abstract [Display omitted] [ABSTRACT FROM AUTHOR]

• A configuration of multi-resonant meta-shell is proposed. • Generalized theoretical model of meta-shell is established. • Equal ratio gradient is used for lightweight and broadband design. • Broadband vibration suppression is experimentally verified. This paper presents the design of a meta-shell with spring-mass resonators periodically attached onto a cylindrical shell to achieve low-frequency, broadband vibration suppression. The dispersion relations of the meta-shell are calculated using Hamilton's principle in conjunction with the plane wave expansion (PWE) method, which is verified by the finite element method (FEM). The bandgaps in different wave propagation directions are observed which is induced by the dynamic negative effective mass density. The effects of different meta-shell parameters on bandgap behavior are investigated, from which the fine-tuning of bandgaps can be achieved. The vibration propagation in finite meta-shells is then studied using FEM and the attenuation of vibration is demonstrated in the frequency range of the bandgap. To further broaden the bandgap frequency range, we propose a gradient configuration of a multi-resonant meta-shell in which the resonant frequencies of multiple sets of resonators comply with equal ratio distribution. Compared with the single-resonator meta-shell, it is shown that a 170.7 % expansion in bandwidth can be achieved while the total mass of the resonators is reduced by 41.5 %. Finally, the vibration suppression performance of the multi-resonant meta-shell is experimentally verified, demonstrating the broadband vibration attenuation in corresponding bandgap frequency ranges. This work shows promising application potentials for the multi-resonant meta-shells in vibration control engineering. [Display omitted] [ABSTRACT FROM AUTHOR]

• The theoretical equations governing the post-rocking stiffness of a multiple-rocking-column system (MRCS) were derived and validated experimentally. • Scaled shaking-table tests were performed to investigate dynamic responses of MRCSs with positive, quasi-zero and negative post-rocking stiffness. • Low frequency and broadband effective vibration isolation can be achieved through quasi-zero or negative post-rocking stiffness. • Seismic design of the MRCS should consider the balance between displacement and acceleration demands. Ancient wooden pagodas have shown remarkable seismic resistance, surviving strong earthquakes over millennia. This impressive performance is credited to the unique seismic mitigation and isolation mechanism. The discontinuity between the timber columns allows each story to rock freely like a "balancing toy", effectively reducing inertia forces. Inspired by this fascinating phenomenon, an innovative steel multiple-rocking-column system (MRCS) has been designed. This system includes continuous beams, discontinuous columns, and springs. The post-rocking stiffness of the MRCS can be adjusted to be positive, quasi-zero, or negative by varying the stiffness of the springs. This paper mainly focuses on the effects of post-rocking stiffness on the dynamic behavior of the MRCS, both theoretically and experimentally. Initially, analytical models were developed to assess the stiffness properties of the MRCS. After that, a scaled MRCS model consisting of three stories and featuring seven different post-rocking stiffness levels was designed. Shaking-table tests were conducted to investigate the dynamic response of the model under seismic excitations. The equations governing the post-rocking stiffness of the MRCS demonstrated good accuracy with test results. As the post-rocking stiffness decreased, displacement response increased gradually but significantly mitigated horizontal acceleration responses along the structural height. Wavelet transform-based time-frequency analysis provides a comprehensive understanding of the dynamic features of the MRCS. Furthermore, a finite element model was established to verify the proposed theoretical model, and the numerical results agree well with the experimental findings. This study provided valuable insights into the design of innovative multiple-rocking systems for post-rocking stiffness. [ABSTRACT FROM AUTHOR]

• Developed a micro‑meso-macro framework for RPV steel. • Predicted ART for RPV steel over 40 and 60 years. • Demonstrated correlation between irradiation and DBTT. • Evaluated yield stress changes under varied temperatures and irradiation dose. • Applied CPFEM for nano-indentation simulation. Irradiation can induce microscopic defects in reactor pressure vessel (RPV) steel, resulting in macroscopic hardening and embrittlement. This paper proposes a micro‑meso-macroscale calculation framework for the mechanical properties of irradiated RPV steel based on experimental and numerical investigations. The mean size and number density of Fe-ion-irradiation-induced dislocation loops were measured using transmission electron microscopy (TEM). These parameters were described by a power-function relationship with the irradiation dose at various temperatures and were used as input parameters for the crystal plasticity finite element model (CPFEM). Nano-indentation tests of A508-Ⅲ steel under different irradiation conditions were successfully simulated. In addition, microstructural characterization and molecular dynamics (MD) simulations revealed the phenomenon of dislocation pinning and the sweeping of irradiation defects during dislocation migration, implying that the dislocation-loop interactions could be responsible for the formation of dislocation channels and curved dislocation lines. Furthermore, increase in yield stress and the ductile-brittle transition temperature (DBTT) at various temperatures were investigated. Results indicated that yield stress, DBTT, and the degree of irradiation hardening and embrittlement increased with the irradiation dose and decreased with irradiation temperature. Finally, the adjusted reference temperature (ART), a significant design parameter for nuclear reactors, was calculated and evaluated using the multiscale framework. The framework can serve as a reference text for extending the life of nuclear reactors. [Display omitted] [ABSTRACT FROM AUTHOR]

• The nonlinear vibro-acoustic problem of a buckled beam is studied. • A finite element method in an arbitrary Lagrangian-eulerian framework is adopted. • Effects of acoustic pressure on beam vibration are discussed. • Sound radiation efficiencies of quadrupole and dipole directivity patterns are much different. • Internal resonance can be used to adjust acoustic directivity patterns. Although the nonlinear vibration of buckled beam has been thoroughly studied, its acoustic radiation does not get much attention. This paper deals with the nonlinear vibro-acoustic problem of an internally resonant buckled beam immersed in an infinite fluid. A finite element method based on an arbitrary Lagrangian-Eulerian framework is adopted to analyze the nonlinear interaction between the large-deformed buckled beam and the finite-amplitude acoustic waves in the fluid. The effects of acoustic pressure excitation, external harmonic excitation, and internal resonance on the vibro-acoustic responses of the buckled beam are discussed in the first and second primary resonances. It is found that the amplitude of the acoustic pressure can be comparable to the amplitude of the external harmonic force. This leads to an increase in the critical harmonic excitation amplitude for the occurrence of quasi-periodic responses and an increase in the second mode frequency component of quasi-periodic responses compared to the case neglecting the acoustic pressure excitation on the beam. Saturation phenomena are discovered in the second mode frequency components of beam displacement and acoustic pressure. Due to the 2:1 internal resonance, different time-frequency characteristics, quadrupole acoustic directivity patterns with low radiation efficiency, and dipole acoustic directivity patterns with high radiation efficiency can be observed at different harmonic excitation amplitudes and frequencies. Understanding these phenomena will help design loudspeakers and recognize sound sources. [Display omitted] [ABSTRACT FROM AUTHOR]

