Mode I Fracture Response of Polymer Based Gelatins as a Function of Loading Rate

Extended Abstract

Traditional collagen-based ballistic gelatin has been used extensively to determine the effectiveness of bullets and firearms because of its similar density to natural tissue. In these investigations, the gel is subjected to a projectile penetration experiment, during which temporary and permanent cavities are observed in the gel medium. The tensile failure mode dominates the damage mechanisms in the formation of these cavities. However, the mechanical response of ballistic gelatin is sensitive to temperature and the gel has a limited shelf life. Synthetic polymer-based gelatins alleviate these issues and thus are good candidates for an alternative tissue simulant. The ability to closely control the synthesis of these polymer gels gives them a distinct material structure, which governs mechanical characteristics on the macro-scale (i.e. strength, compliance). This ability to tune mechanical properties deems them suitable for many other applications such as in sensors, robotics, chemical, and biomedical uses. In order to determine the tensile failure properties of these materials, a Mode I experimental method was developed. The present work builds upon prior studies to incorporate styrene-ethylene-butylene-styrene (SEBS) gelatins at low and high loading rates. Using a digital image correlation (DIC) technique to quantify the full-field surface strains around a crack tip, the critical strain required for initiation of failure and crack growth was determined as a function of loading rate. The experimental methods are presented with results from Mode I fracture experiments, including energy and strain based criteria for failure initiation and growth and their corresponding loading rate dependence.