1. Fatigue design of welded joints

1.1 Fatigue damage – Steps – Influencing factors

While under increasing monotonic static loading, internal damage to a metallic material only appears after the possibilities for plastic deformation have been exhausted, i.e., very late when triaxiality is low, fatigue damage manifests itself above a certain load variability threshold and accumulates over the course of loading cycles in a three-stage process:

• initiation of a microcrack;

• propagation (stable growth) of the crack;

• fracture (unstable crack growth) in a ductile and/or brittle manner.

Below a certain threshold of load variability, damage to a sound structure does not occur...