Numerical Modeling of Fatigue Crack Growth in Single Crystals Based on Microdamage Theory

Proper life-time prediction modeling of single crystalline components is of increasing importance due to their common use in turbine industry. Viscoplastic damage approaches are of great interest in that context. However, mechanical properties of single crystals are strongly anisotropic and nonlinear in service conditions, bringing certain complexity into constitutive and numerical modeling. The aim of this work is to develop a thermodynamically consistent constitutive model based on generalized continua in order to simulate fatigue crack initiation and growth in single crystals. For that purpose, a standard crystal plasticity model is taken as a basis and coupled with the continuous damage model developed by Marchal et al. (2006a) [Marchal, N., Forest, S., Remy, L. and Duvinage, S. (2006a). Simulation of Fatigue Crack Growth in Single Crystal Superalloys Using Local Approach to Fracture, In: Moinereau, D., Steglich, D. and Besson, J. (eds.), Local Approach to Fracture, 9th European Mechanics of Materials Conference, Euromech-Mechamat, Moret-Sur-Loing, France, Presses de l'Ecole des mines de Paris, pp. 353-358]. As a variant of micromorphic theory, microdamage approach is applied to the model in order to obtain a regularized continuum damage formulation which solves mesh dependency problem by introducing an intrinsic length scale. A detailed finite element implementation procedure and its validation for monotonic crack growth are-shown. Fatigue crack growth analyses have been performed on a single edge notched geometry and a comparison between numerical and experimental results is presented.