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.

Metamaterials with both reversible deformation and a long load plateau meet the demand for cyclic buffering, offering great application prospects in protective engineering. However, current metamaterials generally suffer from low material utilization, which limits their load-bearing and energy absorption performance. To address these limitations, a novel buffering metamaterial with a long load plateau is proposed in this work. Composed of bilaterally symmetric double-arc structures and vertically symmetric curved plates, the metamaterial is capable of recoverable large deformation and overall cooperative load-bearing deformation, thereby improving material utilization and optimizing structural load capacity and energy absorption performance. Experimental tests and numerical simulations were conducted to validate the long load plateau and recoverable large deformation characteristics of the metamaterial. The influences of structural geometric parameters on its mechanical behavior were also systematically analyzed. The results indicate that the long load plateau can be effectively tuned by adjusting the thickness of lateral double arcs, the thickness of intermediate curved plates, and the central transverse span. Once the intermediate curved plates are removed, the long load plateau feature disappears, and the force-displacement curve presents an approximately linear variation. Finite element simulations at equal mass confirm that the proposed metamaterial possesses better buffering performance than similar structures without a long load plateau, and the underlying buffering mechanism is clarified. The findings provide a novel design strategy for improving the performance of metamaterials with a long load plateau, and facilitate their application in protective engineering.

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.

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.

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.

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 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.

To enhance the prediction accuracy of low-velocity impact performance and improve the structural design efficiency of triangular corrugated sandwich beams, this paper proposes a machine learning modeling and optimization process for the impact response of sandwich beams based on a hard-parameter-sharing multi-task learning (MTL) framework. A sample dataset is generated using finite element models, and the rationality of the models is validated against existing experimental results. Subsequently, an MTL model is trained to simultaneously predict the structural specific energy absorption (SEA), the maximum deflection of the top panel, and the initial peak load. The results show that the MTL model optimized via Bayesian optimization demonstrates strong predictive performance under a 50 J impact energy condition. The predictions align well with the finite element simulation results, with the coefficient of determination R² for all output variables in the test set exceeding 0.989, thereby validating the effectiveness and reliability of the model in response prediction and engineering optimization analysis. Parameter sensitivity analysis reveals that the core cell count and core wall thickness have the most significant influence on structural stiffness, followed by the top panel thickness, while the bottom panel thickness has a relatively minor impact. Moreover, the core wall thickness exhibits a certain saturation threshold in terms of performance enhancement. In combination with the non-dominated sorting genetic algorithm Ⅱ (NSGA-Ⅱ), multi-objective optimization analysis are conducted focusing on deformation characteristics, energy absorption performance, and comprehensive performance, and yields optimal parameter configurations that meet different engineering design requirements for sandwich beams.

A bio-inspired fractal multi-cell circular (BFMC) tube with embedded regular polygons is proposed to address the gap between the need for high absorption and the limited performance of traditional thin-walled circular tubes. Inspired by biological structures and fractal hierarchy theory, geometric models of BFMC tubes embedded with square, pentagonal, and hexagonal cells are constructed. Numerical simulations are carried out to systematically investigate the effects of mass, fractal dimension, and the number of sides of the embedded polygons on the axial crushing performance, and the results are compared with those of typical multi-tubes. The results indicate that, under approximately equal mass conditions, the BFMC tube can significantly enhance the specific energy absorption and the load-bearing capacity owing to its fractal hierarchical and bio-inspired configurations. Its crashworthiness increases with mass, first decreases and then rises as the fractal dimension increases, and improves further as the number of polygon sides increases, while the peak force is only weakly affected. A theoretical model for predicting the mean crushing force of BFMC tubes is developed based on the super folding element theory and is validated through numerical simulations. This study provides theoretical support and structural design guidelines for developing high performance thin-walled energy absorption structures.

The choice of aluminum alloys used as the interlayers significantly influences the interfacial bonding properties and dynamic impact mechanical properties of 7B53 aluminum alloy composite plates (7A52/interlayer/7A63). In this study, the influence mechanism of different aluminum alloy interlayer materials (7A01, 6061, 2024 aluminum alloy) on the interfacial metallurgical bonding quality and the dynamic mechanical behavior at high strain rates (1700−3200 s⁻¹) was systematically investigated using tensile-shear tests, Charpy impact tests, split Hopkinson pressure bar (SHPB) tests, and scanning electron microscopy (SEM). The results show that the composite plate with the 6061 interlayer exhibits the optimal interfacial bonding performance, achieving a maximum shear strength of 109.6 MPa, which is 36.5 MPa higher than that of the plate with the 7A01 interlayer (73.1 MPa). This improvement is attributed to the fact that the 6061 alloy promotes the formation of fine and uniform grains at the interface, thereby effectively strengthening the interfacial region. SHPB tests reveal that the inhomogeneous deformation of the interlayer interrupts the penetration of cracks into the 7A52 layer and promotes crack deflection along the interface. The composite plate with the 7A01 interlayer shows low strain rate sensitivity. The plate with the 6061 interlayer, while decreases in flow stress due to thermal softening within the strain rate range of 1700–2700 s⁻¹, maintains stable deformation under high-velocity impact owing to its excellent ductility. Compared to the composite plate with the 2024 interlayer, the plate with the 6061 interlayer achieves higher plastic strain while retaining relatively high yield strength. The 6061 interlayer composite plate successfully achieves an effective integration of the high toughness of 7A52 and the high strength of 7A63, providing an important theoretical basis for the design of impact-resistant protective structures for armored vehicles.