Fatigue life prediction methodology using entropy index of stress interaction and crack severity index of effective stress

Abstract

Fatigue life in critical parts of structure components, which is subjected to variable amplitude loading, is a very complex subject. When a fatigue life is influenced by these load variations, accelerations and/or retardations in crack growth rate can occur. Thus, an accurate prediction of fatigue life requires an adequate evaluation of these stress interaction effects. There are many different indexes for calculating fatigue damage at critical locations. The crack severity index based on crack growth is one of the methodologies implemented for modern military aircrafts to define mission severity relative to a known reference usage. But, this index cannot consider stress interaction. In this study, a novel index was proposed to evaluate an effect for stress interaction by using entropy concept, and fatigue life prediction methodology was developed by using entropy index of stress interaction and crack severity index of effective stress.

Stochastic fatigue life and reliability prediction based on residual strength

“…The number of cycles to failure life N at any given stress level can be obtained from Eq. (17). Therefore, considering both S-N curve model and the linear damage accumulation model, a linear relationship model between the damage accumulation and the number of usage cycle at any given stress level can be derived by combining Eqs.…”

“…Because of the stochastic nature of the fatigue damage processes, it is generally inadvisable to formulate a deterministic approach to predict fatigue damage and fatigue life [15][16][17] . Thus, many stochastic mathematical expressions for fatigue life and fatigue damage process have been developed.…”

An Entropy-Based Damage Characterization

“…Discussion of the underlying mechanism of fatigue damage accumulation and crack initiation is beyond the scope of this paper. Interested readers may refer to a comprehensive review by Sangid [3] and discussions by Mughrabi [75] and McDowell and Dunne [76] Gomez and Basaran [79,83] and other works [77][78][79][80][81]. Let us assume that fatigue damage is caused by plastic deformation of bulk material.…”

Development of fatigue prediction model for steel bridges based on characteristics of variable stress spectra

“…To account for stress interaction for various stress spectra, entropy index was proposed as novel index by using entropy concept in author's paper (Kim et al, 2013). The relation between entropy index and fatigue life was proved by examples of single crack model and multiple site damage model for real stress spectra from a part of the trainer aircraft.…”