The Effect Of Large Strain Cycling On The Fatigue Strength Of Welded Joint

Earthquakes sometimes create damages to steel structures. The structures which have not been seriously damaged are still used after an earthquake. The fatigue strength of these structures, however, might have been decreased due to the cyclic loads during an earthquake. In order to clarify the effect of seismic loading on the fatigue strength of the welded joint of a steel structure, a high cycle fatigue test of welded joint after large straining was performed. Although a large residual tensile stress induced by plastic deformation caused little effect on the fatigue limit even in gross plasticity condition, the cyclic application of large strain substantially decreased the fatigue limit. An application of large straining for a small number of cycles initiated a short crack at the weld toe in the low cycle fatigue manner, which acted as a trigger for high cycle fatigue failure after seismic loading. The reduction of fatigue limit depended on the size of the crack. The linear elastic fracture mechanics was used to evaluate the fatigue strength of welded joint. Although the short crack was initiated by cyclic application of plastic straining and the crack was in gross plasticity, the ?Kth of the small crack determined the fatigue limit of small-cracked welded joint after seismic loading.