Nonlinear fatigue crack propagation in a baffle module of Wendelstein 7-X under cyclic bending loads

摘要

Simulation of the fatigue crack propagation in a Wendelstein 7-X baffle module is performed in this study using both a finite element method-based software and the UniGrow nonlinear model for small-scale yielding (SSY) conditions. Some experimental fatigue tests of several cracked baffle modules have been performed through a servo-hydraulic machine. One of these experimental tests has been considered to simulate fatigue crack propagation in the baffle module. Before starting the experimental test, a first crack partly contained in the welding seam and partly in the steel pipe is found. Subsequently, owing to the applied load, the crack propagated both into the welding seam and into the steel pipe until the plastic zone in the near field attains SSY conditions. Finally, owing to the increase in the extension of the plastic zone, SSY conditions are not more valid, and the breakage of the steel pipe is produced by plastic collapse.