Analysis of Time-Resolved Shearographic Methods with Controlled Thermal Stressing

Electronic shearographic interferometry is a nondestructive evaluation (NDE) technique in which qualitative detection of subsurface defects is readily achieved. In both industrial and laboratory environments, various full field stressing methods, including vibration, vacuum, thermal and mechanical loading, have been employed to produce characteristic deformations which can be monitored shearographically [1,2]. However, quantitative measurements of parameters such as defect depth are difficult to make with these techniques. This paper presents the results of using controlled thermal stressing with shearography in an effort to expand the quantitative capabilities of the technique. The use of controlled thermal-stressing allows a totally noncontact inspection technique with a large standoff distance to monitor the time-dependent deformations of test specimens. Typically laser power levels of tens of milliWatts are sufficient to generate measurable deformations.