Flaw characterization by thermography and shearography

The results of a study comparing the techniques of thermography and shearography are presented. Disk shaped samples made of PVC have been irradiated by a high energy light pulse. Surface temparature as well as deformation gradient have been measured as a function of time. For thermography the time delay between light pulse and highest temperature contrast induced by the flaw correlates well with FEM calculations for the different flaw sizes and flaw depths. The deformation gradient picked up by shearography shows also a maximum at the time delay. However, by shearography the flaws are revealed also directly after the light pulse which can be explained by the thermoelastic effect. The time delay when half the value of maximum temperature contrast is achieved is found out to be most suitable for determining the flaw depth.