Search

Paper-like electronics with thin multi-layer structures, which can be repeatedly bent and twisted like paper, are promising for diverse innovation application. Employing surface-mounted flexible strain sensors is a general way to monitor the bending characteristics of each layer inside paper-like electronics, however, the deviation of measured strain will reach up to 15% on account of the layer-to-layer interface sliding, neutral axes offset resulted from the extra effect of the flexible strain sensor. Here, we proposed a precise measurement method to evaluate the surface bending strain of paper-like electronics by using flexible sensors. In combination with the effects of the thickness, length, etc, a strain compensation model has been established to compensate the measurement deviation. Meanwhile, a slip failure model has been developed to guide the design of the sensitivity unit within the non-sliding area of the flexible sensor. Validated by finite element analysis and experiment, the bending strain of paper-like electronics (eg., ∼50 μm) can be evaluated much more accurate compared to the frequent access one. The newly-proposed method provides a powerful basis for further research of paper-like electronics. [ABSTRACT FROM AUTHOR]

• The first-ever systematic experimental program on the transverse tension tests of PGFRP profiles using non-standard short coupons was presented. • Size effects on transverse tensile properties in terms of coupon width and gauge length were examined. • Finite element models were developed to provide a better understanding of the failure mechanisms of the transverse short coupons under tension. • Recommended short coupon configuration for transverse tension tests of PGFRP profiles was eventually proposed. Pultruded glass fiber-reinforced polymer (PGFRP) profiles, manufactured via a pultrusion process, are increasingly used in civil engineering. However, due to the anisotropic nature, their transverse material properties are weaker than the longitudinal ones, necessitating robust material characterization methods for transverse properties. Commercially available PGFRP profiles often have insufficiently large cross-sections for standard-sized transverse tensile tests, prompting the need to investigate the effect of coupon size on transverse tensile properties and propose a feasible shorter coupon size. This paper therefore aims to examine the coupon-size effects and propose suitable short coupon geometries for transverse tensile tests. Standard material characterization tests were conducted on channel-section PGFRP profiles, followed by transverse tensile tests on six types of non-standard short coupons. The effects of coupon width and gauge length on transverse tensile properties were evaluated and compared across six aspects, with potential failure mechanisms further explored using finite element analysis (FEA). The paper concludes by proposing a feasible short coupon configuration for transverse tensile tests. [ABSTRACT FROM AUTHOR]

Applying the hybrid flux finite element method(HF-FEM) and hybrid thermal stress finite element method (HTS-FEM) is not prevalent in analyzing heat conduction and thermal stresses in particle-reinforced composite materials. Most of the research on this technique is confined to two-dimensional problems. This paper proposes the HF-FEM and HTS-FEM, based on 3D polyhedron-octree, to calculate the steady-state heat conduction and thermal stress of particle-reinforced composites. In addition, this paper presents a method for partitioning spherical particle-reinforced materials into polyhedron-octree elements, each of which contains only one type of material. Each element is divided into multiple Delaunay tetrahedrons, and hammer integration is used to perform the integrals. Additionally, this paper presents a technique to construct the heat flux function for polyhedral elements, and the effectiveness of the above methods is demonstrated by comparing it to several numerical examples of traditional finite element methods. [ABSTRACT FROM AUTHOR]

Anisotropic stiffness properties of carbon fiber-reinforced polymer composites (CFRPCs) can be designed by arranging the fiber path. In this paper, we propose a novel method to optimize the fiber path using the genetic algorithms (GA) and simulated annealing algorithms (SAA) combined with the quasi-uniform cubic B-spline curves. The optimization goal is to obtain the largest reaction force of an open-hole plate under uniaxial tensile loading. After the finite element method (FEM) and experimental verifications, the optimized variable-stiffness specimen owes the higher strength and stiffness, compared with the unidirectional one. Besides, the stress concentration can be reduced. One of the key points of this paper is to use the GA and SAA to control the slight data points to optimize the B-spline curve. By reducing the number of optimization variables, the computational efficiency is improved greatly. Moreover, by increasing the interval variables of the B-spline curve, we further improve the accuracy of optimization results. The range of values for the control points can be easily adjusted according to the manufacturing and design requirements. We also compare the optimization results of GA and SAA. Both of them can get the similar optimization results, and the SAA has a better convergence speed and accuracy. The proposed optimization method can be extended for three-dimensional preform and structure design in the future. [ABSTRACT FROM AUTHOR]

End-anchors have been widely used to prevent/postpone debonding failures in FRP-strengthened RC structures. The bond behavior between FRP and concrete with end-anchors can be investigated through FRP-concrete bonded joint with such anchors. Existing studies have found that deformation of FRP and the anchor, as well as slip of FRP-concrete interface at the anchored end can happen when the FRP is under external loading; therefore, the simple assumption that end-anchors provide a rigid end to FRP may result in significant overestimations of the bonding stiffness and strength. Against this background, this paper presents an analytical study on the closed-form solution to the full-range bond behavior of CFRP-concrete bonded joint with a non-rigid anchor. The obtained analytical solution was first verified through finite element analyses and test results, and then was adopted in a comprehensive parametric study to investigate the effect of mechanical properties of end-anchors on the overall bond behavior of the joint. This paper provides a better understanding of the bond behavior between FRP and concrete with a non-rigid anchor and shows that the design of such end-anchors should be based on CFRP-concrete interfacial characteristics for a desired bond behavior. [ABSTRACT FROM AUTHOR]

Bi-functional metamaterials with programmable coefficients of thermal expansion (CTEs) and Poisson's ratios (PRs) have garnered significant attention among researchers due to the ability to manifest desired deformations under thermal and mechanical loads. Nevertheless, a current challenge lies in efficiently achieving the inverse design of these metamaterials to meet diverse application requirements. This paper presents a machine learning (ML) model that can establish a logical mapping relationship between geometric/material parameters and mechanical properties, and it is applied to the inverse design of bi-functional metamaterials with desired CTEs and PRs. Furthermore, the inverse design capability of the ML model was validated by the finite element analysis and experimental test. The results demonstrate that the geometric models obtained from the inverse prediction can effectively exhibit the desired deformation behavior under thermal and mechanical loads. And the ML model proves to be a valuable tool, offering effective guidance for the design of bi-functional metamaterials with specific CTEs and PRs. [ABSTRACT FROM AUTHOR]

Damage monitoring during the service life of Type III composite overwrapped pressure vessels (COPVs) is crucial for ensuring their safe operation. This paper focuses on the damage localization in COPVs using ultrasonic guided waves structural health monitoring (SHM) techniques. Firstly, dispersion curves were plotted to establish a foundation for experiments and simulations based on the propagation theory of guided waves in multilayered anisotropic structures. Subsequently, a 3D finite element model of COPV was constructed to capture the propagation characteristics of guided waves within the COPV and their interaction with damage. The effects of different fiber angles and fiber layer numbers on guided waves propagation were analyzed, and their interrelationships were established. Furthermore, the "Wave Velocity Directionality" effect of the A 0 mode was identified during its propagation in COPV. The monitoring signals obtained from experiments were analyzed to assess the impact of damage on the time-domain and frequency-domain signals of guided waves. Finally, a damage localization algorithm based on mode-matching was proposed, and its localization accuracy was verified in COPVs with different damage locations and fiber layer numbers. The results demonstrate the significant potential of the proposed damage localization algorithm in the damage monitoring of COPV structures. [ABSTRACT FROM AUTHOR]

