Fatigue Damage Initiation in Waspaloy Under Complex Cyclic Loading

Abstract

The low-cycle fatigue damage initiation in Waspaloy under complex cyclic loading (out-of-phase) is studied from experimental and theoretical viewpoints. Special emphasis is put on the transgranular damage development and results are compared to those reproduced in the literature. A physico-phenomenological model based on slip theory is used to predict the damage initiation lives as well as the directional aspect of the damage distribution. In this model, the micro-damage is supposed to initiate and then evolve on the activated crystallographic slip systems. The theoretical results are compared to both the experimental ones concerning the same material (Waspaloy) as well as other experimental results extracted from the literature.

Effects of Microstructure Variability on Intrinsic Fatigue Resistance of Nickel-base Superalloys – A Computational Micromechanics Approach

“…Abdul-Latif et al (1999) presented a homogeneous (i.e., precipitates not explicitly modeled) crystal plasticity approach to predict fatigue crack initiation in Waspaloy under uniaxial and multi-axial cyclic loading. Manonukul and Dunne (2004) explicitly modeled the grain structure of a Ni-base superalloy using a rate-independent crystal plasticity constitutive model for individual grains.…”

“…The total life (crack initiation life plus propagation life) was found to be the same for both microstructures. Abdul-Latif et al (1999) conducted uniaxial and 90 • out-of-phase LCF tests on Waspaloy at room temperature. They studied two microstructures and observed that the LCF life (defined as number of cycles to form a macro-crack observed by the naked eye, which differs from the definition used in other studies mentioned above) associated with a microstructure with smaller precipitates was about twice that of a microstructure with larger precipitates.…”

Modeling of the Heterogeneous Damage Evolution at the Granular Scale in Polycrystals under Complex Cyclic Loadings

“…The experimental observations, related to the low-cycle fatigue for FCC polycrystals like the Waspaloy (see, Ferney, 1994;Abdul-Latif et al, 1999) and austenitic stainless steel, demonstrate that microcracks initiate and orient along the slip planes (for example, Heino and Karlsson, 2001).…”

“…Regarding the low-cycle fatigue crack nucleation modeling, the selfconsistent approach has not received enough attention from researchers till date and is still in its immaturity. However, some attempts have been made, using the above-mentioned approach in characterizing the stress, strain, and damage responses for polycrystals subjected to different cyclic loading paths (simple and complex) using continuum damage mechanics (CDM) (Abdul-Latif and Saanouni, 1994, 1997Abdul-Latif et al, 1999, 2002bAbdul-Latif, 1999;Saanouni and Abdul-Latif, 1996). The microcrack initiation criterion is based on the accumulated slip on the crystallographic slip system.…”

“…Despite adopting the isotropic damage concept, the model describes the damaged behavior emphasizing the advantages to predict correctly the fatigue life related to the complexity of the loading path, i.e., the greater the complexity of the loading path, the greater the additional hardening; the shorter the fatigue life becomes consequently. However, the aboveproposed model reveals some restrictions because it can only describe the damaged behavior of those materials like the Waspaloy (Abdul-Latif et al, 1999) and nickel-base alloy C263 (Manonukul and Dunne, 2004) in which the damage initiation takes place at the slip system level. Hence, this assumption makes this approach quite limited in its application for other metals.…”