Search

• Accurate prediction of tape-spring folding behavior with new analytical model. • Proposed model outperforms classical models in predicting peak and steady-state moments. • Stretching and bending strain energy studied and analyzed during folding process. • Three key geometric parameters identified for optimizing tape-spring design. The tape-spring is widely used in aerospace, mechanical, and civil engineering due to its unique mechanical properties and compact size. This paper aims to establish a new analytical model to more accurately predict the folding behavior of the tape-spring, including the geometric configuration, folding moment versus longitudinal curvature curve, peak moment, and propagation moment. This model comprehensively considers the influence of stretching strain energy and bending strain energy on the total strain energy, and determines the folding behavior of the tape-spring through the minimum energy principle. The proposed analytical model was compared with Wuest's model, Yee's model, and Yao's model. Experiments of tape-springs made from two different materials were utilized for validation. The study shows that the proposed model has the highest prediction accuracy compared with the classical models, with the error of approximately 10%. The reason for the significant difference in the prediction results between the proposed model and Yao's model was given, and the relationship between stretching strain energy and bending strain energy during the folding process of the tape-spring was analyzed. The proposed model has broader applicability than classical models and provides new insights and solutions for accurate prediction of the folding behavior of the tape-spring. [ABSTRACT FROM AUTHOR]

Metallic lattice structures are garnering increasing attention across various research domains for their potential to create lightweight yet high-strength solutions. Their appeal largely stems from a range of beneficial attributes, including their low weight, substantial specific strength and stiffness, and superior energy absorption qualities. These characteristics have facilitated their widespread use in industries like aerospace, shipping, defense, and automotive, particularly in scenarios demanding weight minimization, multifunctionality, and enhanced safety in intricate environments. The mechanical properties of these structures are, therefore, of paramount importance. This paper offers an exhaustive review and synthesis of existing research approaches, production techniques, and evaluations of both static and dynamic mechanical properties associated with metallic lattice structures. It starts by delineating the various types and manufacturing methods, followed by an analysis of factors impacting their mechanical properties. The paper concludes by exploring prospective research avenues concerning the static and dynamic mechanical performance of metallic lattice structures. [ABSTRACT FROM AUTHOR]

Since carbon fiber woven composite panels contain complex fiber bundle structures, the aim of this paper is to investigate the factors influencing the macro-equivalent properties and topological flexibility of composite panels resulting from variations in fiber bundle configuration. Firstly, the structural topology optimization design of carbon fiber composite plates was achieved using a multi-scale modeling approach with the variable density method. Nonlinear relationships between carbon fiber bundle configuration parameters and macroscopic equivalent properties, as well as macroscale topological flexibility, were determined using deep learning methods, respectively. The maximum error in the predicted values of the deep learning network model does not exceed 0.5% when compared with the results of the finite element calculations. In addition, utilizing deep learning networks to predict macro-equivalent properties of composites can significantly decrease computational time. The impact of varying the number of filaments in fiber bundles and the spacing of the fiber bundles on the flexibility of the topology was determined using a deep learning network. The optimal topological flexibility, along with its corresponding fiber bundle spacing and number of fiber bundle filaments, are globally searched within the design domain using an adaptive genetic algorithm. The study in this paper can provide a reference for designing fiber bundle configurations of composites for practical applications. [ABSTRACT FROM AUTHOR]

• The cohesive bond model demonstrates good agreement with experimental results. • Significant dynamic enhancement occurs at the concrete-CFRP strip interface during blast loading. • Blast wave propagation induces interface damage between concrete and CFRP strip. • A dynamic increase factor (DIF) is necessary for modelling CFRP-concrete interface behaviour under blast loading. The paper is structured into two main sections. In the first part, the focus is on the finite element (FE) analysis of bond slip in a single bond shear test between concrete and carbon fiber reinforced polymer (CFRP) strips under static loads. To model the test set-up, a plastic damage material model and an elastic material model are used for the concrete prism and the unidirectional CFRP strip respectively. Three approaches, including a perfect bond model, a cohesive bond model, and contact algorithms based on recent bond slip models, are employed to simulate the bond interface. The numerical model's validity is confirmed through comparison with experimental results from the literature. The paper predicts the debonding failure mode, the strain evolution along the bond length, and the delamination loads of the CFRP strip. The cohesive bond model exhibits good agreement between numerical and experimental data. In the second part of the paper, the developed FE model is tested under blast loading and compared to the experimental results of the blast tests conducted by the authors. The experimental and numerical findings highlight a significant dynamic enhancement effect on bond-slip properties due to the propagation of the blast wave within the concrete and the high loading rate. [ABSTRACT FROM AUTHOR]

Accurately predicting Cure-Induced Distortion (CID) is paramount to ensuring manufacturing precision. Existing prediction models heavily rely on material parameters associated with the CID, which presents challenges for newly developed composites due to the time-consuming, expensive, and limited accuracy of parameter characterization processes. With recognizing the shared curing mechanism across various composites, this paper introduces a transfer learning-based approach that leverages a small dataset of practical CID data from the newly developed composite and historical knowledge from existing composites to achieve rapid and accurate CID predictions. This approach was validated for two typical CID prediction cases by implementing a transfer learning framework, and various sampling methods were explored to assess the stability and repeatability of prediction results. The results indicate that the proposed method can predict the CID within a 5% margin of error. This paper offers a promising approach for predicting CID in the design and manufacturing processes. [ABSTRACT FROM AUTHOR]

