A Local Fatigue Strength Concept for Evaluation of Post Weld Treatments of Fatigue Loaded Welds

摘要

Many investigations have revealed the beneficial effect of mechanicalrnsurface hardening in combination with induced compressive residualrnstresses which lead to an improved fatigue strength as more, as thernhigher the quality of the weld is. On the other hand methods like shotrnpeening are useless, if the weld toe profile is poor and the connectedrnnotch effect strong. Then an increased fatigue strength is only possiblernafter a post weld treatment which produces a smoother shape of thernweld toe. Experiments reveal that methods which are working in orderrnto increase the intensity of the penetration depth must not necessarilyrnproduce the best fatigue performance. The paper introduces a modelrnwhich enables the estimation of the resulting fatigue strength of arnwelded joint as a result of a post weld treatment with help of a mechanicalrnor thermal surface treatment like the described peening or toerngeometry improvement methods. Based on a model which has beenrndeveloped for the application in quenched and tempered steels forrnautomotive parts after mechanical surface treatments it can be shownrnthat the model is principally applicable as well for welded joints. Arnreliable estimation of the benefit of post weld treatments can be givenrnin relation to the as-welded condition if the weld toe geometry and thernnear surface residual stress and hardness profiles of the treated weldrnare known. The results show, that the model gives an explanation, thatrnnot necessarily the highest treatment intensity must produce the bestrnfatigue performance. The amount of the fatigue strength improvementrnhowever depends on the agreement between the local load stressrnprofile and the profile of the local fatigue strength.