13th International Conference on Fracture (ICF13) June 16–21, 2013, Beijing, China Investigations of Subcritical Crack Propagation under High Cycle Fatigue Attilio Arcari1, Nagaraja Iyyer1, Madan Kittur2, and Nam Phan2 1Technical Data Analysis Inc., Falls Church, VA, USA 2Structures Division, Naval Air Systems Command, Patuxent River, MD, USA Abstract Most of the fatigue life in high cycle fatigue (HCF) is expended in growing subcritical defects to a detectable damage size, followed by rapid growth to failure. This is a significant challenge in design as this leads to concerns with respect to the efficacy of planned inspections and routine repair operations. The variability of the damage phenomena in HCF can impact the characterization of the long fatigue life regimes, as the extent and severity of damage depends on the intensity of the operating loads, and on the intrinsic variations in material characteristics at different scales. In this paper we propose a methodology to account for stochastic variability in HCF by using the framework of the Kitagawa-Takahashi diagram, and the El-Haddad formulation as the design curve for subcritical crack propagation in fatigue and in environmentally assisted cracking (EAC). Moment-based reliability, based on first order and second order reliability methods, as well as Monte Carlo simulation is used to handle stochastic variability in applied stress and defect size. The calculation of a probability of defect propagation at each instant of the subcritical growth process is the goal of the developed framework. Preliminarily validation with available data and an application of the framework to stochastic defect growth for block loading is presented. 1. Introduction Designing against HCF can be challenging, particularly for dynamic components subjected to a large number of small amplitude or vibratory solicitations. While the growth of cracks from the subcritical level to a detectable size level has been extensively investigated in literature, current models show difficulties in estimating the fatigue life in HCF regimes and innovative solutions are sought [1-4]. The characterization of the fatigue behavior of materials in the long fatigue life regime is critical for fatigue life prediction models, but the investigation of damage phenomena in the proximity of the endurance stress can be experimentally intensive. Furthermore, crack growth under high R-ratios and near threshold is not well captured by currently employed frameworks [5, 6]. Therefore, certification becomes difficult for damage tolerance of components Figure 1: Kitagawa-Takahashi diagram for fatigue.
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