Jialin Chen

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.

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.

To study the effect of the addition of potassium perchlorate (KClO₄) on the performance of nano thermites, Al/Bi₂O₃ nano thermites with different mass fraction (wt%) of KClO₄ was made by ultrasonic dispersion method. Then, all samples were tested by SEM, DSC and rapid excitation ignition. DSC results showed Al/Bi₂O₃/10 wt%KClO₄ had the highest heat release. Compared with Al/Bi₂O₃, the heat release increased by 28.32%. The results of activation energy calculations showed Al/Bi₂O₃/30 wt%KClO₄ had the lowest activation energy (Ea). Its activation energy was reduced by 30%, mere about 149.17 KJ mol⁻¹. Finally, it can be seen from the combustion situation that the addition of KClO₄ reduced the intensity of burning. This work found a way to increase the heat release or reduce the activation energy of nano thermites by controlling the amount of KClO₄ added.

To investigate the effect of the addition of poly (vinylidene fluoride) (PVDF) on nanothermites, Al/MoO₃/PVDF energetic nanocomposites were prepared using electrospraying method. As a control group, Al/MoO₃ was also designed. Then, both samples were tested by FE-SEM, XRD and TG-DSC. TG-DSC results showed that the Al/MoO₃/PVDF energetic nanocomposites released more than 934.0 J g⁻¹ with two obvious exothermic peaks. Compared with the control group of 800.7 J g⁻¹ heat, it changed the thermal performance to some extent. There were Mo₂C among the residues products after the reaction via XRD. The activation energy (Ea) was analyzed using the Kissinger method under different heating rates by DSC. The addition of PVDF reduced the Ea of the thermites. To explore the combustion performance, a preliminary experiment was designed. The Al/MoO₃/PVDF energetic nanocomposites were easier to ignite and the burning was more durable, which was significant in solid propulsion and applications requiring extended combustion time.