Predicting fracture in structural fillet welds using traditional and micromechanical fracture models

Traditional JJ-integral based fracture mechanics approaches and novel micromechanics-based simulations featuring the Stress Modified Critical Strain (SMCS) model are examined to evaluate their effectiveness in predicting fracture deformation capacity of structural fillet welds. This study represents one of the first detailed applications of these novel modeling techniques to fillet weld materials and details commonly used in civil construction. The study is based on experiments on twenty-four fillet welded cruciform specimens featuring a sharp root notch transverse to the direction of loading. The tested parameters include two weld filler materials, two weld sizes and two root notch lengths. The cruciform tests are complemented by detailed finite element simulations as well as ancillary tests (including sharp cracked fracture mechanics tests, Charpy V-Notch tests and notched tension coupons) to calibrate weld material toughness properties. The results indicate that the SMCS model can predict fracture in the structural fillet welds with good accuracy, while the JJ-integral based methods result in somewhat conservative and inaccurate predictions of fracture. The inaccuracy is higher, especially for the tougher fillet welds where extensive yielding prior to fracture invalidates the JJ-integral as a measure of fracture toughness. The results suggest that if calibrated and applied appropriately, micromechanics-based models such as the SMCS show promise in predicting fracture in fillet welds, when traditional approaches may not be reliable.