• A novel setup to measure the local static mechanical pressure (SMP) exerted by earplugs is proposed. • The setup allows measuring the SMP at any location of any artificial rigid earcanal. • The SMP of several types of commercially available earplugs are measured. • The SMP of roll-down foam earplugs depends on the diameter to which the earplugs are compressed prior to insertion. Earplugs are used in various critical industrial sectors, such as construction, aviation, military and defense, transportation, and healthcare. However, they present inherent drawbacks, notably discomfort that can lead to inconsistent and incorrect use, thereby leaving a significant proportion of workers vulnerable to irreversible hearing damage, ranging from tinnitus to deafness. This discomfort is closely linked to a physical parameter known as static mechanical pressure (SMP), representing the pressure exerted by earplugs on the earcanal walls. Determining the SMP is crucial for developing earplugs that prioritize comfort. However, experimental studies in this area are scarce and there is no experimental set-up capable of measuring the SMP whether in vivo or ex vivo. The objective of this paper is to fill this gap by presenting a novel experimental system designed to mimic a real earcanal, equipped with an optical probe for precise pressure measurements at various points along the earcanal. This precision-targeted methodology holds the promise of yielding a comprehensive pressure map spanning the entirety of the contact area between the earplug and earcanal, thereby offering unprecedented insights into SMP distribution. To validate our test bench, we conducted experiments using cylindrical rolled-down PVC earplugs inserted into a rigid cylindrical earcanal replica of varying radii. We compared our results with data obtained from a commercially available radial force tester commonly used in investigating stent grafts. Once validation was achieved, we expanded our investigation to measure SMP across various types of earplugs. Additionally, we designed and measured the SMP using roll-down foam earplugs in an artificial earcanal shaped to resemble the human anatomy. Our experimental findings were corroborated with data from finite element method (FEM) numerical calculations. Apart from providing the first comprehensive characterization of the static mechanical pressure exerted by earplugs, our research reveals that with roll-down foam earplugs, increased compression prior to insertion leads to reduced SMP. The versatility of our specially designed test bench allows for mapping SMP caused by earplugs across diverse earcanal shapes. Integration of this instrument into design frameworks holds promise for enhancing the physical comfort of earplugs and, consequently, improving their overall efficacy in hearing protection. [Display omitted] [ABSTRACT FROM AUTHOR]

• Introduction of new machine learning-based sampling method to perform virtual experiments within the full stress state. • Comparison with two state-of-the-art sampling methods demonstrated the enhanced sampling efficiency and reproducibility of this new method. • Consideration of the full stress state led to a degraded representation of the in-plane anisotropy for the Yld2004–18p yield function. • Identification of Yld2004–27p as suitable to represent the anisotropic yield surface of DX56D with respect to the full stress state. This paper presents a new machine learning-based approach to investigate anisotropic yield surfaces of sheet metals by means of virtual experiments. The new sampling approach is based on the machine learning technique known as active learning, which has been adapted to efficiently sample virtual experiments with respect to the full stress state in order to identify parameters of anisotropic yield functions. The approach was employed to sample virtual experiments based on the crystal plasticity finite element method (CPFEM) for a DX56D deep drawing steel and compared with two state-of-the-art sampling methods taken from the literature. The resulting points on the initial yield surface for all three sampling methods were used to identify parameters of the anisotropic yield functions Hill48, Yld91, Yld2004–18p and Yld2004–27p. These parameters were then applied to a cylindrical cup drawing simulation to analyse the effect of the three sampling methods on a typical sheet forming simulation. The results show that the new machine learning-based sampling approach has a higher sampling efficiency than the two state-of-the-art sampling methods. Consequently, fewer computationally expensive crystal plasticity simulations are required. By comparing different variants of the Hill48, Yld91, Yld2004–18p and Yld2004–27p yield surfaces, it was also found that identifying parameters of anisotropic yield functions based on virtual experiments sampled within the full stress state can lead to a degraded representation of the in-plane anisotropy. With respect to DX56D deep drawing steel, this degradation was observed for the Yld2004–18p yield function. The negative implications following from this degraded in-plane representation were further demonstrated by the results of the cylindrical cup drawing process. As a consequence, the representation of the in-plane anisotropy must be carefully reviewed when taking the full stress state into account. In this context, Yld2004–27p was identified as being sufficiently flexible to simultaneously represent the plastic anisotropy of DX56D with respect to the in-plane and out-of-plane behaviour with high accuracy. [Display omitted] [ABSTRACT FROM AUTHOR]

This paper applies an energy method based on the high-order smooth curvature model to address the challenges of kinetostatically modeling the complicated nonlinear post-buckling behavior of inclined compliant beams. The proposed energy method is grounded in the principle of minimum strain energy, implying that the total strain energy is minimized at the equilibrium configuration. In this work, the high-order smooth curvature model is adopted to accurately model the bending strain energy of large deformation beams. Subsequently, the Lagrange multiplier method is employed to ascertain the minimum of strain energy while concurrently determining the corresponding tip loads. Additionally, the deformation shape and maximum stress are determined via the smooth curvature model. The proposed method is introduced for the first time in modeling compliant bistable mechanisms, and it is proven that the method can be used for modeling compliant beams with inclined angles ranging from 0 to 90 degrees. Following the modeling, finite element analysis and experimental tests are conducted to verify the accuracy of the proposed energy method. A comprehensive comparative analysis between proposed method and existing methods is conducted. The comparison results prove that the model is more computationally efficient without compromising modeling accuracy The proposed modeling method can not only be used for modeling compliant bistable mechanisms but also has extendable applications in modeling initially-curved compliant beams, contact-aid design problems, and distributed load problems.The present work not only advances the practical application of the proposed energy method but also lays the foundation for future research in modeling compliant mechanisms. [Display omitted] • Accurate and comprehensive nonlinear large-deflection modeling via the SCME method. • Efficient modeling capability without discretization. • Application to full inclined angles from 0 to 90 degrees. • Extensive comparisons with existing models, FEA and experiments. [ABSTRACT FROM AUTHOR]

• The specially designed 3D negative poisson's ratio corrugated metamaterial (3D-NPRCM) tube has the ability to make an impulse impact process into a quasi-static one. • A novel crash box is designed with a 3D-NPRCM tube, which produces excellent crashworthiness performance. • The peak crushing force of the 3D-NPRCM crash box is reduced by 18.076 % from 206.9 kN to 169.5 kN, compared to the conventional crash box. • The compressive displacement of the 3D-NPRCM crash box is decreased by 9.457 % from 235.8 mm to 213.5 mm, compared to the conventional crash box. The conventional impact process is a quintessential impulse process that causes substantial damage due to the high initial impact force. However, the impact effect can be significantly diminished by making the impulse process quasi-statically by using a three-dimensional negative Poisson's ratio corrugated metamaterial (3D-NPRCM) structure. This paper proposes a novel 3D-NPRCM obtained by folding the 2D-NPRCM. This study examines the crashworthiness properties and impact force of 3D-NPRCM subjected to impact using the finite element method (FEM). The results reveal that the sequential matrix structure has the ability to make impact impulse processes quasi-statically. The effects of various folding angles, arrangements, and geometrical parameters on the properties are also explored. Finally, the 3D-NPRCM is employed in an automobile crash box design. Through axial quasi-static compression simulation, the peak crushing force of the 3D-NPRCM crash box is reduced by 25.374 % from 211.652 kN to 157.946 kN, and the energy absorbed is increased by 23.830 % from 11.259 kJ to 13.942 kJ, compared to the conventional crash box. Through cart lateral impact simulation, the peak crushing force of the 3D-NPRCM crash box is reduced by 18.076 % from 206.9 kN to 169.5 kN, and the compressive displacement is decreased by 9.457 % from 235.8 mm to 213.5 mm. This work presents a novel design proposition for a crash box in vehicle engineering and demonstrates a fresh approach to expand the design of three-dimensional mechanical metamaterials. [Display omitted] [ABSTRACT FROM AUTHOR]

• A robust beam element is developed based on the 3D exact deformation field. • The generalized hyperelastic Rivlin model is integrated into the FE model. • A general unit cell (UC) is designed to simulate all hexagonal lattice structures. • The geometrical parameters effect of UC on the mechanical properties are studied. • UC with a broad range of large and negative Poisson's ratios are studied. • The lattices under large deformation are analyzed using experiment and FE model. This paper addresses the intricate analysis of lattice structures, pivotal components in engineering applications, confronted by challenges arising from their diverse unit cells (UCs) and complex behavior across micromechanical and macro-scale dimensions. The present study deals with a comprehensive analysis of lattice structure with honeycomb and re-entrant auxetic unit cells under large deformation via both a robust finite element analysis (FEA) and experimental tests. The proposed FEA is developed based on the hyperelastic Mooney–Rivlin strain energy function and the novel exact motion field that can fully describe the projection of cross-section. The results demonstrate that mechanical parameters such as Young's modulus, Poisson's ratio, and shear modulus have significant nonlinear behaviors with respect to UC geometrical parameters that are crucial for optimization across varied operational conditions. Additionally, the lattices made of TPU material and fabricated by Fused Deposition Modeling are tested under three-point bending and compression considering contact interaction. The results reveal highly nonlinear responses due to instabilities in some links and material nonlinearity. Furthermore, the behavior of lattice structures is exceedingly dependent on the orientations and types of UCs. It also can be found that both of the proposed FEA and constitutive model are in good agreement with experimental data. [Display omitted] [ABSTRACT FROM AUTHOR]

