A Short Review on Fracture and Fatigue Crack Growth in Welded Joints

Abstract

Welded joints are increasingly employed in nuclear power plants, process industries, engineering structures including automotive and aerospace. The integrity and service life of the joints in such critical applications is paramount. The engineering structures made of welded joints are mostly subjected to fatigue loads. Welds have defects such as cracks, porosity among others. Under fatigue loads, cracks initiate at the pre-existing defects and grow to the size at which unstable crack-growth results and fracture occurs. In this context, it is relevant to also evaluate the resistance of the weldments against fracture viz. fracture toughness. In addition, the life of the weldments with growing fatigue cracks is also of interest. Thus, study of the behaviour of welded joints under fatigue loads has been the topic of interest of researchers for decades. This paper reviews the developments in the field of fracture and fatigue crack growth rates (FCGRs) of the joints. It is well known that the heterogeneous properties of the weldments make their characterization more challenging and time consuming. Two types of crack configurations viz., normal cracks and interface cracks are considered. Normal cracks are oriented perpendicular to the weld, while the interface cracks, parallel. In the case of normal cracks, the welded joints offer greater resistance against fracture and fatigue than base metals. Dissimilar metal welded (DMW) joints, display higher resistance when crack is in the weaker metal and grows toward the stronger one due to crack shielding. Lower fracture toughness and fatigue resistance are obtained for the opposite crack direction due to crack-amplification. Crack path deviates from its plane and is deflected in the former and do not deviate and grows straight in the latter. Strength mismatch, residual stresses and geometric constraints influence the toughness and FCGRs of the weldments with interface cracks. These cracks deviate into the nearby areas of lower strength and, perhaps higher toughness.