Methods for estimating the fatigue properties of UNS C70600 copper-nickel 90/10

Abstract

Most existing methods for estimating the strain life parameters of a material are dependent on the material’s monotonic tensile properties. However, a few of these methods yield quite complicated expressions for calculating fatigue parameters, and are specific to certain groups of materials only. The Universal Slopes method, Modified Universal Slopes method, Uniform Material Law, the Hardness method, and Medians method are a few existing methods for strain-life fatigue prediction, which use monotonic tensile material properties and hardness of material. In the present study, nine methods for estimating fatigue life and properties are applied to determine the best method for estimating the strain life parameters of UNS C70600 Copper-Nickel 90/10, which is a ductile material. Experimental strain-life curves are compared with the estimations obtained using each method. Muralidharan-Manson’s Modified Universal Slopes method and Ba¨umel-Seeger’s method for unalloyed and low-alloy steels ae found to provide better accuracy in estimating fatigue life with a deviation of less than 25%. However, prediction via both these methods yields much better accuracy only for a cycle of less than 1000 or for strain amplitudes of more than 1%. Manson’s Original Universal Slopes method and Ong’s Modified Four-Point Correlation method are found to predict strain-life fatigue with better accuracy for a high number of cycles of strain amplitudes of less than 1%. The differences between mechanical behavior during monotonic and cyclic loading and the complexity in deciding the coefficient of equations are probably the main reasons for the lack of a reliable method to estimate fatigue behavior based on the monotonic properties of a material. It is therefore suggested that a differential approach and new expressions be developed to estimate the strain-life fatigue parameters of ductile materials such as copper.