The deformation of textile composite reinforcement is influenced by its fibrous composition. In-plane bending behaviour is an inherent aspect of textile reinforcement, yet it is frequently overlooked. The paper elucidates the significant influence of in-plane bending behaviour on fibre orientation during forming process and emphasizes the necessity of accounting for in-plane bending virtual work to prevent non-physical deformation mode. To this purpose in-plane bending calculation is implemented into a fibrous shell finite element by using the neighbouring elements method. Numerical spurious mode involving in-plane shear is avoided due to the new approach. Finally, the model is validated by comparing with composite reinforcement draping experiments: fibre orientations and distributions of shear angles are simulated in good agreement with experiments and give better results than the simulations neglecting the in-plane bending behaviour. [Display omitted] • Neglecting in-plane bending energy in fibrous reinforcements forming simulations often lead to spurious modes. • In-plane bending contribution is highlighted through dedicated patch tests and forming simulations tests. • Enhanced fibrous shell considering the in-plane bending behaviour is proposed. • Forming simulations accounting for in-plane bending energy led to better results. [ABSTRACT FROM AUTHOR]

• A method is described to solve the transient thermoelectric coupling problem. • The heat flux concentration rises as the crack's thermal permeability falls. • The crack's electrical permeability has a limited effect on the TE performance. • As thermal permeability of the crack goes up, the efficiency falls significantly. Thermoelectric (TE) materials have a broad range of application in engineering such as cooling for thermal protection. Due to the brittle nature, TE semiconductors are prone to crack/voids under thermal shock. The investigation of the transient problem in cracked thermoelectric materials is essential for engineering applications. This paper describes a thermal-mechanical coupling method to analyze the transient response of the TE medium of finite size with an arbitrarily located inner crack. Based on the Fourier and Laplace transform, the crack problem is simplified into a system of singularity integral equations which can be solved by simple allocation. Besides, the results of this paper are verified through the finite element method (FEM). Furthermore, the effects of the crack position, crack's thermal and electrical permeability are discussed. Also, the effect of crack on the thermoelectric energy conversion efficiency is studied. Results show that the field concentrations at the crack tip become more significant when the crack is centrally located in the vertical direction. The electrical permeability of the crack has a limited influence on the energy conversion efficiency. However, as thermal permeability of the crack goes up, the efficiency falls significantly. [ABSTRACT FROM AUTHOR]

Highlights • Bulging formation can be prevented in a bilayer tube of arbitrary thickness while retaining moderate extensibility. • Several critical parameters for avoiding localized bulging are determined. • The applicability of an explicit bifurcation condition to layered tubes is validated. Abstract This paper studies the bifurcation behavior in an inflated bilayer tube of arbitrary thickness under inflation and uni-axial extension. It is assumed that both layers are composed of the Gent material with each layer having its own J m , where J m is a material parameter in the Gent model that signifies the maximum extensibility. First, we determine several critical parametrical regions where localized bulging disappears for a single-layer tube. Then we investigate localized bulging in an inflated bilayer tube, where one layer (layer I) of the tube cannot bulge whereas the other part (layer II) can. Surprisingly, we find that such a composite tube is still susceptible to localized bulging and localized bulging can be prevented only if the proportion of layer I exceeds a critical value, no matter whether layer I occupies the inner side or the outer side. Even for a very thin bilayer tube, the same feature holds. The cases of fixed axial force and fixed axial stretch are both studied, and the critical geometrical parameters marking the transition between bulging and no bulging are determined. Moreover, we carry out a numerical analysis by use of the finite element method to verify the applicability of an explicit bifurcation condition and the predicted bifurcation behavior. This paper offers a possible way to avoid bulging formation in a cylindrical tube while retaining moderate extensibility. [ABSTRACT FROM AUTHOR]

Highlights • A soft pneumatic gripper having automatic conversion mechanism is designed with four convertible grasping modes. • The grasping methods of multi-finger and adsorption for the designed gripper are investigated. • A simplified kinematic modeling approach to analyze the workspace of the soft finger tip is proposed. • The finite element analysis and experimental verification for the bending deformation of the soft finger is discussed. Abstract This paper proposes a novel soft pneumatic dexterous gripper that consists of four soft fingers and a movable sucker. Compared with rigid dexterous hands and other soft grippers, the soft pneumatic dexterous gripper has four convertible grasping modes, which can grasp a wide range of objects due to the proposed conversion mechanism. Most parts of the dexterous gripper are 3D-printed with resin in order to make it lighter. The soft finger is made of silicone rubber with the pleated channel, making the grasping process more flexible and safer. The curvature performance of single finger is predicted through finite element analysis (FEA) before making a prototype. The simplified kinematic model and tip workspace of the gripper are obtained to reveal its grasping range. Then, a mathematical model of the soft bending finger is proposed in order to explain the relationship between input air pressure and the finger bending angle. Finally, the single finger bending and the gripper grasping experiments results validate the accuracy of the model, consistency of finite element analysis, and rationality of the design. Graphical abstract This paper proposes a novel soft pneumatic dexterous gripper with the automatic conversion mechanism, which has four convertible grasping modes. In perpendicular mode, the Plane 1 and Plane 2 are orthogonal to each other. In this case, the gripper is more suitable for grasping sphere, cube, and the cylinder in vertical, etc. In parallel mode, where the Plane 1 and Plane 2 are in parallel to each other, the gripper can grasp objects with large aspect ratio. In two-finger mode, Finger 2 and Finger 4 bend inwardly to form the grasping gesture in the Plane 2. In this mode, the gripper is fit to grasp small bulk objects. In sucker mode, four fingers extend outwardly and the sucker moves down to make the gripper grasp small or light objects more easily. In addition, a simplified kinematic modeling approach is proposed to analyze the workspace of the soft finger tip, and the finite element analysis and experiments validate the superior performance of gripper under four grasping modes. The proposed soft gripper has extensive applications in automatic production lines such as grasping food, handing glass, and electronic components assembly, therefore, the work presented in this paper has a high practical value. Image, graphical abstract [ABSTRACT FROM AUTHOR]

Highlights • The equivalent thermophysical properties are calculated analytically. • The equivalent properties are applied to creep-fatigue design. • The equivalent method is verified by finite element analysis. • Equivalent thermophysical properties are dependent on geometrical parameters. • The result of creep-fatigue design satisfies the design criteria. Abstract Creep-fatigue life prediction is essential to plate-fin heat exchangers (PFHE) work at high temperatures and pressures in addition to thermal cycles. As the core of PFHE, the plate-fin structure is a complex pore structure and it is pretty difficult to carry out the stress analysis by conventional finite element method. Thus in this paper, a homogeneous method is proposed to do the strength design for plate-fin structure. This method treats the pore structure as an equivalent solid structure, and the key is to calculate the equivalent material properties and the equivalent stress. The equivalent mechanical properties have been obtained in our previous work [1], and in this paper the equivalent thermophysical properties including thermal conductivity, coefficient of thermal expansion, specific heat and density have been derived. This equivalent method is also verified by the three-dimensional finite element method. Besides, creep and fatigue tests of plate-fin structure are applied to calculate the stress and strain magnification factors. Basing on the equivalent material properties, a full scale stress analysis of PFHE by the equivalent finite element model has been carried out successfully to calculate the equivalent stress. After that, we multiply the equivalent stress-strain by the stress and strain magnification factors to calculate the local stress and strain. Then the creep and fatigue damages are predicted according to design curves of base metal. The result of equivalent model agrees well with that of the classical model, which concludes that this homogeneous method is effective to predict the macroscopic performance of plate-fin structure. Graphical abstract Image, graphical abstract [ABSTRACT FROM AUTHOR]