This paper proposes a study on the thermal buckling of Variable Angle Tow (VAT) composite plates using high-order theories. Here, the governing equations are derived via the principle of virtual work. Under the assumption of linear pre-buckling, the stability problem is reduced to a linear eigenvalue analysis considering proportional geometric stiffness. In contrast, a constant thermal load is assumed to be known along the plate thickness, and the uncoupled thermo-mechanical formulation is used, where the thermal effects are described as external loads. The plate is discretized using the Finite Element Method (FEM) and high-order theories are developed using the Carrera Unified Formulation (CUF). Using the CUF, the equations are expressed as an invariant of the plate theory approximation order. Therefore, Equivalent Single Layer (ESL) and Layer-Wise (LW) models can be easily implemented. Several geometries and lamination cases are considered for verification purposes, including different side-to-thickness ratios and fiber orientations, which result in various anisotropy effects. In addition, the effect of changing constraints and materials is evaluated. Particular attention is paid to the effect of the structural theory approximation on the evaluation of the thermal buckling load. It is shown that the correct evaluation is highly dependent on the edge-to-thickness ratio and on the anisotropy given by both the fiber orientation and the material properties. As a final remark, sensitivity analysis and best fiber angle solutions are discussed to highlight the importance of the LW modeling approach. [ABSTRACT FROM AUTHOR]

Composite laminated thin-walled structures, widely used in high-speed aircrafts, undergo a complex thermal–mechanical coupling environment. Geometrical nonlinearities with a thermal effect bring significant challenge to finite element analysis of structures. In this paper, a novel hybrid-stress method based on the solid-shell element is proposed for nonlinear thermoelastic analysis. An eight-node solid-shell element (CSSH8) is developed based on the assumed natural strain method and hybrid-stress formulations to overcome various locking problems and achieve an effective 3D simulation for structures with a large span-thickness ratio. The Green–Lagrange displacement-strain relation is selected to take the geometrical nonlinearities into account. The modified generalized laminate constitutive model is extended to consider both the thermal expansion and temperature-dependent material properties. A temperature variation along the laminate thickness can also be assumed in the constitutive model. Nonlinear thermoelastic equilibrium equations are derived using the Hellinger–Reissner variational principle, in which five different coupling cases for thermal–mechanical loads can be fully involved. Numerical examples demonstrate that the proposed method with CSSH8 element is insensitive to various distorted meshes and numerically robust to pass the buckling point; meanwhile large step sizes can be achieved in the path-following nonlinear thermoelastic analysis. • A hybrid-stress solid-shell element is developed for nonlinear thermoelastic analysis of structures. • The modified generalized laminate constitutive model is extended to consider thermal effects. • Nonlinear thermoelastic equilibrium equations are derived for five thermal–mechanical cases. • The method is fully tested using various examples compared with displacement based FE methods. [ABSTRACT FROM AUTHOR]

[Display omitted] • Predictive FE models for compressed wood dowel-laminated timber structures. • Verification and Validation of finite element models for dowelled timber structures. • Development of solid-shell and solid-beam approaches for industrial cases. • Numerical model using a mix of solid, solid-shell and solid-beam elements. • Reduction of finite element models thanks to solid-shell and solid-beam approaches. This paper presents a numerical approach to assess efficiently the vibration performance of adhesive-free engineered wood products assembled through compressed wood dowels. Predictive finite element models are obtained by applying the Verification and Validation methodology. The models are first developed using solid elements. Then, solid-beam and solid-shell approaches based on standard solid elements are developed with first-order or higher-order theories. Beam or shell kinematic assumptions are applied throughout the cross-section of the dowels and through the thickness of the layers. From a numerical point of view, a modification of the system of algebraic equations, based on the concept of independent and dependent nodes, is developed. Dependent nodes are eliminated, resulting in a significant reduction in the number of degrees of freedom and floating-point operations. The methodology is evaluated for the calculation of frequencies and mode shapes of adhesive-free laminated timber beams and timber panels with a mix of solid elements, solid-shell and solid-beam approaches. The study highlights the efficiency of the proposed modelling approach in terms of quality of results and model size reduction. [ABSTRACT FROM AUTHOR]

• Shear behavior of RC beams strengthened with U-wrapping PET FRP was studied. • Effects of shear span ratio on shear performance of U-wrapping PET FRP-strengthened RC beams were investigated. • Seven design models of FRP shear contribution were evaluated and a modified model was proposed. • An FE model incorporating the bond-slip relationship between FRP and concrete was developed. This paper reports the investigations of experimental and numerical programs on the shear performance of U-shaped Polyethylene Terephthalate (PET) FRP-retrofitted RC beams. Twelve RC beams were fabricated and tested under monotonic three-point loading with the test parameters being FRP strip width and shear span-to-effective depth ratio. A comprehensive analysis and investigation were conducted in terms of the failure modes, shear load–deflection responses, shear capacities, the strain evolution of FRP and stirrups, and the interaction of shear contributions among FRP, stirrups and concrete. Larger debonding strains were observed for PET FRP. Five design guidelines and two models available in the literature were assessed against the measured PET FRP shear contribution. A modified model of the shear contribution for PET FRP was developed and verified by the test results. Finally, a finite element model was established to further understand the shear performance of retrofitted beams, in which the bond-slip relationship between concrete and FRP was considered. The FE model was validated by comparing the test and FE results. The proposed FE model could accurately capture the propagation of shear critical cracks and FRP debonding failure for the specimens with medium and large shear spans. [ABSTRACT FROM AUTHOR]

This paper presents a fully coupled thermodynamically consistent diffusion–reaction-deformation cohesive model for pyrolytic carbon (PyC)/SiC interfacial coating in fiber-reinforced composites. Arrhenius function is used to capture the chemical kinetics and the Kuhn-Tucker conditions is exploited to describe the damage evolution of interfacial coating. A strong connection between the diffusion–reaction process and interfacial mechanical deformation is established by the cohesive model, and the rules of the model parameters are discussed in detail. Implementation of the cohesive zone model is conducted in ABAQUS finite element software through the use of UEL subroutines. A mesh convergence for the model is tested and the model is validated by the comparison with the experimental results. A Representative Volume Element (RVE) model for fiber-reinforced composites at different temperatures, equipped with custom cohesive elements, is constructed to investigate the impact of PyC/SiC coating during oxidation. Two-step simulation is adopted to solve the chemo-mechanical behaviors of interfacial coating. The impact of the interfacial coating on stress transfer between the matrix and fibers is highlighted by numerical results that demonstrate an initial decline in mechanical properties followed by an upward trend with increasing temperature. The model also captures the coupling mechanisms between the diffusion–reaction process and the interfacial deformation in the interfacial coating. Theoretical insights for fiber-reinforced composites in chemical environments are provided, guiding the design of interfacial coatings for potential engineering applications. [ABSTRACT FROM AUTHOR]

