Thickness Effect Analysis on Fatigue Crack Propagation of 7475 Plate Material under Variable Amplitude Loading

VZLÚ – Czech Aerospace Research Centre, Beranových 130, Prague 9, 199 05, Czech Republic

^* Corresponding author: sedek@vzlu.cz

Abstract

In the crack growth prediction models, the effect of variable amplitude loading is taken into account by different ways. One of them the Newman’s model is used very often, but in its original form it is not able to take into account the effect of specimen thickness. The new modification which involves the specimen thickness is presented. The study of variable thickness impact is based on the FE – analysis of M(T) specimen. The variability of constrained factor α was analysed for several load levels and specimen thicknesses. The value of α is governed by the ratio of thickness B versus plastic zone size r_p. The effect of overloads on the plastic zone and relevant constraint factor value is analysed as well. During loading, it was found, that the constraint factor value is lower after overloads than when creating monotonic plastic deformation on the same load level in a large part of the cycle. The influence of thickness effect based on different α value after overload was successfully implemented into the strip yield model. Simulation of crack growth taking into account the thickness of the specimen under variable amplitude loading shows similar behaviour like the experimental data.