Highlights • FEM based model with and without van der Waals interaction is developed and validated for SWCNTs and DWCNTs. • FEM modeling of VACNTs with and without van der Waals forces are presented. • Influence of arrays size of VACNTs on elastic modulus is studied. • Influence of arrays size, intertube spacing and tube diameter on buckling strength of VACNTs is studied. Graphical abstract Image, graphical abstract Abstract Vertically aligned carbon nanotubes (VACNTs) have been explored widely in various applications due to their unique anisotropic properties. However, its application is limited due to large aspect ratio of nanotubes which lead to buckling phenomena. In this paper, we perform a finite element analysis to predict the variation of elastic modulus and critical buckling load of VACNTs. While elastic modulus is obtained from the slope of stress–strain variation of tubes when one end is fixed and another end is subjected to longitudinal loading, critical buckling load is found using eigenvalue analysis corresponding to first buckling mode. We also perform study to show size dependence of elastic modulus and buckling load of single walled carbon nanotubes (SWCNTs) using FEM approach and compare the results with MD results found in the literature. After validating FEM approach with available results of single-walled and double-walled carbon nanotubes, we apply the same method to arrays of VACNTs. It is found that elastic modulus of VACNTs increases from 1.18 TPa to 2.02 TPa when the size increases from 4 to 36 tubes and then it becomes nearly size independent. The variations of critical buckling load versus other parameters such as tube diameter, intertube spacing, etc., are also obtained. It is found that with the increase in diameter, there is a steep rise in the buckling load for the case of VACNTs arrays. In order to show the influence of non-linear van der Waals force in VACNTs, we compare the above results with and without the presence of van der Waals force and discuss its significance. The modelling and analysis presented in the paper can be used to optimise the number density of VACNTs for different applications. [ABSTRACT FROM AUTHOR]

• A novelty model coupling CFD and faulty gear dynamics is presented. • The vibration-cavitation mechanism considering pitting and crack is studied. • Effects of speed, pitting depth and crack depth on cavitation vapour are discussed. In high-speed gear transmission, cavitation occurs easily due to vibration. When gear has pitting or crack fault, the cavitation will be more violent due to stronger vibration, causing potential safety hazards. However, researches on gear cavitation mechanism considering pitting and crack are limited. For studying the cavitation mechanism of faulty gear, a model combined computational fluid dynamics and faulty gear dynamics has been proposed, being regarded as the innovation of this paper. The dynamic characteristics of the faulty gear is obtained by solving the gear finite element model, and the results will be applied to the analysis of lubricating oil flow characteristics as boundary conditions. For proving the validity of the proposed model, the simulation results are compared with the available experimental results. Moreover, the novelty of this paper is to consider the influence of gear failures on cavitation, factors such as rotational speed, pitting depth and crack depth are discussed, tooth profile changes are also considered. The results indicate that gear faults have greater impact on cavitation at high speeds. At 10,000 rpm, with the deepening of pitting, the cavitation intensity will increase firstly and then decrease. When the pitting depth increases from 0.2 mm to 0.3 mm, the root mean square value of average vapour volume fraction decreases from 0.0752 to 0.0724. For cracked gears, the crack depth will affect the cavitation enhancement rate. The increase rate of cavitation decreases from 17.4 to 1.1% when crack depth increases from 1 to 4.5 mm. This study provides an effective tool for gear cavitation suppression and high reliability. [Display omitted] [ABSTRACT FROM AUTHOR]

• A generalized model of bolted variable-stiffness flanged-cylindrical shells is established. • A simplified modeling method for bolted flanges is proposed. • The proposed modeling method is incremental validated by FEM and testing. • The influence of key parameters on natural frequencies and modal shapes is discussed. A general semi-analytical modeling method for the bolted variable stiffness composite cylindrical shell, incorporating precise modeling of the boundary and connecting flanges, is proposed in this paper. The coupling between shells and flanges is achieved through a spring-based penalty function method. A novel bolted joint model for flange connections is introduced, enabling the simulation of non-uniform pressure distributions at the joint interface. The joint model features a stiffness characterization technique that effectively improves adjustability and computational efficiency. The correctness and accuracy of the proposed modeling method are systematically validated through finite element analysis based on the ANSYS commercial software and experimental testing approaches. The series of parameter influence analyses on the bolted variable stiffness composite cylindrical shell with flanges, conducted using the proposed modeling method, accurately demonstrate the influence of geometric dimensions, fiber layup parameters, and bolt parameters on the free vibration behavior of such structures. Furthermore, these analyses aid in a deeper understanding of the dynamic characteristics of such structures, partially highlighting key design considerations and offering valuable guidance for their dynamic optimization design. [Display omitted] [ABSTRACT FROM AUTHOR]

• Gradient-shaped thin-walled origami tubes are formed by cutting and folding technique. • Thin-walled origami tubes with gradient shape possess significantly improved energy absorption capability and deformation mode. • Gradient shape leads to increased specific energy absorption and decreased peak force. • Specific energy absorption can be increased by 39.96% with hourglass-shaped origami tube H8-0.5/1.0. Introducing origami with outstanding flexibility into thin-walled tubes can enhance their energy absorption performance. This paper first proposes a cutting and folding-based design route of thin-walled origami tubes which enables geometry gradients such as uniform, tapered, hourglass-shaped, and ellipsoidal shapes. Subsequently, the finite element model of the proposed tube is established and verified through comparisons with experimental results. Numerical simulation results demonstrate that the quasi-static energy absorption capability of the graded thin-walled origami tubes is closely related to the folding angle, the total number of layers, and shapes. Compared with the conventional octagonal tubes (COT), the initial peak force in the proposed origami tube experiences a dramatic reduction, reaching a maximum decrement of 70.75%, while achieving a 39.96% boost in specific energy absorption (SEA). Moreover, the incorporation of gradient shapes within the origami tubes facilitates a more predictable and controlled collapse pattern, leading to an enhanced energy-absorbing efficiency than conventional uniform origami tubes. This study provides new insights into the design of thin-walled tubes that balance energy absorption and shape. [Display omitted] [ABSTRACT FROM AUTHOR]

• Novel methodology was developed to address geometric nonlinearities in multilayered plates via Hamiltonian framework. • Symplectic duality provides accurate determination of in-plane displacements and stress under non-mechanical stimuli. • Analytic power series of out-of-plane deflections capture nonlinear response rapidly, aligning well with FEM. • Purposed analytical method elegantly unveils complex interplay between membrane and bending parameters. • Framework can be readily extended to incorporate asymmetrical deformations due to general material orthotropy. Bistable multilayered plates have attracted significant attention as morphing and adaptive structures, renowned for their unprecedented exceptional performance. However, accurately predicting both their shape and internal stresses poses formidable challenges due to their geometrically nonlinear nature. For the first time, this paper introduces a Hamiltonian formalism aimed at achieving high-resolution analysis of nonlinear multilayered plates subjected to non-mechanical stimuli, including hygro-thermo-electro-magneto-elastic responses. A canonical system is strategically developed to compute membrane behaviors, yielding symplectic dual differential equations for in-plane field variables. This method elegantly decouples out-of-plane variables from the full-state vector, leading to an exact analytical solution in the membrane problem. To predict the bending behaviors, the first variation of the Hamiltonian energy density function, expressed as a power series of the transverse deflection, ensures flexural equilibrium. The power series effectively captures all admissible out-of-plane deformations, enabling a smooth transition between linear and nonlinear plate responses, including pitchfork bifurcation and limit points. The validity and accuracy of the proposed method are rigorously assessed through convergence tests and satisfaction of boundary conditions across various equilibria, ranging from monostability to bistability. It is cross-verified with high-fidelity finite-element methods (FEM), showing excellent agreements in both deformations and stress resultants. This research presents a physics-based methodology that unveils a parametric interplay between in-plane and out-of-plane field variables, serving as an efficient approach for analyzing adaptive and morphing structures. [Display omitted] [ABSTRACT FROM AUTHOR]

