| Abstract Scope |
Recent experimental studies on the extent to which materials can deform under combined shear and axial loadings have shown that strains inside localization zones that precede failure are much higher than previously reported. The measured strain at failure for Al-6061-T6 reported in these studies monotonically decreases as the triaxiality increases, a trend that is contrary to previously-reported results (Haltom et al. [1]; Scales et al. [2]). In addition, scanning electron microscopic evaluation of the failure zones showed that void formation and coalescence is delayed until very close to the onset of failure for this material. This presentation first reviews the tension-torsion experiments and associated experimental challenges such as measurement of strains in narrow localization zones of the order of the wall thickness of the specimen. Numerical simulations of the experiments are used to evaluate the extent to which continuum plasticity can reproduce the measured responses and the associated localization. The results demonstrate that reproduction of the measured responses requires a careful calibration of an appropriate non-quadratic anisotropic constitutive model, a properly extracted material hardening response to large strains, and demands a fine 3-D discretization of the structure in order to capture the large strains and high strain gradients in the localization zones (Chen et al. [3]). Accurate prediction of such local strains forms the basis for the use of a ductile failure criterion. In the way of closing the loop, the constitutive model is implemented in a finite element analysis of the concertina folding crushing response of aluminum tubes. The modeling framework is evaluated based on its ability to reproduce the overall response, the sites of the most deformed zones, and the prediction of the onset of failure at these sites (e.g., Haley & Kyriakides [4]). |