A Finite Element Based Methodology for Combined Crack Initiation and Crack Growth Prediction in Welded Structures

Understanding total fatigue life of welded joints is crucial to developing durable products. Traditional fatigue analysis methods have focused independently on either crack initiation or crack growth. Each of these methods has strengths but neither method predicts the total life of the part from fabrication to fracture. Recently the SAE Fatigue Design and Evaluation committee evaluated and validated a fatigue analysis technique that can predict the total life of the weld, from microscopic crack initiation to crack growth and finally to fracture. This paper describes a finite element-based (FE) methodology for implementing this total life fatigue analysis in a CAE environment. This new method offers numerous benefits over traditional weld fatigue analysis techniques, such as:

• recognizing fatigue life as being dependent on both crack initiation and crack growth
• the use of fracture mechanics-based crack growth and crack tip plasticity modeling
• insensitivity to initial crack length assumptions
• incorporating the influence of weld geometry and residual stress on life
• the use of simplified FE modeling techniques
• the ability to include multiaxial loading

This paper describes how this total life method has been implemented in a software solution, including descriptions of the required inputs for FE modeling, material properties, residual stresses, and applied loading.