Practical Applicability and Limitations of the Elastic Modulus Degradation Technique for Damage Measurements in Ductile Metals

The use of damage models require a number of material parameters the identification of which should be made, when possible, based on direct measures of the damage that develops in the material. Among the possible experimental techniques to measure the occurrence of ductile damage in metals, the measure of the damage through the degradation of the material Young's modulus has been indicated as one of the more effective technique and used by several authors. In this paper, this technique is critically reviewed highlighting the number of issues that may affect the measure of damage. In particular, the attention is focused in the case where damage process initiates at the onset necking and develops in the post-necking regime where stress, strain and damage are no longer uniform in the gauged section. Since geometry variations alter the reference base length for both stress and strain definition, a procedure based on the use of finite element simulation is proposed in order to account for this effect on the measure of the stiffness loss. The procedure has been applied to two class of metals: a high strength steel and high purity copper.