Measurement of the Dynamic Bulk and Shear Response of Soft Human Tissues

Traditionally, Kolsky bars are used to study the dynamic response of hard materials in uniaxial compression, tension or torsion. We present modifications to the technique that allow loading of a soft tissue specimen in (a) hydrostatic compression and (b) simple shear. The first modification is designed to determine the pressure vs. volume behavior of each material, and thence to extract a measure of the dynamic compressibility or equivalently of the bulk modulus. The second modification is designed to develop the shear stress versus shear strain behavior for a near-simple shear experiment. The critically important questions of the proper acquisition of human tissue samples and protocols for appropriate experimentation have also been addressed. The experimental techniques and the results are discussed in detail and the results compared to finite element simulations. We present examples of the dynamic response of typical tissue simulants as well as human liver and stomach tissues.