Modeling of stress ratio effect on Al alloy SAE AMS 7475-T7351: Influence of loading direction |
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Authors: | E. Di Todaro C. T. O. F. Ruckert M. T. Milan W. W. Bose Filho J. R. Tarpani D. Spinelli |
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Affiliation: | 1. NEMAF — Núcleo de Ensaios de Materiais e Análises de Falhas, Departamento de Engenharia de Materiais, Aeronáutica e Automobilística, Escola de Engenharia de S?o Carlos, Universidade de S?o Paulo, CEP, 13566-590, S?o Carlos, SP, Brazil
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Abstract: | The main goal of this work was to evaluate the effectiveness of Walker’s equation in collapsing the fatigue crack propagation data of a SAE AMS 7475-T7351 aluminum alloy loaded either longitudinally (L-T) or transversely (T-L) to the rolling direction. T-L orientation testpieces presented lower ductility and fracture toughness values than L-T orientation. As a consequence, during the fatigue crack propagation tests, T-L testpieces exhibited a stronger influence of monotonic modes of fracture, resulting in higher Paris exponent values,m. Walker’s model was able to collapse fatigue crack propagation data of L-T test pieces at different applied stress ratios,R. However, for the T-L orientation, due to theR ratio dependency onm andC, simply averaging ofm values for the calculations of Walker’s exponent proved to be inefficient. A simple analytical procedure was proposed by the authors to modify Walker’s model to take into account such effect. For T-L test pieces, when Walker’s model is modified by considering both Paris’s exponent as well the coefficient as a function of theR ratio, the fatigue crack growth data collapses within a narrow band, thus allowing predictions to be made satisfactorily. The collapsed band is even narrower if the empirical relationm=a+blogC is used instead of simple polynomial equations due to a better correlation coefficient. |
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Keywords: | aluminum alloy fatigue crack propagation R ratio Walker’ s model |
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