Applied Composite Materials最新文献

In this paper, an architecture-based approach is proposed to enhance the quasi-static crushing behaviour of trigger-free composite energy-absorbing structures. To validate the proposed methodology, specimens with an inner diameter of 32 mm and a wall thickness of ~ 1 mm were manufactured and tested under axial quasi-static compression (20 mm/min) using a filament winding technique. Two sets of samples were fabricated by including an external CFRP mesh to enhance the hoop strength and promote progressive crushing. By comparing the test results with those of the base material, a remarkable influence of the outer layer on the crash performance (> 50% of the SEA) was registered, despite a negligible increase in weight. Furthermore, since geometric modifications (e.g., edge chamfering) were unnecessary to achieve progressive crushing because of the contribution of the outer mesh, this approach can be further explored to simplify the manufacturing process of energy-absorbing structures.

Curing is a reaction leading to a hardened material in mixtures of two or more components known as themosetting polymers. The specific choice of components allows to regulate the speed of reaction. In some applications, fast kinetics are chosen to achieve a fully hardened product within seconds. Yet in other applications, where the mixture is cast in larger volumes, a slower curing rate is needed to allow the cast or mold process to be completed before significant hardening has been occurred. Specifically in the latter case, such a reaction is of importance to model accurately; yet an interplay of several mechanisms makes it challenging to predict the correct model to be used in curing. Such a polymer comprising multiple components has been analyzed by listing different models available. Based on them, a phenomenological model is proposed that resembles a slowly reacting thermosetting polymer. An inverse analysis approach is developed for acquiring a fit representing the data with a good agreement.

The methods and approaches used for composite repairs depend on the sector of industry, and exhibit both common elements and distinctions. Here we consider the repair methods used in four exemplary applications: marine, wind, automotive, and aerospace. Repairs are often overlooked as a means of imparting greater sustainability to composite products, but they are generally the least costly route for doing so. Approaching each industry from a common repairs perspective, the similarities are highlighted while the different approaches are compared. The problems associated with current approaches are examined, along with active research methods for each application. Areas for potential to increase efficiency of repairs through automation and introduction of new materials are identified. The review of repair methods is intended to stimulate new approaches and opportunities to transfer the approaches and practices employed across industries.

Carbon Fiber Reinforced Plastic (CFRP) is particularly suitable for replacing metal materials in the safety lap bars of amusement rides due to its excellent mechanical properties and lightweight nature. To ensure the safety and dependability of the CFRP lap bar, the mechanical characteristics of the lap bar were investigated through a combination of experimental and simulation methods, and the damage behavior is analyzed using acoustic emission (AE) and X-ray micro-computed tomography (micro-CT). Simulation results revealed that the maximum principal stress of the tubular element and lap bar arm was 132.27 MPa, located at the profile alteration point beneath the lap bar arm. The damage behavior of the lap bars was investigated through an analysis of the AE signals generated during the five experimental stages. With the increase in load, a large number of signals with frequencies exceeding 300 kHz appeared, indicating irreversible damage such as fiber pull-out and matrix cracking. In addition, the number of AE signals captured by Sensor 3 corresponding to the bent portion of the lap bar arm exceeded 6,000, representing the largest proportion and indicating that the damage in this area is relatively intensive. Furthermore, the internal damage morphology was reconstructed using micro-CT. The observed damage was primarily caused by interlayer damage. The failure of the CFRP lap bar is attributable to the cumulative effect of multiple damage modes, validating the reliability of the damage mode characterized by AE signals. Eventually, the damage evolution mechanism of the CFRP lap bar was clarified, providing a basis for design optimization and service evaluation.

Over-molded composites are produced by injecting short fiber composites over continuous fiber-reinforced composite inserts through an injection molding process. These composites are suitable for load bearing structural applications because of their high specific strength, stiffness, lightweight nature, and the ability to form complex structures through simple manufacturing processes. However, their performance is highly dependent on the interface adhesion between the short and continuous fiber-reinforced composite inserts. This study investigates the effect of preheating on the load bearing capacity of over-molded composites under tensile and flexural loads using experimental and numerical approaches. The damage mechanism of the over-molded composites is characterized using Hashin and cohesive zone failure criteria within ABAQUS/Explicit to capture the failure mechanisms. The experimental results revealed that preheated over-molded composites demonstrated a significant increase in tensile and flexural properties compared to non-preheated composites. For the non-preheated specimens, the primary failure mechanisms were interfacial debonding, insert delamination, and short fiber composite failure. Conversely, in the preheated specimens, both short and continuous fibers experienced simultaneous damage, owing to the strong cohesive bond formed by preheating. The predicted numerical results align well with the experimental results in terms of load-displacement behavior, strength, and damage morphologies, suggesting that the numerical simulation is a valuable tool for assessing the performance of over-molded composites.

