<title>Laser speckle interferometry for welding inspection</title>

Abstract

Degradation processes of welded materials from the beginning of tensile until fracture were investigated by laser speckle interferometry (LSI). In the LSI system, speckle patterns are acquired continuously by a CCD camera while the tested object is deformed. A series of speckle correlation fringe patterns are obtained by subtracting couples of two interfering speckle patterns while the reference speckle patterns are renewed successively. The localized strain can be identified occasionally as the remarkably white band (WB) or irregular patterns in the correlation fringe patterns. The behavior of deformation on the specimen surface was visualized on a video monitor as moving correlation fringe patterns. In the experiment of welded specimens, the WB or irregular fringe patterns due to the localized deformation was observed for the first time at the welding part of the specimen in the elastic stage of deformation. The position of the WB was stationary although the loading progresses. Finally the specimen fractured at the position of the WB or the location of the welding. The LSI system is expected to be applicable to identify defect in the solid materials.© (1999) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.