Investigation of Heterogeneous Joule Heating as the Explanation for the Transient Electroplastic Stress Drop in Pulsed Tension of 7075-T6 Aluminum

Abstract

The electroplastic effect can be predicted and modeled as a 100% bulk heating/softening phenomenon in the quasi-steady-state; however, these same models do not accurately predict flow stress in transient cases. In this work, heterogeneous Joule heating is examined as the possible cause for the transient stress drop during quasi-static pulsed tension of 7075-T6 aluminum. A multiscale finite element model is constructed where heterogeneous thermal softening is explored through the representation of grains, grain boundaries, and precipitates. Electrical resistivity is modeled as a function of temperature and dislocation density. In order to drive the model to predict the observed stress drop, the bulk temperature of the specimen exceeds experiment, while the dislocation density and grain boundary electrical resistivity exceed published values, thereby suggesting that microscale heterogeneous heating theory is not the full explanation for the transient electroplastic effect. A new theory for explaining the electroplastic effect based on dissolution of bonds is proposed called the Electron Stagnation Theory.