Investigation of work hardening behavior and failure analysis of billets due to biaxial stresses in simple upsetting process

Abstract

The present work focuses on the work hardening behavior of the AA2014-T6 billets deformed plastically between two flat cylindrical rigid dies under cold working condition. Three sets of billets of different aspect ratios (height (h) to the diameter (d)), namely h/d=1, h/d=0.75, and h/d=0.5 were deformed to the different strain levels. Upon severe plastic deformation, the cylindrical billets will start cracking from the middle, and the crack will propagate to the surface. The hydrostatic stress and deviatoric stresses influence the failure of the billets resulting in poor ductility and distorting the shape of the billet. To analyze the effect of shear bands on the failure of the billet, maximum shear stress theory was applied. A detailed investigation has been carried out to study the influence of the tensile nature of the hoop stress, axial stress, and hydrostatic stresses. The critical paths for different aspect ratios of the deformed billets were plotted, and the failure of the specimen was well explained. The effect of anisotropy on the formability was studied by constituting the anisotropy factor with the ductile fracture models such as Gurson-TvergaardNeedleman model and Lemaitre model. The influence of anisotropy on the void failure was studied, and critical damage was evaluated for different anisotropy ratios.