Space debris is a major threat to the safety of spacecraft in orbit, and advanced protective materials with lightweight and high impact resistance are effective passive protection solutions. In order to investigate the hypervelocity impact protection performance of aluminum matrix ceramic ball composite materials plate, this paper has carried out the hypervelocity impact test of aluminum matrix ceramic ball composite materials plate, and verified the accuracy of the numerical model based on the FE-SPH adaptive method, and then carried out a comparative study on the hypervelocity impact protection performance of aluminum plate and aluminum matrix ceramic ball composite materials plate with the same area density. The results show that: compared with the aluminum plate conditions, the composite materials plate has a better ability to broken the projectile. Compared with the aluminum plate, the kinetic energy absorbed by the composite materials plate is increased by 37.04%, and the kinetic energy of the generated debris cloud decreased by 69.57%. The proportion of the internal energy dissipation of the composite materials impact system reaches up to 72.03%. The secondary pollution generated by the composite materials plate is less and the hazardous debris have less threat to the rear wall. The research in this paper can provide reference for the selection of hypervelocity impact protection materials. [ABSTRACT FROM AUTHOR]

Auxetic materials are attracting increasing interest due to their extraordinary or even abnormal mechanical properties. Different from the traditional truss-lattice structures, this paper proposes a series of novel auxetic plate-lattice structures with an excellent auxetic effect. Utilizing a dual-materials glue-free assembly design involving hyperelastic and plastic materials, these plate-lattices exhibit numerous advantages such as disassembly, assembly, replacement, recyclability, reusability, excellent energy absorption, high specific stiffness, and impact resistance performances. Quasi-static/dynamic tests and simulations are conducted to assess mechanical properties, including elastic constants, deformation modes, and mechanical responses. Simultaneously, the effect of the principal geometric parameter, concave angle, on the structural response was analyzed with various impact velocities. Findings suggest that the concave angle influences the structural elastic constants under compressive loading. The stress–strain response exhibits a distinct dual-plateau phenomenon. Taking the A65 (concave angle is 65°) configuration as an example, the stress on the second plateau is approximately 2.7 times that of the first plateau, significantly enhancing the structure's energy absorption capability. Under dynamic impact loadings, different configurations and varying impact velocities affect the structure's energy absorption performance. This paper introduces a series of assemblable plate-lattice structures with an auxetic effect, offering design insights and guidance tailored to the convenient transportation, unconventional structures, and rapid assembly needs of lightweight, impact-resistant mechanical metamaterials. [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]

The aim of this paper is the multiscale investigation of composite pressure vessel structures wound with varying fibre tension. The paper explores the potential of "programming" the fibre tension force during the winding process of a high pressure hydrogen storage vessel. Two series of vessels were wound with two different tensions: Two series of vessels wound with forces of 3 N and 80 N respectively were experimentally investigated. Other technological factors, such as the type and weight of carbon fibre used, were kept constant throughout the study. Quasi-static burst tests were used to measure the elastic deformation of the vessel surface. Microscopic studies were also carried out to analyse the structure of the composite at different length scales. The fibre content, the geometric parameters of the voids and the distribution of the three main components of the composite – carbon fibre, technological defects and resin – were also determined. Representative RVE elementary cells were generated for both materials using statistical modelling. The composite was then homogenised and elasticity matrices were obtained for the fibre tensile forces in both materials. [ABSTRACT FROM AUTHOR]

This paper presents an extensive experimental performance study of bonded joints (BJs), only bolted joints (OBJs) and hybrid bonded-bolted joints (HJs). For each joint type, three test configurations are considered: namely, short, medium and long overlap lengths. In each case, the adherends comprise quasi-isotropic twill woven CFRP. For each joint type/overlap length combination, three specimens are tested for statistical representation. HJs demonstrate 1.4, 1.5 and 1.5 times higher failure load and 1.5, 1.6 and 1.9 times higher stiffness than OBJs, for short, medium and long overlap, respectively. In all test cases, HJs outperform BJs except for short overlaps where BJs outperform both HJs and OBJs. OBJs perform poorly in terms of failure load and Hooke's stiffness. Nevertheless, due to bearing deformation at bolt hole locations, OBJs experience higher failure displacements than BJs and HJs leading to a desirable energy absorption mechanism compared to HJs and BJs. This is thanks to the bearing failure mode of the joint despite much lower failure load in OBJs. It was found that increasing the overlap length generally benefits BJs. However, for medium length overlap specifically, HJs show better performance than BJs. Stress–strain behaviours show a linear behaviour for all test groups with significant joint rotation for OBJs compared to BJs and HJs. Failure mechanism studies presented in the paper show that BJs fail in cohesive failure mode for all test groups. OBJs fail in bearing mode, which is followed by net tension failure. OBJs experience matrix cracking and delamination at bolt hole locations. On the contrary, HJs experience considerably less bearing failure at bolt holes due to the load bearing contribution from the adhesive. [ABSTRACT FROM AUTHOR]

This paper introduces quasi-periodic homogenization schemes for quasi-periodic media, those without strict periodicity, but that can be mapped to a parent periodic medium. Quasi-periodic homogenization relies on the conceptual idea of mapping a non-periodic domain to a reference periodic one through a point mapping of material points within the domain of an identified repetitive unit cell. The theoretical background of quasi-periodic homogenization introduced in the first part of this paper relies on expressing the microscopic position of micropoints within a physical unit cell as a sum of the macroscopic position (the center of area of the unit cell) and the relative position of micropoints with respect to the center of area. This decomposition parameterized by the small-scale parameter entails a corresponding additive decomposition of the tangent map defining the geometrical transformation of the periodic UC into the quasi-periodic one in terms of an additive decomposition into macroscopic and microscopic contributions. The quasi-periodic homogenized effective moduli are then determined, starting from the average of the microscopic energy, those being expressed in terms of the periodic moduli and a perturbation term, both expressed in a volumetric format as surface integrals over the reference unit cell domain in a 2D context. In the second part of this contribution, a surface formulation of the quasi-periodic moduli is derived, based on the notion of shape derivative of the total potential energy stored within the unit cell. This approach relies on introducing a shape velocity field at the boundary of the periodic unit cell to change its design, driven by the normal projection of Eshelby stress onto both the internal and external boundaries of the unit cell. This second scheme offers comparatively to the first one a simpler way to compute the quasi-periodic moduli as it only requires the evaluation of the mechanical fields on the unit cell boundaries. Application of the proposed homogenization schemes are done for inclusion-based composites, underlining the importance of strain gradient energetic contribution in the situation of a micrograding of the unit cell geometry. [ABSTRACT FROM AUTHOR]

[Display omitted] • Honeycomb panels with discrete arranged block reinforcements were numerically designed. • The elastic moduli of the new honeycomb panels are higher than those of heavier panels with slatted. • Tables with new cellular panels are characterized by a stiffness of 85 % of the stiffness of heavier tables with slats. Furniture manufacturers indicate they know the benefits of lightweight honeycomb panels but still expect their higher mechanical properties. This work presents a numerical and experimental approach to designing new tables manufactured of paper honeycomb panels with discreetly arranged reinforcing blocks in the core. The main goal was to determine whether the discrete arrangement of the blocks affects the strength and amount of energy absorbed by the newly designed tables and stiffness of honeycomb panels. Optimization reduced the weight of the panels by up to 30 %. At the same time, their linear elastic modulus was increased from 1579 MPa to 1771 MPa. After ten load cycles, tables with discrete reinforcements have a stiffness up 86.85–87.20 % of the stiffness of the reference table. After destructive tests up 89.96–91.16 %. Ultimately, the test results demonstrate the effectiveness of replacing wide slats with discreetly placed reinforcing blocks in the core structure. [ABSTRACT FROM AUTHOR]

This paper investigates the effect of compaction and curing states on the mechanical properties and void content of AFP-manufactured laminates. For the mechanical characterization, tensile tests, 4-point-bending tests and interlaminar shear strength (ILSS) tests were applied. The internal structure was evaluated via micro CT. For the surface structure evaluation, an optical profilometer was used. The void content was determined via segmentation of the micro CT images. The paper is subdivided into the description of the applied materials and methods, the results and their discussion and a conclusion. The study showcases the potential of AFP-manufactured aerospace composites to attain high-quality results even without the need for an autoclave, making them well-suited for unmanned applications. [ABSTRACT FROM AUTHOR]

• A highly efficient and exact search algorithm of inter-fiber fracture criterion is proposed. • A progressive damage model considering fracture toughness is promoted. • Experimental and simulation data proved the accuracy of the proposed model. This paper presents a quick search algorithm of the fracture angle of inter-fiber fracture (IFF) criterion and a progressive damage model considering the dynamic fracture toughness effect. The fracture angle determination of the IFF criterion is necessary and time-consuming, which has limited its practicality. Therefore, to accurately calculate stress exposure factors under various combinations of stress states, a highly efficient algorithm is needed. In this paper, a novel algorithm using stress tractions on the fracture plane and the golden section search (GSS) is promoted. Through a series of simulation tests, this novel algorithm has been proven to be exact and efficient compared with other two common algorithms, which saves an average of 63.2 % and 28.1 % of the time in 1 million calculations and 2 h 2 min 4 sec and 39 min 2 sec in simulations. Additionally, fracture toughness, which controls material damage evolution process, also has strain-rate effect like elastic modulus and strength. Hence, a new progressive damage model considering the dynamic fracture toughness effect is proposed. The results of dynamic compression and ballistic impact tests and simulations demonstrate the fidelity of the novel damage model. [ABSTRACT FROM AUTHOR]

A unique strategy of low-frequency wideband vibration control by harnessing the concept of feedback control between the piezoelectric bimorph sub-cells which are acting as sensors and actuators is conceptualized in this paper. In the unit cell, voltages from the sensing bimorph are fed back to actuate another bimorph through operational amplifier-based gain circuits. The prime novelty of the paper is the non-trivial formulation of the spectral element of the non-reciprocal piezoelectric beam (NRPB), having electro-mechanically coupled sensing and actuating bimorph in the unit cell, derived from the exact solution of the governing differential equations. The analytical formulation employing the spectral element method enables the elementary assembling of the NRPB units to simulate different boundary conditions and various configurations arising due to the alteration of the position of the sensing and actuating bimorph. The direct frequency responses for various configurations are obtained for a cantilevered and a simply-supported beam with varying feedback gain. The feedback gain induced damping to the system, hence sharp peaks and drops are flattened. Most promisingly, the amplitude of the displacement response for the entire frequency range can be brought down below its corresponding static deformation with the application of positive gain for certain configurations. Hence, the proposed system could potentially be used for application in the field of vibration and acoustics. • Emergence of superior vibration control by non-reciprocal piezoelectric beam (NRPB). • Realization of the constant gain sensing and actuating piezo bimorph via an electrical circuit. • Spectral element formulation for the complete NRPB, including actuating cell. • Ultra-wide bandgap starting from very low frequency. [ABSTRACT FROM AUTHOR]

Bistable laminates have attracted considerable interest among researchers as prospective candidates for delivering exceptional performance within the domain of morphing structures. These laminates exhibit a distinctive characteristic of featuring two stable states, sustaining their configuration until the application of a critical force that triggers a transition to their second stable position. Before discussing the practical applications involving bistable composite laminates, this paper presents analytical modeling for predicting the room-temperature shape and simulating the snap-through phenomena. The main aspects of the room-temperature shape simulation are discussed, and various snap-through triggering methods are shown. At this point, the paper focuses on a comparative analysis of numerical predictions in contrast to experimental data aimed at discerning the reliability of existing models. Furthermore, this paper not only elucidates existing challenges but also delineates potential avenues for future research. As the investigation into bistable composites progresses from comprehending intrinsic phenomena to practical, real-world applications, this study outlines both the present and potential future research concerning bistable composite laminates. [ABSTRACT FROM AUTHOR]

