Effect of weld metal mis-matching on crack driving force

This paper presents the results of a comparative study on the application of CTOD and J design curves as well as the Engineering Treatment model for Mis-Matched joints (ETM-MM) procedures to mis-matched weld joints. Inhomogeneous through thickness centre-cracked tensile (CCT) panels are prepared by electron beam welding (EBW) a transverse strip of austenitic steel of 18 mm height to the middle of the panel of another austenitic steel of different mechanical properties. The crack tip opening displacement (CTOD) and the experimental J values obtained from such bimaterial panels which simulate the 20 percent undermatched (UM) and 25 percent overmatched (OM) welds are compared with those predicted by the three above-mentioned procedures. Design curves, developed to predict the failure of homogeneous structure, only use the mechanical properties of one material as an input. Moreover, the predictions of such procedures are very sensitive to the mechanical properties and applied strain definitions. Therefore, the significance of the choice of the mechanical properties (weld or base metal properties) to be used in those procedures on the predictions of the crack driving force are discussed. In contrast to the design curves, the recently developed ETM-MM for welded structures includes the mechanical properties of the weld and base metal. Its predictions of the CTOD (#delta#_5) are compared with the experimental results. The mechanical properties of the base or weld metal in the design curves have no significant influence on crack driving force predictions for undermatched specimens. In contrast, for overmatched specimens, the use of mechanical properties of the base metal provides conservative predictions. The predictions obtained using ETM-MM are reasonably conservative for small cracks in an undermatching weld. (orig.)Reprinted from: Mis-Matching of Welds, ESIS 17 (edited by K.H.Schwalbe und M.Kocak) 1994, Mechanical Engineering Publications, London, pp.589-607 / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman