Analysis of hole expansion limit through biaxial test

Predicting failure of a material is one of a challenge in the metal forming area. Also advancement of a material for higher strength and ductility could not be achieved without bringing the complexities at the micro level. This complexity at the micro level is due to the multi phases in a material. Due to which it creates the heterogeneity in a material which hugely affects the mechanical behaviour and creates a challenge on determining the limits of the material and their failure characteristics. In this paper hole expansion technique is investigated to observe the limits of a material. Hole expansion process is one of the material mechanical characterization method which provides the material edge characteristics during forming/stretching. The specimen used in this process was cruciform shape with hole at the centre. The specimen arms were then pulled to create the three deformation modes i.e., uniaxial, plane strain and biaxial. The strain evolution for the critical element in all three deformation modes was analysed. Also the hole expansion was monitored for the whole process. From the results it was observed that the critical element predicts the forming limit however hole expansion predicts the fracture behaviour of the material and found one of the useful tool to predict the fracture limit.