Analysis of the mesoscopic high cycle multiaxial fatigue strength of fcc metals with crystal plasticity and generalized extreme values probability

摘要

Multiaxial high cycle fatigue modeling of materials is an issue that concerns many industrial domains (automotive, aerospace, nuclear, etc) and in wich many progress still remains to be achieved. Several approaches exist in the litterature: invariants, energy, integral and critical plane approaches all of there having their advantages and their drawbacks. These different formulations are usually based on mechanical quantities at the micro or meso scales using localization schemes and strong assumptions to propose simple analytical forms. This study aims to revisit these formulations using a numerical approach based on crystal plasticity modelling coupled with explicit description of microstructure (morphology and texture). This work has three steps: First, 2D periodic digital microstructures based on a random grain sizes distribution are generated. Multiaxial cyclic load conditions corresponding to the fatigue strength at 107 cycles are applied to these microstructures. Then, the mesoscopic Fatigue Indicator Parameters (FIPs), formulated from the different criteria existing in the literature, are identified using the FE calculations of the mechanical fields. These mesoscopic FIP show the limits of the original criteria when it comes to applying them at the grain scale. Finally, a statistical method based on extreme value probability is used to redefine the parameters of these criteria. These new criteria contain the sensitivity of the microstructure variability.