Experimental Validation Technique for Constitutive Models Describing Behavior of Soft Tissue Surrogates During Projectile Penetration

Numerical simulations of ballistic penetration of soft tissues are particularly difficult to validate because relevant experimental data is not readily available. Efficient, controlled, high strain rate experiments involving large deformations must be developed for that purpose. This paper proposes an axisymmetric experiment to validate constitutive models describing the bulk mechanical behavior of soft tissue surrogates. The need to use techniques such as element erosion and re-meshing or to consider material failure is avoided by using a cylindrical target with a small pre-made cylindrical channel along its axis. Cavitation is excited by firing a spherical projectile through the pre-made channel whose diameter is smaller than that of the projectile. The transient response of the channel is recorded using a high speed camera and the images collected are analyzed using a digital image tracking software to measure the channel deformations. As an example to demonstrate the usefulness of the proposed experiment, measurements from a test involving a ballistic gelatin cylinder are used to evaluate the quality of numerical results produced by finite element analyses performed with ABAQUS/Explicit. The mechanical behavior of the soft tissue surrogate is represented in the simulations using a single-term Ogden model. Different values are attempted for the required material properties and friction coefficient based on data available in the literature and simple sensitivity studies. The experimental results are used to assess the results corresponding to each set of model parameters.