1989 年 38 巻 434 号 p. 1303-1308
Plastic strain-controlled low cycle fatigue tests and cyclic tension (C.T.) tests with various plastic strain ratio Rε (Rε=Δεm/Δεp: Δεm being a tensile plastic strain per cycle and Δεp a controlled plastic strain range) were carried out on rod specimens with a small hole which were machined from austenitic stainless steel 316L. The effects of the Rε value on fatigue deformation properties, final fracture mode and surface crack growth behavior were investigated from the C.T. test results.
In the C.T. tests (Rε=0-0.667), the stress amplitude in the cyclic work hardening curve showed a notable decrease after a peak stress, and a cyclic strain exponent n' in the cyclic stress-strain curve was lower (about n'=0.17) than that of a constant amplitude test (n'=0.50). In the case of the low Rε value (Rε<0.25), the specimen was fractured with the surface fracture mode by fatigue, while in the high Rε value (Rε≥0.25) it was fractured with the internal fracture mode by the effect of accumulative tensile deformation, and the estimated Δεp-Nf relation from the linear accumulation of the fatigue damage Df and the tensile damage Dt indicated fairly good agreement with the experimental data for the range of these C.T. tests. Moreover, in the range of the low Rε value, the surface crack growth rate da/dN was evaluated successfully by plotting against the parameter of modified J integral range ΔJ*(ΔJ*=ΔJ/(1-Rε)n, where n is a constant), after considering the effect of Rε value.