Time-Dependent Springback

Abstract

Draw-bend tests performed some years ago on four aluminum alloys (2008-T4, 5182-O, 6022T4, and 6111-T4) revealed that specimens can continue to change shape for long periods, up to 15 months, following forming and unloading [1]. Contemporaneous tests of autobody steels (DQSK, AKDQ and HSLA steels) tested under identical conditions showed no such time-dependent springback over a 7 year period [2]. Current, preliminary results for a few advanced high strength steels (DP600, DP800, DP980 and TRIP780) revealed time-dependent springback at room temperature; the sign of the springback reversing for certain combinations of process conditions. Time-dependent behavior of four advanced high strength steel was measured and creep-simulated for various test conditions. Comparisons show qualitative agreement, but the simulations over-predict the magnitude of the effect