Real-time thermal deformation monitoring plays a crucial role in calibrating phase signals and maintaining satellite performance for large spaceborne antennas. The inverse finite element method (iFEM) represents a promising shape-sensing methodology applicable to monitor the three-dimensional displacement of structures through surface-measured strain. However, the high-accuracy reconstruction of large-scale structures involves a large number of inverse elements, which leads to the low level of computational efficiency. To address this issue, a displacement-gradient-based variable-size iFEM is proposed in this paper. According to the characteristics of deformation, this method optimizes the size of each inverse element to reduce the number of inverse elements required, which improves real-time performance and maintains the high accuracy of reconstruction. The real-time performance of the proposed method is verified by conducting a simulation test on a large-scale honeycomb antenna. According to the simulation results, the variable-size iFEM is applicable to achieve the same accuracy of reconstruction using fewer inverse elements than conventional iFEM. An experimental test is performed and the optimal variable-size discretization that balances accuracy and efficiency is determined. The results show that the maximum error of reconstructed displacement is less than 7.3 % and the reconstruction time is in no excess of 0.1 s. [ABSTRACT FROM AUTHOR]

[Display omitted] • A semi-analytical method for dynamic modeling of variable stiffness composite flanged-cylindrical shells is proposed. • The correctness and efficiency of the proposed method are verified by finite element method. • The vibration test of a composite cylindrical shell with flange is carried out. • The effects of various design parameters on the variable stiffness composite cylindrical shell are analyzed. Variable stiffness composite structures show great application potential due to their flexible spatial stiffness adjustment ability. In this paper, the accurate and efficient dynamic models of variable stiffness composite cylindrical shells considering the effects of the flange are established based on a semi-analytic frame. Then, the finite element models of the corresponding structures are established by using the ANSYS commercial software. Through the comparison of the calculation results between models under two analytical frameworks, the correctness and efficiency of the proposed modeling method are well verified and reflected. In addition, an instant hammering test of a composite cylindrical shell with flange is carried out to verify the accuracy of the modeling method at the experimental level. Then, the influence of design parameters on frequency trajectories and modals of the variable stiffness composite cylindrical shell with flange is studied. The analysis results show rich and interesting phenomena, among which, the circumferential variable stiffness composite cylindrical shell with and without flange exhibits complex frequency veering behavior under continuous variations of design parameters. The research work has a certain guiding significance for the dynamic optimization design of the variable stiffness composite cylindrical shell with flange. [ABSTRACT FROM AUTHOR]

This paper establishes a geometrically nonlinear bending analysis framework using the deep energy method and the classical laminated plate theory (CLPT) for laminated plates. Inspired by the transfer learning technique, a load applied to a laminated plate can be divided into multiple load steps. The network parameters for the current load step, with the exception of the initial step, are initialized by inheriting values from their preceding steps. Including both von Kármán and Green-Lagrange strains, the plate strains are computed using the automatic differentiation and integrated along the thickness direction per laminate plate based on the constitutive theory. By combining the outputs of neural network, the external potential energy can be obtained, and the optimized network parameters are given by minimizing the total system potential energy of the laminated plate. In order to validate the proposed approach, several numerical examples are calculated, and the present solutions are compared with those given by the literature and the Finite Element Analysis (FEA). The results show that the proposed approach is indeed feasible, can reach high levels of precision under varying loads while offering a simplified calculation strategy. [ABSTRACT FROM AUTHOR]

[Display omitted] • Twisting effects caused by material gradients are first explored in this study. • An advanced line element is introduced to capture the geometrically nonlinear behaviors considering twisting effects. • A new cross-section analysis method for arbitrary functionally graded sections is proposed. • The proposed geometrically nonlinear analysis method has good accuracy and efficiency. • The proposed approach has been integrated into a new software, MSASect2 to provide a user-friendly tool. Functionally graded materials with spatially varying properties have gained widespread use in various engineering disciplines due to their exceptional mechanical characteristics. Nevertheless, these materials can lead to non-symmetric properties of cross-sections and an offset between centroid and shear center of functionally graded (FG) members, thereby significantly affecting the mechanical behavior. This phenomenon, known as twisting effects, poses a substantial challenge for the geometrically nonlinear analysis of FG members, as existing methods rely on traditional line elements that assume the centroid and shear center of the section coincide. Thus, this paper proposes a new framework for geometrically nonlinear analysis of FG members, incorporating twisting effects through a novel Timoshenko line element. An efficient finite-element-based approach that employs the nonhomogeneous plane triangle (NPT) element for calculating the cross-sectional properties of arbitrary FG cross-sections is presented. These cross-sectional properties are then utilized within the advanced line-element formulation to perform geometrically nonlinear analysis of FG structures considering twisting effects. The accuracy of the proposed method is validated through three examples, followed by several case studies to examine the impact of twisting effects on FG members. Furthermore, the proposed cross-section analysis method is integrated into a new structural analysis software MSASect2 to facilitate its application. [ABSTRACT FROM AUTHOR]

Due to their outstanding mechanical properties, fiber-reinforced polymer composite (FRPC) structures have become a prominent research topic. Yet, to surpass existing performance limits, their design potential should be expanded beyond conventional empirical methods. Moreover, because of the high manufacturing costs, the protection of FRPC structures should be considered in the design phase to extend their service life. In this paper, we introduce an innovative configuration wherein metal coatings are strategically applied to the surfaces of FRPC structures. This technique aims to protect the internal matrix and fiber materials, and to inhibit the interlaminar delamination of composite laminates. Then, a corresponding full-scale topology optimization framework is built based on a density-based method. The coating, matrix, and fiber materials are considered collectively, avoiding issues such as excessive computation, non-convex optimization, and fiber discontinuity. Furthermore, a dual variable scale filtering (DVSF) method and its simplified scheme are presented to optimize coating thickness based on the physical information obtained from finite element analysis. Meanwhile, the co-evolution of solid topology and fiber morphology, driven by algorithms, facilitates the parallel optimization of multiple geometric features. Several typical examples, including wing ribs, are provided to illustrate the effectiveness and superiority of our approach, highlighting its engineering relevance. [ABSTRACT FROM AUTHOR]

• Exact solution of non-uniform/inhomogeneous rod with linear variation is derived. • Effects of non-uniformity/inhomogeneity on bands of periodic rods are discovered. • Inverse design of periodic non-uniform/inhomogeneous rods is proposed on Q-Learning. The existing researches on controlling the longitudinal waves through periodic rods with frequency bands mainly focus on the analysis of band structures together with their influences by various geometrical/material parameters and on the corresponding forward design via passive/active modulations. This paper originally proposes the interactive inverse design method by virtue of the Q-Learning algorithm for catering required objectives with introducing the cross-sectional nonuniformity and material inhomogeneity to the constituent components in periodic rods. Firstly, theoretically analyzing the frequency bands of periodic non-uniform/inhomogeneous rods with linear variations to the cross-sectional area and to the Young's modulus and material density, is presented using transfer matrix method (TMM). After verifying the analysis method by comparing it with the finite element method (FEM) for obtaining band structures in three kinds of exemplified periodic rods with non-uniform/inhomogeneous components, the effects of non-uniformity and inhomogeneity of components on the frequency bands are discussed. These effects provide qualitative judgment criteria to the results of inverse design. Secondly, the inverse design method by the Q-learning algorithm for periodic non-uniform/inhomogeneous rods is proposed as the optimization objective is the maximum of the first bandgap width. The optimization results of the periodic rods with only non-uniformity, with only inhomogeneity or with both non-uniformity and inhomogeneity are provided to validate the accuracy and efficiency of the proposed Q-Learning algorithm that has the advantages of obtaining the optimal result from any initial states and giving the evolutionary path along the gradient to the objective. It should be pointed out that our proposed inverse design method can actually be extended for other optimization objectives and to other kinds of periodic structures for controlling diversified elastic waves. [ABSTRACT FROM AUTHOR]

