進行性引張り塑性ひずみを伴う塑性疲労特性と表面き裂進展挙動

抄録

Plastic strain-controlled low cycle fatigue tests and cyclic tension (C.T.) tests with various plastic strain ratio R_ε (R_ε=Δε_m/Δε_p: Δε_m being a tensile plastic strain per cycle and Δε_p 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 R_ε 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 (R_ε=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 R_ε value (R_ε<0.25), the specimen was fractured with the surface fracture mode by fatigue, while in the high R_ε value (R_ε≥0.25) it was fractured with the internal fracture mode by the effect of accumulative tensile deformation, and the estimated Δε_p-N_f relation from the linear accumulation of the fatigue damage D_f and the tensile damage D_t indicated fairly good agreement with the experimental data for the range of these C.T. tests. Moreover, in the range of the low R_ε 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-R_ε)ⁿ, where n is a constant), after considering the effect of R_ε value.