The continuous advancement of modern armor protection technology has imposed severe challenges on the damage power of shaped charge warheads. Traditional liner materials have become a major constraint in improving penetration depth due to their limited comprehensive performance. High entropy alloys (HEAs), owing to their unique multi-principal element design, exhibit core potentials, such as high strength, high hardness, and excellent dynamic fracture toughness, thereby making them highly promising candidate materials for new-generation liners. In this study, the CoCrFeMnNi high entropy alloy was prepared via selective laser melting (SLM) technology, and the mechanical properties of the alloy were tested under quasi-static and dynamic loadings. The Johnson-Cook (J-C) dynamic constitutive model and related parameters for the CoCrFeMnNi HEA were determined. Using LS-DYNA, shaped charge jet formation models for both copper and high entropy alloy were established, and numerical simulations were carried out on the processes of jet formation and target penetration for copper and HEA. The research results indicate that, when compared with copper, the CoCrFeMnNi HEA liner can form a more stable and continuous jet. Its unique formation and stretching-breakup mechanisms ultimately result in greater penetration depth, confirming the significant advantage of high entropy alloys in the enhanced damage effect.

Grain size effect is one of the key factors governing the dynamic mechanical response of metallic materials. Phase transformation iron is selected as the model material, and a series of nanocrystalline polycrystals with identical topology and grain orientation distributions but different grain sizes are constructed to investigate size effects under a fixed grain configuration. Molecular dynamics simulations show that, under high strain rate uniaxial compression, all models undergo elastic deformation, α→ε phase transition, and high-pressure phase plastic deformation. During the elastic stage, grain boundaries act as a soft layer, leading to lower stresses in the fine grain models than in the coarse grain model. After the structural phase transition, grain boundaries hinder the plastic development of the new phase, so that the fine grain models exhibit higher stress than the coarse grain models. At the onset of phase transition, the threshold of phase transition of smaller grains is lower, and the transformed phase in fine grains mainly forms stacking fault structures, whereas twinning structures appear in relatively larger grains. With increasing strain, the disappearance of twinning and the reconstruction of stacking faults are observed in large grains. Under high strain rate tension, shear strain of grain boundary in the large grain models is highly localized, readily forming continuous shear bands that serve as preferred paths of crack propagation. After grain refinement, shear strain of grain boundary gradually evolves into a diffuse mode, and the effective paths of crack propagation are constrained by the network of grain boundaries. The change of grain boundary effects leads to a non-monotonic variation of fracture strength with the grain size.

Deep space exploration faces challenges from extreme temperatures and complex high-speed operating environments, placing higher demands on the low-temperature impact resistance of materials. In this study, a low-temperature Hopkinson bar impact experimental device was developed to achieve dynamic loading of materials under ultra-low temperature conditions within a vacuum liquid helium environment. The dynamic mechanical response of 301 stainless steel produced by two rolling processes was investigated under the combined effects of low temperature (30–298 K) and high strain rates (4000–5000 s⁻¹). Experimental results show that the yield strength of both materials exhibits a significant negative correlation with temperature and a positive correlation with strain rate. The unidirectionally rolled samples displayed an anomalous increase in toughness at 77 K. The study indicates that the unidirectional rolling process induces a higher content of martensitic phase, thereby endowing the material with greater strength. Microstructural characterization results reveal that the anomalies in macroscopic mechanical behavior stem from the competition of deformation mechanisms. At room temperature, the samples mainly exhibit a toughness fracture mechanism, dominated by ductile dimples, whereas at low temperatures, they transition to a brittle fracture mode, dominated by quasi-cleavage. Based on this, the Johnson-Cook constitutive model was used to fit the mechanical properties, demonstrating good consistency with the experimental results. This research provides important experimental methods and theoretical support for the dynamic strength and toughness design of metallic materials under extreme low-temperature impact conditions.