In this paper, the wave propagation mechanics theoretical model of Y-shaped core sandwich metabeams with local resonators is established based on the spectral element method, and the flexural wave bandgaps and vibration isolation characteristics are studied. The reliability of the theoretical model of Y-shaped core sandwich metabeams is verified by the finite element method and experiment. On this basis, a deep learning-based intelligent design method for predicting the vibration transmission characteristics and structure design of Y-shaped core sandwich metabeams is proposed. A dataset is created using the theoretical model of wave dynamics, and deep neural networks are constructed to forward prediction of transmission characteristics and intelligent design of Y-shaped core sandwich metabeams, respectively. Results indicate that the bandgap range of Y-shaped core sandwich metabeams is 2.5 times that of Y-shaped core sandwich beams, and the start frequency of bandgap is reduced by 578 Hz. The prediction of the transmission characteristic curve is in good agreement with the target, and the average relative error of intelligent design is below 3 %, which verifies the precision of the intelligent design method. The innovative, intelligent design method provides a novel way to realize engineering vibration reduction design of acoustic metamaterials rapidly. [ABSTRACT FROM AUTHOR]

• FE solution of harmonic vibrations for VE layered plates with exponential complex-conjugate form and refined zig-zag theory. • Effective application of the continuation method to solve the discretised amplitude equation. • Numerous analyses of the influence of various plate and formulation parameters on the resonance behaviour of laminate plates. The paper is devoted to the numerical analysis of the harmonic vibrations of laminate plates with viscoelastic layers in the von Kàrmàn geometrically non-linear regime. The amplitude equation derived in the prequel paper Part 1 – theoretical background is discretized using the 8-noded bi-quadratic plate finite elements. The response curves are obtained using the continuation method to solve the discretised amplitude equation treated as the equation with the frequency of vibrations as a parameter. The proposed method of solution is verified by comparing the results with those from available literature. Furthermore, several numerical analyses are performed, including testing of FE mesh density, plate aspect ratio, various VE materials, support conditions and layers layout as well as the possibility of simplification of the complex-valued zig-zag function used in the description of plate kinematics. Several results of practical importance are found and discussed in the conclusions. [ABSTRACT FROM AUTHOR]

The composite shell is one of the crucial components of solid rocket motors. Its design goal is to reduce the shell mass as much as possible while ensuring technical and cost requirements. This paper proposes a damage analysis method for the thin-walled composite shell secondary loading process based on a refined finite element model to verify the damage caused by the thin-walled composite shell secondary loading process and the performance decline of the shell and to assist in the lightweight design of the thin-walled composite shell. The shell's damage failure state and crack propagation path are analyzed by establishing the acceptable finite element model and introducing the damage failure criterion and the stiffness degradation model. Based on the model, the damage state of the shell during the secondary loading process is described, and it is determined that the re-loading has little effect on the blasting performance of the shell. For composite shells used in small quantities, the effects of damage due to initial loading can be of no concern during design. This method can provide a theoretical basis for thin-walled composite shell safety factor selection and damage state assessment to achieve the thin-walled composite shell lightweight design goal. [ABSTRACT FROM AUTHOR]

• The composite has a good energy dissipation characteristic. • The von Mises stresses on the skull are not enough to induce injury. • The Back Face Signature obtained are in line with standards. The research involved analyzing a material solution for a 9 mm Full Metal Jacket (FMJ) Parabellum loaded with ballistic impact on a resin laminate strengthened with extra aramid layers. The goal of this research is to determine the impact of material (aramid/DCPD) layer thickness on the energy absorption performance of the laminate for blunt trauma as blunt criterion (BC). For this purpose, aramid fiber laminate with dicyclopentadiene (DCPD) resin matrix was prepared. Laminate samples were tested on the drop test and were subjected to ballistic loads. The ABAQUS/Explicit program and finite element method were used to conduct the study. Individual material systems' optimal solutions were created using numerical analysis, and they were then classified using the mass-efficiency criterion. The numerical results were compared with the experimental using samples prepared according to the modeling methods. Selected results were shown and discussed in the later part of the paper. [ABSTRACT FROM AUTHOR]

Laminated composite structures, while offering weight savings compared with their metal counterparts, are susceptible to ply separation, (i.e., delamination mode of failure) due to the lack of through-thickness fiber reinforcements. In this paper, numerical simulations are used to gain an enhanced understanding of angled composite beam delamination when subjected to four-point bending consistent with the ASTM D-6415 test standard, with an expectation that the learning gained from this work is extensible to laminated composite components in general. While illustrating mesh sensitivity, manufacturing and frictional effects, four items of interest are examined: (1) the undamaged state/pre-peak load response, (2) the through-thickness peak tensile capability, (3) the post-peak load drop, and (4) the subsequent post-peak damaged response. A Finite Element Analysis (FEA) model is developed that incorporates the Smeared Crack Approach (SCA) to capture progressive failure modes within the element formulations directly, effectively eliminating the need for a priori specification of discrete delamination zones. The ability to incorporate failure directly within the element structure is particularly notable where laminates may not realistically permit a high number of interface layers or where geometry may be complex. Leveraging experimental data of curved composite laminates subject to four-point bending, the proposed approach successfully predicts the correct behavior throughout the damage progression. Additionally, this study offers an insight into effects of manufacturing-induced imperfections and frictions between the specimen and fixture on the prediction of inter-laminar strength of a curved composite part. [ABSTRACT FROM AUTHOR]

• The bird-strike experiments on various M40J CFRP laminated square plates were performed with a wide range of impact velocities. • Numerical predictions of the bird-strike tests by the Finite Element (FE) Models agreed well with the experimental results. • The numerical model was employed to obtain a ply stacking sequence optimal in anti-bird-strike stiffness by the global optimization method. In this paper the anti-bird-strike behavior of M40J 12 K/7901 carbon fiber reinforced plastic (CFRP) laminates was investigated numerically and experimentally. Gelatin artificial birds were used to perform the bird-strike tests on various M40J CFRP laminated square plates with a wide range of impact velocities. Ultrasonic C-scan was utilized to measure the damage of the tested plates. Finite Element (FE) Models were created to simulate the bird-strike tests and the numerical predictions agreed well with the experimental results. The threshold values of bird's impact velocity V 0 when fibers begin to break were studied for 4 types of plates under normal and oblique bird-strikes to evaluate the anti-bird-strike capability of the laminates. The fiber damage after a flock-strike of two small birds was then investigated and the results suggest that the investigation of one large bird strike is more convincing in qualifying the anti-bird-strike resistance than that of a flock-strike of two small birds. Finally, a ply stacking sequence optimization in anti-bird-strike stiffness was obtained by the global optimization method. [ABSTRACT FROM AUTHOR]

