Experimental Investigation of Fatigue Crack Propagation in Residual Stress Fields

This work is on the interaction of residual stresses and fatigue cracks in welded steel plates. A longitudinal dummy weld was used to create high tensile residual stresses in axial loading direction. The fatigue crack was trained to start at an artificial notch and propagated through a field of high tensile residual stresses. The fatigue crack propagation as well as the re-distribution of residual stresses were studied in detail by combined experimental methods. The mean stress was varied as well as the residual stress state of the samples used. Samples were tested as-welded as well as stress-relieved at R = (σmin/σmax) = 0, R = -1 and R = -3. The materials used were a typical fine grained construction steel S355J2+N as well as a high strength quenched and tempered steel S960QL.It is shown how residual stress are degraded and in which way moderate residual stresses affect the fatigue strength of welded steel plates. The combined effect of residual stresses and load mean stresses is discussed.