Shutao Li

This study aims to clarify the mesoscopic damage evolution mechanisms of concrete subjected to rigid projectile penetration and provide support for the optimal design of high-performance protective structures. Based on the ABAQUS/Explicit finite element framework, a three-phase mesoscopic numerical model of concrete considering aggregate, mortar matrix, and interfacial transition zone (ITZ) is constructed. By combining the random convex polygon algorithm with the background mesh mapping technique, the intrinsic geometric features of stochastic materials such as crushed stone and pebble are accurately characterized. The effects of aggregate geometric characteristics, volume fraction, and projectile motion/geometry parameters (velocity, length–diameter ratio, curvature radius of the warhead CRH) on the damage evolution of the target, penetration depth, and velocity attenuation law are systematically investigated. The results reveal that increased aggregate angularity substantially enlarges both tensile and compressive damage zones and promotes crack bifurcation, which collectively enhances kinetic energy dissipation, reduces penetration depth, and accelerates projectile deceleration. Increasing the aggregate volume fraction can significantly enhance the anti-penetration resistance of the target. A high proportion of aggregate grains effectively enhances the structural toughness by blocking the crack propagation path. Penetration velocity, length–diameter ratio, and CRH are the core elements determining the penetration efficiency, and the increase in their values will lead to a significant increase in penetration depth and induce a change in the damage mode from local failure to large-scale cracking. The mesoscopic model and related conclusions established in this study can provide a theoretical foundation and numerical benchmark for the impact resistance design, optimization, and damage assessment of high-strength concrete protective structures.

Existing mesoscopic numerical models still exhibit shortcomings in terms of the aggregate geometric fidelity, interface transition zone (ITZ) characterization, and modeling efficiency. To solve these problems, this paper establishes a two-dimensional mesoscopic model and analysis method for concrete, considering randomly distributed convex polygons of aggregate grains and a three-phase structure comprising aggregate, mortar, and ITZ. An efficient random placement algorithm based on background meshing is proposed to enable rapid and accurate model construction. The effects of aggregate geometry, spatial distribution, and ITZ on mechanical properties and damage evolution have been systematically studied. A quantitative relationship has been established between damage energy and the decay of strength and stiffness, and damage quantification indices have been proposed. The damage rates of mortar and ITZ, along with the variation characteristics of the damage variable d_c at each stage, have been quantified. Neglecting the ITZ leads to overestimation of the peak strength and stiffness of concrete while exacerbating its post-peak brittle behavior. The most significant increases occur in both stiffness decay and damage growth at 90% of peak stress. A sudden change occurs at approximately 0.17% axial strain (corresponding to 80% of peak stress). This study offers a meso-scale foundation for understanding concrete failure and designing high-performance concrete.

The random inhomogeneity of rubble stone–concrete targets is the fundamental cause of the significant randomness in anti-penetration performance, thereby limiting the engineering application of rubble stone–concrete. Here, to study the penetration damage effects and the anti-penetration mechanisms of the rubble stone–concrete, a random inhomogeneity modeling method is proposed, which constructs high-fidelity hexahedral mesh models of rubble stone–concrete targets. The reliability of the numerical simulation methodology and parameters is validated by comparison with penetration test data. The effects of corundum rubble size, corundum rubble volumetric percentage, concrete strength, and projectile impact velocity on penetration damage and penetration depth are discussed. The results reveal that the optimal corundum rubble size should equal 1.0 times the projectile diameter to balance the performance and stability of anti-penetration at the 30% volumetric percentage. As the concrete strength increases, corundum rubble gains more support during the penetration process, which also makes significant contributions to improving anti-penetration performance. The percentages of the penetration resistance impulse contribution from concrete and corundum rubble are unrelated to the projectile impact velocity. Moreover, an empirical formula for predicting penetration depth in corundum rubble–concrete targets is proposed, which provides a reference for evaluating the anti-penetration performance of corundum rubble–concrete.

The damage ability of hypervelocity kinetic energy projectile penetrating ground has become a hotspot in modern military research. In this study, a hypervelocity impact test on a granite target subjected to projectiles using a two-stage light gas gun is conducted to study the stress wave evolution in granite under hypervelocity penetrations. The parameters of the *MAT_JOHNSON_HOLMQUIST_CERAMICS(JH-2) constitutive equation are calibrated using the results of the splinter impact test and the static test, and numerical simulations are performed using the smoothed particle hydrodynamics method coupled with finite element method (SPH-FEM coupled method) to extend the resulting data. A formula for calculating the stress wave peak attenuation is established, indicating that the maximum impact pressure produced by the hypervelocity impact decreases exponentially with scaling distance, and the attenuation coefficient is related to the degree of rock damage. Additionally, the attenuation of the speed of sound is used to characterize rock damage, and the damage deterioration law of granite under hypervelocity impact is analyzed based on the damage factor.

With the extensive application of composite laminates in protective structures, new materials and new structures have been developed rapidly. As an excellent impact-resistant material, aramid fiber is widely used in the field of protective structures. Aramid laminates show excellent performance in anti-penetration, but there is no research on its anti-explosive characteristics. In this paper, a kind of aramid–steel composite target (ASCT) plate protective structure is proposed innovatively. The failure mode and damage mechanism of three kinds of ASCT plates with equal area density and single-layer steel plates under a local explosion load are studied, and the most effective composite mode is given. The results show that the aramid laminates stuck on the back explosion surface ASCT (SA) exhibit the best anti-explosion effect, which is center deflection reduced by 12% and 18% compared with a single-layer steel plate (S-1) and an equal-thickness steel plate (S-2), respectively. Plate ASCT (SA), plate ASCT (AS), and ASCT (SAS) plate center tear failure did not occur. The analysis shows that different combinations change the propagation of stress waves in the structure, which in turn affects the failure of the composite plate. The critical failure dose of different structural configuration plates is obtained by simulation. The influence of explosion center distance, explosive charge, and bonding thickness of aramid laminate on the central deflection of steel plate was discussed by dimensional analysis, and the empirical formula of central deflection of the aramid–steel composite target plate was obtained. The research results can provide a theoretical basis and reference for the lightweight and efficient protection of composite structural armor.