The paper deals with the application of a new method of necking detection and strain measurement based on digital image analysis used for the determination of forming limit diagrams at the necking of thin aluminum sheets. The two analyzed images usually correspond to the initial, unstressed specimen, and the image just before the necking. For pure a luminum sheets was established two situations regarding the onset of necking: one in the area where the planar state of deformation, and other where the biaxial extension is predominant. It is assumed that a transition's point characterized by the parameter s2 / s1 exists.