• This paper provides insight into the conventional methods for predicting critical buckling loads of pultruded FRP columns. • A comprehensive test database of 365 for global flexural buckling of pultruded FRP struts is proposed. • Based on the machine learning algorithm and the database proposed in this paper, the critical load of pultruded FRP struts is predicted. Pultruded fiber-reinforced composites (FRP) are widely used in structural engineering due to their excellent properties along the fiber direction. Its global buckling performance has received increasing attention from academia and engineering. This paper reviews the prediction methods for the critical buckling load of pultruded FRP struts, including the Euler formula critical load prediction method, the shear-corrected critical load prediction method, the Southwell plot method, and the critical load prediction method based on the strength failure mode. Summarizes the basic principles of each method, discusses the internal relationship and difference of each method, and analyzes the critical factors of each method with experimental data. In addition, a unified generalized Ayton-Perry theoretical model is proposed through induction and summary. Finally, based on the experimental database, a Machine learning model for predicting the buckling critical load is established. The results show that the machine learning algorithm can predict the buckling critical load with high prediction accuracy. [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]

• Investigates the mechanical performance of sandwich beams with PET FRP facings and recycled PET cores. • Examines two types of PET FRP facings with bio-resin and partial bio-resin matrices. • Compares mechanical properties of beams with recycled PET honeycomb and foam cores. • Analyzes parameters like core type, thickness, orientation, and facing thicknesses. • Provides experimental data validated by finite element modelling, aiding sustainable construction practices. The objective of this paper is to assess the mechanical performance of new forms of sandwich beams predominantly comprised of recycled plastic polymers. These beams feature two types of polyethylene terephthalate (PET) fiber-reinforced polymer (FRP) facings: one with a bio-resin matrix and the other with a partial bio-resin matrix. The core of the beams is a focal point of the study as well, comprised of recycled PET (R-PET). Fifteen different types of sandwich beams were tested, with three identical specimens from each type, totaling 45 beams. Each beam, measuring 240 mm in length, was fabricated and categorized based on its core composition: either an R-PET honeycomb or an R-PET foam core. The study investigated key parameters including the core type (honeycomb or foam), core thickness (12 mm or 15 mm), core orientation, and facing thicknesses (1 mm or 2 mm). The mechanical testing of these beams involved a four-point bending setup to assess their flexural performance. This included analyzing mid-span load–deflection, moment–curvature behaviours, and changes in tension and compression strains in the facings during bending. The results demonstrated that core density, type, and facing thickness significantly impact the beams' stability and failure modes. High-density foam cores primarily failed through core shear, while lower density cores showed both core shear and wrinkling, dependent on facing thickness and core type, highlighting the complex influence of material properties on structural behaviour. A finite element (FE) model was developed to verify the experimental findings, effectively corroborating the test results. The research data is intended as a reference for structural designers seeking to incorporate sustainable alternatives into traditional building materials, thereby promoting a more environmentally conscious approach within the construction industry. [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]

In this paper, the effect of intra-yarn fibre hybridisation on the homogenised elastic properties and micro- and meso-scale matrix stress fields in 2D woven composite laminae (i.e. plain, 2/2 basket, 2/2 twill and 5-harness satin) is studied with a two-scale homogenisation scheme—employing a representative volume element model at micro-scale and a repeating unit cell model at meso-scale. The study is focused on S-glass/polypropylene/epoxy woven laminae with intra-yarn fibre hybridisation. A modified random sequential expansion algorithm generates microstructure for the micro-mechanical model, and a periodic meso-structure is used to generate the weave architecture for the meso-mechanical model. Both models are verified using analytical models. It is found that intra-yarn fibre hybridisation can significantly alter the homogenised properties as well as the micro- and meso-scale matrix stress fields—depending on the degree of hybridisation (i.e. the combination of S-glass and PP fibre volume fractions). Moreover, the homogenised lamina properties are found to be less sensitive to weave architecture and yarn thickness, but more so to the degree of intra-yarn fibre hybridisation, yarn width and yarn spacing. It is shown that the lamina properties can be tailored, and the micro- and meso-stress fields can be manipulated, by intra-yarn fibre hybridisation and weave architectures. [ABSTRACT FROM AUTHOR]

Reinforced glass beam (RG beam) is a type of structural glass member that has been developed in recent years. This RG beam consists of a glass beam to which reinforcement material, such as steel, is adhesively attached in the tensile side to improve crack resistance. The adhesive plays a critical role in the structural performance of RG beam. However, the effect of non-linear shear-slip behavior of the adhesive layer remains unclear and has been neglected in most previous studies, which can result in inaccurate estimations. To address this issue, this paper presents a finite difference model (FDM) that utilizes an explicit step-by-step method and trial-and-error iterative method for interfacial stress analysis. The model predicts the static structural response of a simply-supported RG beam that simulates the adhesive with non-linear stress-slip behavior. Furthermore, the model describes the adherend's shear deformation in elastic. The FDM results are then compared with the finite element method (FEM), adopting discrete nonlinear connectors (springs) to simulate the adhesion, and available analytical methods. Detailed parametric studies are further conducted to investigate the influences of glass strength, load pattern, reinforcement ratio and height-to-span ratio for proposing design recommendations. [ABSTRACT FROM AUTHOR]

