PSI - Issue 19

Available online at www.sciencedirect.com Available online at www.sciencedirect.com ScienceDirect Structural Integrity Procedia 00 (2019) 000–000 Available online at www.sciencedirect.com ScienceDirect Structural Integrity Procedia 00 (2019) 000–000

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Procedia Structural Integrity 19 (2019) 472–481

© 2019 The Authors. Published by Elsevier B.V. Peer-review under responsibility of the Fatigue Design 2019 Organizers. Abstract Predictive models in the past for stress ratio effect on S-N fatigue life have been subject to modifications since the 19 th century. Many of them have been developed with limited experimental verifications or beyond the theoretical limit. Also, they have employed weak S-N curve models for the development, resulting in inefficiency for applications. There has been, as such, a gap in the development of predictive models between S-N curve behaviour and stress ratio effect. In this paper, an efficient procedure is proposed for predicting S-N curves at different stress ratios. The characteristics of the constant fatigue life (CFL) diagram were clarified for theoretical capability and limitations, and dependence of experimental fatigue behaviour. The Kim and Zhang S-N curve model was dovetailed with the linear CFL lines of the four segments for predicting S-N curves for the whole range of stress ratios. With the benefits of damage parameters in the Kim and Zhang S-N curve model, analytical expressions for CFL as functions of two independent variables (i.e. applied stress and stress ratio) were derived for theoretical predictions. The theoretical predictions were found to be in agreement with the experimental results . © 2019 The Authors. Published by Elsevier B.V. Peer-review under responsibility of the Fatigue Design 2019 Organizers. 1. Introduction The S-N fatigue studies in history have been somewhat disorderly in sequence as already pointed out by Burhan and Kim (2018). For example, the research of stress ratio effect on fatigue life (Gerber, 1874) mostly appears earlier than that of S-N curve modelling (Basquin, 1910) although S-N curve modelling should be a prior task to the stress ratio effect for fatigue life prediction. One would be surprised to find the fact that the stress ratio effect modelling for fatigue life prediction has still been a contemporary research topic since the 19th century. It would not be surprising, however, to find the fact that the knowledge advancement in the area has been slow. The earlier disorderly sequence of events has still been continued. For example, some researchers (Bond, 1999) have already progressed on to the research on S-N fatigue life prediction for the variable amplitude loading while some other researchers (Adam et al., Fatigue Design 2019 Prediction of S-N curves at various stress ratios for structural materials Ho Sung Kim Mechanical Engineering, School of Engineering, The University of Newcastle, Callaghan, NSW 2308, Australia Abstract Predictive models in the past for stress ratio effect on S-N fatigue life have been subject to modifications since the 19 th century. Many of them have been developed wit limit d experim ntal verifications or bey nd the the retical limit. Also, they have employ d weak S-N curve mod ls for the dev lopment, resulting in inefficiency for applicatio s. There has be n, as such, a gap n the development of predictive models betw en S-N curve behaviour nd stress ratio ffect. I this paper, an efficient procedu is proposed for p dicting S-N curves at d ffere t stress ratios. Th characteristics o the constant fatigue life (CFL) diagram were larified for theoretical capability and limitations, and dependence of experimental fatigue behaviour. The Kim and Zhang S-N curve model was dove ailed with the linear CFL lin s of the four segments for predicting S-N curv s for the wh le range of stress ratios. With the benefits of damage param ters in the Kim a Zhang S-N curve mod l, analytical expressions for CFL as functions of two independent variables (i.e. applied stress and stress ratio) were derived for theoretical predictions. The theoretical predictions were found to be in agreement with the experimental results . © 2019 The Authors. Published by Elsevier B.V. Peer-review under responsibility of the Fatigue Design 2019 Organizers. Keywords: S-N curve; constant fatigue life; stress ratio; fatigue damage; life prediction 1. Introduction The S-N fatigue studies in history have been somewhat disorderly in sequence as already pointed out by Burhan and Kim (2018). For example, the research of stress ratio effect on fatigue life (Gerber, 1874) mostly appears earlier than that of S-N curve modelling (Basquin, 1910) although S-N curve modelling should be a prior task to the stress ratio effect for fatigue life prediction. One would be surprised to find the fact that the stress ratio effect modelling for fatigue life prediction has still been a contemporary research topic since the 19th century. It would not be surprising, however, to find the fact that the knowledge advancement in the area has been slow. The earlier disorderly sequence of vents has still been continued. For example, some researchers (Bond, 1999) have already progressed on to the research on S-N fatigue life prediction for the variable amplitude loading while some other researchers (Adam et al., Fatigue Design 2019 Prediction of S-N curves at various stress ratios for structural materials Ho Sung Kim Mechanical Engineering, School of Engineering, The University of Newcastle, Callaghan, NSW 2308, Australia Keywords: S-N curve; constant fatigue life; stress ratio; fatigue damage; life prediction

2452-3216 © 2019 The Authors. Published by Elsevier B.V. Peer-review under responsibility of the Fatigue Design 2019 Organizers. 2452-3216 © 2019 The Authors. Published by Elsevier B.V. Peer-review under responsibility of the Fatigue Design 2019 Organizers.

2452-3216 © 2019 The Authors. Published by Elsevier B.V. Peer-review under responsibility of the Fatigue Design 2019 Organizers. 10.1016/j.prostr.2019.12.051