Impact Fatigue Strength and Behavior of Plastic Deformation due to Cyclic Creep for Copper under Repeated Impact Tensile Loads at High Temperatures

Abstract

The impact fatigue tests for oxygen-free copper and high strength copper were carried out at various temperatures between 100 and 250°C as well as at room temperature. The fatigue strength and plastic deformation due to cyclic creep under impact tensile loads were analyzed in consideration of temperature-dependence and static tensile properties.
The impact fatigue strength was found to be expressed by the formula of σ(N_fT)^m₀=D₀, where m₀ and D₀ are the material constants for impact fatigue strength at each high temperature T_θ(K). The values of m₀ and D₀ depended on the temperature and were expressed by the formulas of m₀=m₀^*+m₁^*(T_θ-273) and D₀=D₀^*exp(Q/kT_θ).
The behavior of cyclic creep plastic deformation was expressed by a formula including only plastic strain ε_p and normalized number of cycles N/N_f, which is independent of impact stress σ, duration time T and temperature T_θ. The values of m₀, D₀ and main material constants (a₁, a₂), which appear in the formula expressing the cyclic deformation, had distinct relationships with the ultimate strength σ_B, reduction of area φ and elongation δ in static tension. Impact fatigue strength and cyclic creep plastic deformation at high temperatures can be well estimated through these relationships from the static tensile properties at room temperature.