• Experimental longitudinal tensile stress–strain curves fluctuated obviously before final failure. • Micromechanical model considers the dispersions of fiber strength and spatial distributions. • Predicted stress–strain curves agree well with experiments in modulus, initial failure and final failure. • Simulations show the progressive failure process of fibers before the final failure of the unidirectional composite. Longitudinal tensile failure prediction has always been the focus of research on unidirectional (UD) Carbon Fiber Reinforced Polymer (CFRP). In this paper, the longitudinal tensile tests of unidirectional T800 grade carbon fiber reinforced epoxy resin composite were carried out first. The experimental stress–strain curves show that there are obvious progressive damages before the final failures of the specimens. However, this phenomenon is usually neglected in most of the existing investigations and tests to only obtain elastic modulus and ultimate strength. Thus, a Representative Volume Element (RVE) model based on micromechanics was established using finite element method, considering the randomness of fiber spatial distribution and fiber strength. The tensile strength of fiber monofilaments was assumed to follow a statistical two-parameter Weibull distribution. The failure process of UD composite under longitudinal tensile load was simulated by explicit finite element method. The stress–strain curves obtained by simulation are in good agreement with the experimental results. Finally, the influence of different boundary conditions on the calculation of the RVE was studied. It is found that the final failure strengths of the RVE with uniform displacement boundary conditions are similar to the case of periodic boundary conditions, while the former has higher computational efficiency. [ABSTRACT FROM AUTHOR]

• Two novel auxetic structures with different arrangements of a new enhanced trigram frame unit-cell were proposed. • The mechanical performance of the designed structures was evaluated through theoretical analysis, finite element simulation, and experimental tests. • Single and multi-objective optimization methods were implemented to optimize the geometry parameters of the selected auxetic structure. • The exceptional mechanical characteristics of the present proposed structures, surpassing previous designs in terms of stiffness and specific stiffness, highlight their tremendous potential for load-bearing applications. Superior stiffness is deemed essential for structures intended for several applications. The stiffness enhancement can be achieved by adopting structures that deform based on the stretching-dominated mechanism instead of the bending-dominated mechanism. This paper proposes a novel auxetic unit cell design and two distinct lattice structures dominated by stretching when subjected to quasi-static compressive and tensile loadings. The structures are manufactured via the fused deposition modeling (FDM) 3D printing method with the use of polylactic acid (PLA) filament as the patent material. The investigation also includes theoretical analyses and finite element (FE) simulations, all yielding consistent results. Response Surface Methodology (RSM) is also employed to understand the influence of three geometric parameters. Besides, single-objective optimization is conducted to maximize the stiffness through geometry design, and multi-objective approaches are implemented to improve the stiffness while simultaneously reducing relative density. Finally, different unit cells, which deform based on the stretching-dominated mechanism, are selected to represent their respective classifications, enabling a comparison of their potential stiffness capacity with the designed structures in this study. Remarkably, it is highlighted that the proposed unit cells and structures outperform others in terms of specific stiffness, making them a promising choice for use in structural engineering. [ABSTRACT FROM AUTHOR]

Macro fiber composites (MFCs) are widely used in various fields due to their excellent piezoelectric performance. This paper presents a novel method that combines analytical and finite element analysis to accurately model MFCs. The method iteratively calculates the nonlinear poling field generated by interdigital electrodes (IDEs), leading to reliable estimates of the local orientation and properties of the piezoceramic. The local poling state is then incorporated into a 3D representative volume element (RVE) model to determine the strain response of the device under realistic loading conditions. The influence of the poling voltages, piezoceramic fiber thickness, and IDE geometries on the poling and actuating performance of the device is studied. Furthermore, considering the complexity of the modeling the entire MFC device, a simplified method is further presented that is much more efficient and maintains the same level of accuracy. [ABSTRACT FROM AUTHOR]

Bending-active elastica beam is a structural configuration that is based on the elastic deformation of an initially straight beam. This deformation occurs when horizontal displacements are applied to a sliding support, causing the beam to bend into an arched shape. Previous research has focused on the stability of small-scale bending-active structures, thus not considering material strength, which is crucial in real-scale applications and structural design. This paper investigates the short-term structural behavior of bending-active elastica beams using pultruded glass fiber-polymer composite profiles, as used in real-scale structures. A series of short-term bending and service load application experiments were performed considering different bending degrees and loading scenarios. These results were used to validate finite element modeling. They demonstrated that steeper bent beams experience material failure, while shallower ones exhibit snap-through buckling. Material failure initiates on the tensile side of the beams, with cracks initiating at locations of maximum curvature. Higher bending degrees and symmetric loading result in higher maximum loads than lower bending degrees and asymmetric loading. A strain-based failure criterion, which can serve for structural design, is derived. [ABSTRACT FROM AUTHOR]

This paper presents the Green's Functions Stiffness Method (GFSM) for solving linear elastic static problems in arbitrary axially non-uniform Timoshenko beams and frames subjected to general external loads and bending moments. The GFSM is a mesh reduction method that seamlessly integrates elements from the Stiffness Method (SM), Finite Element Method (FEM), and Green's Functions (GFs), resulting in a highly versatile methodology for structural analysis. It incorporates fundamental concepts such as stiffness matrices, shape functions, and fixed-end forces, in line with SM and FEM frameworks. Leveraging the capabilities of GFs, the method facilitates the derivation of closed-form solutions, addressing a gap in existing methods for analyzing non-uniform reticular structures which are typically limited to simple cases like single-span beams with specific axial variations and loading scenarios. The effectiveness of the GFSM is demonstrated through three practical examples, showcasing its applicability in analyzing non-uniform beams and plane frames, thereby broadening the scope of closed-form solutions for axially non-uniform Timoshenko structures. [ABSTRACT FROM AUTHOR]

In this paper, crack growth in orthotropic materials subjected to dynamic loading is numerically studied using an adaptive phase-field method. The study starts with a coarse structured mesh and the adaptive refinement strategy based on a user-defined threshold on the phase-field variable is proposed for computational efficiency, and variable-node elements are employed to treat the hanging nodes as a result of local adaptive refinement. The Hughes-Hilbert-Taylor (HHT) time integration scheme is adopted for temporal discretization. The directionality of orthotropic materials is represented by a penalized second-order structural matrix, which is incorporated in the crack face energy density. Through numerical examples, the influence of the material orientation on the dynamic crack growth in orthotropic materials is studied and the reliability of the proposed framework is validated. • An adaptive PFM is proposed to simulate dynamic crack growth in orthotropic materials. • Time integration method HHT is combined with a staggered solving scheme. • A robust local adaptive refinement strategy is used based on a phase-field threshold. • Variable-node elements are used to overcome incompatibility in the refined mesh. • Performance of the proposed framework is demonstrated by numerical examples. [ABSTRACT FROM AUTHOR]

This work presents a novel numerical methodology to model the degradation and failure of composite materials like GFRP submitted to monotonic and high cycle fatigue loads. This is done by using the Serial–Parallel Rule of Mixtures homogenisation technique together with a proper mechanical characterisation of the constituent materials of the composite. This paper also proposes an efficient way of estimating the fatigue properties of each of the material constituents (fibre or matrix) to comply with the experimental results obtained at composite level; this enables to estimate the fatigue strength of any stacking/orientation of fibres with only one mechanical characterisation of the material properties. A comparison of the results obtained analytically and experimentally for GFRP is presented. The results show the applicability and accuracy of the proposed methodology in this field. [ABSTRACT FROM AUTHOR]