• A deep learning-based design framework is introduced for random porous metal. • The optimal structure exceeds CT scan ones by 17.71 % in energy absorption. • The proposed inverse hunt is 575 times more efficient than FEM traversal search. • Uniform pores indicate high energy absorption and no obvious yield bands occur. • Structural homogenization method generates structure with higher energy absorption. Due to its remarkable energy absorption properties, porous metals have widespread applications in engineering. However, the high randomness of pore morphology greatly hinders the effective design and analysis of high energy absorption structures. To address this challenge, this paper first introduces a deep learning-based framework for high energy absorption-oriented design of random porous metals structures. The framework comprises two steps: (i) a generator powered by Wasserstein deep convolutional generative adversarial network is developed to swiftly generate a vast design space (∼one million samples) of porous metals with real random pore morphology. (ii) an inverse search strategy based on convolutional neural network is applied to quickly pick out the optimal structure with the best energy absorption from the design space. Results show that the optimal energy absorption is about 17.71 % higher than the maximum value of initial structures from CT scan. Additionally, a 575-fold increase in computational efficiency is achieved compared to the traversal search using finite element method. Subsequently, the deformation process of the optimal structure is analyzed focusing on the pore morphology and compression performance, showing that random porous metals with uniformly sized pores are capable of withstanding higher stress under the same strain and exhibit no yield band during compression. Inspired by this, a structural homogenization method is introduced and validated to create porous metal structure with stable microstructure evolution, extended plateau stress and high energy absorption. [Display omitted] [ABSTRACT FROM AUTHOR]

The underlying size-dependent mechanism of viscoelastic porous metamaterial structures is still unclear, and the solution to their response using the high-fidelity numerical method is time-consuming, even prohibitive. This paper explores how the size-dependent effect of metamaterial structures emerges from the underlying nonlocal interactions in metamaterial microstructures, and then develops an accurate but efficient homogenization method for analyzing their size-dependent and time-dependent mechanical behaviors of viscoelastic porous metamaterial structures. By accounting for the nonlocal interaction between different representative volume elements and the history-dependent effect, a spatiotemporally nonlocal discrete element model is developed to analyze the mechanical behavior of viscoelastic porous metamaterial structures. With the help of the spatiotemporally nonlocal discrete element model, a spatiotemporally nonlocal homogenization method is proposed to accurately yet efficiently assess the size-dependent mechanical behavior of the porous metamaterial structure. The remarkable potential of the spatiotemporally nonlocal homogenization method is illustrated by simulating the stress relaxation of a viscoelastic porous metamaterial structure under axial strain. Results indicate that the size-dependent phenomenon can be significant, and the spatiotemporally nonlocal homogenization model can efficiently capture the size-dependent relaxation stress evaluated by the high-fidelity finite element model without loss of accuracy. [Display omitted] • Size-dependent stress relaxation behavior is observed in metamaterial structures. • The size-dependent effect emerges from the underlying nonlocal interactions. • A spatiotemporally nonlocal discrete and continuum method is developed. • Proposed method is accurate yet efficient for predicting the size-dependent behavior. • Stress relaxation can be directly analyzed in time domain instead of frequency domain. [ABSTRACT FROM AUTHOR]

• A novel mechanical metamaterial with a broad QZS platform is proposed. • Theoretical analysis, finite element simulation and experimental verification are conducted. • Broad QZS platform and isolation capabilities of the metamaterial confirmed. • Discuss the influence of critical parameters on the QZS properties. Adaptability and reliability are challenges in designing vibration isolation structures, and mechanical metamaterials featuring broad quasi-zero stiffness (QZS) platforms are among the most promising candidates for addressing this issue. This paper proposes a novel design of vibration isolation metamaterials featuring a broad QZS platform to achieve vibration control in complex environments. The metamaterial unit cells are designed by integrating horizontal and diagonal beams based on the mechanism combining Euler buckling and flexural deformation. Herein, the component made of diagonal beams is configured to exhibit negative stiffness behavior, while the designed support components aim to relax the boundary constraints of the diagonal beam component, thereby mitigating the negative stiffness effect. By tuning the synergistic effects between horizontal and diagonal beams, QZS features can be achieved over a broad range of displacements. A combination of theoretical analysis, finite element method and experiment is employed to investigate the payload and QZS features of metamaterials comprehensively. Notably, the designed unit cell maintained a considerably broad QZS platform, with static experiments revealing that this platform accounts for approximately 55 % of the total loading range. Furthermore, the designed metamaterials exhibit excellent vibration isolation performance in the low-frequency range, with vibration experiments demonstrating that the unit cell can effectively shield vibrations across almost the entire range when the support mass corresponds to the QZS payload. The geometric parameters of the metamaterial configuration that influence the range of the QZS platform are also explored. In conclusion, the proposed mechanical metamaterials have a tunable and broad QZS platform with considerable potential for use in customized low-frequency vibration isolation applications. [Display omitted] [ABSTRACT FROM AUTHOR]

• The proposed approach reveals the location, severity, and type of damage through real-time electrical resistance data. • Cross-validation of experimental, failure, and self-sensing analyses verify the validity of electrical resistance in health monitoring. • An effective self-decision system is established using unsupervised machine learning tools free from data labeling or imbalance. • The proposed algorithm accurately identifies the damage timing, location, severity, and types with an accuracy exceeding 96 %. The growing usage of carbon-fiber-reinforced polymers (CFRPs) has necessitated the development of structural health monitoring (SHM) for ensuring their integrity and safe operation. This paper presents a novel technique for monitoring the structural health of 3D CFRP pipe structures subjected to multiple impacts based on real-time electrical resistance monitoring. Damage characteristics such as its location and type were identified using the monitoring data and machine learning techniques. Additionally, finite element analysis was deployed to rationalize the electromechanical behaviors of pipes with varying stacking types and thus different fracture mechanisms. Analysis of the electrical resistance data coincided with the results of the finite element analysis in terms of damage modes and types. Therefore, a simple real-time electrical resistance measurement can detect the damage type without numerical analysis. A damaged section was identified by comparing the intensity of the data. Through machine learning techniques, the timepoints of damage severity demarcation were accurately predicted within error of 10 s and accuracies over 96 %. The machine-learning tools applied are unsupervised, thus reducing the effects of data dependency, labeling, and imbalance, as well as ensuring flexibility and general applications. The proposed technique was able to detect the damage location, severity, and type in real-time; hence, it has various potential applications in structural health monitoring including CFRP materials and is one of the few methods used to assess 3D structure characterization using self-sensing, which can result in mature technology and the optimal operation of CFRP systems. [Display omitted] [ABSTRACT FROM AUTHOR]

• Non-harmonic triangle and trapezoidal vibration trajectories are generated and control. • Effect of 2D tool vibration trajectory on the nano-grating formation is revealed. • Triangle tool vibration trajectory can fabricate nano-gratings with typical sawtooth profile. • Trapezoidal tool vibration trajectory can fabricate nano-gratings with specific duty cycle. • Structural color attributes are flexibly manipulated via innovative tool trajectory designs. Nano-gratings induced structural color is of great value in various anti-counterfeiting and decoration applications. Despite the attractive rendering performances, the manipulation strategy for vibration-assisted diamond-cutting structural color is far from complete due to the intrinsically limited tool trajectory designs. The novelty of this paper lies in the precise generation and control of non-harmonic triangle and trapezoidal two-dimensional vibration trajectories to shape typical blazed nano-gratings and nano-grating with specific duty cycles. A two-degree-of-freedom non-resonant vibration tool with closed-loop control was employed to reveal the effect of tool vibration trajectory on the machined nano-grating topography, and establish a sound framework for diamond-cutting structural-color to manipulate color attributes through innovative tool trajectory designs. Triangle and trapezoidal vibration trajectories are utilized for the first time to generate nano-gratings, which will be systematically compared to the common utilization of elliptical vibration trajectory throughout the trajectory generation, kinematical modelling and finite element analysis. Then, various vibration-assisted diamond cutting experiments were carried out to validate the identified differences of nano-grating topography induced by different tool vibration trajectories. The results show that smooth triangle and trapezoidal trajectories can be accurately generated for texturing nano-gratings with typical sawtooth topography and specific duty cycle, which can hardly be achieved using conventional elliptical trajectory. Ultimately, the manipulation of structural color effect via varying tool vibration trajectory was successfully demonstrated using the comparisons of color palette and diffractive spectrum. The revealed effects of tool vibration trajectory are beneficial to guide the process parameter designs for deterministically manipulating the vibration-assisted diamond-cutting structural color effect. [Display omitted] [ABSTRACT FROM AUTHOR]

