Photomechanical Approaches to Dynamic Viscoelastic Material Identification*

In most areas of engineering, materials undergo deformation at high rates.  At the same time, high-rate material characterization comprises of a relatively limited toolbox of test procedures that leverage assumptions developed decades ago.  For example, traditional Kolsky (or split-Hopkinson) bar methods to examine dynamic compression still dominantly rely on strain gauge readings away from the material of interest and assume uniform loading with mitigated inertial effects.  This talk will present new methods for characterizing materials at high rates that instead leverage inertial effects and combine full-field imaging with inverse identification techniques.  Focusing on polymers, two examples of dynamic viscoelastic material identification will be presented.  First, the quantitative microstructural characterization of open-cell polyurethane foams, its relation to the bulk response, and the compressive behavior across six orders of magnitude in strain rate will be presented. The second part of the talk will introduce the extraction of multiple viscoelastic constitutive parameters of polymers using the Image Based Inertial Impact Test (IBII).  Using polymethyl-methacrylate (PMMA) as a model material, both numerical simulations with a generalized Maxwell model and experimental validations will be presented to demonstrate the successful determination of viscoelastic parameters across multiple time constants in a single experiment.