Max Edvardsson

Abstract

A technique to calculate fatigue life of continuous laser welds has been investigated. The fatigue life for three new weld patterns are evaluated in a FE-environment and the results are compared to fatigue life from experimental tests. In the technique the structural stresses 5 mm in front of the weld is extracted using 5x5 mm shell elements. The stress is then related to the fatigue life with a previously developed Wöhler curve. The Wöhler curve was developed using fairly simple weld patterns. This report investigates if the Wöhler curve still can give accurate fatigue life predictions using these new weld patterns.

One weld pattern had a much longer fatigue life than expected and one had a much shorter. The last pattern was in fairly good agreement with the expected fatigue life.

The weld direction on the pattern with long fatigue life is not aligned with the loading direction. This allowed for a slower crack growth rate and longer cracks before failure.

The weld pattern with the short fatigue life has the welds close to the edge of the plate. When a crack reached the edge the specimens failed instantly.

It was concluded that the geometry and placement of the welds have a significant impact on the fatigue life. It was recommended to not have welds closer than 10 mm to the edge of the plate.

Because it was shown that the fatigue life is geometry dependent it is possible to find a geometry dependant constant to improve this calculation technique.