Mechanism of nanoscale helium bubbles influencing dynamic tensile response of polycrystalline copper

This work investigates the mechanism of nanoscale helium (He) bubbles influencing the dynamic tensile response of quasi two-dimensional (2D) polycrystalline copper (Cu), based on molecular dynamics simulations. The dynamic fracture behaviors are explored under two different loading conditions (uniaxial tensile loading and shock loading). For uniaxial tensile loading, it's found the effect of He bubble on the tensile strength gets weaker with the increasing strain rate. A strain rate-dependent fracture mechanism that transforms from the growth and coalescence of He bubbles to the cleavage fracture of grain boundaries (GBs) as the strain rate increases is investigated. Under shock loading, the effect of He bubble on reducing the spall strength of polycrystalline Cu is more significant at lower impact velocities and will disappear as the impact velocity increases higher. The mechanism of spall damage is investigated by comparing the effect of He bubbles, voids and GBs under different impact velocities. Additionally, the dynamic response under the above two loading conditions is compared. The results indicate that the effect of He bubble distribution on the strength is more significant under shock loading than uniaxial tensile loading.