The ABD matrix is a fundamental method to characterize the overall stiffness behavior of laminated composite structures. Although classical laminate theory has been widely used, it has limitations in predicting the ABD matrix for woven composites. To address this issue, this paper presents a mesoscale homogenization approach aimed at computing the ABD matrix for thin woven composites accurately. The mesoscale representative volume element (RVE) of the woven composite is generated using TexGen and imposed with periodic boundary conditions to enforce the Kirchhoff thin plate assumption. The ABD matrix is computed by conducting six separate finite element simulations, each representing one simple in-plane or out-of-plane deformation in a specified direction. Moreover, to facilitate the implementation of the method, an open-source plugin tool was developed within ABAQUS CAE, automating the ABD matrix calculation for various types of woven composites including 2D weave, 3D weave, and multiaxial. The accuracy of the proposed method was validated through benchmark calculations against existing literature results. [ABSTRACT FROM AUTHOR]

As studies on the damage behaviors of composites during screw type blind riveting are notably absent, this paper seeks to fill this gap by combining experimental tests and numerical simulation methods. A three-dimensional finite element model was proposed, and the simulation results were obtained and validated by experimental data. The light microscope and scanning electron microscope were used to observe the stress state, axial deformation, damage modes, and damage distribution in two load-bearing regions at the initial contact and after installation. The results demonstrated that the preload showed a four-step "zero -steep rise -decline -steep rise" development during installation. The stress and deformation were concentrated in two circular zones, with the maximum axial stress component and deformation of 321 MPa and 0.046 mm, respectively. In two pressed zones, there were three failure modes, with out-plane matrix crushing being the most severe. In-plane matrix cracking damage is seen at a 45° direction in the first layer, with a damage index of 0.745. In addition, the effect of two geometric parameters of the sleeve on the blind head shape, load-bearing regions, and CFRP damage was investigated. The results would build confidence in reducing CFRP damage and enhancing joint integrity. [ABSTRACT FROM AUTHOR]

In three-dimensional problems, regular tetrahedron, pentahedron, and hexahedron elements are used in standard finite element software. In practice, however, the three-dimensional model is irregular. Traditional regular elements cannot accurately describe model structure. The field function integral accuracy of traditional displacement finite elements is low, and the number of elements considerably affects the integral results. As the number of elements increases, the computational efficiency decreases as well. Therefore, based on the hybrid stress element method, this paper proposes a new numerical calculation element for three-dimensional problems–a three-dimensional arbitrary polyhedron element. The corresponding calculation scheme is the 3-Dimensional Voronoi Cell Finite Element Method (3DVCFEM). This paper first verifies the effectiveness of the scheme. The stress field model with a singular solution is further simulated, and the change rule of the number of stress terms is obtained. On this basis, 3DVCFEM is introduced into calculating octree elements to solve complex classification problems and difficult calculation of octree elements. Moreover, the efficiency of the octree elements is investigated. [ABSTRACT FROM AUTHOR]

In this paper, a novel multiscale tri-level finite element (FE) numerical analytical method is proposed to study the mechanical performance of SiCp/CNT dual-scale hybrid reinforced aluminum matrix composite materials. The analysis is ranging from nano-scale CNT reinforcement to micro-scale SiCp particles to macro-scale composite systems. The microstructures of the CNTs and 6061Al matrix at the nano-RVE and the SiCp particles, interfaces, and 6061Al matrix at the micro-RVE are established. At the macro-scale, the structural model is established, whose elastic–plastic material properties and damage state are derived from the homogenization calculation of the representative volume element (RVE) at the micro-scale. Multi-scale progressive damage simulation of the macro-scale model is achieved by invoking the micro-scale and nano-scale RVE. The stress–strain curve of one finite element in the macro-structure model is randomly extracted and comparing it with the calculated micro-material-properties of SiCp (CNT)/ 6061Al, the good consistency verifies the effectiveness and accuracy of the multi-scale tri-level FE calculation method proposed in this paper. Using this multi-scale tri-level FE model, we can see the load-bearing and fracture process of the macrostructure, and the damage evolution process of the microstructure, which enables us to further carry out the research work of composite microstructure design, interface regulation, etc. [ABSTRACT FROM AUTHOR]

[Display omitted] • Hybrid densified wood-filled aluminium dowels have been developed and characterized through three-point bending tests. • The developed wood-filled aluminium dowels have been tested in context of slotted-in aluminium plate timber connections. • Confinement of wood into aluminium tube contains the brittle failure of wood and improves the ductility of the hybrid dowel. • Hybrid densified wood-filled aluminium dowels are potential substitute for conventional steel dowels in timber connections. • LS-DYNA and its MAT-143 are suitable to model the failure behaviour of the hybrid dowels. This paper deals with the finite element modelling of the structural response of timber connections assembled using a novel hybrid dowel, made of densified wood filled aluminium tube, for the first time. Predictive and comprehensive finite element models, using the LS-Dyna Software, are developed to thoroughly investigate the non-linear 3D mechanical behaviour and optimize the design of the aluminium-to-timber connections. The materials parameters of the models are, first, identified based on experimental data from three-point bending tests. Then the models are validated by comparison to experimental data from slotted-in aluminium plate timber connections assembled either using steel dowel or hybrid densified wood filled aluminium tube dowel. The results are compared in terms of load-slip curves as well as in terms of failure modes. In addition, a parametrical study is conducted using the validated finite element model to investigate the influence of some material and geometrical parameters. The results showed that the hybrid densified wood filled aluminium tube dowels can be a potential substitute for conventional steel dowels. The study highlights the efficiency of the proposed finite element model in terms of quality of results and efficiency of use upstream the design process of such structures. [ABSTRACT FROM AUTHOR]

The property measurement and structure optimization of composite materials are difficult topics due to the diversity of combinations of composite constituents and complexity of their application environments. The distribution of composite constituents and heat sources can cause heat aggregation phenomenon which may lead to failure of materials. In this paper, we first propose a deep learning-based surrogate model (DLBSM) which can quickly and accurately achieve the end-to-end prediction between the layout of composite materials under multiple heat sources and its temperature field. The prediction result depicts that the coefficient of determination for the maximum and average temperature of all cases exceeds 0.996. Then, the layout optimization is transformed into a combinatorial optimization problem, and the DLBSM is combined with optimization algorithm to optimize the maximum temperature, temperature gradient, and uniformity of the temperature field. The optimized maximum temperature and temperature gradient are significantly reduced, while the temperature uniformity is improved. These enhancements effectively reduce the probability of failure in composites. This approach can significantly improve the efficiency of thermal behavior prediction of composite and its layout optimization compared with finite element method (FEM). [ABSTRACT FROM AUTHOR]

• Mode II fatigue crack growth is characterized at the steel-to-composite interface. • Displacement and load controlled ENF and 4ENF test methods are compared. • Novel method is proposed to determine crack growth by shear strains from DIC. • Friction and geometrical non-linearity is considered by finite element models. In this paper, mode II fatigue crack growth properties of the composite-to-steel interface are characterised through different test configurations, namely ENF and 4ENF tests. Different loading types including force control and displacement control methods are compared. An innovative shear strain based method is proposed for monitoring the mode II crack growth at the bi-material interface through Digital Image Correlation (DIC). A 3D finite element model with Virtual Crack Closure Technique (VCCT) is built and used for obtaining the strain energy release rate (SERR) to investigate the effect of geometrical nonlinearity, friction at the interface and steel yielding, as well as to verify the mode mixity. The results show that the standard 3-point bending ENF specimen can be unstable under force control and sweeps narrow SERR range by a single test under displacement control. The 4-point bending 4ENF test shows stable crack propagation and clear SERR developing trend. More pronounced geometrical nonlinearity and friction effect exist for 4ENF test which can be considered when interpreting the Paris curves by a nonlinear finite element model. [ABSTRACT FROM AUTHOR]

