Test MethodOn the use of a four-cameras stereovision system to characterize large 3D deformation in elastomers

The mechanical behavior and volume change of filled elastomers were studied thanks to a four-cameras stereovision system. The device allows measuring simultaneously the displacement field on two faces of the sample using 3D Digital Image Correlation (3D DIC). Subset size, step size and filter size, associated with DIC calculations, are carefully calibrated to ensure efficient analysis of the displacement fields. The smoothing parameter (i.e. filter size times step size) appears to be a discriminating criterion with an upper limit below which the strain field can be appreciably estimated. Within the appropriate choice of analysis parameters, volume changes under large deformation can be evaluated. For sufficiently large deformation, volume change exhibits an upturn during stretching which could be the sign of a significant increase of void fraction. Volume change appears to be reversible during unloading phase when maximum stretch ratio is low enough. So cavities that could have been open under tension are closed when elastic deformation is released. Conversely, for high stretching ratio, volume change exhibits a hysteresis loop-like evolution indicating that either some plastic cavities remained or closure kinetics is slower.