Applied Composite Materials最新文献

Despite being invented several decades ago, fiber metal laminates (FMLs) still encounter challenges in large-scale manufacturing, especially in forming small and complex-shaped components. These challenges arise from the limited strain rate of the fiber layers compared to the metallic layers. Consequently, conventional approaches to form FML parts are often inadequate. To produce parts free of defects such as fractures and wrinkles, this study investigates the effects of Thermo-stamping (TH-S), in addition to fiber orientation, on the forming behavior of FMLs, employing two different aluminum layer thicknesses. A comprehensive approach combining finite element simulations and experimental analyses was employed. The study investigated thinning of aluminum alloy layers, stress distributions across different layers, and the influence of fiber orientation. The FML blanks are made of a middle woven glass fiber prepreg with a thickness of 0.2 mm, using a thermosetting epoxy system, and Al 2024-T3 alloy sheets with varying thicknesses of 0.3 mm and 0.5 mm. Material behavior was evaluated using Abaqus software, applying the Johnson-Cook criterion for damage initiation in ductile metals and Hashin’s theory for damage initiation in fiber-reinforced composites. These simulations were then compared with experimental results. The findings highlight the potential of the TH-S process to enhance the forming performance of FMLs, particularly evident in the case of the 0°/45° middle layer fiber, which exhibits a higher forming depth and a more uniform thickness distribution. Additionally, a greater flexibility of the glass fiber under the 0°/45° layup compared to the 0/90 layup was detected. This flexibility provides the aluminum layers with more freedom of deformation in the plastic domain. These advancements hold promise for widespread industrial applications of FMLs.

The integration of carbon nanomaterials with flexible polymers has received intensive attention as a promising research direction in developing materials with novel properties for advanced applications. Herein, we report on the fabrication and characterization of flexible porous polydimethylsiloxane (PDMS) coated with graphene nanoplatelets (GNPs). We explore the mechanisms affecting its various properties under deformation, and propose new applications for it. The results show lightweight and excellent flexibility characteristics for the obtained GNP-PDMS composite. Measurements of its electrical resistance revealed a change in the electrical resistivity from 2.35 × 10⁶ Ω·m to 194 Ω·m under a strain change from 10 to 80% illustrating its ability to shift behavior from an electrical insulator to a relatively low resistivity material and demonstrating the considerable potential for use as a flexible electrical switch. Moreover, the thermal conductivity of GNP-PDMS was found to be significantly enhanced (up to ∼ 110%) by changing the level of compression from 20 to 80%, proving a strain-tunable thermal performance, allowing its utilization as an insulation material of variable conductance for unique thermal management applications.

Optimal design study of vibro-acoustic resistance of porous foam composite laminates (PFCLs) is presented in this paper. A dynamic model of the PFCLs subjected to the plane acoustic excitation load is firstly proposed with consideration of upper and lower composite skins and a uniform porous foam. The vibration and acoustic solutions of the PFCLs with acoustic energy excitation are further acquired using the first-order shear deformation theory, the finite element method, the Rayleigh integral approach, the mode superposition technique, etc. Subsequently, a vibro-acoustic optimization model is established by accounting for appropriate design variables and constraints, in which resonance responses, sound transmission losses, and overall structural mass are taken as objective functions, respectively, and the artificial immune clonal selection algorithm is adopted to improve the efficiency in the optimization calculations. After such an algorithm and the current model are thoroughly validated, single-objective, dual-objective, and multi-objective optimizations are undertaken on the PFCLs to achieve the optimal design parameters. The research results indicate that it is hard to enhance the vibro-acoustic resistance and lightweight property of the PFCLs simultaneously, which means some compromise results of design parameters need to be chosen. It is suggested to determine the concerned optimal design results by referring to the nearby turning points associated with the Pareto-optimal solutions.