• A new silica/phenolic pyramidal lattice reinforced silicone rubber based ablative material composite structure is proposed. • The lattice enhances the high-temperature stiffness of ablative materials dramatically. • Effects of geometrical parameters and heating rates are obtained. Besides aerodynamic heating, ablative materials are always exposed to aerodynamic pressure. This paper proposes an effective method to improve the high-temperature compressive performance of silicone rubber based ablative materials using silica/phenolic pyramidal lattice. Composite structures of silica/phenolic pyramidal lattice reinforced silicone rubber based ablative material were fabricated and tested with the high-temperature material testing machine. To determine the stiffness of lattice reinforced ablative materials at different temperatures, a theoretical model was developed and validated by comparison with experimental results. Results show that silica/phenolic pyramidal lattices can significantly improve the stiffness of ablative materials at high temperatures. The changes in the stiffness of ablative materials reinforced with silica/phenolic pyramidal lattices at high temperatures can be divided into four stages. The composite lattice has a reinforcing effect on the mechanical properties of ablative materials up to 1000 °C, with optimal enhancement observed at 681 °C. Furthermore, the effects of geometrical parameters of the lattice and heating rates on stiffness at high temperatures are also discussed. [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]

Although honeycomb is a kind of lightweight structural material with great potential, its specific strength is not always able to meet the requirements, especially in the weight-sensitive field. Inspired by the bionic idea of cuttlebone, the curved-wall configuration design is proposed to strengthen the buckling impedance of honeycomb, which can effectively prevent the premature occurrence of buckling failure mode induced by thin walls. Compared with the straight-wall honeycomb materials of the same geometric size, the probability of buckling failure in curved-wall honeycomb materials proposed in this paper is reduced by more than 22 %. Moreover, to achieve the preparation of curved-wall configuration, a processing strategy that uses stretching process to prepare ultralight carbon fiber honeycomb (Carbcomb) material is firstly introduced. Compared to the Hexcel Corporation's aluminum honeycomb with a density of 21 kg/m3, for the Carbcomb, the specific compressive strength and specific shear strength along both the L and W directions respectively improved by 57 %, 61 % and 77 %. In addition, the minimum density of fabricated Carbcomb (14.6 kg/m3) is less than that of the Hexcel's products (16 kg/m3), and the research findings fill the gap of the carbon fiber honeycomb material in low density areas (10 ∼ 30 kg/m3). More importantly, this process which does not require much manual operation can effectively avoid the problems of unstable mechanical properties, difficult mass production and high preparation cost of the existing carbon fiber structural parts. This curved-wall configuration design and fabricated approach widens the potential of carbon fiber honeycomb as a structural material, and makes it possible for lower cost and higher efficiency in aerospace and transportation applications. [ABSTRACT FROM AUTHOR]

• A molecular simulation method to analyze deterioration mechanism of carbon fiber/matrix interface in humid environments is developed. • The decrease of interfacial interaction energy, the increase in hydrogen bonds between water and interface, and anomalous diffusion of water together lead to interface deterioration. • The moisture resistance of modified interface by distribution function and diffusion coefficients of water molecules is elucidated. Extended exposure to moisture could harm the carbon fiber/matrix interface, threatening CFRP's reliability service. This paper introduces a method that develops molecular dynamics models to analyze the deterioration of the interface and the influence of the silicon coupling agent. The mechanical properties of the interface in humid environments are obtained through simulations. The interfacial shear strength decreases by 25.68% and 26.96% respectively, demonstrating good consistency between experiment and simulation. The free volume and water distribution function characterize the extent of interface deterioration under varying moisture levels. The water molecules weak interface interactions through hydrogen bonding, leading to abnormal swelling of nanoscale structure. This inhibits the stress transfer between the fiber and matrix, weakening the interfacial shear strength. Additionally, the silane coupling agent reduces the pathway for water transmission, diminishing water diffusion. It can enhance the water damage resistance capability of interfacial strength. [ABSTRACT FROM AUTHOR]

Increasing throughput in wind turbine blade production can be achieved by separately manufacturing pre-shaped binder-stabilised dry preforms, and subsequently placing them in the blade mould. To avoid manufacturing defects, a trade-off between the formability and the handleability of the preform is necessary. In this paper, an experimentally validated preform model is used to study how variations in material properties, tool geometry, and placement tolerances influence defect generation. The results from three studies are presented. In the first study, a preform is formed over a ramp transition with variations in geometry. The results from this study indicate that a short ramp promotes transverse shearing of the preform. In the second study, the material properties of the preform are varied. The results indicate that a high mode I cohesive law of the binder and a high bending stiffness of the fabric promote transverse shearing and remove wrinkles. In the last study, placement tolerances for a pre-shaped preform are studied. The results show that if the preform can shear between the preform edge and the tool edge, it can conform to the mould even with large placement offsets. Process engineers and blade designers can readily use these results to help reduce forming-induced wrinkles. [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]

Fiber-reinforced plastic sandwich structures (FRPSSs) are increasingly used in marine applications thanks to their high levels of stiffness, lightweight, buoyancy and damage resistance to penetration and impacts. This paper investigates the effect of exposure to seawater conditions on mechanical behavior of FRPSSs with various core configurations loaded with indenters with different geometries. A new in-situ acoustic emission (AE) methodology is applied to monitor the moisture evolution process, while X-ray micro-computed tomography validated its influence on out-of-plane failure modes observed in quasi-static indentation experiments. Results indicate that AE velocity can effectively monitor the moisture uptake, serving as an in situ structural health monitoring approach. It was also revealed that the core configuration had a limited effect on moisture ingress. Samples exposed to sharp indentation exhibited the greatest decrease in load-bearing capacity (in excess of 50% in some cases) while that for blunt indentation was the lowest. This can be explained by reduced penetration forces resulting from matrix plasticization and degraded matrix/fiber interface, exacerbated by a smaller contact area. Also, early damage initiation and intensified damage progression were observed for sharp indenters after the seawater exposure. The core of FRPSSs significantly influenced localized damage in samples indented with conical and flat indenters, unlike those subjected to hemispherical ones. The seawater exposure adversely affected the energy absorption and penetration performance, enhancing macroscale damage mechanisms. These findings offer valuable insights for design and optimization of FRPSSs for marine applications. [ABSTRACT FROM AUTHOR]

