Browse Publications Technical Papers 2006-01-0146

The Effective Unloading Modulus for Automotive Sheet Steels 2006-01-0146

In stamping advanced high strength steels (AHSS), the deviations from desired part geometry caused by springback from a radius, curl, twist, and bow are major impediments to successfully producing AHSS parts. In general, the conventional elastic modulus is used to quantify the strain that occurs on unloading. This unloading strain causes deviations from desired part geometry. Considerable evidence in the literature indicates that for tensile testing, the conventional elastic modulus does not accurately describe the unloading strain. The present study uses new data and results from the literature to examine the average slope of tensile stress strain curves on unloading. This slope is termed the effective unloading modulus. The results from this study quantitatively describe how the effective unloading modulus decreases with increasing strength, prestrain, and unloading time. Calculations are also included that describe the relative contributions of: 1) dislocation related phenomena, 2) thermal contraction, and 3) conventional elasticity. The effective unloading modulus can be used as an engineering estimate to replace the conventional elastic modulus in mechanics equations that predict springback from a radius, curl, twist, and bow. The results from this study also indicate a need for evaluating the effective unloading modulus for other strain paths. Determination of the effective unloading modulus for other strain paths is needed before quantitative relationships suitable for finite element analysis codes can be precisely specified.


Subscribers can view annotate, and download all of SAE's content. Learn More »


Members save up to 16% off list price.
Login to see discount.
Special Offer: Download multiple Technical Papers each year? TechSelect is a cost-effective subscription option to select and download 12-100 full-text Technical Papers per year. Find more information here.
We also recommend:

The Influence of the Bauschinger Effect on Springback Prediction for Dual Phase Steel


View Details


Finite Element Simulation of the Bending and Springback Behavior of Advanced High Strength Steels (DP780)


View Details


Evaluation of Stress Saturation Effect with a Stress Based Failure Criterion for Sheet Metal Using Numerical Simulations


View Details