On the necessity of taking into account the variation in the Young modulus with plastic strain in elastic-plastic software Original Research Article

Work hardening of steel involves modifications of the elastic properties of the material, e.g. an increase in its yield stress. It can also be the cause of an appreciable decrease in the Young modulus. However, this property diminishes as the plastic strain increases. Experiments with a microcomputer-controlled tensile test machine indicate that the diminution can reach more than 10% of the initial value after only 5% plastic strain. In spite of this fact, a lot of elastic-plastic software does not take into account the decrease in the Young modulus with plastification even though it may lead to obvious differences among results. As an application we have developed a software which computes the deformation of steel sheet in press forming after springback. This software takes into account the decrease in the Young modulus and its results are very close to experimental values. Quite arbitrarily, we noticed a recovery of the Young modulus of plastified specimens after few days, but not for all steels tested.