To address the issue of weak interfacial bonding and insufficient ballistic performance in poly-p-phenylene ben-zobisoxazole (PBO) fiber composites caused by the chemically inert fiber surface, the waterborne polyurethane impregnation followed by a hot-pressing process was employed to fabricate PBO composite laminates with varying resin mass fractions (18.40% and 20.45%) and numbers of fiber layers (10, 20, and 30 layers). The tensile properties, ballistic limit, failure modes, and energy absorption mechanisms of the composites were investigated through quasi-static tensile testing, ballistic experiments, and X-ray computed tomography (CT). The results indicate that this process can effectively improve the formability and protective performance of the PBO fiber composite laminates. In comparison with the specimen exhibiting a resin mass fraction of 20.45%, the 30-layer specimen with a resin mass fraction of 18.40% demonstrated a 14.86% increase in tensile strength and a 28.33% increase in elastic modulus. The ballistic limit increases with resin content. The ballistic limit of the 10-layer and 20-layer specimens with a resin mass fraction of 20.45% increases by 9.9% and 5.3%, respectively. However, the increasing effect diminishes with a greater number of layers. For the 30-layer specimens, the difference in resin mass fraction between the two resins was less than 1%. The primary failure modes of the composite laminates include fiber shear fracture, matrix cracking and delamination, and fiber tensile fracture. Energy absorption is achieved through the synergistic mechanisms of fiber compressive deformation, shear, and tensile fracture. Efficiency of the energy absorption decreases with increasing impact velocity, while it increases with the number of layers under the same impact velocity. The effect of colloid content diminishes significantly for numerous layers. The study can provide a reference for the design of ballistic protection using PBO fiber composites.

To investigate the influence of backplate mechanical properties on the formation mechanism of ceramic cones in boron carbide ceramic composite armor, four typical backplate materials, including 6061 aluminum alloy, 7075 aluminum alloy, T300 carbon fiber board, and ultra-high molecular weight polyethylene (UHMWPE) were selected. A combination of ballistic impact experiments conducted via a one-stage light gas gun and numerical simulations performed with LS-DYNA was adopted to systematically study the effects of backplate yield strength, stiffness, and wave impedance on the morphology and evolution of ceramic cones. The results indicate that: the load transfer from the ceramic cone to the backplate is not solely dependent on a single outer cone but is achieved through the synergistic action of multiple cracks, including the outer and inner cones; the yield strength of the backplate has no significant effect on the crack propagation of the main cone; regarding stiffness, the outer cone angle decreases linearly with increasing elastic modulus, while the inner cone angle increases exponentially; wave impedance alters the internal stress field of the ceramic by modulating stress wave reflection/transmission, resulting in a linear increase in the inner cone angle and an exponential decrease in the outer cone angle with increasing impedance.

Carbon fiber reinforced polymer (CFRP), as an advanced composite material, are widely used in engineering applications. However, research on the dynamic mechanical behavior of ultrathin CFRP laminates remains relatively limited. In this study, unidirectional ultrathin prepreg and hot-pressing molding processes were employed to fabricate ultrathin CFRP laminates with a single ply thickness of only 0.1 mm. The strain rate effects on specimens with five different ply orientations—0°, 90°, 0°/90°, 45°, and ±45°—were systematically investigated. Quasi-static compression experiments indicated that the 45° ply orientation enhanced plastic behavior but reduced material strength and modulus, whereas the 90° ply orientation contributed to increased modulus and strength while reducing plastic deformation. Dynamic impact tests revealed that the 90° ply orientation improved both dynamic modulus and strength while decreasing yield strain. Although the 45° ply orientation reduced dynamic yield strength, it significantly increased the sensitivity of dynamic modulus and yield strain to strain rate. Compared with conventional CFRP laminates with a 0°/90° ply layup (ply thickness is 0.295 mm, and dynamic strength and modulus are 900 MPa and 10.12 GPa, respectively), the ultrathin CFRP composites developed in this study exhibited a 66% increase in fiber content per unit thickness; under the 0°/90° ply configuration, dynamic strength and modulus were enhanced by 123% and 926%, respectively. Based on the experimental data, a constitutive model for the ultrathin CFRP composites was established, and corresponding constitutive parameters were provided, offering a basis for predicting the mechanical behavior of CFRPs under different ply orientations and strain rates.

