Observing Load Sequence Effects on Simulated and Experimental Fatigue Crack Growth Occurrence

Abstract

Load cycle interactions can have a significant effect in fatigue crack growth (FCG) under variable amplitude loading. Studying of FCG and fatigue life calculation under spectrum loading is important for the reliable life prediction of engineering structures. Many models have been proposed, but yet no universal model exists. In this paper, a fatigue life predicted under various load spectra, using three different fatigue crack growth models namely, the Austen, modified Forman and NASGRO models. These models are validated with fatigue crack growth test data under various amplitude loadings. This application is performed with aids of three-point bend specimens of ASTM A533 steel material. The results clearly show the load sequences effect and the predicted results agree with some discrepancies between the different models as well as with the test data. Thus, neglecting the effect of cycle interaction in fatigue calculations under variable amplitude loading can lead to invalid life predictions.

The effect of compression stresses, stress level and stress order on fatigue crack growth of multiple site damage

“…Although we did not conduct experiments for the ascending and descending stress spectra in multiple site damage, the trends mentioned above, i.e. enhanced crack growth retardation under ascending stress spectra in comparison to descending ones, are in agreement with the experimental results of single crack specimens obtained by Schijve, 71 Borrego et al 72 and Beden et al 54 The reason for the difference in results computed by the Forman and NASGRO equations is, once again, that the Forman equation considers only LEFM and neglects the load sequence effect for the threshold SIF and retardation effect while the load sequence effects are considered in the NASGRO equation.…”

“…When we analysed load sequence effects of multiple site damage, the NASGRO fatigue equation was used because it is the most reliable method among other fatigue equations. [50][51][52][53][54]…”

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

“…in which f denotes the crack opening function; R is the stress ratio; C, n, p, and q are material parameters; ÁK is the stress intensity factor range; ÁK th is the threshold stress intensity factor range; and K C is the critical stress intensity factor. For evaluation of stress sequence effects (stress interaction) in variable stress spectra, the NASGRO equation is the most reliable method among other fatigue equations (Abdullah et al, 2011;Beden et al, 2010Beden et al, , 2011Beretta and Villa, 2010;Rui and Xiang, 2010).…”

“…For evaluation of stress sequence effects (stress interaction) in variable stress spectra, the NASGRO equation is the most reliable method among other fatigue equations Beden et al, 2010Beden et al, , 2011Beretta and Villa, 2010;Rui and Xiang, 2010).…”

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

“…When we analyzed stress sequence effects (stress interaction) in stress spectra, the reason to use NASGRO fatigue equations is the best reliable method among other fatigue equations (Abdullah et al., 2011; Beden et al., 2010, 2011; Beretta and Villa, 2010; Rui and Xiang, 2010).…”