Total fatigue life prediction for welded joints based on initial and equivalent crack size determination

Abstract

When the linear elastic fracture mechanics-based approaches are used to predict the fatigue life of welded joints, initial crack size is a key point, which eventually affects the accuracy of total fatigue life prediction. Meanwhile, the life prediction process under random loading is complicated. In this paper, a novel method is proposed to determine the initial crack size, which is based on the results of back-extrapolation approach. The proposed method expresses the stress intensity factor, and the boundary between crack initiation and propagation period is taken into consideration. Based on the proposed method, deterministic total fatigue life can be obtained with fewer tests and less cost. In addition, the concept of equivalent crack size and its calculation model are proposed to reduce the complexity of the calculation process of fatigue life prediction under random loading, and model uncertainty is included into the prediction model of probabilistic fatigue life based on equivalent crack size. It is feasible, which has been verified, to take the influence of stress level into account when determining the initial crack size. Meanwhile, the proposal of equivalent crack size simplifies the calculation process of probabilistic fatigue life, and the consideration of model uncertainty is more conducive to assess the safety and reliability of the materials or structures.

Low-Cycle Fatigue Life Prediction of 10CrNi3MoV Steel and Undermatched Welds by Damage Mechanics Approach

“…Thus, the life for welded joints and components is dominated by fatigue crack growth. Further, it illustrates the reliability and popularity of fatigue strength and fatigue life assessments for different failure modes in welded joints (Zhang et al, 2018;Ahola et al, 2019a;Chapetti and Steimbreger, 2019;Liu et al, 2020). The contribution of either fatigue crack initiation or propagation onto the fatigue life is strongly influenced by the material properties and loading conditions.…”

Fatigue life assessment method of in-service mechanical structure

“…Through the construction of the payload process, cyclic stress is determined for fatigue life estimation. 19–21 The existing life prediction models primarily include the average stress affect life prediction model, 22 the fatigue life cycle model, 23 the multi-axial fatigue life model, 24 the state-space model, 25 the high cycle fatigue model, 26 the fatigue thermal response model, 27 residual life model 28 as well as the damage parameter life prediction model. 29 These models are applied to the fatigue life analysis of mechanical equipment.…”

Evaluation of surface energy for formation of multiple edge cracks using Medg-integral

“…Also, the influence from the finite size effects becomes more considerable when the cracks are located closer to the boundaries. For interior cracks, studies on the size effects have extensively presented (e.g., Juhász et al., 2018; Zhang et al., 2018, etc.). As to the edge cracks, such effects appear to be more significant and therefore needs to be deliberately addressed.…”