This paper focuses on the vibration control of an L-shaped composite structure, which is a simplified part of the motor support structure in an electric airplane. NiTiNOL steel wire rope (NiTi-ST) is employed as the vibration control mechanism. The study begins with a natural frequency and modal analysis using the Rayleigh-Ritz approach, which is subsequently validated using finite element analysis and experimental hammering methods. The dynamical equations are derived through the Lagrange method and then discretized using the Galerkin truncation method (GTM). Vibration responses of the simplified model are obtained through the harmonic balance method (HBM), and these results are confirmed through validation with the Runge-Kutta method (RKM). Based on the theoretical analysis, the experiments are carried out to optimize the vibration control scheme of L-shaped composite beam. The results demonstrates that the NiTi-ST wire rope effectively controls vibrations without affecting the system's natural frequency. [ABSTRACT FROM AUTHOR]

This paper proposes a parameterized simulation framework for predicting the load-bearing capacity of 3D scarf-repaired composite laminates which remarkably reduces the modeling time from several hours to just a few seconds. The specific implementation is demonstrated through a detailed step-by-step explanation. The main contribution lies in: (1) By introducing a reusable geometric partitioning method for composite layers and implementing a partitioning method-based numbering scheme for element and node, the effective management of element and node IDs of elements and nodes in such complex 3D models is greatly facilitated; (2) By ingeniously combining open-source meshing tools and text rewriting techniques, a highly efficient approach has been developed to construct complete models for such structures, showcasing the remarkable potential of these existing techniques in this field. The reliability of the efficient parameterized simulation framework proposed in this study is verified through the comparison between strength values acquired from progressive damage analysis (PDA) and experiment data reported in the existing literature. [ABSTRACT FROM AUTHOR]

This paper extends sublaminate-based variable kinematics plate finite elements towards the buckling analysis of composite structures. Robust locking-free 4-node and 8-node interpolations are used to build the finite element matrices in terms of fundamental nuclei, invariant with respect to the employed kinematic model of the composite plate. Geometric nonlinearities are accounted for in the von Kármán sense. The classical linearized stability analysis is mainly conducted for sandwich panels, for which different kinematic assumptions are employed for the skins and the core. Global buckling of the sandwich panel as well as short-wavelength wrinkling of the skins are investigated by referring to a variety of case studies, including homogeneous and laminated skins as well as isotropic and orthotropic cores. Convergence studies are performed to establish the minimum number of elements for the local instabilities to be grasped. The proposed computational framework requires a simple 2D mesh and is capable of providing quasi-3D response patterns. This is as demonstrated by numerous case studies that address the transition from global to local buckling, the onset of wrinkling in flat sandwich panels with anisotropic skins under various loading conditions as well as the local face sheet instability occurring in sandwich panels working in bending. It is concluded that he proposed FEM-based tool is computationally efficient and can be advantageously employed in pre-sizing design phases without resorting to full 3D models. • Global buckling and wrinkling of sandwich structures is investigated. • Robust locking-free finite plate elements are implemented. • Reduced-order modelling strategies are assessed against 3D solutions. • Guidelines for determining effective computational models for wrinkling are proposed. • Skew wrinkling and one-sided wrinkling under bending are successfully computed. [ABSTRACT FROM AUTHOR]

The working environment of industrial fields where the Particulate Reinforced Composites (PRCs) are commonly used is complex. In these harsh environments, PRCs produce some nonlinear strains, such as plastic, thermal, and creep strains, which affect the performance of PRCs to some extent. In addition, the actual structure of PRCs contains a massive amount of inclusions, and the number of inclusions could reach the magnitude of millions or even tens of millions. For the large-scale numerical simulation of PRCs, ordinary displacement finite element requires a large number of meshes, which increases their computational complexity and unsolvability. For real PRCs with random particle distribution, homogenisation theory does not accurately capture the true state of stress concentration in PRCs. The Voronoi cell finite element method (VCFEM) can be a good solution to the drawbacks of the above two numerical simulation methods. The subject of the present work explores a modified complementary energy generalized function that takes the constitutive relationship of nonlinear strain into account, proposing a two-dimensional VCFEM, formulated with plastic, thermal, and creep strain. The simulation results are compared with the computed results of a commercial finite element software Marc to verify the validity and accuracy of the VCFEM. Results of the comparison show that the VCFEM has the advantages of simple meshing and faster computation under the same precision. The VCFEM, considering plastic, thermal, and creep strains proposed in this paper, lays the foundation for future large-scale numerical simulations of PRCs containing a large quantity of inclusion structures and can realistically capture the stress concentration state of PRCs. At the end of the article, the impact of the order of stress function on the calculation results is discussed. [ABSTRACT FROM AUTHOR]

• Investigating laminated glass failure under blast loading, optimizing accuracy and computational efficiency. • Hybrid techniques (FEM with erosion/deletion, SPH) yield optimal results for extreme loading. • Models replicate peak displacement, considering mesh distortion and energy dissipation. • Adaptive meshing crucial for accurate, homogeneous crack distribution in blast-loaded laminated glass. • Findings enhance understanding of laminated glass behavior, aiding protective structure design. Modeling laminated glass response to extreme loading scenarios is a computationally demanding process in designing and analyzing protective structures. Therefore, an optimal modeling scheme requires a delicate trade-off between accuracy and computational demand. This article investigates the failure modeling of laminated glass layups of thin and thick panels (three and 11 layers) under blast loading. This is done by implementing various simulation techniques: the finite element method with element erosion/deletion, the mesh-free method of smoothed particle hydrodynamics, and the hybrid implementation of mesh-based and mesh-free simulation through element conversions into particles. This Article examines the feasibility and limitations of each method, considering both the aspects of accuracy and computational cost in light of experimental testing results obtained from both arena and shock tube scenarios. Mesh sensitivity and the significance of adaptive meshing in capturing the fracture patterns are evaluated. The present paper suggests that using hybrid techniques leads to optimal modeling results. Furthermore, the stability of the modeling results under diverse blast conditions is verified. [ABSTRACT FROM AUTHOR]

This paper presents the coupling between curvilinearity and effective modulus for a set of mathematically admissible high-symmetry and low-symmetry fiber architectures. The contour of the fiber is decomposed into a series of unidirectional short segments, and its effective modulus is determined using an integration scheme that combines theoretical analysis and finite element simulations. Results show that the modulus of low-symmetry sinusoidal and hyperbolic tangent fibers varies nonlinearly with orientation and controlled by the segments forming the smallest direction cosine with the loading direction. Both the orientation of the midline and amplitude of the fibers strongly influence the effective behavior. For unidirectional fiber reinforced composites, results reveal the existence of a critical fiber-orientation angle of 60 ° where the modulus is minimum. Fibers are the majority stress carrier below 60°, and above this angle, the matrix carries the load. The integration scheme can be applied to determine effective modulus of composites comprising fibers of arbitrary geometries and orientations, and the findings are expected to advance the design of additively manufactured complex composite structures. [ABSTRACT FROM AUTHOR]