• A full characterization diagram of beam impact responses is first proposed. • Multiple impact phenomenon are considered. • The proposed diagram can fast identify types of wide-ranging impact responses. • The proposed diagram can fast predicting the maximum impact force. • The proposed diagram proves to be a powerful analytical prediction tool. This paper presents a methodology for characterizing the responses of elastic-plastic beams to low-energy impacts. The objective is to construct a new full impact characterization diagram by considering the effects of multiple impacts. The diagram shows the relationship between normalized maximum impact force and non-dimensional parameters. It is applied to fast identify the types of impact responses for selecting adequate simple models and to fast predict the maximum impact force for designing safer structures and operations. Through the asymptotic solutions and numerous finite element simulations, the full impact characterization diagram is first constructed. It consists of the new relationship of non-dimensional parameters, characteristic curves and regional boundaries. It is found to be intrinsically different from the plate impact characterization diagram. Some conflicts have been revealed without considering the effect of multiple impacts as was done for plate impacts. A jump region is first observed between the region of infinite beam impacts and the regions of transition impacts and quasi-static impacts. Several new distinct evolution modes of response types are observed as well. These new phenomena are caused by the nature of beam impact responses and the effects of multiple impacts. The full impact characterization diagram is validated by the numerous experimental data and intensive numerical results of a wide range of the complicated beam impacts. The validations show that the full impact characterization diagram is a powerful analytical prediction tool to minimize the enormous computational and experimental efforts in tests and analyses. [Display omitted] [ABSTRACT FROM AUTHOR]

• The first three harmonics of mass defects induce adverse vibrations in shell resonators. • Extracts eccentricity-induced vibration from composite signals leveraging dynamic properties. • Presents a streamlined, low-damage approach to identify eccentric mass, bypassing the need for initial frequency split trimming. • Establishes an integrated platform combining harmonic identification with ion beam etching for mass balancing. • The quality factors are improved by suppressing the undesired mode, demonstrating its potential for engineering applications. This paper presents a novel method to identify and suppress the undesired spurious mode caused by the 1st and 3rd harmonics of eccentric mass defects in shell resonators. This approach eliminates the need for pre-trimming of frequency split, simplifying the identification and trimming process, with the advantages of high efficiency and minimal structural damage. Firstly, the influence of the mass defects on the dynamics of resonators is analyzed using the mass ring model. The shear force caused by the 1st and 3rd harmonics of the eccentric mass, as well as the axial force caused by the 2nd harmonic, result in forced bending vibration and axial vibration of resonators. These two types of vibrations are superimposed as spurious modes with the operating mode. The bending vibration caused by eccentric mass is decoupled from the mixed vibration signal by analyzing the dynamic characteristics. An analytic scheme is proposed to identify the 1st and 3rd harmonics without eliminating frequency split. To validate the proposed scheme, the identification and trimming process for eccentric mass is simulated by the finite element method based on the geometric model with preset first four harmonics. Finally, experimental identification and trimming of the eccentric mass for the hemispherical resonator are performed based on the laser Doppler vibrometer and ion beam etching process. After multiple iterations, the 1st and 3rd harmonics are reduced by 87.2% and 49.8%, and the quality factors of the operating modes increase by 26.7% and 40.7%, respectively, demonstrating the effectiveness of the proposed method. [Display omitted] [ABSTRACT FROM AUTHOR]

The mechanical properties of fiber-reinforced composites are significantly affected by hygroscopic exposure. Recent experimental findings reveal that the diffusion of water molecules results in void formation at the fiber–matrix interface, contributing to ∼ 1% increase in porosity. This paper presents a computational micromechanics framework to analyze the damage behavior of unidirectional composites under hygroscopic aging and transverse loads. First, a mathematical relation for the porosity evolution with moisture content in the composite is obtained. Leveraging this correlation, the aged composite is modeled as a porous microstructure consisting of fiber, matrix, and voids at the fiber–matrix interface in finite element simulations. The fiber is considered elastic, and the matrix is modeled as an elastoplastic material using a pressure-dependent yield model to capture tension–compression asymmetry. A cohesive interface is considered between the fiber and matrix. Simulation results indicate that a void at the interface significantly influences plastic strain evolution and stress distribution, leading to early damage initiation and reduced strength. Previous works have indicated that matrix and inter-fiber voids do not have a significant impact on the strength of composites when their combined porosity is below 1%. On the contrary, this study demonstrates that a porosity of as low as 0.1% at the fiber–matrix interface can result in an 11% decrease in the transverse tensile strength of the composite. A parametric study is conducted to understand the fundamental effects of pore size, location, and relative position on the transverse tension, compression, and shear loading responses of a unidirectional composite. For a given moisture content, the predicted strength of the hygroscopic aged composite exhibits a lower and upper bound. The strengths observed in the experiments fall within the model-predicted range. Additionally, a computational method is proposed that incorporates the effects of porosity at the fiber–matrix interface into a modified cohesive strength. This method allows efficient computations and failure predictions for water or moisture-aged strength degradation of unidirectional composites. [Display omitted] • A novel micromechanics framework to account for hygroscopic effects. • Correlated hygroscopic-induced porosity and water content for a unidirectional composite. • Simulated strength and failure mechanisms are consistent with experiments. • Proposed a computationally efficient probabilistic method to predict the strength of aged unidirectional composites. [ABSTRACT FROM AUTHOR]

The frictional receding contact problem for two graded layers pressed by a rigid punch is considered in this paper. The punch is subjected to both normal and tangential loads thereby resulting in frictional contact with the upper layer. It is also assumed that the contact between the layers is frictional and the lower layer is fixed. It is further assumed that the gradation in the layers follows an exponential variation through the thickness with different profiles while Poissons ratios are taken as constants. Using standard Fourier transform, the contact problem is converted to a system of two singular integral equations in which the contact pressures and the contact widths are the unknowns. The integral equations are then solved numerically using Gauss–Jacobi integration formula. The Finite Element Method was additionally employed and both exponential and power law material gradation is used to solve the investigated problem and the obtained numerical and analytical results are in good agreement. The primary intention of this paper is to investigate the effect of material gradation, friction coefficients, layers thicknesses and material property mismatch at the interface between the layers on the contact pressures and contact widths. [ABSTRACT FROM AUTHOR]

This paper investigates the designing of Superplastic Forming pressure cycles in order to propose rapid forming sequences that suit industrial strategy, and which enable the control of microstructure evolutions. An optimization algorithm using ABAQUS ® coupled with MATLAB ® has been developed in order to improve forming cycles while allowing superplasticity. The numerical strategy is based on an algorithm controlling a statistical maximum of the distribution of strain rate of non-formed elements of part mesh instead of the maximum strain rate on the whole mesh for classical optimization algorithms. The objective of this method is to exclude numerical singularities that are used for pressure controlling in traditional techniques. This paper details firstly the new algorithm and then presents numerical and experimental results for different forming conditions obtained from industrial, classical, and optimized pressure cycles. These tests were performed on Ti-6Al-4V titanium alloys. [ABSTRACT FROM AUTHOR]

