Abstract
It is shown how double exposure laser speckle photography, when used with an automatic image processing system, can provide detailed information on both in-plane displacement components around the tip of a crack. This paper describes the results of the analysis of six speckle photographs of sharp cracks in polymethylmethacrylate (PMMA), each on a mesh of 16 × 16 datapoints. Two numerical methods for calculation of the mode I stress intensity factor ( K I ) from the measured displacement field have been investigated. Least-squares fitting of the theoretical displacement field gave good estimates of K I , with low systematic and random errors (~1%). Evaluation of the J-integral around square paths enclosing the crack tip was found to result in larger errors (up to 5%). It is thought that laser speckle photography together with J-integral calculations may find applications in nondestructive testing, as a method of automatically detecting the presence of a crack.
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