Quantitative analysis of a class of subsurface cracks using shearography and finite element modeling
The application of a full field non-contacting measurement system for nondestructively evaluating (NDE) subsurface flaws in structures has been conducted using Electronic Shearography. Shearography has primarily been used as a qualitative tool for locating areas of stress concentration caused by anomalies in materials[1–4]. NASA has been applying optical techniques such as these to NDE inspection of aircraft lap joint integrity, composite material defects, and pressure vessel quality assurance. This paper examines a special class of defects manufactured in thin metal panels and serves as a testbed for interpreting the displacement gradients produced on a simple well-characterized sample with known defects. Electrode discharge machining (EDM) notches were cut into panels to simulate subsurface cracks. Shearography was used to determine the detectability of subsurface cracks ranging in size from 0.8 mm to 25.4 mm fabricated in both steel and aluminum test panels. Finite element modeling was used to verify and quantify experimental results obtained in these tests. Very good agreement existed between both the experimental and predicted displacement models.