科研之友
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摘要
In this study, we investigate the mechanical responses of copper based alloy, NARloy-Z, under cyclic loadings at different strain rates and strain amplitudes, and also creep at different levels of stresses. We examine the effect of temperature changes, as a result of energy dissipation during loading, on the overall cyclic and creep responses of NARloy-Z. A phenomenological viscoplastic model, developed by Freed et al. (1994), is adopted and modified in order to incorporate the effect of energy dissipation on the viscoplastic response of NARloy-Z. An adiabatic process is assumed to convert the dissipated energy into temperature increase, and the resulting temperature changes alter the elastic modulus and plastic flow of NARloy-Z during loading. A numerical method is also presented in order to implement the above nonlinear constitutive model. Experimental data reported by Conway et al. (1975) for cyclic loading and Ellis and Michal (1996) for creep loading are used to examine the viscoplastic responses of NARloy-Z. From the analyses, it is concluded that the amount of energy dissipation is much more pronounced under cyclic loading, especially for long-term duration of cyclic loading, while it is negligible under creep loading. Higher strain rates result in higher energy dissipation, which is expected as higher strain rates accumulate more hysteretic cycles at the same loading duration. Large amount of energy dissipation leads to a pronounced stress softening behavior due to significant increases in temperatures. The stress softening is one of the sources for material failures. It is also seen that the energy dissipation, and its corresponding temperature increase, is an important component in determining fatigue failure of NARloy-Z.
- 出版日期2016-4-1
