Comprehensive knowledge of strain rate-dependent viscoelastic properties of bony materials is necessary to understand the mechanisms of bone fracture under impact loading conditions (e.g., falls, traffic accidents, and military environments). Although the mechanical properties of bones have been studied for several decades, the high strain rate data and corresponding material parameters of the rate-dependent constitutive models are still limited. In this study, split Hopkinson pressure bar technique was used to test bovine cortical bones, to obtain the rate-dependent stress–strain curves in two directions (along and perpendicular to the bone fibers). A constitutive relationship comprising two terms was then applied to identify the material constants with strain rate effect and viscoelastic properties. In this model, the linear elasticity was combined with nonlinear viscoelasticity components to describe the overall nonlinear strain rate dependence. The presented data give strong experimental evidence and basis for further development of numerical biomechanical models to simulate human cortical bone fracture.

Titanium Ti6Al4V alloy is a superior material that has extremely high strength, hardness and good anti-corrosion resistance. Dynamic shear-compression experiments were carried out on the alloy to investigate the micro-mechanisms of adiabatic shear banding (ASB) formation. The split Hopkinson pressure bar (SHPB) setup were used for the tests at high strain rates. It was found that the shear deformation localization (SDL) was considerably affected by the complex loading conditions. The micro-mechanisms for the ASB formation relied on different shear compressive proportion of loadings (SCLPs). Scanning electron microscope (SEM) observations showed that the ASB width was related with the SCLP and the fracture failure of alloy was induced by the nucleation and growth of microvoids. In transmission electron microscope (TEM) analysis, the microstructural changes of material within the ASB were characterized by dynamic recrystallization (DRX) and twining grain formation, dislocation migration, and stacking and grain refining processes. The results in this article demonstrates a complex image of microstructural evolution of alloy in the shear localization process.

Based on the modified Hopkinson torsion bar, a high-temperature dynamic shear test method was proposed for the Ti-1023 alloy, and the microstructural evolution of the tested material at different temperatures was studied. By using the modified high-temperature Hopkinson torsion bar, high-temperature testing within 1000 °C can be achieved. As the specimen-heating rate was fast, and the temperature gradient of the experimental environment was small, valid experimental data can be ensured during the experiment. The experimental results show that stress-induced martensite can significantly enhance the strength of the Ti-1023 alloy. Dynamically recrystallized grains similar to those in adiabatic shear bands appear in the microstructure of the Ti-1023 alloy after severe plastic deformation. Therefore, it is possible to regulate the content of stress-induced martensite in the microstructure to improve the mechanical properties of other alloys that are similar to β titanium alloys.