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research-article

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

[+] Author and Article Information
Brandt Ruszkiewicz

Clemson University Department of Automotive Engineering, 4 Research Drive, Greenville, SC 29607
brandtruszki@gmail.com

Laine Mears

Clemson University Department of Automotive Engineering, 4 Research Drive, Greenville, SC 29607
mears@clemson.edu

John T. Roth

The Pennsylvania State University-Erie Department of Mechanical Engineering, 4701 College Drive, Erie, PA 16563
jtr11@psu.edu

1Corresponding author.

ASME doi:10.1115/1.4040349 History: Received September 04, 2017; Revised May 15, 2018

Abstract

Increasing fuel economy standards are pushing automotive OEMs to lightweight designs, necessitating the use of new materials with good strength-to-weight ratios. These metals come with challenges of decreased ductility and increased springback, making them difficult to form using traditional manufacturing processes. Electrical augmentation is a possible solution for processing these new materials using traditional manufacturing infrastructure. Electrical augmentation increases ductility and decreases forming loads in metals. 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 the pulsed tension of 7075-T6 aluminum. A multi-scale 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.

Copyright (c) 2018 by ASME
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