Applied Composite Materials最新文献

Poly(lactic acid) (PLA) was melt-blended separately with low concentrations of polypropylene (PP) and low-density polyethylene (LDPE) that maintained the total biopolymer content above 89 wt%. Additionally, a multifunctional reactive chain extender was also incorporated to assess the potential compatibility among the constituents. The blends were exposed up to five reprocessing cycles to simulate recycling, with material collection occurring at one and three recycling stages for characterization. Rheology, thermal, and mechanical properties were then evaluated to assess the processing – properties of the resulting materials. In addition, wood flour powder (≤ 250 μm) was compounded into two different system types (PLA: PP and PLA: LDPE) at 30 and 40 wt% to fabricate high-biopolymer content wood-plastic composites (WPCs). The entire composite was then subjected to up to five recycling cycles to elucidate the effects of recycling on different systems. The simulated recycling process induced crosslinking reactions in the case of LDPE, evidenced by an increase in melt viscosity and changes to the zero-shear viscosity ratio of the blended polymers. In the case of PP, recycling led to reduced viscosity likely attributed to temperature and shear mediated chain scission inducing changes in both the matrix and dispersed phase’s viscosity. The study provided valuable insights into the behavior of the materials and composites undergoing through recycling.

To ensure a strong adhesive bond, most standards and adhesive manufacturers specify a maximum adhesive gap of 1 mm when bonding fiber reinforced composite structures. In manufacturing large components, such as joining two halves of wind turbine blades, meeting this gap tolerance specification is impractical; gaps larger than 10 mm are common in large adhesively bonded composite structures using state-of-the-art manufacturing techniques. Currently, there is a lack of fundamental understanding of the failure mechanics of adhesive gaps larger than 3 mm. To create such understanding, glass fiber – acrylic thermoplastic composite panels bonded using different epoxy adhesives within single-lap joint samples with adhesive thicknesses of 0.1 mm, 0.3 mm, 1 mm, 3 mm, 5 mm, and 10 mm were sheared to failure. A transition from cohesive to adhesive failure was observed to occur about 1 mm to 3 mm joint thicknesses. Plotting the shear stress normalized by the ratio of the joint width to thickness as a function of the joint thickness normalized by the joint length is shown to result in the ability to fit simple empirically derived models of the cohesive-to-adhesive failure transition, regardless of the adhesive. Furthermore, using these normalized variables, all the observed cohesively failed specimens collapse to a single master curve, as do the adhesively failed specimens.

In this work, a novel unsupervised machine learning (ML) method for automatic image segmentation of low velocity impact damage in carbon fiber reinforced polymer (CFRP) composites has been developed. The method relies on the use of non-parametric statistical models in conjunction with the so-called intensity-based segmentation, enabling one to determine the thresholds of image histograms and isolate the damage. Statistical distance metrics, including the Kullback–Leibler divergence, the Helling distance, and the Renyi divergence are used to formulate and solve optimization problems for finding the thresholds. The developed method enabled rigorous and rapid automatic image segmentation of the grayscale images from the micro computed tomography (micro-CT) scans of the impacted CFRP composites. Sensitivity of the segmentation results with respect to the thresholds obtained using different statistical distances has been investigated. Based on the analysis of the segmentation results, it is concluded that the Kullback-Leibler divergence is the most appropriate statistical measure and should be used for automatic image segmentation of impact damage in CFRP composites.

The structural design of the brake disc of urban rail trains, especially the design of the heat dissipation rib structure, affects the heat dissipation performance of the brake disc. Unreasonable design can lead to poor heat dissipation performance and generate energy consumption caused by large air-pumping resistance. However, the current structural design method for brake discs does not consider material characteristics and continues with materials such as steel and iron. There is no long-term service performance testing applicable to brake disc service conditions for lightweight and high-strength materials such as aluminum matrix composites. In addition, there is no comprehensive and systematic analysis of the structural design of cooling ribs. Therefore, a structure of SiCp/A356 brake discs for urban rail trains was designed in this work. Different from the previous design method, long-term performance testing of materials was conducted first, and then the heat dissipation performance and energy loss performance of different cooling rib structures were systematically analyzed to select the appropriate cooling rib structure. Based on long-term performance testing results, cooling rib optimization, and material forming process, a new brake disc structure was designed. The thermal-fluid–solid multi-field coupling simulation was conducted on the new structure brake disc under emergency braking and full round-trip conditions, and bench tests were conducted to verify the reliability of the simulation. Based on comprehensive simulation and bench test results, the new structure SiCp/A356 brake disc meets the established operating conditions. This design method considers material properties, multi-field coupling simulation, and engineering practice, which can a provide reference for the design of other brake discs and has high engineering application value.

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.