高温における間欠ひずみ波形下の損傷評価法

概要

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In order to establish a life prediction method for gas turbuine blades, fatigue tests using inter-mittent strain wave forms which simulated the service loading of gas turbine blades were carried out for SUS 316 stainless steel and two Ni-base superalloys (IN 738 LC and Inco. 713 LC) at elevated temperatures. The fatigue behavior and fatigue strength in these tests bad been reported in the PreVious papers by the present authors. In this paper, several methods of damage evaluatlon using intermittent strain waveforms were examined on the basis of a linear cumulative damage concept, and the following conclusion was obtained; The failure life (N^^-_<es>) in the intermittent strain cycling can be predicted by the equation below, which takes the acceleration of crack propagation rate due to the superposed small strain cycling into consideration. [numerical formula] where N_h and N_2 are the fatigue lives observed under trapezoidal and constant strain waves respectively. η is the ratio of crack propagation rate under superposed small strain cycling to that under constant strain amplitude cycling, which is represented by the following equations. [numerical formula] where α is the Paris's exponent and R is the stress ratio calculated by using the cyclic stress-strainrelationship
社団法人日本材料学会の論文
1986-03-15