LAUSR

Abstract This study investigates the material characteristics across the thermite welded joint and discusses the inherent correlation between the material properties and the mechanism of the fatigue cracking occurring at the fusion line. Various material regions across the welded joint are identified and the characterization of the mechanical and fatigue properties are conducted. The weld defects are investigated, and it is found that the defects lead to a reduction of fatigue limit and the local severe stress concentration which acts as potential crack initiation sites at the fusion line. The fatigue crack propagation behaviors were studied and the result reveals that the moderate material strength overmatch is detrimental for interfacial cracks propagation. The interfacial cracks, once initiated, grow towards the base rail metal and away from fusion line resulting in a shorter fatigue propagation life. It is concluded that the fatigue cracks occurred at the fusion line of the thermite welds are caused by the high density of weld defects and the mismatch of strength and fatigue properties.