Discussion of Fatigue Analysis Techniques in Automotive Applications

This paper is targeted to engineers who are involved in predicting fatigue life using either the strain-life approach or the stress-life approach. However, more emphasis is given to the strain-life approach, which is commonly used for fatigue life analysis in the ground vehicle industry. It attempts to discuss, modify and extend approaches in fatigue analysis, so they are best suited for structural durability engineers. Fatigue analysis requires the use of material fatigue properties, stress or strain results obtained from finite element analyses or measurements, and load data obtained from multi-body dynamic analysis or road load data acquisition. This paper examines the effects of these variables in predicting fatigue life. Various mean stress corrections, along with their advantages and disadvantages are discussed. Different stress/strain combinations such as signed von Mises, and signed Tresca are examined. Also, advanced methods such as Fatemi-Socie and Bannantine are discussed. Analyses based on uniaxial and biaxial calculations are compared and conclusions are reached. Finally, different methods of accelerating fatigue analysis such as time history reduction (for example peak-valley slicing) and element elimination techniques (removal of elements suspected of having negligible damage from the actual damage calculation) are discussed. Examples and comparisons are provided for the major methods discussed in this paper.