Hui Wang

To address the low interlaminar strength and catastrophic failure of traditional 2D laminated carbon fiber composites, 3D braided and 2D laminated T700/GE-7188A epoxy composites were fabricated via identical RTM-autoclave curing, and their bending properties and failure mechanisms were compared. Results show that 3D braided composites achieve bending strength of 916.48 MPa and modulus of 98.17 GPa, 69.37% and 66.79% higher than 2D laminates. 2D laminates exhibit catastrophic interlaminar delamination failure, while 3D braided composites enable multi-directional load transfer via spatial fiber networks, showing progressive diffuse damage and better damage tolerance. This work provides experimental support for aerospace applications of 3D braided composites.

This study comparatively analyzes the effects of a dendritic polymer and polyolefin elastomer (POE) on the mechanical properties and melt flowability of polypropylene/talc (PP/talc) composites. The microscopic morphology of the two toughening systems is characterized via scanning electron microscopy (SEM). The results indicate that, compared to POE, the dendritic polymer exhibits a less pronounced detrimental effect on the flexural modulus of the PP/talc composites. Furthermore, at loadings of 10 wt% and above, the dendritic polymer-toughened system exhibits significantly higher impact strength. Microstructural observations reveal that dendritic polymer exhibits a finer particle size within the PP matrix, concurrently promoting a more uniform dispersion of the talc platelets throughout the composites.

This study proposed an ultrasonic adhesive‐impact bonding process tailored for carbon nanotube (CNT)‐reinforced epoxy adhesive joints. A predictive model for shear strength was established using the response surface methodology (RSM), and the optimal process parameters were determined. Under optimal conditions, the fabricated 6061 aluminum alloy/carbon fiber‐reinforced polymer (CFRP) joint exhibited a shear strength of 30.77 MPa, representing a 16.46% improvement over conventional bonding processes. The molecular dynamics (MD) simulation results indicate that ultrasonic vibration not only effectively enhances the filling behavior of adhesive molecular chains but also significantly promotes chemical reactions at the interface and within the adhesive layer. Compared with the model without ultrasonic vibration, the number of KH550 molecules participating in crosslinking increased by 57.14%, and the number of CN bonds formed increased by 63.64% under ultrasonic vibration. Meanwhile, the number of amino groups on the CNT participating in crosslinking and the associated CN bonds formed increased by 60% and 33.33%, respectively. The experimental results on interfacial microscopic morphology and chemical composition were consistent with the findings from MD simulations.

Fiber metal laminates (FMLs) are an innovative hybrid material formed by laminating metal with fiber‐reinforced plastics. Due to their excellent functional characteristics, FMLs are extensively employed in the automotive and aerospace industries. Nevertheless, the strength of FMLs is significantly influenced by various interfaces, making it crucial to explore strategies for further enhancement and conduct an in‐depth mechanism analysis. Consequently, this research proposes a novel multi‐field‐assisted forming method for thermoplastic fiber metal laminates (TFMLs) composed of 5052 aluminum alloy, carbon fiber PA6 prepreg, and hot‐melt adhesive film. A multi‐field‐assisted forming platform was established comprising a hot‐press unit, an ultrasonic device, and a pulsed current device. Orthogonal experiments were conducted to optimize the forming process parameters for improving the multi‐fields coupling formability. The results demonstrate that the multi‐field‐assisted forming method enhanced tensile and bending strengths by 19.76% and 17.55%. To explore the effect of the ultrasonic field and electromagnetic field acting separately, the mechanisms by which multi‐fields enhance the mechanical properties of TFMLs are elucidated independently. Additionally, the multi‐field‐assisted forming analysis indicates that both ultrasonic and electromagnetic fields improved the forming quality of curved components. The present study can provide an initial research foundation for the multi‐field‐assisted forming process of FMLs.Highlights: A novel multi‐field‐assisted forming method for TFMs was proposed. The forming process parameters were optimized. The multi‐field‐assisted forming method improved the forming quality. The enhancement mechanisms of forming quality were elucidated.

