Study On Biaxial Fatigue Assessment Of Butt Joint Based On Strain Field Intensity Approach

Welding is widely used in engineering, because of the advantages such as nice connectivity and convenience making etc. The welded structures are in larger amounts in the field of modern industrial equipment. However, the structural fatigue failures,as a result of the failure with welded joints, have occurred from time to time. In the engineering, welded structures usually bear complicated multiaxial cyclic loading. Consequently it is full of valuable significance to study the fatigue life prediction of the welded joints under complicated stress or strain state.Strain field intensity approach is introduced and improved in this paper, which has a good effect on welded structures fatigue life assessment. With the new approach,both of the stress and strain gradients and multiaxial stress state——the two main factors which affect the welded joints fatigue life prediction, can be taken into account. Besides, based on a certain welded joint of fatigue test, a good fatigue life prediction using the improved Strain field intensity approach is achieved. The field of high-strength steel is given at the first time and it can be a reference for the life prediction of the high-strength steel in the future.First, on the basis of the fully understanding about the existing main methods of evaluation of the fatigue life of welded joints, this paper points out their respective advantages and disadvantages in engineering applications with a comparison. After comprehensive consideration about those methods, strain field intensity approach is introduced to assess the fatigue life of welded joints. In this paper you can see there is a brief introduction about the principle and process in application of fatigue life prediction by strain field intensity approach, as well as the problems which should be paid attention.Then, given the strain field intensity approach can not make allowance for the multiaxial stress state, this paper gives a new failure function, in order to improve strain field intensity approach, by combining with the critical plane method. The critical plane method is commonly used in the multiaxial fatigue life prediction, for its the actual physical meaning.It gives a way to solve the theoretical analysis of stress or strain state of a arbitrary point, as well as the location of the critical plane. Finally, this paper introduces the whole algorithm flow according to the new strain function. Based on a high strength steel low cycle biaxial fatigue test, the fatigue life prediction is obtained by the improved strain field intensity approach. Meanwhile, it makes a comparison about the assessment value of fatigue life between the results predicted by local stress-strain method, critical plane method and experiments, The result shows that the improved strain field intensity approach is proved to be a method with higher precision of fatigue life prediction in this welded joints. As a whole, the method has a certain practicability in the multiaxial fatigue life prediction of welded joints.