Composite Structures最新文献

The occurrence of peak-split or distortion in the reflected light of fiber Bragg grating (FBG) sensors with metallic coatings embedded in composites is inevitable during the curing process, regardless of protection layers. In this study, we present a comprehensive methodology to numerically predict the reflected spectrum of metallic-coated FBG sensors, considering the process-induced residual stress in carbon fiber/epoxy composites. The finite element analysis was utilized to simulate the residual stress, which primarily arises from mechanical, thermal, and chemical cure mechanisms of the composites, including the thermosetting resin. Subsequently, the reflected spectra were calculated using the coupled mode theory. Contrary to common expectations, our findings indicate that the coating thickness has minimal influence on the reflected spectrum, while the residual stress and embedding position significantly impact it. By employing this proposed methodology, the number of experimental trials can be reduced, enabling the development of robust structural and state monitoring systems for composites using metallic-coated FBG sensors.

Robotic arms have remarkable applications in diverse fields such as medical rehabilitation, disaster relief, and space exploration. Enhancing their rigidity, load-bearing capacity, and motion simplicity is key to broadening their usage. Utilizing the admirable flexibility and strength of tensegrity structures, made of rigid bars and elastic strings, we introduce a new type of flexible robotic arm. This arm is constructed using a sequence of two-dimensional X-tensegrity inspired modules. Each module comprises two sets of triangular bars linked by three strings, enhancing the arm’s ability to deform and resist impact forces. The joints between modules are stiff, allowing for angular adjustments to create three-dimensional configurations with adjustable stiffness and curvature. Through theoretical analysis, simulations, and experiments, we have shown that this tensegrity-based robotic arm exhibits superior stability, flexibility, and scalability.

This study aims to identify the influence of resin permeation on ballistic responses of fabric laminates. According to experimental results, when the resin permeation degree was improved, the yarn mobility was greatly constrained due to increasing of the bonding force, and the specific energy absorption of laminates under ballistic impact was degraded in comparison with that of the neat fabric. Different resin permeation states in a single yarn and fabric were simulated through Finite Element (FE) modeling at a fiber-bundle level. For a given resin ratio of 15%, semi-permeation of resin in a single yarn was benefit for energy absorption due to even distribution of impact load at the early impact, but full-permeation of resin resulted in energy absorption degradation due to high stress concentration and premature failure. For laminate models, the yarn mobility was severely constrained not only by resin bonding but also by yarns interlacement. In comparison with the neat fabric, stress distribution area on laminates was decreased 30–70%. Yarns contribution to energy absorption was significantly reduced in particular for principal yarns. Such results indicated that perfect resin permeation in armor-grade composite played a negative effect on ballistic energy dissipation due to low material utilization efficiency.

Pentamode metamaterials are a class of extremal materials exhibiting fluid-like mechanical behavior. The mechanical properties of pentamode metamaterials arise from their unique micro-architecture, rather than their constituent material. In this research, we present closed-form analytical relationships for the elastic modulus and Poisson’s ratio of pentamode lattice structures with double-cone struts based on cubic diamond morphology. To validate our analytical solutions, we performed numerical simulations and experimental tests, which confirmed the accuracy of the derived relationships. Our findings indicate that increasing the smaller diameter ($d$) and the larger-to-smaller diameter ratio ($\alpha$) of the double-cones increases the elastic modulus of pentamode metamaterials. However, within the considered range of $d$ and $\alpha$, the Poisson’s ratio is nearly constant and lies within the range of approximately 0.5. These analytical relationships provide valuable insight into the mechanical behavior of pentamode metamaterials, which can aid in the design and optimization of new materials with unique properties.

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.

Agglomeration and interphase region of fillers are two important factors that affect the mechanical properties of metal matrix composites reinforced with carbon nanotubes (CNT-CMMs). However, most of the existing theoretical models predict an ascending linear in strength for composites with increasing filler content, which disagrees with the experimental results, especially at high filler loading. In fact, at high CNT concentrations, agglomeration and weak interphase region bonding reduce the strength and consequently degrade the mechanical properties of composites. Based on the mean-field theory, we present a novel micromechanical model to predict the elastic modulus of CNT-CMMs by considering the effects of these two factors. Furthermore, we investigate the effect of other parameters such as CNTs aspect ratio, agglomeration amount, interphase layer thickness and modulus, and matrix modulus on the elastic modulus of CNT-CMMs. Finally, we validate our model by comparing it with numerous experimental outcomes from the literature signifies good precision. Using this model, it is possible to optimize the filler value and also maximize the elastic modulus, which can be a powerful tool for designing the CNT-CMMs.

Poor thermal stability limits the application of CuCr alloys at high temperatures. In this work, non-stoichiometric TiC particles (7 vol%) reinforced CuCr matrix composites were fabricated. The effects of TiC powders with different particle size (1 μm, 2 μm, 4 μm) on the microstructure and properties were studied. The diffusion of supersaturated Ti atoms induced the formation of Cu (Ti) solid solution transition layer at the interface, which improved the interface bonding. Dislocations caused by thermal mismatch promoted heterogeneous nucleation, which led to the precipitation of coarse Cr clusters. The strength and plasticity of composites increased with the reduction of TiC particle size. Strengthening and fracture mechanisms were discussed, and the strength difference was mainly attributed to thermal mismatch strengthening. Meanwhile, TiC particles refined the matrix grains and improved the activation energy of grain growth. The strength and softening temperature of CuCr alloy were 520 MPa and 540 °C, while that of CuCr-1TiC composite were 530 MPa and 915 °C. CuCr-TiC composites displayed much superior thermal stability than the CuCr alloy. These findings provide practical approaches for developing particle-reinforced copper matrix composites with excellent interfacial bonding and thermal stability.

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.

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.

Isogeometric Analysis is a numerical method that integrates the concepts of geometric modeling and structural analysis. It approximates the displacement field using the same basis functions employed by CAD systems to describe the structure’s geometry. This work proposes an isogeometric formulation for analysis of functionally graded panels based on rational Bézier triangles, allowing the exact geometry representation and automatic discretization of topologically complex models. The formulation is applied to the free vibration and stability analysis of functionally graded plates and curved panels. Monotonic convergence under mesh refinement was observed in all examples. Furthermore, results show that curved functionally graded panels display a complex nonlinear behavior and can present bifurcation buckling before reaching the limit load.