A practical approach to modeling aluminum weld fracture for structural applications

This paper addresses the numerical simulation of plasticity and ductile fracture of large scale structures (e.g. ships, railcars, automobiles) fabricated with welds that exhibit appreciably lower strength than the plate material, often referred to as weld undermatching. It has been observed, both numerically and experimentally, that for such structures the weld undermatching often leads to plasticity and fracture being limited to the weld and heat affected zone (HAZ). While the large size of the structures of interest precludes the use of a refined three-dimensional element mesh capable of capturing the details of the weld/HAZ behavior, cohesive zones are ideal for capturing the overall effects of undermatched weld plasticity and fracture on a structural scale. This paper focuses on establishing a systematic calibration process for determining the cohesive zone constitutive behavior and examining the validity of this approach in the context of mode I tearing of a large welded two-layer AA6061-T6 sandwich panel. First, test data from a welded coupon is used to calibrate the cohesive law. Tearing fracture of this panel is examined using the established cohesive law to represent weld/HAZ along with elastic-plastic shell elements, with in-plane dimensions much greater than the layer thickness, to represent the parent metal. It was verified that, for this structure, plasticity was indeed confined to the welds and heat affected zones, and that the behavior of the panel was captured with reasonable fidelity.