Experimental investigation of elastic wave propagation and inertia effects in extra soft gelatin material

Abstract In this paper, elastic wave propagation and inertia effects in gelatin-based soft material under impact loading is investigated. The dynamic test is principally performed by the classical SHPB (Split Hopkinson Pressure Bars) technique with highly sensitive piezoelectric polyvinylidene fluoride (PVDF) pressure sensors placed on the interfaces between the specimen and the bars. Digital image correlation (DIC) technique is conducted to measure the strong non- homogeneous strain field, the particle velocity, the the strain rate, the strain acceleration under transient stress state using high speed photography. The particle velocity and its gradient are used to extract the elastic wave velocity. Additionally, we derive closed-form equations for the additional axial stress produced by transverse inertia in the rectangular parallelepiped specimen under the non-equilibrium stress state. The amplitude of transverse inertial stress depends strongly on the strain rate and the strain acceleration. The transverse inertia results in a significant spike-like stress in the initial portion of inertial stress history and in the zone of the specimen near the impact side due to the acceleration stage of the impact test. It is obvious that the degree of inertia effects depends strongly on time steps and spatial positions.