This paper presents an analysis of the transient contact solutions of wheel-rail frictional rolling impacts calculated by an explicit finite element model of the wheel-insulated rail joint (IRJ) dynamic interaction. The ability of the model to simulate the dynamic behavior of an IRJ has been validated against a comprehensive field measurement in a recent paper (Yang et al., 2018). In addition to the measured railhead geometry and bi-linear elastoplastic material model used in Yang et al. (2018), this study adopts a nominal railhead geometry and an elastic material model for the simulations to provide an overall understanding of the transient contact behavior of wheel-IRJ impacts. Each simulation calculates the evolution of the contact patch area, stress magnitude and direction, micro-slip distribution, and railhead nodal vibration velocity in the vicinity of the joint during the wheel-IRJ impacts. The simulations apply small computational and output time steps to capture the high-frequency dynamic effects at the wheel-IRJ impact contact. Regular wave patterns that indicate wave generation, propagation and reflection are produced by the simulations; this has rarely been reported in previous research. The simulated waves reflect continuum vibrations excited by wheel-rail frictional rolling and indicate that the simulated impact contact solutions are reliable. [ABSTRACT FROM AUTHOR]

This paper presents a novel periodic auxetic cellular structure (PACS) whose cells were spanned as warp and woof. Warp and woof periodic auxetic cellular structure (WWPACS) is compressed in two transverse directions when quasi-static compressive loading is applied. In this paper, among different available manufacturing processes of auxetic structures, interlocking assembly method was used to fabricate the periodic cellular structure. To this end, the effects of NPR and mechanical behavior of auxetic structure were investigated and results compared with 3D finite element simulation. Good agreements were found between the experimental and FE results. The total energy and specific energy absorbed for experimental works and FE simulation were calculated. Furthermore, the effect of re-entrant angle on NPR was also obtained. The results show that the NPR increases and reaches to maximum value and then, due to overlaying the cellular, decreases. FE simulations show that the effect of structural geometry on NPR is more important than that of the materials used in the structure. [ABSTRACT FROM AUTHOR]

Recent studies have shown the coupling of optical and mechanical energy in a class of liquid crystal elastomers that contain light-sensitive molecules. As shown experimentally in the literature, these materials can undergo large, reversible elastic deformation under light illumination, and therefore geometric nonlinearity effects can be significant. In this paper, we present a large deflection model for the light-induced bending vibration of a liquid crystal elastomer beam. In this regard, the von Karman's nonlinear strain–displacement relationship is used to account for the large deflection of the beam. The effect of light on the liquid crystal elastomer beam is modeled as an inhomogeneous and time-dependent light-induced contraction strain and the dynamic equations of the beam are derived using the Hamilton's principle. Finite element formulation is developed to analyze the nonlinear dynamic response of the beam under uniform light illuminations. In addition, numerical results are presented and effects of different physical and geometrical parameters, including light intensity, light source position, contraction coefficient, and the thickness of the beam on the vibration characteristics of the beam are investigated. The model developed in this paper can be used to design liquid crystal elastomer based structures such as optically sensors, photo-mechanical energy harvesters, or other reversible opto-mechanically active structures. [ABSTRACT FROM AUTHOR]

• Intelligent metamaterials are developed by bio-inspired design concept and 4D printing method. • A novel theoretical calculation model of coupling of intelligent material and structure is proposed. • Tunable mechanical properties are verified by theoretical calculation, experiments and finite element analysis. • Various mechanical properties are large-scale controlled by regulating parameters and temperature. 4D-printed intelligent metamaterials possess a multitude of potential applications in the engineering fields due to their novel structures and functions. In this paper, a multifunctional intelligent metamaterial inspired by arc-bearing structure in human spine and tortoise shell has been established based on 4D printing technology. The innovative metamaterial exhibits programmable shape, significantly tunable mechanical properties, reusable characteristics with good loading, energy absorbing and vibration damping ability. Theoretical models of the metamaterial are developed to describe its intelligent mechanical properties. The relationship between structural parameters and the temperature field in relation to the tunable mechanical properties and functionalities of metamaterials were displayed and analyzed by experiments, theoretical calculation and finite element analysis. The stiffness, energy absorption and vibration damping effects are regulated by varying the structural parameters and temperature field. This multifunctional and tunable metamaterial is expected to be widely applied in related fields such as aerospace engineering and intelligent robots. [Display omitted] [ABSTRACT FROM AUTHOR]

• Folding stability mechanics of a bistable composite tape-spring towards its full tape-length range is revealed. • Novel features in terms of critical transitional length and stable folded angle are observed and identified. • Theoretical criteria for folding stability are determined from the established strain energy model. A bistable composite tape-spring (CTS) structure is stable in both extended and coiled configurations, which can be fully coiled or folded. Its bistable coiling feature has been employed in a Roll-Out Solar Array and successfully deployed in space; its foldable characteristics is analogous to a flexible mechanical hinge, showing great potential to be applied in an aircraft landing gear. Both the structural coiling and folding mechanics are dependent on tape geometry; whilst the correlated scale effect has not been investigated, which significantly constrains its foldable mechanical hinge designs and smart driving analysis in order to further reduce weight and complexity for conventional mechanical hinges. Here, we studied the folding stability mechanics of the CTS structure towards its full tape-length range, where novel stress and shape transitional mechanisms are revealed. This is achieved by investigating the quasi-static folding process of the CTS, where new stable shape features in terms of critical transitional length and stable folded angle are observed and identified through experimental observations, finite element model, as well as theoretical analysis. Theoretical criteria were then determined from the strain energy analysis in comparison to the predefined folded tape shape features. The folding stability mechanisms towards its full tape-length range were proposed in order to facilitate customized flexible hinge design and in-situ smart driving analysis in order to replace conventional mechanical hinges. [Display omitted] [ABSTRACT FROM AUTHOR]

• Contact radius and pressure are sensitive to normal jumping coefficients. • Stress distributions are significantly affected by all jumping coefficients. • The maximum von Mises stress is a piecewise function of friction coefficient. • Coupled imperfect interface has synergistic / dominative effect on contact response. This paper establishes a contact model between a rigid sphere and transversely isotropic layered material with imperfect interface. Interfacial displacement and stress of the coating-substrate system are transmitted discontinuously because of coupled dislocation-like and force-like defects. General solution of elastic field for transversely isotropic material was derived first, which was further converted to frequency response functions (FRFs) by performing the Fourier transform. Considering coupled dislocation-like and force-like interfacial condition, closed-form analytical expressions of elastic field for transversely isotropic layered material with imperfect interface in the Fourier frequency domain were obtained, and the discrete convolution-fast Fourier transform (DC-FFT) algorithm was employed to calculate FRFs. A conjugate gradient method (CGM) was used to solve contact equations iteratively. The reduced model with perfect interface was validated by carrying out a corresponding example with the analytical solution method and the finite element method (FEM). Effects of uncoupled / coupled dislocation-like or/and force-like interface conditions on contact behaviors and stress distributions were investigated employing the proposed model. [Display omitted] [ABSTRACT FROM AUTHOR]

