The Effect of Discontinuities on the Fatigue Behavior of Transverse Butt Welds in Steel

The primary objectives of this study were to identify and evaluate the variables that influence the fatigue behavior of transverse butt welded steel members containing various weld discontinuities, and to formulate fatigue based weld quality rating crite ia. Mathematical models for evaluating the fatigue strength of welds containing discontinuities have been developed from empirical fatigue relationships. Empirical relationships for welds with nonplanar discontinuities are used to relate fatigue strength zones to known discontinuity severities; welds containing planar discontinuities are modeled by partitioning the fatigue life into initiation and propagation phases for given discontinuity severities. An experimental program was conducted to examine the accuracy of the mathematical models. Fatigue tests were conducted on notched mild steel plain plate specimens, welded mild steel and quenched and tempered steel.specimens containing artificial discontinuities, and quenched and tempered transverse butt-welded steel specimens containing slag inclusions. Strain relaxation tests were conducted also to determine the magnitude and distribution of residual stresses in the quenched and tempered steel welds. A simple-to-use method is suggested to relate weld fabrication quality to the reduction in mean fatigue strength of a sound weldment. The recommendations are formulated from fatigue strength rating curves which relate predicted fatigue strength~ for welds containing discontinuities to mean fatigue strengths of sound welds. Use of the suggested weld fabrication quality levels provides a simple means of assessing the effect of different types of discontinuities on the weldment fatigue strength.State of Illinois Department of Transportation, Division of HighwaysU.S. Department of Transportation. Federal Highway AdministrationDavid W. Taylor Naval Ship Research and Development Center. The U.S. Nav