A novel numerical method at the microscale for studying the mechanical behavior of an aluminum-particle-reinforced polytetrafluoroethylene (Al/PTFE) composite is proposed and validated experimentally in this paper. Two types of 2D representative volume elements (RVEs), real microstructure-based and simulated microstructures, are established by following a series of image processing procedures and on a statistical basis considering the geometry and the distribution of particles and microvoids, respectively. Moreover, 3D finite element modelling based on the same statistical information as the 2D simulated microstructure models is conducted to show the efficiency and effectiveness of the 2D models. The results of all simulations and experiments indicate that real microstructure-based models and simulated microstructure models are efficient methods to predict elastic and plastic constants of particle-reinforced composites.

Polytetrafluoroethylene/aluminum/tungsten (PTFE/Al/W) reactive materials of three different component mass ratios (73.5/26.5/0, 68.8/24.2/7 and 63.6/22.4/14) were studied in this research. Different from the PTFE/Al/W composites published elsewhere, the materials in our research were fabricated under a much lower sintering temperature and for a much shorter duration to achieve a brittle property, which aims to provide more sufficient energy release upon impact. Quasi-static compression tests, dynamic compression tests at room and elevated temperatures, and drop weight tests were conducted to evaluate the mechanical and impact-induced initiation characteristics of the materials. The materials before and after compression tests were observed by a scanning electron microscope to relate the mesoscale structural characteristics to their macro properties. All the three types of materials fail at very low strains during both quasi-static and dynamic compression. The stress-strain curves for quasi-static tests show obvious deviations while that for the dynamic tests consist of only linear-elastic and failure stages typically. The materials were also found to exhibit thermal softening at elevated temperatures and were strain-rate sensitive during dynamic tests, which were compared using dynamic increase factors (DIFs). Drop-weight test results show that the impact-initiation sensitivity increases with the increase of W content due to the brittle mechanical property. The high-speed video sequences and recovered sample residues of the drop-weight tests show that the reaction is initiated at two opposite positions near the edges of the samples, where the shear force concentrates the most intensively, indicating a shear-induced initiation mechanism.

Dynamic fracture and fragmentation characteristics of explosively driven rings and cylinders are important issues in the field of weapon effectiveness and protection. However, the comparison of fracture characteristics between metal cylinder and rings, and the fracture characteristics of the metal shells at different axial positions, are rarely touched. In the present work, a recovery tank was used to collect fragments, and witness plates were used to investigate the fragment spatial distributions. Before the test, the representative positions of metal shells were plated with copper layers to locate the original position of the recovered fragments. After the test, scanning electron microscopy and optical microscope were used for characterizing the microstructure of the recovered fragments from different positions. Then, the recovered fragments were weighed and measured to investigate their mass and size characteristics. In addition, numerical simulation was used to further investigate the fracture mechanisms of explosively driven cylinders and rings. It was found that the projection angle axial distribution of the fragments for the metal cylinder was similar to that of the fragments for the metal rings. However, the fracture characteristics of the metal rings were significantly different from those of the metal cylinder. The adiabatic shear band played a key role in the fracture process of the metal cylinder, whereas the adiabatic shear band had little chance to initiate in the fracture process of the metal rings because the metal rings could deform uniformly with much fewer strain localizations due to their much lower length. The fracture surfaces of the fragments from different positions of the metal cylinder were very smooth, whereas dimples were found in the fracture surfaces of the fragments from different positions of the metal rings. The mass distribution of the fragments from the metal rings was more uniform than that of the fragments from the metal cylinder, and the circumferential rupture strains of the metal rings were much larger than those of the metal cylinder.

The impact response of a composite structure consisting of a metal-packaged ceramic interlayer and an ultra-high molecular weight polyethylene (UHMWPE) laminate has been studied through a ballistic test and numerical simulation. The studied structure exhibits 50% higher anti-penetration performance than the traditional ceramic/metal structure with the same areal density. The metal-packaged ceramic interlayer and the UHMWPE laminate are key components in resisting the penetration. By using a metal frame to impose three-dimensional constraints on ceramic tiles, the metal-packaged ceramic interlayer can limit the crushing of the ceramic and contain the broken ceramic fragment to improve the erosion of the projectile. The large deformation of UHMWPE laminate absorbs a large amount of energy from the projectile. By decreasing the amplitude of the shock wave and changing the distribution of the impact load in the structure, the projectile has longer residence time on the interlayer. The anti-penetration performance shows within 10% variation when the impact position is varied. Due to the asymmetric deformation and high elastic recovery ability of the UHMWPE laminate, the projectile trajectory deflection is increased, and the broken ceramic fragments are restrained, thereby mitigating after-effect damage caused by the projectile after penetrating the structure.

Adiabatic shear bands in uranium alloy projectiles/penetrators, during penetration, allow them to “self-sharpen,” a process that is absent in most tungsten alloy projectiles/penetrators. U-0.75 wt % Ti alloy samples have been accelerated to impact steel targets, and the distribution of adiabatic shear bands in residual samples has been studied in detail to understand the effect of self-sharpening on penetration. In our study, self-sharpening was evidenced by the distribution of the shear bands in the recovered sample. The shear bands formed during impact were observed to change direction when they crossed grain boundaries, which indicated that the grain boundaries had an influence on the adiabatic shear bands of U-0.75 wt % Ti. Micro-hardness test results showed that the Vickers micro-hardness in the adiabatic shear zone was 18% lower than that in the matrix. In the split-Hopkinson pressure bar (SHPB) experiment, a strain rate of around 2891 s⁻¹ was the threshold strain rate that triggered the formation of adiabatic shear bands in the U-0.75 wt % Ti alloy.