Weld Fatigue Analysis

Description:

This webinar discusses factors related to calculating weld fatigue over a wide variety of industries and applications.

Weld Fatigue Analysis | Code-based and FEA Methods

• How to approach weld fatigue analysis using both traditional code-based methods and finite element analysis methods.
• Fatigue assessments are critical to cyclically loaded structures.
• Fatigue life prediction can be particularly challenging in welded structures.
• Welded joints contain residual stresses, material property changes, and other factors which add significant complexity to the fatigue problem.

Fatigue Analysis of Seam-Welded Structures

The fatigue strength of seam-welded junctions is typically much lower than that of the parent plate or the weldable portions themselves.

There are several causes for this:

• A stress concentration is typically caused by a weld’s shape (unless it is a butt weld, ground flat).
• The welding process can frequently produce flaws that can act as fracture initiation sites, such as slag inclusions, incomplete fusion, porosity, etc.
• The stress will typically be strongest at the toe or root of the weld, and the shape in this area may not be well controlled. There is a vast array of evidence to suggest that fracture propagation frequently dominates the fatigue life of welds.
• There is a heat affected zone (HAZ) surrounding the fusion zone where the parent material has been heated to a high temperature and allowed to cool relatively quickly. This could override any prior heat treatment and result in significant changes to the microstructure and characteristics in this area.
• Remaining tensions from the welding process may be on the order of the material’s yield strength.

Fatigue Strength of a Welded Connection

Due to all of these elements, the fatigue strength of a welded connection differs significantly from the fatigue strength of the components it links.  As a result, it is unreasonable to anticipate being able to accurately forecast the fatigue life of a joint based on the characteristics of the plates or other components being joined.

To characterize the fatigue behavior of whole joints, typically in the form of S-N curves, is the foundation of the bulk of historical methodologies and standards. These curves successfully account for all faults, unknown residual stresses, notches, and changes in material properties that are introduced during the welding process. In addition, the supporting webinar video outlines the key components of this kind of approach.