PSI - Issue 21

Mehmet F. Yaren et al. / Procedia Structural Integrity 21 (2019) 31–37 Yaren M. F. et al / Structural Integrity Procedia 00 (2019) 000 – 000

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Fig. 4. Comparisons of crack retardation models with experimental results, a) F OL /F da/dN = 1.28, b) 1.57, c)1.71, d)1.85 .

5. Conclusion Retardation effect is related to overload plastic zone size at crack tip. In the experimental part of this study, single overload tests are done. Different overload magnitudes are applied to each test. The effect of different overload ratios are investigated. Increasing of overload magnitude causes larger overload plastic zone size at the crack tip, which results in retarded and longer crack growth life. After single overload tests, crack growth life prediction is done by seven different crack retardation models. All models considered predicted the crack growth life well for low to mid levels of overload ratio. Willenborg and its modified versions underestimate crack growth life for high levels of overload ratio. It can be said that while overload ratio is increasing the error between models and experiments are also increasing for some models. 6. Acknowledgement The financial support by The Scientific and Technological Research Council of Turkey (TUBITAK) under Project Number: 217M690 for this study is gratefully acknowledged. References ASTM International, 2016. E647 − 13, Standard Test Method for Measurement of Fatigue Crack Growth Rates. Forman, R. G., 1972. Study of fatigue crack initiation from flaws using fracture mechanics theory. Engineering Fracture Mechanics, 4(2), 333-345. Forman, R. G., & Mettu, S. R., 1990. Behavior of surface and corner cracks subjected to tensile and bending loads in Ti-6Al-4V alloy. Gallagher, J. P., 1974. A generalized development of yield zone models (No. AFFDL-TM-FBR-74-28). Air Force Flight Dynamics Lab Wright Patterson Afb Oh.,. Huang, X., Torgeir, M., & Cui, W., 2008. An engineering model of fatigue crack growth under variable amplitude loading. International Journal of Fatigue, 30(1), 2-10. Walker, K., 1970. “The effect of stress ratio during crack propagation and fatigue for 2024 -T3 and 7075- T6 aluminum”. In Effects of environment and complex load history on fatigue life. ASTM International. Wheeler, O. E., 1972. Spectrum loading and crack growth. Journal of basic engineering, 94(1), 181-186. Willenborg, J., Engle, R. M., & Wood, H. A., A crack growth retardation model using an effective stress concept (No. AFFDL-TM-71-1-FBR). Air Force Flight Dynamics Lab Wright-Patterson Afb Oh. Paris, P., Erdogan, F., 1963. A critical analysis of crack propagation laws. Journal of basic engineering, 85(4), 528-533. Sander, M., & Richard, H. A., 2006. Fatigue crack growth under variable amplitude loading Part II: analytical and numerical investigations. Fatigue & Fracture of Engineering Materials & Structures, 29(4), 303-319,. Sheu, B. C., Song, P. S., & Hwang, S., 1995. Shaping exponent in wheeler model under a single overload. Engineering fracture mechanics, 51(1), 135-143.