Technical Note(Vol.60 No.9 pp.777-782)

A Validity of Estimation Methods of Total Strain-Fatigue Life Curve about Copper and Copper Alloys

Yoichi TAMIYA

Abstract: Before now, several estimation methods of total strain-fatigue life curve (Δε_t-N_f curve) formulated by mechanical properties have been proposed. In these estimation methods, Universal slopes method, Modified universal slopes method and Medians method can be utilized effectively for preliminary fatigue design. However, it appears that the validity of three estimation methods about copper and copper alloys has been not investigated. Accordingly, in this report, actual fatigue life (N_f) of copper and copper alloys were compared to predicted fatigue life (N_p) obtained by each three estimation methods in order to investigate their validity. The conclusions are obtained as follows:
(1) Equation approximated on Medians method by strain controlled fatigue test results of copper and copper alloys was suggested as follows.
　　　　　　Δε_t=(2.70σ_B/E)N_f^-0.0805+0.543N_f^-0.529
(2) Precision of N_p obtained by Universal slopes method was the worst in three estimation methods. In addition, this N_p was non-conservative prediction under 10⁴ cycles and conservative prediction over 10⁵. cycles. Consequently, It is decided that Universal slopes method was not practical for preliminary fatigue design.
(3) Precision of N_p obtained by Modified universal slopes method was better than one of N_p obtained by Medians method. But, the advantages and disadvantages of two estimation methods could not be judged, because precisions of two may be change according to increase of experimental results. At the present time, It is thought that there is no difference of a practical use for preliminary fatigue design between Modified universal slopes method and Medians method.

Key Words:Total strain-fatigue life curve, Low cycle fatigue, Mechanical properties, Copper, Copper alloys, Universal slopes method, Modified universal slopes method, Medians method