Full-field bulge testing using global digital image correlation

Abstract

The miniature bulge test is an acknowledged method for characterizing freestanding thin films. Nevertheless, some discrepancies in the quantitative results from such tests can be found in literature, explained in part by erroneous assumptions in the analytical description used to compute the global stress and strain from the membrane pressure and deflection. In this research, a new method is presented which renders the analytical description obsolete. A specialized Global Digital Image Correlation technique on high resolution, confocal microscopy, surface height maps of bulged membranes, has been developed. This method is able to capture full-field continuous deformation maps, from which local strain maps are computed. Additionally, local stress maps are derived from full-field curvature maps and the applied pressure. The local stress-strain maps allow the method to be used on inhomogeneous, anisotropic membranes as well as on exotic membrane shapes.