This study investigates the heating (i.e. discharging) of Lithium-ion (Li-ion) polymer batteries (e.g. pouch and 18650 cells) embedded in sandwich composites made of carbon fibre laminate facesheets and polymer foam cores (Polyvinyl Chloride or PVC, Polyethylene Terephthalate or PET). The effects of facesheet thickness, foam core thickness and density, and battery type and orientation on the heating of sandwich composites are systematically investigated. Heat can be rapidly dissipated from sandwich composites when the Li-ion polymer battery has a large area of contact with the carbon fibre facesheets. However, rapid internal heating, potentially leading to thermal runaway and fire, may occur when the battery is fully embedded within the foam core and physically separated from the facesheets. The optimal foam core thickness to prevent overheating can be predicted using the numerical thermal design maps. This study builds on our previous work which investigated the thermal performance of monolithic carbon fibre laminates.

The progressive fatigue damage (PFD) model effectively simulates the fatigue behavior of laminated composites under multiaxial cyclic stress. This model employs the generalized material property degradation (GMD) technique to calculate the residual properties of unidirectional (UD) plies subjected to cyclic stress. The present study enhances the PFD model to simulate the fatigue behavior of polymer matrix composite (PMC) materials under cyclic stress at various temperatures by executing it at a single temperature. The equivalent cycle time (ECT) method evaluates property changes in PMCs across different temperature settings, utilizing data from isothermal loading. In the present study, a novel approach based on the ECT concept, termed equivalent cycle number (ECN), is developed and integrated into the GMD technique. Additionally, a combined fatigue life model is employed to improve the predictive capability of the PFD model. This model is constructed by evaluating the results of three commonly used fatigue life models in predicting the fatigue life of UD plies under uniaxial cyclic stress at both room and elevated temperatures. The proposed PFD model effectively predicts the residual properties and fatigue life of a PMC subjected to multiaxial cyclic stress at two distinct temperatures. The findings demonstrate that the ECN method significantly reduces the model's computing load while maintaining a high level of predictive capability compared to available experimental data. Furthermore, the results indicate that using the combined fatigue life model substantially enhances the predictive capability of the PFD model.

An analytical model is developed to predict the ballistic performance of fiber-reinforced plastic (FRP) laminates under normal impact of rigid penetrators with various nose shapes. The model formulation is based on the localized interaction model incorporated with the spherical cavity-expansion model. Experimental validation of the analytical model is performed on experimental data obtained by own ballistic tests on Twaron/epoxy laminates and previous studies on ballistic performance of other FRP laminates. The model predictions for the ballistic limits and residual velocities are in good agreement with the experimental data, with discrepancies remaining within 10%, demonstrating the robustness and reliability of the present model.

This study employs numerical methods to model through-the-thickness reinforcements in CFRP tubular structures under axial impact, investigating the influence of reinforcement configurations on crashworthiness performance. Experimental validation involves testing unpinned tubular structures to establish a baseline model. LS-DYNA finite element models simulate low-velocity axial impacts, incorporating energy-based tiebreak contacts or solid cohesive elements to describe interlaminar bridging. Through-the-thickness are introduced through a homogenous mesh system or locally refined mesh at pin locations. Various reinforced tube designs with different pin diameters and areal densities are examined to identify the optimal pinned design for crashworthiness. The research demonstrates numerically that pinning enhances crashworthiness performances in axial crushing of composite tubes.

Carbon fibre reinforced polymers (CFRP) are increasingly being used in different industries, including the automotive and aerospace sectors. One important reason for this is because they have interesting structural and mechanical properties compared to metallic materials. Their high strength-to-weight ratio makes them a preferred choice for high-stress applications. However, CFRPs are often subjected to various defects during their manufacturing that can significantly alter their structural integrity and durability. Amongst these defects, the occurrence of void formation (known as porosity) is the most common. Many methods have been developed for the characterisation of porosity including the ones based on the use of ultrasound data. The present work aims at providing a comprehensive review of the application of machine learning (ML) techniques to the mapping and characterisation of porosity across CFRP composites. The types of ML used, and their potentials for improving the accuracy of porosity detection are presented and discussed. It is particularly noted that ML techniques can extract unique features from CFRP complex ultrasound data with a relatively good level of accuracy. This result suggests that these techniques, particularly the convolutional neural network (CNN), would overcome the limitations of traditional signal processing techniques.