Surface Discontinuity Detection via Direct Strain Imaging

Direct strain imaging is a recently developed full-field strain measurement method that accomplishes full field measurement of the strain tensor on the surface of a deforming body, by using arbitrarily oriented engineering strain measurements. This new approach doesn’t make any assumption on the compatibility of the strain field and thus it allows for consistent representation of media that may be or may not be discontinuous. In this paper, we present a novel method for detecting whether a discontinuity exists on a deformed body by evaluating the validity of the compatibility conditions over the imaging field. This approach can also be used for quantifying the shape and length of the discontinuity or crack. Synthetic numerical experiments based on the exact solution of a slant crack under biaxial loading were conducted to establish the detectability performance and the associated uncertainty of detection. Very encouraging results were derived indicating that for realistic levels of noise the method was found to be able to detect discontinuities as small as 0.3 mm long with very high confidence.