This paper proposes a multiphase material topology optimization (MMTO) method for thermal–mechanical structures that takes into account the effect of the temperature field under stress and frequency constraints. Thermoelastic coupling occurs when an engineering structure is concurrently subjected to thermal and mechanical loads. This work focuses on the following: (1) the derivation of three interpolation schemes that use stress, dynamic, and thermal loads based on the extended solid isotropic material penalization (SIMP) method; (2) the incorporation of stress and dynamic constraints of multi-material thermal-elastic structural designs; and (3) the effective control of the impact of thermal loads on structures based on stress and frequency levels. Numerical experiments show that a clear distinction exists in the final topologies for mechanical and thermal loads among materials. Coupled and uncoupled mechanical and thermal behaviors can be predicted using finite element models based on materials' coefficients of thermal expansion. We see this method is capable of optimizing a structure's strength and stability while solving the issue of a thermal environment. In addition, it allows for the precise management of stress and vibration levels when structures are not exposed to a thermal environment. [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]

• The static behaviour of notched PPS/GF specimens was investigated. • V-shaped notched specimens were manufactured and tested. • Different notch root radii and manufacturing processes were considered. • Different approaches for the static strength assessment were compared. In this paper the static behaviour of polyphenylenesulfide reinforced by 40% wt. short glass fibre net-shaped plain and notched specimens was investigated. The specimen geometries were obtained by injection moulding and the experimental results were compared with data obtained from machined specimens with the same material and geometries. All data were reanalysed according to several models available in the literature for orthotropic materials, to find a rapid and efficient assessment tool for predicting the strength of short glass fibre reinforced materials in the early design stages. To this end, approaches based on orthotropic linear elastic stress analysis were considered, namely the linear elastic peak stress criterion, the nominal net-stress criterion, the point stress criterion, the average stress criterion, the strain energy density criterion, the generalized stress intensity factor-based approach, the inherent flaw model, the damaged zone criterion and the Hitchen criterion. Among the models, the average stress criterion and the generalized stress intensity factor-based approach provided the most accurate predictions of the static strength, ranging from −10% to +9% and from −19% to +2%, respectively, compared to the experimental data. [ABSTRACT FROM AUTHOR]

Perforation in cylindrical shells is commonly a typical technique to fulfill relevant functional requirements. However, how the perforation influence the mechanical performance of thermoplastic composite cylindrical shells (TPCCS) is incompletely understood. Hence, a systematic investigation through quasi-static compression and low-velocity impact (LVI) experiments was carried out in this paper. The full-field strain distributions of TPCCS intact tubes (IT) and perforated tubes (PT) were monitored by using 3D-DIC, and the residual properties were also characterized by compression-after-impact (CAI) tests. The results show that under quasi-static compression, the structural stiffness decreases significantly with increasing perforation diameter. The perforation reduces the interference of internal random defects on the structural deformation mode, which leads to a significant strain concentration in PT. The peak force and initial stiffness under LVI are smaller than those under quasi-static compression, with IT displaying higher sensitivity to dynamic loading compared to PT. At the impact energy of 100 J, IT and PT exhibit "S"- and "X"-shaped deformation modes, respectively. CAI tests indicate that although PT has a poorer residual load-carrying capacity than IT, it retains good structural integrity and secondary energy absorption capacity. This study provides a valuable reference for the assessment and application of perforated TPCCS. [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]

Vibration control plays a vital role in engineering structures, especially for low-frequency range, because designing structures with small dimensions makes it difficult to control large-wavelength vibrations. The present study seeks another road to realize low-frequency vibration control from the view of the real vibration responses. Similar to mode shapes, deflection modes are the main distributions of vibration amplitudes on structures in low frequency. Therefore, they are also essential vibration characteristics of structures. This paper proposes an effective passive vibration control method under both non-resonant and resonant excitations based on deflection mode theory and optimal algorithm. In fact, it is just like an axially functionally graded design for structures. The equations of motion for non-uniform beam structures are formulated by Hamilton's principle. Firstly, a desired deflection mode is artificially designed, and the beam structure is discretely divided into subunits. Then, by adjusting the thickness or elastic modulus of each subunit to make the deflection mode of the beam coincide with that of the desired one. This process is completed by the genetic algorithm (GA). After that, by experimental and simulation analyses, the deflection mode of the optimally designed beam structures coincides with that of the desired one. Therefore, the present vibration control method is verified to be correct and effective. [ABSTRACT FROM AUTHOR]

Fretting fatigue pertains to the behaviour of engineering components undergoing cyclic loading while in contact with each other. This intricate contact-related phenomenon often results in premature failure compared to conventional fatigue issues. Moreover, when these components operate in high-temperature atmospheres and experience high wear conditions, such as the heat transfer tubes in the nuclear reactor, the application of Functionally Graded Material (FGM) coatings becomes essential. Consequently, it is imperative to investigate how FGM coatings influence the initiation and propagation behaviour of fretting fatigue cracks. This paper employs the Critical Plane (CP) method to calculate the damage parameter. Additionally, Linear Elastic Fracture Mechanics (LEFM), specifically the Extended Maximum Tangential Stress (E-MTS) criterion, is utilized to examine how FGM coatings affect the paths of fatigue crack propagation in the presence of fretting conditions. Meanwhile, due to the unavailability of material properties of FGM coatings, the damage parameter and stress intensity factors are utilized to indirectly assess the effect of FGM coatings on crack initiation and propagation lifetimes. The FGM coating significantly influences tangential stress, thereby affecting the length of the stick zone, while having minimal impact on the distribution of normal stress along the contact surface. Furthermore, it is observed that adjusting the variation in composition of FGM coatings and the elastic modulus of the first FGM coating layer provides a potential technique for enhancing both crack initiation and propagation lifetimes. [ABSTRACT FROM AUTHOR]

