PSI - Issue 14

2

Author name / Structural Integrity Procedia 00 (2018) 000–000

430 This is an open access article under the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0/) Selection and peer-review under responsibility of Peer-review under responsibility of the SICE 2018 organizers. A.N. Savkin et al. / Procedia Structural Integrity 14 (2019) 429–434

Keywords: crack growth rate, crack closure, stress intensity factor, variable amplitude loading.

1. Introduction The machines and structures are experienced variable loads in operation. The microcracks can arise in stress concentrators areas, which are the overstrained micro-entities of metal structures. The growth of such cracks under service loading can lead to catastrophic failure. Crack growth kinetics depends on the magnitude as well as sequence of applied loads (Panasjuk, 1991). For example, overloads promote crack growth retardation while underloads accelerate growth. Random loading contains all those elements and analysis of their interaction is made difficult by gaps in understanding. Therefore, experimental studies of the effect of load history continue to be relevant. A common approach to handling the mix of load amplitudes under random loading is to ignore their interaction and merely apply the linear damage accumulation rule. 2. The crack closure model and the near-tip stress influence Currently, among other models for crack growth life estimation, crack closure models that consider the decrease in the stress intensity factor (SIF) magnitude are more popular (Kiciak et al. (2003). One of the negative sides of these models is the impossibility of considering the loading history.

Fig. 1. The ralationship between near-tip stress and Δ K th

The Sunder’s crack resistance model, considering the local near-tip stress, explains the nature of crack slowing based on the active particles from moisture accumulates at the crack tip in the most stressed volume under increasing load, which affects the dependence of the threshold SIF K th = f ( *  ) from stresses near the crack [Sunder (2005) and (2012). Theory bound threshold SIF Δ K th and local near-tip stress and postulated that the overloading effect at the threshold crack growth rates caused by local residual stresses. The proposed model applies the local stress and strain approach to estimate the stress σ* in the stress concentrator region in the fatigue analysis. In this study, the Neuber and Ramberg-Osgood equations were used for making associating SIF K or its range Δ K with the local stress σ* at a distance from the crack tip r * for static and cyclic loading, respectively: