Quantitative Evaluation of Strain Rate Change during Creep and Relationship between Extrapolated Life to Failure and Monkman-Grant Constant

The shape of creep curve was quantified using the Strain Acceleration and Transition Objective-index, α , and the extrapolated life to failure were estimated from the creep curve near the minimum creep rate.In a two-phase Mg-Li-Al-Zn alloy, where the strain dependence of creep rate varies depending on stages, α varies in each stage.It indicates that the index α reflects the state of the microstructure.The relationship between the extrapolated life, the minimum creep rate and the index α was systematically clarified, and shows that the Monkman-Grant constant is inversely proportional to the square root of α and to the minimum creep rate.To improve the life to failure, in addition to reducing the minimum creep rate, reducing the α in primary and tertiary creep is effective.