Acceleration rate effects on Rayleigh-Taylor instability in elastic-plastic solids

Rayleigh-Taylor instability (RTI) is a hydrodynamic instability that can also occur in elastic-plastic (EP) materials and soft yield-stress solids. Most theoretical and numerical studies of RTI in EP materials assume a uniform, constant acceleration field. However, several applications of RTI in solids occur at variable and impulsive acceleration fields. A novel rotating wheel experimental setup that allows for imposing variable acceleration profiles and adjustment of the rate of increase in the driving acceleration is used to study the transition from the stable plastic regime to the instability regime of RTI in EP materials. The instability acceleration and the instability strain are measured for different single-mode perturbation geometries in a soft EP yield-stress material under linearly increasing acceleration profiles. From the instability experiments, it is observed that for larger wavelengths, the effect of the initial amplitude is more prominent. A larger wavelength allows stress concentrations at the base of the perturbations to dissipate, delaying the necking behavior observed at the instant of instability. Within the parameters space investigated, no systematic dependence of instability strain on acceleration rate was observed.