Concerning strain-controlled creep-fatigue conditions of a notched specimen, since cycle sequential characteristics of stress reduction are affected not only by materials and test conditions but also by a dimension of notch, estimation of experimental result by conventional method is not feasible. In order to establish a unified measurement method of the cycle sequential characteristics of the stress reduction for a notched specimen under strain-controlled creep-fatigue condition, the stress range Δσ (=σmax-σmin) and its reduction ratio η has been proposed. In this study, strain-controlled creep-fatigue crack growth tests were conducted for the CNS (Circular sharp Notched round bar Specimen) using two types of the extensometers which has different gauge lengths, and the effect of gauge length on cycle sequential characteristics of the stress reduction and failure life was investigated in relation to the crack length. In addition, the optimum gauge length was discussed using FEM.
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