Aspects of automated measurement of proportional and non-proportional deformation in sheet metal forming

This paper evaluates techniques of surface strain analysis in sheet metal forming based on a two-dimensional grid. Deficiencies of circle grid analysis, which in general cannot be used to measure non-proportional deformation, are discussed. An improved technique utilising a grid of squares or quadrilaterals for the automatic measurement of strains and stresses is presented. The advantage of applying a stress limit curve (SLC), instead of the forming limit curve (FLC), in the experimental analysis of deformation and in the evaluation of forming severity is discussed. (C) 2003 Elsevier B.V. All rights reserved.