Dynamic mechanical response and constitutive model of (Ti_37.31Zr_22.75Be_26.39Al_4.55Cu₉)₉₄Co₆ high-entropy bulk metallic glass

In this work, the mechanical response and fracture characteristics of (Ti_37.31Zr_22.75Be_26.39Al_4.55Cu₉)₉₄Co₆ high-entropy bulk metallic glass (HE-BMG) were investigated in detail over a wide range of strain rates (10⁻⁴–10⁵ s⁻¹). The HE-BMG exhibited a negative strain rate sensitivity under uniaxial compression, with the strength showing more significant rate dependence under dynamic conditions. The shear band behavior translated from the dominance of multiple shear bands propagations under quasi-static compression to the rapid propagation of a single shear band to form cracks under dynamic compression. Under dynamic loading, the shearing velocity increased along an arc-shaped displacement path, and the local stress state on the shear fracture surface shifted from compressive-shear to tensile-shear, accompanied by changes in fracture morphologies. The spall strength of HE-BMG decreased as flyer impact speed increased, while the long-term dependence of spall strength on strain rate may be positive. With the increase of impact speed, the main microstructural features of the spalling surface translated from flat regions accompanied by dimples to cup-cone structures. Furthermore, the complete parameters of the Johnson–Holmquist II (JH-2) model for HE-BMG were obtained based on experimental data. Numerical simulations of planar impact, penetration, and hypervelocity impact are in good agreement with experimental results, demonstrating the validity of the JH-2 model parameters. The current work has important guiding value for the application of HE-BMG in space debris protection.