To date, research on the physical and mechanical behavior of nickel-titanium shape-memory alloy (NiTi SMA) has focused on the macroscopic physical properties, equation of state, strength constitution, phase transition induced by temperature and stress under static load, etc. The behavior of a NiTi SMA under high-strain-rate impact and the influence of voids have not been reported. In this present work, the behavior evolution of (100) single-crystal NiTi SMA and the influencing characteristics of voids under a shock wave of 1.2 km/s are studied by large-scale molecular dynamics calculation. The results show that only a small amount of B2 austenite is transformed into B19’ martensite when the NiTi sample does not pass through the void during impact compression, whereas when the shock wave passes through the hole, a large amount of martensite phase transformation and plastic deformation is induced around the hole; the existence of phase transformation and phase-transformation-induced plastic deformation greatly consumes the energy of the shock wave, thus making the width of the wave front in the subsequent propagation process wider and the peak of the foremost wave peak reduced. In addition, the existence of holes disrupts the orderly propagation of shock waves, changes the shock wave front from a plane to a concave surface, and reduces the propagation speed of shock waves. The calculation results show that the presence of pores in a porous NiTi SMA leads to significant martensitic phase transformation and plastic deformation induced by phase transformation, which has a significant buffering effect on shock waves. The results of this study provide great guidance for expanding the application of NiTi SMA in the field of shock.

It has been found that there are two kinds of interfaces in a Cu/Pd multilayered film, namely, cube-on-cube and twin. However, the effects of the interfacial structure and modulation period on the mechanical properties of a Cu/Pd multilayered film remain unclear. In this work, molecular dynamics simulations of Cu/Pd multilayered film with different interfaces and modulation periods under in-plane tension are performed to investigate the effects of the interfacial structure and modulation period. The interface misfit dislocation net exhibits a periodic triangular distribution, while the residual internal stress can be released through the bending of dislocation lines. With the increase of the modulation period, the maximum stress shows an upward trend, while the flow stress declines. It was found that the maximum stress and flow stress of the sample with a cube-on-cube interface is higher than that of the sample with a twin interface, which is different from the traditional cognition. This unusual phenomenon is mainly attributed to the discontinuity and unevenness of the twin boundaries caused by the extremely severe lattice mismatch.

The thermo–chemo–mechanical coupling on the thermal shock resistance of 20 vol%-ZrB₂–15 vol%-SiC–graphite composite is investigated with the use of a self-developed material testing system. In each test, a specimen under prescribed constant tensile pre-stress (σ₀ = 0, 10, 20 and 30 MPa) was subjected to 60 cycles of thermal shock. In each cycle, the specimen was heated from room temperature to 2000 °C within 5 s in an air atmosphere or an Ar atmosphere. The residual flexural strength of each specimen was tested, and the fracture morphology was characterized by using scanning electron microscopy (SEM). There were three different regions in the fracture surface of a specimen tested in the air, while no such difference could be observed in the fracture surfaces of the specimens that were tested in Ar. The residual flexural strength of the composite that was tested in Ar generally decreases with the increase of σ₀. However, in the range of 0 ≤ σ₀ ≤ 10 MPa, the residual flexural strength of the composite that was tested in the air ascended with the increase of σ₀ due to the healing effect of oxidation, but it descended thereafter with a further increase of σ₀, as the effect pre-stress that became prominent.

The mechanical properties of metal multilayers change significantly when the modulation period decreases to a nanoscale. As is well known, the lattice misfit between Ni and Cu is~2.7%, it means that the coherent and semi-coherent interfaces can form between the Ni and Cu atomic layer. Hetero-twin interface Cu/Ni multilayer film with a modulation period of several nanometers and grown along the[111] direction is realized experimentally, and the mechanical properties change significantly due to the effect of interfaces. In this study, molecular dynamics simulations on Cu/Ni multilayers with coherent, coherent twin, semi-coherent, and semi-coherent twin interfaces under nanoindentation are carried out to study the deformation evolutions of different interfaces and the interactions between dislocation and interfaces. Furthermore, the influence of Cu/Ni interface on the mechanical property is investigated. The simulation results show that the different interface structures exhibit different strengthening and/or softening mechanisms at different indentation depths. The hardness values of the Cu/Ni multilayer films with four different interface structures are different, and the hardness of the coherent interface is larger than the semi-coherent interface's. The hardness values of the four interface structures reside between the pure Cu and pure Ni. For the coherent twin interface, with the increase of the modulation ratio, the strengthening effect of the twin interface is enhanced. The softening effect for the coherent interface is mainly attributed to the generation of parallel dislocations and their proliferation. While for the semi-coherent interface, the mismatched networks are formed at the Cu/Ni interfaces, the softening effect on the movable dislocation is mainly the repulsion of the mismatched network, while the strengthening effect on the movable dislocation is the hindrance of the mismatched dislocation network. The strengthening of the coherent twin interface is attributed to the limited effect of twin interface on the movable dislocation within the monolayer. Unlike the coherent twin interface, the strengthening effect of the semi-coherent twin interface is mainly due to the mutual repulsion between the arched dislocation, which is generated within the twin interface, and the mismatched network. Furthermore, the pinning effect of misfit dislocation network will impede the migration of twin interfaces and will also enhance the mechanical property of Cu/Ni multilayer film.