The Forming Limit Curve

Abstract

In a deforming sheet, the strain state is defined as the ratio between minor strain and major strain. The formability depends on this strain state and can be expressed as the so-called forming limit curve (FLC). In complex strain states the deformation is limited by an instability just as in a tensile test. In cases of negative minor strain this can be analyzed simply, in cases of positive major strain a more complex analysis is required. Two strain states allow high formability: deep-draw and equi-biaxial, in case of the first one the formality is infinite in theory. The FLC however is only valid under certain conditions: no bending, straight strain path, planar stress, no shear.