The fracture behaviour of specimens with a notch tip partly in the base metal of strength mis-match welded joints

The relevant parameter for the safe service of a welded structure is the cr itical crack tip opening displacement (CTOD). This value is dependent on th e microstructure present along the front of the fatigue pre-crack, which is also in the same locality where the strength mis-matching has a substantia l influence. In the case of a specimen containing a through thickness notch , embedded partly in the heat affected zone and partly in the base metal, t he fracture behaviour strongly depends on a portion of the ductile base met al and the size and distribution of the mis-matching factor along the vicin ity of the crack front. Therefore, if local brittle zones are located in th e process zone the ductile base metal cannot prevent pop-in instability, bu t it can reduce it to an insignificant level during the fracture toughness testing and it can provide higher critical CTOD values.