Spall strength of a zirconium-based bulk metallic glass under shock-induced compression-and-shear loading

We present results of a series of plate-impact experiments conducted to understand spall threshold in a zirconium-based bulk metallic glass (BMG), Zr41.25Ti13.75Ni10Cu12.5Be22.5, following normal shock-induced compression and combined compression-and-shear loading. The experiments were conducted using a 82.5 mm bore single-stage gas-gun. A multi-beam VALYN VISAR was used to measure the particle–velocity at the free-surface of the target plate. For the normal shock-compression experiments, the impact velocities were chosen to span the elastic to the elastic–plastic range of the BMG during impact; the spall strength was inferred, at different levels of shock-induced compression, from the measured particle–velocity history of the free-surface of the target plate. For the combined compression-and-shear experiments the shock-induced normal stress was kept constant at ∼5 GPa (i.e. below the HEL for the BMG), while the projectile skew angle was varied from 6° to 24°. These skew angles are expected to result in a maximum shear strains of up to 3.18%. Under normal impact, at impact stress levels below the HEL, the spall strength of the BMG was found to decrease with increasing levels of the impact stress. However, at impact stress levels above the HEL the spall strength is observed to remain constant with increasing impact stress at ∼2.3 GPa. In the case of the combined compression-and-shear loading, with increasing levels of shear strain (at a constant shock-compression level below the HEL), the spall strength of the BMG was found to initially decrease, increase dramatically in the shear strain range of 2–2.4%, and then fall again as the shear strain is increased from 2.4% to 3.18%.