• The influence law between IPCF and tubular parameters is clarified. • A universal multi-cell cross-section characterization scheme is proposed. • The mapping mechanism between IPCF and multi-cell configuration is revealed. • The generalization ability of the prediction model is validated. Accurately predicting the initial peak crushing force (IPCF) of the CFRP/metal hybrid structure is of great significance for the high-efficiency energy absorption of energy-absorbing elements and ordered deformation of combined energy-absorbing devices. Due to the significant differences in material properties between CFRP and metal and the high complexity of cross-sectional shape, a combined method of machine learning and mechanism analysis is proposed for predicting the IPCF of CFRP/Al hybrid energy-absorbing tube. First, a high-precision finite element model validated by the axial and oblique experiments is conducted to generate the dataset for predictive analysis. Second, a sample space through the design of experiment (DOE) is established for data fitting between structural parameters and IPCF based on traditional response surface model (RSM). It is found that traditional RSM method can successfully predict the IPCF of the single-cell hybrid tube, but cannot effectively predict the IPCF of the multi-cell tube due to the strong coupling effect between inner and outer plates. To address the issue of the lack of accurate correspondence between structural parameters and IPCFs in multi-cell hybrid tube, the indicator of relative density is proposed to characterize complex cross-sectional features. Surprisingly, there is a strong correlation between relative density and IPCF where multi-cell tubes with the same relative density have almost the same IPCF. Third, different artificial neural networks (ANN) are trained by a pre-simulated IPCF database of CFRP/Al hybrid energy-absorbing tube depending on the parameter characterization scheme based on mechanism analysis. In order to enhance the network's performance, the optimal configuration parameters of the neural network, including the number of layers and nodes, are ascertained through a combination of K-fold cross-validation and the Grid Search method. As a result, compared with the traditional RSM and Kriging model, the IPCF of CFRP/Al hybrid energy-absorbing tube can be predicted in small samples with high accuracy using the optimal ANN model. Finally, Through the comparative analysis of the IPCF of hybrid tubes with reported multi-cell configurations, it is found that the prediction model proposed in this paper has good generalization ability, which can be used to predict more complex types of multi-cell tube configurations. The present study offers important suggestions for the overall control of multi-materials hybrid energy-absorbing tube and the ordered deformation of combined energy-absorbing devices. [Display omitted] [ABSTRACT FROM AUTHOR]

• Buckling behavior of spherical shells with patterned surface under indentation is investigated. • Shells with discontinuous protrusions exhibit unique multiple snap-through due to local buckling. • Mechanical response and buckling morphology can be controlled by tuning surface patterns. A well understanding of instability mechanics of soft shell structures is key issue due to its important implications in functional shape morphing, flexible electronics, soft robotics, nanotechnology, biological engineering, etc. Despite abundant studies, buckling analysis of flexible shells with patterned surface under indentation is rare, primarily because of the complexities of high nonlinearities in geometry, material, and surface contact. In this paper, buckling behavior of spherical shells with patterned surface under indentation is comprehensively investigated by using experimental, numerical and theoretical analyses. It is found shells with stripes show similar variation in the force-displacement curves and post-buckling morphologies like perfect shells. Unlike perfect ones, shells with discontinuous protrusions exhibit multiple snap-through due to local buckling under indentation. What is more, mechanical response and buckling morphology can be well controlled by tuning shell thickness as well as positions and sizes of protrusions. These results can not only deepen understanding of mechanism of spherical shell buckling under local loads, but also provide a designing guidance for flexible electronics, soft robotics, and other future devices. [Display omitted] [ABSTRACT FROM AUTHOR]

• Versatile method for dispersion curve extraction in diverse structures. • Numerical examples cover a range of materials, including layered composites and functionally graded materials. • Examining how initial stress affects dispersion curves in the structures. • Provides insight into how band gaps influence wave propagation. • Viscoelasticity and damping effects are included in dispersion calculations. Guided waves play a crucial role in non-destructive testing, offering a reliable and efficient means for inspecting structures and materials. In this paper, we present the implementation of a wave finite element method for extracting dispersion curves, providing a feasible approach for analysing guided wave propagation in structures characterized by complex geometries and diverse material properties. Various numerical examples are investigated, including layered composites, functionally graded materials, rail sections, and metastructures, showcasing the versatility of the method. Mode sorting is a serious problem associated with this method crucial for distinguishing different guided wave modes. A mode sorting algorithm based on modal assurance criteria is implemented which can effectively trace different guided wave modes. To enhance accuracy, dispersion calculations are assisted by incorporating micro-modelling techniques for composite materials. Furthermore, the influence of initial stress on dispersion curves is examined, revealing that the effects of tensile and compressive stresses can vary at different frequencies and for different modes. Attenuation or damping is inherent in every structure and material, significantly influencing wave propagation. The article also investigates viscoelasticity and damping, expanding the method's applicability by introducing a novel approach to calculate attenuation using the frequency domain modulus for computing complex angular frequencies. The present method offers a fast, accurate, and feasible solution for extracting dispersion curves in structures with intricate geometries and material properties. [Display omitted] [ABSTRACT FROM AUTHOR]

This article presents the results of study of natural vibration and aeroelastic stability of isotropic shallow cylindrical shells interacting with a supersonic gas flow. The examined systems are equipped with piezoelectric elements which are located on the inner surface of the structure, and can be connected to a passive electric circuit. The mathematical formulation of the problem is based on the variational principle of virtual displacements taking into account the work of inertia forces, aerodynamic pressure and electric field. The solution is developed in a three-dimensional formulation using the mode-superposition technique and finite element method. The non-classical problem on complex eigenvalues is solved using the Muller method. The validity of the obtained results is confirmed by solution convergence with increase of the nodal unknowns and by comparison with the literature. The influence of the piezoelectric element location on the frequency and critical pressure of the gas flow leading to the onset of flutter instability is analyzed at different combinations of kinematic boundary conditions. The applicability of shunt R and R L -circuits for controlling the aeroelastic stability boundary and the damping rate of free vibration in the subcritical region are evaluated. The methodology described in this paper allows obtaining higher damping ratios and provides the smallest difference between the natural vibration frequencies of the shell and the electric circuit, compared to solutions based on the known analytical expressions. [Display omitted] • Panel flutter of isotropic shallow shells is investigated by the finite element method. • Different combinations of kinematic boundary conditions on shell edges is analyzed. • Location of the piezoelement is determined from the solution of optimization problem. • Change of the flutter boundary due to the use of shunt circuits is insignificant. [ABSTRACT FROM AUTHOR]

• Shear bands' morphology in amorphous polymer under four-point bending is concerned. • Physical mechanisms of detour and strength decay of bands at intersections are analyzed. • Constitutive model can predict the morphology of shear bands under four-point bending. As a significant means of plastic deformation in polymers, shear bands play a crucial role in material failure and performance optimization. In this paper, the finite element method is utilized to numerically investigate the morphology of shear bands in an amorphous polymer plate under plane strain four-point bending. Amorphous polymers are characterized by the elastic-viscoplastic constitutive relationship that takes into account the effect of pressure on yielding, including intrinsic softening and subsequent orientation hardening. The impact of material parameters including intrinsic softening, orientation hardening, and initial imperfections on the evolution of shear bands and the undulations of the specimen's surface are explored in detail. In addition, the physical mechanisms responsible for the detour and strength decay of shear bands after passing the intersections are described. It appears that intrinsic softening is the driving force promoting the detour of shear bands at intersections, while orientation hardening is the driving force inhibiting the detour. By comparing the simulations with experimental observations, it is demonstrated that the model can qualitatively depict the morphology of the shear band during the four-point bending of amorphous glassy polymers. [Display omitted] [ABSTRACT FROM AUTHOR]

• An original ICVI algorithm reproducing the pyrolytic carbon deposition process is proposed. • The relationship between the process parameters and mechanical properties of unidirectional carbon/carbon composites is investigated. • The transverse modulus and tensile strength increase with an increase of the infiltration time, pressure, and temperature. • Interfacial debonding and propagation of multiple cracks result in the complete failure of unidirectional carbon/carbon composites. This paper proposes an innovative algorithm derived from the isothermal chemical infiltration process to generate quasi-real microstructures of unidirectional carbon/carbon composites. This algorithm, which can predict the relationship between the composite density and infiltration time, is termed the isothermal chemical infiltration algorithm. To further evaluate the relationship between the process parameters and the mechanical properties, a mesoscale finite element model of the unidirectional carbon/carbon composite is established based on the isothermal chemical infiltration algorithm. After validation, the developed numerical model is employed to study the effects of the infiltration time, pressure, and temperature on the effective mechanical properties. The results show that the transverse modulus and tensile strength increase with an increase in the infiltration time, pressure, and temperature, with the effect of temperature being the most significant. In parallel, it is revealed that the complete failure of unidirectional carbon/carbon composites results from interfacial debonding and propagation of multiple cracks during transverse tension. The proposed model has potential applications in the process design and optimization of high-performance carbon/carbon composites. [Display omitted] [ABSTRACT FROM AUTHOR]