Creep behavior of thin metal sheets during laser bending

An experimental study of the deformation phenomenon during laser bending of 0.5 mm metal sheets is presented here. The thermal gradient mechanism, i.e. ratio of the laser beam diameter to the sheet thickness less than unity, was used to deform the samples. Sheets made of AISI 304 stainless steel, 1100 aluminum and 1010 carbon steel, were scanned several times by a focused CO2 laser beam (up to 95 W and 10 mm/s). Results are presented as plots of the bending angle vs. scan number (i.e. 2theta-N curve). 304 stainless steel shows an "inverse" primary creep (i.e. strain softening) type behavior in contrast with the "normal" primary creep (i.e. strain hardening) type curves of 1100 aluminum and 1010 carbon steel. For the latter two materials time dependent deformation should be controlled by thermally activated dislocation climb process, whereas solute-drag creep should be the rate controlling mechanism for 304 stainless steel.