Estimation of In-Plane Strain for Laser Forming

Abstract

To form curved surface, in-plane strain is induced into a plate by line heating, press working or laser heating in shipbuilding or sheet metal working. Laser forming could be a potential useful method by which press working could be replaced. It is thought to be useful to know distribution of in-plane strain added into the thin plate during forming curved surface, so that workers can show a place and amount of additional in-plane strain in their next step. The process to measure in-plane strain in an actual curved surface seems still not to be reported. In this report, in-plane strain distributions existing in bowl shape thin plate made by laser heating is investigated with geodesic lines drawn numerically on the surface. The in-plane strain is calculated from distance change of two geodesic lines. This in-plane strain distribution agrees with a strain distribution measured from shrinkage of the plate when the plate length is long. When plate length is short, these strains do not agree with each other. In this case, existence of some elongations cancelling effective in-plane strains appears as width change of the plate. As a result, in-plane strain measured by geodesic lines is useful to indicate performance of curved surface forming process.