Relationship between a non-spherical collapse of a bubble and a stress state inside a wall

Abstract

This study performed a fluid/material coupled numerical simulation of the first stage of a non-spherical collapse of a bubble near a wall and investigated the stress state inside the elastic material of the wall according to the change in the stand-off distance γ between the bubble and the wall. The relationship between the collapse behavior of the bubble and propagation of stress waves was confirmed for typical collapse modes: pancake-shaped mode at γ = −0.3, hemispherical mode at γ = 0, microjet mode at 0.3 < γ < 1.0, and detaching mode at γ > 1.2. The stress influence area, which is an index of material damage, was estimated. At 0.3 < γ < 1.0, the stress influence area caused by the microjet is narrow and shallow in the material; in contrast, that caused by the pressure waves spreads more widely and deeply, especially inside the material. This means that the pressure wave has a larger influence than the microjet on damage to a material even though the maximum value of the equivalent stress is nearly identical between the microjet and the pressure wave. Additionally, the depth of the stress influence area at 0.3 < γ < 0.5 is larger than that at γ = 0, although the volume and the maximum stress are larger at γ = 0 than at 0.3 < γ < 0.5. This indicates that the case of toroidal bubble rebound attaching to a wall has the potential to cause a deeper damage inside a material in comparison with hemispherical bubble collapse.