A hardening-based damage model for fast-evolving microstructures: Application to Ni-based single crystal superalloys
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2019 Elsevier Ltd. A phenomenological hardening-based damage density function built on a Rabotnov-Kachanov's formulation and coupled to a microstructure-sensitive viscoplastic crystal plasticity model is developed for ductile materials experiencing fast-evolving microstructures. The model seats on the fact that classical continuum damage models, that only consider discontinuities of matter; viz. voids and cracks; as damage, are not able to predict the non-isothermal creep and isothermal dwell/fatigue lifetimes of materials exposed to temperature/stress conditions that trigger microstructure evolutions faster than the nucleation and growth of voids. The hereby-proposed damage model depends on microstructure-sensitive hardening variables that were previously tailored to model changes in the mechanical behavior of a Ni-based single crystal superalloy during non-isothermal loading. Furthermore, the model also proposes to predict lifetime scattering during creep by considering the initial volume fraction of pores obtained by X-ray tomography. Isothermal and non-isothermal uniaxial creep and dwell/fatigue experiments on a Nibased single crystal superalloy are used to calibrate and validate the model. Finite element simulations are also carried out to confirm the lifetime predictive capabilities of the model on an in-plane multiaxial creep test and on multiaxial torsion and tension/torsion dwell/fatigue tests. The numerical results show that the damage model well predicts the lifetime of isothermal and non-isothermal creep as well as dwell/fatigue experiments in uniaxial and multiaxial states of stresses.