• Chaotic snap-through phenomena are studies for bistable cantilever shell. • Transverse foundation excitation subjects to fixed end of bistable cantilever shell. • Analytical results of frequency-amplitude and force-amplitude responses are obtained. • Chaotic, quasi-periodic and snap-through vibrations are presented for bistable shell.5. Vibration experiment is carried out to investigate dynamic snap-though behaviors. The realization of the dynamic snap-through behaviors provides the new design ideas in the fields of the morphing aircraft and piezoelectric energy harvesting. This paper studies 1:2 internal resonance, nonlinear vibrations and chaotic snap-through phenomena of the bistable asymmetric composite laminated (BSCL) cantilever shell with the lower-frequency and higher-frequency primary resonances for the first time. The transverse foundation excitation subjects to the fixed end of the bistable cantilever shell. The perturbation analysis of two-degrees-of-freedom nonlinear ordinary differential equations is carried out by using the first-order approximate multiple scale method. The analytical results of the frequency-amplitude and force-amplitude response curves are obtained under the small foundation excitation. The obtained results reveal that the BSCL cantilever shell exhibits the double-jumping characteristics when 1:2 internal and primary resonances occur. There is a continuous energy exchange back and forth between two modes of the bistable laminated cantilever shell. As the foundation excitation increases, the BSCL cantilever shell exhibits saturation phenomenon. Numerical simulations are finished to further investigate the effects of the large excitation on the chaotic, quasi-periodic and snap-through vibrations for the BSCL cantilever shell. The vibration experiment is carried out to investigate the internal resonance and dynamic snap-though motions of the BSCL cantilever shell. Using the snap-though behaviors of the BSCL cantilever shell, we obtain the morphing structure of the aircraft wing. [ABSTRACT FROM AUTHOR]

Automated Fiber Placement (AFP) is a key additive manufacturing process for the production of complex composite structures. This study focuses on the in-situ AFP process for thermoplastic composites with Hot Gas Torch (HGT), which includes heating, consolidation, and solidification steps. Temperature control is critical to achieving high quality parts as it affects bond quality, crystallization, and solidification. However, previous studies have oversimplified convective heat transfer by assuming a constant coefficient, resulting in discrepancies between simulations and experiments. This paper introduces a novel distribution function to model the convective heat transfer coefficient, thereby improving temperature predictions. An optimization loop is used to determine the parameters of the function, which ensures agreement with experimental data. The proposed approach accurately predicts the temperature distribution, which is validated against unseen experimental results. By incorporating the distribution of the convective heat transfer coefficient, this study improves the understanding of heat transfer mechanisms in AFP for thermoplastic composites, leading to improved manufacturing processes and part quality. [ABSTRACT FROM AUTHOR]

Thermal dimensional stability (TDS) is a crucial issue in the development of high-end industry equipment and precision instruments that work in fluctuating thermal environments. To endow meta -structures with high load-carrying capacity and TDS functionality simultaneously, this paper proposes a topology optimization framework to optimize the topologies of lattice meta -structures at macroscopic structural and microscopic material scales concurrently. An important feature of the current optimization model is the introduction of a material concentration distribution (MCD) constraint to reduce the number of dual-constituent interfaces (DIs), which enables the easy manufacturing of the optimized structures because an additional fabrication process is required for the connection of heterogeneous lattice members. Designs for two dual-scale TDS structures, potentially employed for satellite payload platforms and the supporting structure of space telescopes, are completed. Compared with mono-scale TDS structures, the dual-scale schemes exhibit superior structural performances due to the opening of the dual-scale design space. Numerical experiments are performed to validate the ultra-low structural thermal deformations of the optimized TDS structures with values of 0.0743 μm/℃ and 0.153 μm/℃. Furthermore, the imposition of the MCD constraint significantly reduces the number of DIs from 38 to 10 within a lattice cell, enabling the easy assembly of the demonstrative 3D printing dual-constituent samples. [ABSTRACT FROM AUTHOR]

Deformation of rectangular orthotropic laminate resting on a thin elastic orthotropic foundation with fully fixed bottom plane is studied in this paper. The laminate is subjected to an in-plane uniaxial load uniformly distributed over one of its edges. Models of joint deformation of the laminate and foundation are created based on the equations of plane elasticity for an orthotropic body. The applicability of such equations is justified by the uniformity of edge loading. A laminate model allows for the transverse shear strain, whereas a model created for the foundation considers a nonlinear character of variation of the transverse and axial displacements. A governing system of differential equations modelling the joined deformation of the laminate and foundation is derived using static and kinematic contact conditions. The corresponding boundary value problem is solved using the sweep method. Based on this solution, effects of laminate and foundation thicknesses, and elasticity characteristics on the stress–strain state of the jointed structure are investigated. The model created and the method of its analysis enable the strong oscillating behaviour of stresses and strains to be studied. The results obtained can be utilized for verification of solutions of similar problems found by other numerical methods, including finite-element analyses. [ABSTRACT FROM AUTHOR]

