"A novel approach was taken for introducing discontinuities into test weldments@ since it was found that the introduction of discontinuities into welds by controlling welding procedure and environment was difficult and discontinuity sizes and distribution were not representative of those encountered in practice. An unskilled welder was employed to fabricate the test weldments using an acceptable welding procedure. The resulting weldments contained a random distribution of small discontinuities as a result of unintentional operator errors. The discontinuity sizes and distributions occuring were observed to be more representative of those encountered in practice. Mechanical tests confirmed that the presence of minor discontinuities had little effect upon strength or impact toughness but ductility was reduced. The reduction in ductility was attributed to the formation of low ductility regions or ""haloes"" (fisheyes) surrounding the discontinuities. The haloes were easily detected on the fracture surfaces of the tensile and bend test specimens. The haloes are caused by the interaction of strain and the hydrogen present in the cavities formed by or associated with weld discontinuities. Haloes were also noted in connection with fatigue fractures and may be considered to contribute to a reduction in fatigue life."
BULLETIN 311-1986 history
1986BULLETIN 311-1986 ASSESSMENT OF THE SIGNIFICANCE OF WELD DISCONTINUITIES; EFFECTS OF MICROSTRUCTURE AND DISCONTINUITIES UPON FRACTURE MORPHOLOGY