An experimental investigation of radial deformation of soft materials in Kolsky bar experiments.

摘要

Characterization of soft materials at dynamic rates is of critical importance due to the need for accurate data in constitutive models. Knowledge of dynamic behavior of soft materials can be applied to improve areas ranging from soldier protection in a blast setting, to common car crashes. Commercially available methods to characterize materials extend only to loading rates of about 150 s-1, which covers only a portion of the possible rates of loading. Thus, empirical methods must be used to gather such data. Because empirical data is the only source of dynamic behavior characterization, validity of experimental methods must be closely monitored. Constraints of experimental methods must be closely observed when dealing with soft materials, the deformation of the specimen in particular.;Numerous researchers have acknowledged the presence of radial inertia in Kolsky bar experiments. Several have derived equations to analytically remove the inertia induced stress, and others have validated the removal of this stress from experimental results. Numerical studies have called into question the validity of testing exceedingly soft materials using the traditional compression Kolsky bar experiment, showing inhomogeneous sample deformation. Further studies on accurate portrayal of modulus suggest more problems when using the compression Kolsky bar for soft material characterization.;In this study, standard soft material characterization has been completed on four rubbers each with drastically different shear modulus using the Kolsky bar. Annular samples, and solid samples with extra radial inertia induced stress removed were used to investigate the apparent modulus behavior. Through a modified single pulse loading setup, high speed photography was used to capture the deformation during typical experiments; the deformation profile of each rubber was found. Rubbers having a shear modulus less than 200 KPa were found to experience inhomogeneous deformation, while rubbers having a shear modulus of ∼5000 KPa deformed homogeneously, which validates numerical studies. Despite removing extra stress, disparities between shear modulus obtained from commercially available methods at low rate and the compression Kolsky bar still exist.