Abstract
The authors have applied the laser speckle method to the in-situ dynamic strain measurements during welding. The principal objective of this report is to detect the strain behavior during phase-transformation in welds by using the method.
Specimens were thin plates with 4 mm thickness of 9%Ni steel and SUS304 stainless steel, the former of which undergoes martensitic phase-transformation at about T=325°C in the cooling period whereas the latter does not. A specimen was heated by a moving GTA along its center line. A laser beam illuminates a spot just below the heating line on the bottom surface of the specimen and the speckle patterns formed on a pair of linear image sensors were continually recorded. Several kinds of specimen in different shapes were adopted to compare the effects of the restraint on the strain during phase-transformation.
The laser speckle method could detect the strain behavior during phase-transformation successfully. Differences in the strain curves due to the direction, i.e., along or perpendicular to the heating line, were clearly detected. The amount of expansion during transformation differed considerably according to the heat input, measuring direction or specimen size. In some cases where expansion in one direction is strongly restrained, expansion in the other direction exceeded greatly the value in the case of a stress-free sample. Such anisotropic strains due to phase-transformation were qualitatively in agreement with the predictions by an elasto-plastic finite element analysis.
