TWI Industrial Member Report Summary 99/1979
By J G Wylde
Fatigue tests have been carried out to investigate the effect of axial misalignment on the fatigue strength of transverse butt welded joints. The specimens were manufactured by the manual metal arc (MMA) process from 12.5mm thick material to BS 4360:1968, Grades 43A and 50B containing 3.2, 6.3, 9.5 and 12.5mm of axial misalignment. Results have been obtained to establish S-N relationships for each degree of misalignment under pulsating axial tensile loading, and a limited number of results have been obtained in bending.
The results indicate that the fatigue strength of transverse butt welded joints in axial tension is severely reduced by axial misalignment of the abutting members. The amount of reduction is proportional to the extent of the misalignment. Static tests indicate that the reduction in strength stems primarily from the presence of secondary bending stresses caused by local
deformation during the application of load.
Tests were also carried out on specimens in which the weld had been modified either by toe burr grinding, by adding weld reinforcement behind the misaligned joint, or by a combination of both techniques, in an attempt to reduce the loss in fatigue strength incurred by the misalignment. None of these methods produced a significant improvement in fatigue strength over that obtained from the ordinary misaligned joints. The tests carried out under bending indicated that the fatigue strength of transverse butt welded joints is relatively unaffected by axial misalignment in this loading mode.