Investigation of ductility and damage accumulation by two stage deformation using ECAE/ECAD and the tensile test

Lower-Bound Ductility (LBD) is the critical strain at the moment of fracture as a function of stress state and temperature. Measurements of LED are normally performed by testing in a hyperbaric chamber. There is an alternative approach for determination of the LED based on the cumulative nature of damage. The basic idea of this new approach is to apply two successive loadings with different stress ratios that lead to fracture, and then to calculate the LED function. The processes of equal channel angular extrusion and drawing are used to introduce some damage in the specimen for a specified stress - temperature history. The amount of plastic deformation is determined by the angle between the two intersecting channels, while the stress ratio is varied by applying different back-pressures. The rest of the damage required to cause fracture is introduced by a subsequent tensile test. The LED diagram for continuously cast Al 6061 has been deduced using this method.