Analysis of stable plastic regime of Rayleigh-Taylor instability in elastic-plastic solids

Rayleigh - Taylor instability (RTI) occurs between two materials when their density and pressure gradients are in opposite directions. Most of the past studies involving elastic-plastic (EP) materials have focused on estimating the instability threshold where the material yields and begins to flow. The pure elastic to stable plastic phase transition occurs much earlier than the instability, signifies the first point where the mechanical properties start to vary dramatically, and are rarely addressed in the literature. In this work, the EP transition is explored using a rotating wheel experimental apparatus. The test section attached to the wheel is filled with EP material (mayonnaise) and air such that the free surface of the EP material is driven radially outwards by the centrifugal acceleration. The EP threshold acceleration and the maximum elastic strain that can be fully recovered are explored for different 3D single-mode initial perturbation geometries and acceleration rates. Furthermore, the RT growth of the perturbations in the stable plastic regime is studied by holding the driving acceleration constant at EP transition acceleration until irreversible instability is observed. The perturbation growth is measured continuously, and the driving force based on the material mass, amplitude, and centrifugal acceleration is analyzed.