• A criterion for simulation of delamination is proposed. • An imperfection induced pre-buckling must be incorporated into failure analysis of open-hole laminate under in-plane compression. • Rules for selection of a scale factor for the pre-buckling analysis are set forth. • Various failures of notched laminate under compression are predicted with no parameter adjustment and no iteration. Failure prediction of open-hole laminates under compression still remains a great challenge. A number of unique mechanics theories for composites developed by the author are successfully applied to analyze in plane compression induced various failures of the notched laminates in this paper. A buckling mode must be incorporated into the analysis of the compression induced delamination, and the rules for selecting a scale factor for the buckling analysis through ABAQUS are established. To simulate delamination, the interlaminar matrix stress modification method is applied. A more pertinent criterion for delamination is proposed. When and where is delamination initiated, how can the initiated delamination be propagated and how much is the delaminated area to be attained can be easily reproduced. Intralaminar failures are estimated based on Bridging Model and the matrix true stress theory. The ultimate strength of a notched laminate is assumed when any primary layer element outside neighborhoods of the stress singularity and weak singularity points firstly attains an ultimate failure. A limited, if not the minimum, number of inputs are required all measurable independently and following existing standards with no data calibration. Except for the pre-buckling analysis, no iteration is needed for prediction of all the other failures. The predicted failure modes and ultimate compressive loads of several laminates with single or double holes agree well with our measured counterparts. [ABSTRACT FROM AUTHOR]

• Thermal effects of pin-bar assemblies can be controlled by modifying structural geometry. • Thermal adaptivity is the compatibility between thermal elongation and target displacement. • Eigenvalues of the Gramian matrix of the compatibility matrix are modified. • The relationship between the eigenvalues and nodal coordinates is established. • A numerical strategy is proposed for the form-finding of thermal-adaptive configurations. Lattice structures with tunable expansion properties have been investigated in multidisciplinary fields to control the temperature effects of structures or materials. The expected thermal adaptivity can be achieved by optimizing the structural geometry. A novel method for the form-finding of thermal-adaptive pin-bar assemblies is developed in this paper by considering the control of structural temperature effects as the minimization of the potential energy of the system. Based on the stationarity condition of the potential energy with respect to the nodal coordinates, the compatibility relationship between the thermal elongations of members and the target nodal displacements is proven to be the sufficient and necessary condition for structural thermal adaptivity. The solvability of the compatibility equation is determined by the rank equality between the compatibility matrix and its augmented form, which can be measured by the number of nonzero eigenvalues of its Gramian matrix. The analytical relationship between the eigenvalues of the Gramian matrix and the nodal coordinates is established using the matrix perturbation theory. A numerical strategy based on Newton's method is proposed in which the eigenvalues are gradually modified by adjusting the nodal coordinates until the rank equality is satisfied. To address the existence of multiple solutions with structural thermal adaptivity, structural symmetry and periodicity constraints are introduced to narrow the solution space. The thermal-adaptive configurations of three illustrative pin-bar assemblies are analyzed using the proposed form-finding method, and the expected thermal deformations are verified for the obtained configurations using the finite element software ABAQUS. Comparing the results obtained by the proposed method with those obtained by nonlinear programming and the genetic algorithm validates the advantages of the proposed method in terms of computational time, optimality of the obtained configuration and applicability to complex structural geometries. [ABSTRACT FROM AUTHOR]

In this paper the problem of an antiplane reinforced crack in prestressed and prepolarized piezoelectric materials is considered. Using the boundary conditions of the reinforced crack we get the homogeneous and a nonhomogeneous Riemann–Hilbert problems. Nonhomogeneous linear complex differential equations having the unknown complex potentials are obtained. For a constant value of the applied incremental forces can be obtained the complex potentials, incremental displacement and stress fields corresponding to the third mode of the classical fracture. Extending Sih's strain energy density failure criterion for prestressed and prepolarized piezoelectric materials we study the antiplane reinforced crack propagation in a PZT type piezoelectric material. Using numerical results and the graphical representation of incremental strain energy density, the direction of antiplane reinforced crack initiation can be predicted versus different values of stiffness constant and for different small values of initial mechanical and electrical fields. [ABSTRACT FROM AUTHOR]

Additive manufactured lattice structures offer great potential for impact resistance applications. They exhibit excellent energy absorption characteristics during the elasto-plastic deformation process, providing protection to internal devices. However, the mechanical response of lattice structures undergoes substantial variations during the deformation process, thereby imposing limitations on their energy absorption behavior. This study introduces a novel twist design to modify the energy absorption behavior of rectangular and hollow cylindrical lattice structures. Powder bed fusion was used to fabricate the twisted lattice structures. The study employed a combination of compressive simulations and experimental investigations to systematically explore the impact of the twist angle on the peak crushing force, energy absorption, and crash load efficiency of the structures. Adjusting the twist angle results in a reduction of the peak crushing force and a transition towards a stable loading profile during the deformation process. Moreover, the crash load efficiency is also reduced. The twist design concept presented in this paper provides insight into designing and optimizing lattice structures for energy absorption applications. [ABSTRACT FROM AUTHOR]

Hygrothermal ageing has detrimental effect of the fatigue delamination growth (FDG) in carbon fibre reinforced polymer laminates, and may increase the crack growth rate by a factor of ∼5. The paper examines, how this degradation for Mode I fatigue delamination is affected by the severity of the ageing conditions. Fatigue delamination tests for R = 0.1 and R = 0.5 are conducted after ageing (1) at 70 °C 85 % relative humidity (RH) and (2) immersion in 70 °C water bath (WB). Paris-type FDG characterisation is derived, in the form, which accounts for the effect of fibre bridging. It is demonstrated that parameters of FDG degradation do not differ for these two types of hygrothermal ageing. The physical reasons for this are examined using dynamic mechanical thermal analysis (DMTA) and fractographic analysis, which revealed similar irreversible degradation of the material near the fibre/matrix interface and in the matrix itself, and the similar damage mechanisms in fatigue delamination. Furthermore, this study can highlight the importance of obeying similitude principles in FDG characterisation, and provide extra information for the ISO standard development for mode I fatigue delamination in unidirectional carbon fibre reinforced polymer composites. [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]