TWI Industrial Member Report Summary 145/1981
By R H Leggatt and M S Kamath
Background
Through-thickness and surface measurements of residual stresses transverse to the welding direction have been made in 25mm thick COD specimens in the as-welded and locally compressed states. (The COD specimens were taken from a panel containing a twelve-pass double-V weld deposited in the verticalup position.) Similar specimens were subjected to COD testing, and the shape of the fatigue precracks were compared with the measured stress distributions. The as-welded specimens contained substantial residual stresses, whose peak tensile value was just below the yield strength of the parent metal. The compressive stresses at mid-depth and one surface had clearly retarded the growth of the fatigue precrack in those regions. Local compression was effected using either a single large platen, or the double application of a smaller platen. The single platen reduced the residual stresses to very low levels, but the double compression procedure produced only a partial reduction in the original stress distribution. However, the fatigue precracks in all compressed specimens showed no signs of retardation, and were unaffected by any remaining residual stresses. The differences between the mean COD toughness of the as-welded v. locally compressed specimens was not significant at the 5% level.
The variation of transverse residual stress along the weld (ahead of the crack) was also measured to look at the possible influence of compressive residual stresses on the arrest of brittle cracks or pop-ins. There was no indication which could account for the pop-in phenomena; nor were any pop-ins observed.