Fatigue of weldments with welding defects – defect sizing, crack nucleation and crack growth rate

Abstract

Ultrasonic inspections of weldments in some existing bridges revealed the presence of cold cracks, slag inclusions, and porosities of sizes beyond todays acceptance criteria. We conducted a study on the prediction of the fatigue life of these weldments. This paper presents the models and main findings of the study. An extension of the traditional ultrasonic‐based time of flight diffraction inspection method is developed for accurate sizing and locating of defects. The crack nucleation life in the martensitic heat affected zone is predicted using a crystal plasticity model embedded in a finite element environment. Thermo‐mechanical finite element analyses of the welding process are employed to estimate the residual stress around the imperfections. Fracture mechanics tests are employed to determine the fatigue crack growth rates of the different heat affected zones in these weldments. In addition to the remaining life prediction, the study has given insight into the metallurgical features responsible for crack nucleation and growth.