In the present study, a novel multicomponent accumulative roll bonding (MARB) approach was proposed and successfully applied to prepare a nanostructured Ag/Cu multilayered composite. Microstructure, hardness and conductivity of Ag/Cu multilayered composites with different MARB cycles were investigated by electron backscatter diffraction, transmission electron microscopy, nanoindentation and four-point probe direct current methods. It is demonstrated that the MARB approach is able to effectively suppress the shear band formation and result in a remarkable reduction in the thickness of the Ag/Cu multilayered composite down to 40 nm via only 6 cycles. The as-prepared nanostructured Ag/Cu multilayered composite exhibits an excellent combination of high hardness (2.24 GPa) and high electrical conductivity (equivalent to 84% of international annealed copper standard; IACS). It owes these extraordinary properties to the atomically ordered and chemically sharp heter-ophase interfaces and low density of grain boundaries resulting from the MARB process.

A lightweight composite armor system composed of boron carbide (B4C) ceramic panels, carbon-fiber interlayer, and ultra-high molecular weight polyethylene (UHMWPE) backplate has been widely used. This study aims to explore the effect of different constraint conditions on the ballistic resistance of lightweight composite armor. Thus, ballistic experiments of 12.7 mm armor-piercing incendiary (API) projectiles impacting armor targets under different constraint conditions are designed, and numerical simulations are performed to simulate the structural impact response of composite armor. A satisfied consistency is revealed by comparing the numerical results and the ballistic experimental results. Besides, the numerical simulation method is used to research the influence of the distance between the impact point and the constraint conditions on the ballistic performance of the composite armor. The results demonstrate that the ballistic performance of the composite armor is better if the impact point is farther from the constraint conditions as this can enhance the flexibility of composite armor. In conclusion, the flexibility of the constraint conditions is positively correlated with the ballistic performance of B4C/C/UHMWPE composite armor. This conclusion provides a guideline for the design and application of composite armor.

Abstract Annealing of cold-deformed metals often leads to softening of the metals due to the annihilation of lattice defects produced upon deformation. Here we show that in a shock-loaded CrCoNi-based medium-entropy alloy, the yield strength is enhanced by 33% and ductility is substantially improved by 19% after low-temperature annealing treatment. The improved properties stem from the ultra-high density lattice defects (dislocations, stacking faults and twins) produced upon a novel dynamic equal channel angular pressing at liquid nitrogen temperature under an ultra-high strain rate of 1.17 × 105 s− 1. Reorganization of lattice defects to nanotwins via the expansion of initial nanotwins or the glide of partial dislocations occurs during the annealing treatment. The nanotwins can exert strong interaction with the dislocations and thus produce substantial strengthening and increase the strain-hardening capability of alloys. These results provide insights into understanding the annealing strengthening mechanisms in severely plastic-deformed metals.

Lightweight composite armour systems composed of a B4C ceramic panel and composite back panel have excellent bulletproof performance and are used to resist attacks from armour-piercing incendiary projectiles. Numerical simulations can be used to simulate the process of projectiles impacting armour; thus, this method is widely used in armour ballistic performance analyses. To verify the accuracy of the B4C material model, a finite element method based on two-dimensional smoothed particle hydrodynamics is used to simulate the penetration process of steel projectiles into B4C/Al composite armour. To verify the accuracy of the ultra-high molecular weight polyethylene (UHMW-PE) model, a three-dimensional Lagrange method was used to simulate the penetration of a fragment simulating projectile into the UHMW-PE. The influence of geometric strain in the erosion algorithm on the ballistic performance of the UHMW-PE was investigated, and the erosion geometric strain suitable for the UHMW-PE was identified. The impact of a 12.7 mm armour-piercing incendiary projectile on the B4C/UHMW-PE and B4C/C/UHMW-PE armours was then simulated and tested experimentally. The results showed that the B4C/UHMW-PE armour was penetrated by the projectile, while the B4C/C/UHMW-PE armour was not penetrated. The ballistic performance of the B4C composite armour, damage state of the B4C ceramic, and bulge deformation of the UHMW-PE were accurately obtained in the simulations. A comparison with the experimental results showed that the proposed method could accurately simulate the penetration process of the B4C/UHMW-PE armour, reveal the penetration mechanism of composite armour, reduce the number of projectile tests, and provide a basis and technical means for the design and optimisation of lightweight composite armour.