Fracture Toughness and Fatigue Crack Growth Study of Friction Stir Welded Plates

Friction stir welding has been demonstrated as a viable replacement to conventional fusion welding in various engineering applications. In most cases, the suitable welding parameters were selected based primarily on the tensile tests performed on welded test joints. In this project, a study on Fracture Toughness (FT) and Fatigue Crack Growth (FCG) of friction stir welded A6061 plates of 10 mm thickness will be performed. The tests were conducted according to ASTM Standard Test Methods E399-08 and E647-08. The objectives of the project are to perform Fracture Toughness and Fatigue Crack Growth tests on the plates, determining the plane strain fracture toughness KIC and the rate of fatigue crack growth of the A6061 welded plates and comparing those properties with non-welded A6061 plates. Friction stir welding was conducted using CNC milling machine. The sample plates were fabricated into Compact Tension (CT) specimen configuration using EDM machine. To meet the requirement of sharp notch, precracking was conducted for about 30,000 cycles using a cyclic frequency range of 0.3-4.0 Hz with precracked crack lengths of around 25.2 mm. FT tests were conducted using 0.01 mm sec-1 stroke rate. FCG tests were conducted using the same cyclic rate range with fatigue precracking, with a stress ratio of 0.1. The results indicated that the friction stir welded plates exhibited lower fracture toughness and higher crack propagation rate than non-welded plates.