Re-straining induced triggering of the Portevin-Le Chatelier effect in recrystallised 2198 T3 and T8 aluminium alloy: Experimental observations and FE simulations for smooth and notched samples

Abstract

The susceptibility of 2198 Al–Cu–Li alloys to the Portevin-Le Chatelier (PLC) effect was investigated under various testing conditions, including constant strain rate, relaxation, and strain rate jump tests on tensile specimens. The localisation behaviour in the naturally aged state (T3R) was compared with that in the artificially aged state (T8R) using digital image correlation (DIC). Additionally, the triggering of the PLC effect following a change in the strain path was observed. The T8R grade, which contains various precipitates, exhibits no localisation across temperatures from −50 to 80 °C. In contrast, localisations are observed in the T3R grade, which lacks precipitates, suggesting that dynamic strain ageing (DSA) remains the dominant mechanism responsible for serrated yielding, rather than precipitate shearing. A McCormick-type macroscopic elastoviscoplastic model, implemented in a finite element solver, was calibrated with experimental data to simulate the effects of different loading conditions on tensile specimens. The triggering effect and spatio-temporal patterns were well captured compared to DIC results for both T3R and T8R grades. The model was also employed to simulate the early plasticity during tearing tests of flat compact-tension-like samples in order to make a direct comparison with laminography-DVC (Digital Volume Correlation) experiments. Slant localisation patterns ahead of the notch are predicted by the model but are more mobile than those observed in laminography-DVC experiments of previous studies. The differences between constant strain rate and interruptive loading conditions are evidenced. Interestingly, even for the artificially aged T8 material, strain bands were predicted ahead of the notch after restraining.