In situ X-ray synchrotron tomographic imaging during the compression of hyper-elastic polymeric materials

Cellular structures are present in many modern and natural materials and their proper utilization is crucial within many industries. Characterizing their structural and mechanical properties is complicated, in that they often have a stochastic cellular structure, and in addition, they often have hyper-elastic (i.e., non-linear) mechanical properties. Understanding the 3D structure and the dynamic response of polymer foams to mechanical stress is a key to predicting lifetime performance, damage pathways, and stress recovery. Therefore, to gain a more complete picture, experiments which are designed to understand their mechanical properties must simultaneously acquire performance metrics during loading. In situ synchrotron X-ray computed tomography can image these cellular materials in 3D during uniaxial compression at a 10 −2 s −1 strain rate. By utilizing the high X-ray photon flux and high-speed camera provided by beamline 2-BM at the advanced photon source, it is possible to collect a full 3D tomogram (900 radiographs as the sample is rotated 180°) within 1 s. Rotating the sample stage in a washing machine motion allows for a 1 s tomogram to be collected every fifth second. In this study, a series of 20 tomograms were collected as the sample was continuously stressed to a nominal 60 % compression. Several types of silicone foams with various structures were used to explore this technique. Stress–strain curves, collected simultaneously with the 3D tomograms, can be used to directly correlate the morphology with the mechanical performance and visualize in real-time, the buckling of ligaments. In addition, this method allows for the accurate measurement of the Poisson’s ratio as a function of compression. Coupling this moderate strain rate 3D data with finite element analysis provides a direct comparison between the true mechanical response and the modeled performance and adds a level of robustness that is not possible with other techniques.