Roughening of the free surfaces of metallic sheets during stretch forming

Abstract The roughening behaviour of the free surfaces of metallic sheets during stretch forming was investigated with scanning electronic microscopy and an HL-2204 profilometer. Forming tests were performed by the Marciniak method. Roughness was measured for different strain states and levels, especially in the limiting condition. Results show that grain rotation is the most important source of surface roughening. Variations in roughness are proportional to the applied strain and the maximum roughness increment at the onset of strain instability can be seen to be a material parameter determined by the strain state. The maximum roughness increments of all the tested materials are linearly related to the limit strains, and the rate of surface roughening is also related to the applied strain state and the initial surface roughness.