In response to the issue of the insufficient adhesion strength of polypropylene materials, a plasma–ultrasonic treatment is proposed. Plasma treatment is first conducted to activate the polypropylene adherends, and then ultrasonic vibration is applied to the adhesive to facilitate the interface contact, enhancing the bonding performance of polypropylene. The shear strength of the test specimens was assessed using single-lap shear tests. The bonding samples were characterized by scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS), contact angle, and infrared analysis to explore the bonding mechanism of plasma–ultrasonic treatment. The results show that compared to untreated polypropylene specimens, the plasma treatment process increased the shear strength of the polypropylene specimens by 370.3%, and the addition of ultrasonic-assisted technology further increased the shear strength of the polypropylene specimens by 10.6%. The coefficient of variation decreased from 0.53 in the untreated sample to 0.32 for the plasma–ultrasonic treatment, enhancing the stability of adhesion. Plasma treatment introduces active groups, such as hydroxyl groups, onto the surface of polypropylene and increases the surface roughness of polypropylene. Ultrasonic treatment promotes the penetration of adhesive microstructures on the surface of polypropylene, enhancing the anchoring effect of the adhesive, thereby improving bonding performance. Furthermore, through molecular dynamics analysis, compared to the untreated polypropylene bonding system, the bonding energy of the bonding system under the plasma–ultrasonic treatment was increased by 57%, effectively enhancing the shear strength of polypropylene bonding. Plasma–ultrasonic treatment can effectively improve the bonding strength of polypropylene, providing a new idea for the study of polymer bonding.

Fiber metal laminates (FMLs) are advanced super-hybrid sandwich materials. They have been increasingly used in the aerospace industry. However, the low formability of heterogeneous FMLs in the traditional forming process restricts its large-scale application. This paper proposed the idea of introducing extra normal stresses to improve the formability of FMLs by using flexible die forming. The carbon fiber reinforced aluminum alloy laminates (CARALL) were prepared. A flexible die forming finite element model was established, and a platform was constructed to investigate the effects of laminate layup structures and the flexible die hardness. The mechanism of formability improvement was analyzed. The results indicate that the formability of the FMLs is better compared with the carbon fiber sheets. The formability can be increased significantly with a larger flexible die hardness. The 3 + 2 type laminate showed the highest improvement in formability and ultimate limit states per unit thickness. It is formed by alternately stacking three layers of aluminum alloy and two layers of carbon fiber reinforced plastics (CFRP). The specific order of layers is AL/CFRP/AL/CFRP/AL. The matrix type of CFRP is thermosetting epoxy resin. The maximum improvement in formability and the load limit per unit thickness of the 3 + 2 type layup structures were 28.8% and 4.94 N/mm, respectively. The mechanism of formability improvement was analyzed. The mechanism analysis showed that the additional normal stresses through a flexible die forming reduced the spherical tensor of stress. The additional normal stresses can promote damage closure during plastic deformation. It also improved the material’s Lode parameter, increasing the formability. This study demonstrates that flexible die forming helps enhance the deformation capacity of laminates and is a potential method for preparing high-performance, high-plasticity super-hybrid material components.

Fiber metal laminates have been widely used as the primary materials in aircraft panels, and have excellent specific strength. Bending deformation is the most common loading mode of such components. An accurate theoretical predictive model for the bending process for the carbon reinforced aluminum laminates is of great significance for predicting the actual stress response. In this paper, based on the metal-plastic bending theory and the modified classical fiber laminate theory, a modified bending theory model of carbon-fiber-reinforced aluminum laminates was established. The plastic deformation of the thin metal layer in laminates and the interaction between fiber and metal interfaces were considered in this model. The bending strength was predicted analytically. The FMLs were made from 5052 aluminum sheets, with carbon fibers as the reinforcement, and were bonded and cured by locally manufacturers. The accuracy of the theory was verified by three-point bending experiments, and the prediction error was 8.4%. The results show that the fiber metal laminates consisting of three layers of aluminum and two layers of fiber had the best bending properties. The theoretical model could accurately predict the bending deformation behaviors of fiber metal laminates, and has significant value for the theoretical analysis and performance testing of laminates.