Safety margins of aerospace structures can be improved through altering the laminate parameters of composite materials to increase flutter and divergence velocities. Existing work demonstrates the impact of material uncertainties on low-fidelity structural models that are not sufficient to represent realistic aircraft designs. A gap exists in quantifying laminate parameter uncertainties on aeroelasticity for high-fidelity three-dimensional composite structures in realistic tailored designs. This paper puts forward an efficient methodology for uncertainty quantification on the aeroelastic characteristics of three-dimensional composite structures using FE-based parametric composite models and advanced Kriging surrogate models. The methodology is tested on both low and high fidelity case studies to represent the composite wing structure. Similarities between the case studies are observed in the coefficient of variance of all hard flutter modes being within 0.15-1.4% of each other. The difference was found for divergence and soft flutter velocities where the coefficient of variance could be over ten times higher in the high fidelity case. Global sensitivity results revealed similar physical behavior cases can be produced from both studies at early design stages. • Proposed method for UQ on aeroelastic qualities of 3D composite structures. • Effectively demonstrated methodology on low-fidelity plate composite model. • Effectively demonstrated methodology on high-fidelity Finite Element model. • Found strong agreement in uncertainty for hard flutter behaviour between studies. • Found low agreement in uncertainty for soft flutter & divergence between studies. • Most influential uncertain laminate parameters identified via sensitivity analysis. [ABSTRACT FROM AUTHOR]

Clamping anchorages are commonly used to anchor carbon fiber reinforced polymer (CFRP) plates, and the anchoring performance is significantly impacted by bolt preload. This research presents experimental and numerical investigations of long-term bolt preload relaxation in clamping anchorages for CFRP plates. First, a compression test was conducted to obtain the elastic modulus in the thickness direction of CFRP plates. Subsequently, four types of relaxation tests (single bolt, planar and curved anchorage, external load effect, and thickened anchorage) were conducted, considering the effects of the number of CFRP plates, anchorage type, external load, and initial preload. The elastic interaction during the tightening process was also investigated. The contact pressure distribution was simulated through the finite element method, which is in good agreement with the experimental results obtained from pressure papers. To fit relaxation test results and predict million-hour relaxation, different theoretical models were employed. The results indicate that the number of CFRP plates is crucial to preload relaxation, and the presence of CFRP plates introduces strong elastic interactions between bolts in the anchorage. Preload relaxation also increases under external loads and with the increase in initial preload. Curved anchorage has less bolt preload relaxation in the long term under external loads. Additionally, thickened anchorages have a more uniform contact pressure distribution due to the improved pressure diffusion mechanism. [ABSTRACT FROM AUTHOR]

This paper presents an experimental and numerical study of the failure phenomenon of compressed composite top-hat (CFRP) columns with three different lay-up arrangements of the composite. The research was conducted both experimentally on physical structures and numerically based on advanced numerical models (based on the finite element method – ABAQUS® program). The research was conducted especially in the range of failure of thin-walled structures, with capturing the phenomena directly accompanying the loss of load-carrying capacity: damage initiation and evolution, as well as delamination. As part of the experimental study, the course of a time-shortening (universal testing machine) and acoustic emission signals were recorded (AMSY-5), allowing for an in-depth evaluation of the failure. Numerical simulations were conducted using independent failure models - progressive failure analysis (PFA) and cohesive zone model (CZM). This approach allowed for a comprehensive assessment of the failure phenomena, both in the context of the analysis of phenomena contributing to the loss of load-carrying capacity of the structure, as well as the delamination phenomenon. The main objective and novelty of this paper, was to compare the test results for three different composite lay-ups, in the context of failure studies. The research conducted in this paper on composite profiles with open sections, is a prelude to the research from the project from the National Science Centre (Poland) No. 2021/41/B/ST8/00148 on composite profiles with closed sections. In this paper, a preliminary methodology is presented for the realization of the research to be carried out on profiles with closed sections. [ABSTRACT FROM AUTHOR]

This paper presents an experimental and numerical study of the failure phenomenon of compressed composite top-hat (CFRP) columns with three different lay-up arrangements of the composite. The research was conducted both experimentally on physical structures and numerically based on advanced numerical models (based on the finite element method – ABAQUS® program). The research was conducted especially in the range of failure of thin-walled structures, with capturing the phenomena directly accompanying the loss of load-carrying capacity: damage initiation and evolution, as well as delamination. As part of the experimental study, the course of a time-shortening (universal testing machine) and acoustic emission signals were recorded (AMSY-5), allowing for an in-depth evaluation of the failure. Numerical simulations were conducted using independent failure models - progressive failure analysis (PFA) and cohesive zone model (CZM). This approach allowed for a comprehensive assessment of the failure phenomena, both in the context of the analysis of phenomena contributing to the loss of load-carrying capacity of the structure, as well as the delamination phenomenon. The main objective and novelty of this paper, was to compare the test results for three different composite lay-ups, in the context of failure studies. The research conducted in this paper on composite profiles with open sections, is a prelude to the research from the project from the National Science Centre (Poland) No. 2021/41/B/ST8/00148 on composite profiles with closed sections. In this paper, a preliminary methodology is presented for the realization of the research to be carried out on profiles with closed sections. [ABSTRACT FROM AUTHOR]

[Display omitted] • The building of aircraft wing shape structures made of advanced materials by an analytical approach. • The effects of the change of the aircraft wing shapes, materials factors and thermal environment are considered carefully. • The stable and chaotic states of structures are scrutinized through numerical and graphical results. A new approach for airplane wing shapes is found in this study with an analytical method. The paper studies the dynamical characteristics of aircraft wing plates using boron nitride nanotube (BNNT) reinforced for aluminium. The distribution of reinforcements through the thickness of the plates is considered to be uniform and functionally graded. The plate profile is defined in terms of a rectangular plate, in which an edge following a function is introduced according to arbitrary functions such as linear, circular, or hyperbolic functions. Equations of motion using geometric nonlinearities defined by von Karman-Donnell and theory of elasticity with applying Galerkin's method is used to obtain the dynamic and chaotic properties of the structure. The achieved results are validated with the previous documents and the finite element analyses (FEA) for fundamental frequencies to confirm the accuracy and reliability of the calculation method in this paper. The influence of the thermal environment, the volume of BNNT, the distribution pattern of reinforcement, as well as geometrical parameters are scrutinized in this paper. The research results show the superior properties of BNNT materials in reinforcing aircraft wings. [ABSTRACT FROM AUTHOR]

Buckling resistance of variable stiffness composite (VSC) plates can be significantly improved by designing fiber orientation distributions, which affect structural stiffness and stress distribution. In this paper, a meshless model of VSC plates is developed using a radial basis point interpolation method (RPIM) based on the naturally stabilized nodal integration (NSNI) scheme, and the buckling behavior of the VSC plates with elliptical cutouts is investigated. In this model, a set of nodes is used to discretize the problem domain, which makes the loading response of the VSC plates can be calculated by its exact fiber angle. And the mechanical behavior of the VSC plates with various complex geometries and cutouts can be accurately simulated. This meshless method is verified by comparing with the finite element method (FEM) and semi-analytical solutions. And compared with the traditional RPIM based on the Gaussian integration (GI), NSNI-based RPIM achieves considerable enhancement in computational efficiency while maintaining high accuracy. Employing this efficient meshless method, the buckling behavior of the VSC plates with elliptical cutouts for different boundary conditions is studied. And the effects of size and location of the cutout on the buckling response of the VSC plates are analyzed. The research on the VSC plates with cutouts in this paper has practical implications for the design of cutouts for VSC plates and provides a new method for the numerical research of VSC plates. [ABSTRACT FROM AUTHOR]