Composite structures are extensively used in several industries such as aerospace, automotive, sports, and construction due to their many advantages, including tailorable mechanical properties, high strength-to-weight ratios, and high specific stiffness. However, due to their low interlaminar tensile and shear strength, composites are prone to delaminations, which can degrade the overall mechanical performance of the structure. Through-thickness stitching provides a third-direction reinforcement to enhance the interlaminar tensile and shear strengths. In this study, quasi-isotropic composite test specimens were manufactured with a novel through-thickness robotic chain stitching with different patterns and tested under uniaxial tensile and three-point bend loadings. A design of experiments (DoE) approach was used to investigate the influence of stitch parameters (stitch density, stitch angle, and linear thread density) on the tensile strength, tensile modulus, and flexural strength of stitched composites. Experimental results are then used to develop a statistically informed response surface model (RSM) to find optimal stitching parameters based on a maximum predicted tensile strength, tensile modulus, and flexural strength. This study reveals and discusses the optimum selection of stitch processing parameters to improve the in-plane and out-of-plane mechanical properties.

Crawling robots have great potential in some harsh environments, but there are still some limitations, such as tiny structures that can only produce small deformation and poor load-carrying capacity. A lightweight inchworm-like crawling robot made of bistable structure driven by electrothermal actuation is proposed in this paper. The robot has the characteristics of large deformation and a certain extent of load capacity. The motion of the crawling robot was realized by the common effect of the bistable structure and the designed feet with anisotropic friction. The unstable transition process between snap-through and snap-back processes of the bistable structure was utilized to provide morphological deformation. Meanwhile the feet with anisotropic friction transformed the deformation to unidirectional movement of the crawling robot. Through electric experiments, the electrothermal driving influencing factors of bistable structure are tested, including heating time, maximum temperature and curvature change, which demonstrates the possibility of driving inchworm-like crawling robot with bistable structure and large-deformation. And the structure of the inchworm-like crawling robot assembled by a bistable shell pasted with an electric heating sheet and the designed feet with anisotropic friction. In order to evaluate the motion properties and load-carrying function of the inchworm-like crawling robot, the step length test under different voltages and the experiment of the crawling robot load-carrying capacity were completed. The results show that the crawling robot performs well in load-carrying, can achieve crawling movement under the condition of carrying 10 g and 20 g objects. The inchworm-like crawling robot provides a method to achieve large-deformation and load-carrying and demonstrates it is suitable in some extreme environments.

In this study, an in-depth analysis is carried out to simulate the failure mechanism of T700 carbon fiber-reinforced polymer composite (CFRP) joints with a layup sequence of [45/-45/0/90]_3 s when subjected to tensile loading, both experimentally and numerically. We compared the mechanical performance of three different edge-to-bolt diameter ratios (E/d) of bonded, bolted, and hybrid single lap joints subjected to tensile loading. A finite element-based progressive damage method (PDM) along with the bilinear triangular cohesive zone model (BTCZM) is developed to predict the damage evolution and failure mechanism for all joint configurations. By juxtaposing the simulation outcomes and the experimental data, we observed the failure morphology and assessed the bearing capacity of the joint under tensile loading. The comparison results revealed a minor discrepancy of merely 5.5% in terms of joint load capacity between simulations and experiments, which indicates the high accuracy of our model. The strength of the adhesive and mechanical joints increases with E/d from 3 to 5; however, the strength of the hybrid joints decreases. At E/d = 3, hybrid joints performed significantly better than bonded ones, with a remarkable enhancement of 41.53%. However, for E/d ratios of 4 and 5, both simulation results and test data showed that hybrid joints were inferior to bolted joints. The analytical methodology presented in this paper offers a valuable reference for future analysis and design of composite joints.

This paper presents the theoretical investigations on the free and forced vibration behaviours of carbon/glass hybrid composite laminated plates with arbitrary boundary conditions. The unknown allowable displacement functions of the physical middle surface are expressed in terms of standard cosine Fourier series and sinusoidal auxiliary functions to ensure the continuity of the displacement functions and their derivatives at the structural boundaries. Arbitrary boundary conditions are achieved through the introduction of an artificial spring technique. The first shear deformation theory and Lagrange equations are utilized to derive the energy expression, and the eigenvalue equations associated with free and forced vibration are obtained by Rayleigh-Ritz variational operations. Subsequently, these equations are then solved to determine the natural frequency, mode of vibration, and the steady-state displacement response under forced excitation. The new results are compared with those from references and finite element methods to verify the convergence, accuracy and efficiency of the analytical method. The effects of hybrid ratios, stacking sequences, lamination schemes, fibre orientation, boundary conditions and excitation force on the free and forced vibration behaviours of the carbon/glass hybrid composite laminated plates are analyzed in detail.