Estimation of In-Plane Strain in Laser Formed Thin Bowl Plate

Abstract

To form curved surface, in-plane strain is introduced into a plate by line heating, press working or laser heating in shipbuilding or sheet metal working like nose shape forming for bullet trains. Laser forming could be a potential useful method for sheet metal forming as well as press working.
When forming a curved surface with thin plate in some steps, it is thought to be useful to measure in-plane strain distribution before the forming is finished, to know whereabouts and amount of shortage of in-plane strain. 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 bowl shape thin plate made by laser heating is investigated with geodesic lines drawn numerically on the surface. The in-plane strain is calculated with distance change of two geodesic lines. This in-plane strain distribution agrees with a strain distribution measured by 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 in width change of the plate. In a result, in-plane strain measured with geodesic lines is useful to indicate performance of curved surface forming process.