Fatigue strength of repaired cracks in welded connections made of very high strength steels

For cyclically loaded structures, fatigue design becomes one of the important design criteria. The state of art shows that with modification of the conventional structural design methodology, the use of very high strength steels may have a positive effect on fatigue strength of welded connections. However, there is little known about the repair of fatigue cracks in welded connections made of very high strength steels. In this study, the fatigue strength of the repaired base material and repaired fatigue damaged V-shape welded connections made of very high strength steels is investigated. This thesis consists of four parts. In Part I, the emphasis was put on the effects of the material imperfections on the fatigue strength of materials and this part consists of an extensive literature study and a microscopic examination of the fracture surfaces of the base material of very high strength steels. Part II presents a literature survey on the fatigue crack repair methods and the results of the experimental programme of the current study. The experimental programme comprises fatigue tests on the repaired base material and repaired V-shape welded connections made of very high strength steels. The V-shape welded specimens were made of rolled and cast steel plates. In Part III, fatigue strength prediction models were evaluated and a comparison was made between the fatigue strength curves from the prediction models and the fatigue strength curves of the test results. In the last part, conclusions and recommendations from the study are presented. The analysis of test results revealed that the fatigue strength of fatigue damaged V-shape welded connections made of very high strength steels can be recovered by an appropriate repair procedure.