There are three primary methods for estimating the fatigue resistance of components and structures:
- Stress-Life Analysis: This method assumes that stresses remain elastic, even at stress concentrators. Most of the fatigue life is spent nucleating small microcracks. This approach is typically used for long-life situations (millions of cycles) where fatigue resistance is controlled by nominal stresses and material strength.
- Strain-Life Analysis: This method is used when plastic deformation occurs around stress concentrations, such as in structures that experience a major load cycle every day. Both stress-life and strain-life analyses provide estimates of the time required to form a crack approximately 1mm in length.
- Crack Growth Analysis: After a crack has formed, this method estimates the time required for it to grow to the point of final fracture.
Additionally, fatigue analysis of welds requires special considerations due to their complex shape and loading conditions.