Yuqin Ma

Battery packs for new energy vehicles have evolved from simple load-bearing and protective assemblies into multifunctional safety structures integrating structural support, crash protection, thermal-runaway mitigation, flame retardancy, electrical insulation, electromagnetic interference shielding, waterproof sealing, and long-term reliability. Fiber-reinforced polymer composites are promising for upper covers, underbody shields, trays, cross beams, side frames, and local protective structures because of their low density, corrosion resistance, design flexibility, and functional-integration potential. However, composite-part performance is strongly governed by forming. Resin flow, impregnation, curing or cooling shrinkage, fiber orientation, filler dispersion, and interfacial bonding may induce voids, dry spots, resin-rich regions, delamination, warpage, and fiber waviness, thereby affecting load bearing, sealing, thermal protection, and durability. This review focuses on composite-forming technologies for new energy-vehicle battery packs. It summarizes component-level service requirements and material systems and compares representative forming routes, including sheet molding compound (SMC), prepreg compression molding/wet compression molding (PCM/WCM), resin transfer molding/high-pressure resin transfer molding (RTM/HP-RTM), vacuum-assisted resin transfer molding (VARTM), long-fiber thermoplastic direct processing (LFT-D), glass-mat thermoplastic (GMT), thermoplastic sheet forming, pultrusion, and multi-material joining. These routes are evaluated from six dimensions: material form, forming cycle, typical defects, representative mechanical performance, applicable components, and engineering maturity. The review further discusses defect mechanisms, performance effects, detection and control methods, and the roles of in-line monitoring, non-destructive testing, process simulation, machine learning, and digital twins in closed-loop quality manufacturing. Finally, engineering challenges are examined in multi-material joining, thermal-safety integration, low-carbon recycling, and standard certification. Composite-material battery-pack structures should therefore be developed as coordinated design and closed-loop manufacturing systems linking materials, processes, defects, performance, and validation.

Carbon fiber-reinforced polymer (CFRP) composites are in urgent demand in the aerospace, new energy vehicle, and wind power sectors owing to their superior specific strength, specific modulus, and lightweight potential. However, molding defects, such as voids, dry spots, and delamination, arising from their anisotropy and weak interlaminar bonding, severely constrain their service performance. Advanced molding technologies represent the key to overcoming this bottleneck. This paper systematically reviews typical advanced molding technologies in the field of CFRP composites, including resin transfer molding (RTM) and vacuum-assisted resin transfer molding (VARTM) in liquid composite molding, autoclave molding and compression molding (CM) in prepreg molding, and automated fiber placement (AFP) and material extrusion (ME) in automated molding. From an integrated perspective of “technological evolution–process characteristics–defect mechanisms–optimization strategies,” this review summarizes the technical principles, development trajectories, and core advantages of each process, analyzes the formation mechanisms of typical defects, including voids, dry spots, delamination, wrinkles, warpage, and melt instability, and summarizes multidimensional optimization advances in process parameter regulation, numerical simulation, resin modification, equipment upgrading, path planning, and thermal management. Furthermore, the differences and complementarities among these processes in terms of molding precision, efficiency, cost, and applicable scope are compared. Finally, future development directions, including digital twins, green low-carbon manufacturing, ultra-large integrated structures, multi-process integration, standardized defect characterization, and low-cost collaborative design, are discussed. This paper aims to provide systematic theoretical references and technical support for the optimization and upgrading, process integration, and industrial application of advanced CFRP molding technologies.

In this study, graphene‐carbon fiber/basalt fiber (GO‐CF/BF) hybrid reinforced composites were prepared using fused deposition 3D printing technology with vacuum infiltration hot press molding process. The effects on microstructure and shape memory properties were comparatively analyzed by adding shape memory polymer (SMP) and changing the lay‐up method. The results showed that, in terms of density and porosity, the density and porosity of the composites showed a decreasing trend due to the low density and low porosity characteristics of the SMP, and the density and porosity of the composites increased with the increase of the BF content due to the large bulk density of the BFs and the poor interfacial bonding ability with the matrix. In terms of shape memory properties, the addition of SMP can increase the fixation rate and recovery rate of GO‐CF/BF hybrid reinforced composites, and with the increase of BF content, the fixation rate increases and the recovery rate decreases. In terms of flexural properties, the flexural strength of the composites gradually decreased from 675.58 to 400.45 MPa with the increase of BF content due to the low modulus and strength of BFs and the low bonding rate with the matrix.

Shape memory composites are widely utilized in aerospace, medical equipment, and intelligent structures. In this paper, seven types of graphene oxide‐containing carbon fiber/aramid fiber (GO‐CF/AF) epoxy resin‐based hybrid reinforced shape memory composites (SMCs) with different hybrid ratios were prepared based on the vacuum infiltration hot pressing system (VIHPS), and these seven groups of composites exhibited favorable appearances and the microstructure was more desirable. To investigate the effect of different hybrid ratios on the shape memory properties of the composites, this study was carried out by adjusting the hybrid content of aramid fibers, and the experimental analyses were performed under single and multiple cycling conditions, respectively. The results demonstrated that the composites had the largest modulus of elasticity up to 134.8 GPa, the lowest porosity of 2.7%, the shape fixation rate of 91.59%, the shape recovery rate of 98.18%, and the shape recovery force of 8.99 N when the reinforcement was exclusively carbon fibers. When the reinforcement was solely aramid fibers, the elastic modulus of the composites was 73.58 GPa, and the porosity was the highest at 5.73%. But the shape fixation rate was as high as 98.42%, the shape recovery rate was 79.84%, and the shape recovery force was 6.56 N. In addition, the fiber fracture within the composite became more and more obvious with the increase in the number of cycles. This phenomenon led to crack expansion in subsequent cycling tests, thereby impeding the effective transfer of heat and mechanical properties, and ultimately resulting in a decrease in the shape memory properties of the composite. Highlights: GO‐CF/AF prepared by VIHPS has excellent shape memory properties. The shape memory properties of the composites decreased with an increasing number of cycles. The modulus of elasticity of the fiber affects the shape recovery force of the composites.

In order to study the effect of curing temperature on the shape memory properties (SMPs) of GO‐CF hybrid‐reinforced SMPCs, eight sets of composites were prepared at different curing temperatures (60, 70, 80, 90, 100, 110, 120, and 130°C). The rheological and curing properties of the matrix, and the apparent density, porosity, microstructure, and SMPs of the composite were measured and analyzed, respectively. The results showed that at 100°C, the composite has the highest apparent density (1.52 g/cm³), the lowest porosity (0.47%), the best SMPs, the shape fixed rate of 99.13%, the shape recovery rate of 96.54%, and the maximum shape recovery force (5.15 N). The shape recovery speed and rate of shape recovery are also the fastest. This is because when the curing temperature is 100°C, the viscosity of the matrix can be kept at a low level, and the curing reaction rate is appropriate. This not only ensures that the matrix can be fully infiltrated into the fiber space but also obtains the matrix with appropriate crosslinking degree. Therefore, the microstructure of the prepared composite is ideal, which makes the matrix has a strong ability to restrain the expansion force of the fiber and a high efficiency of the transfer force and heat. Finally, in the test of SMPs, the composite showed higher SMPs. It was concluded that the SMPs of the composites were mainly affected by the infiltration effect of the matrix in the fiber.Highlights: The microstructure of the composite was more ideal at 100 °C. The composite with the lowest porosity has the best shape memory properties. The high porosity weakens the heat and force transfer ability of the matrix. The shape memory properties of composites are the best prepared at 100 °C.