To achieve the synergistic improvement of load-bearing stability and energy absorption in lightweight protective structures, a bio-inspired thin-walled-foam composite structure based on mechanical matching design was proposed. Three configurations of polylactic acid (PLA) bio-inspired shells were fabricated via additive manufacturing, and subsequently filled with polyurethane foam through an in-situ foaming process. Tensile tests, quasi-static compression tests, and drop-weight impact tests were conducted to investigate the foaming-induced thermal effects on the mechanical properties of the PLA shells and the structural response of the composites. Crashworthiness was evaluated using peak crushing force (PCF), plateau force, specific energy absorption (SEA), mean crushing force (MCF), and crushing force efficiency (CFE). Results show that the temperature rise during foaming reduces the elastic modulus and strength of PLA while improving its ductility, thereby enhancing the mechanical compatibility between the shell and foam. Consequently, the composite structures exhibit significantly increased plateau force and MCF, and their collapse mode transforms from local instability to progressive stacked crushing, leading to stable hierarchical energy absorption. Dynamic impact tests further demonstrate the superior load-bearing and energy absorption performance of the composite structures under high-energy impact. The results highlight the synergistic role of geometric configuration, material matching, and thermal-mechanical coupling in regulating the energy absorption behavior, providing guidance for the design of lightweight bio-inspired protective structures.

As lightweight and high-strength functional-structural integrated materials, cellular structural materials are widely applied in aerospace, automotive manufacturing, and biomedical fields. However, traditional single-configuration cellular materials (e.g., honeycomb structures and point-lattice lattices) gradually exhibit performance limitations under complex conditions such as impact shock waves, multi-directional impacts, or nonlinear deformations. Against this backdrop, heterogeneous cellular structure material (HCSM) have emerged as a research hot pot in impact protection. This paper systematically reviews recent design strategies and impact resistance performance of HCSM. HCSMs are primarily categorized into two types: topological configuration heterogeneity (including complementary and enhanced fusion) and material heterogeneity (e.g., filling with foam materials and shear-thickening materials). Through innovative “functional fusion” approaches, they overcome the performance bottlenecks of single-configuration cellular materials. The study further elucidates the synergistic reinforcement effects and deformation mechanisms of HCSM under impact loads, while analyzing their intrinsic mechanisms for improving energy absorption efficiency, stiffness, and stability. Despite significant progress in HCSM research, challenges remain in connectivity optimization, additive manufacturing process compatibility, complex condition validation, and multifunctional integration. Going forward, the integration of artificial intelligence and machine learning technologies holds promise for achieving end-to-end optimization of HCSMs from design to manufacturing, thereby providing new directions for developing next-generation high-performance impact-resistant structural materials.

The self-locking structure achieves interlocking property through ingenious design of the connection mode between cells, which enables the cells to lock with each other without the need for any additional constraints. The self-locking structure possesses significant advantages, such as light weight, portability, rapid assembly, and disassembly. Therefore, this structure is widely applied in various fields, such as shock resistance and explosion prevention. Self-locking structures exist in many structures in nature. The design concepts of self-locking structures are introduced from three aspects: the inspiration from biomimetic self-locking structures, the energy absorption mechanism of periodic structures, and failure of shear bands in periodic structures. The research progress of two-dimensional unidirectional self-locking structures, three-dimensional multi-directional self-locking structures and curved self-locking structures are then respectively introduced based on the classification of self-locking direction. Among them, the multi-directional self-locking structure withstands more complex loading conditions. Therefore, research progress of three representative multi-directional self-locking structures based on dumbbell-type, bone stitching, and origami design are further introduced. Finally, the research on the self-locking structure is summarized, and its future research prospects are discussed.

To achieve the precise generation of high-amplitude impact waveforms required for aviation safety testing and related fields, this study investigates the impact waveform regulation mechanisms of graded cellular metals under different boundary conditions. Based on the conservation laws of mass and momentum, theoretical models for impact waveform generation using graded cellular metals are established for both free and elastic boundary conditions. Furthermore, an inverse design method for density gradient is proposed, which incorporates an average relative density constraint combined with Gauss-Newton iteration, enabling the reverse solution from a prescribed acceleration waveform to the material density gradient distribution. Finite element results demonstrate that the proposed method can effectively generate required waveforms—such as triangular and half-sine waves—under both boundary conditions. The study also reveals that: free boundaries are more suitable for generating high amplitude and long duration waveforms, whereas elastic boundaries can improve the realizability of low-amplitude waveforms through stiffness regulation; boundary conditions do not alter the impact duration but exert a significant influence on waveform shape; and excessive impedance mismatch between adjacent layers will intensify waveform oscillations, thereby compromising the waveform generation accuracy. The proposed inverse design strategy for density gradients exhibits favorable versatility and provides both theoretical support and a practical design tool for the development of high-amplitude impact testing technologies.