Abstract
JIN SNCM439, S35C and SUS304 steels were low cycle fatigued with mean stress and strain under load and displacement controlled conditions. The cyclic J integral range, ΔJ and the crack tip opening displacement range, ΔΦt(200) were not effective for evaluation of the crack growth rate under test conditions accompanied by a ratcheting deformation. Then, the parameter of ΔJ/{1-(Φcmin/Φcmax)}0.2, which can control the acceleration or the crack growth rate due to the ratcheting deformation as well as the crack growth rate under the fully reversed cyclic strain, was usefully proposed here, where Φcmin and Φcmax are minimum and maximum crack center opening displacements. The ΔΦt(200) was correlated with ΔJ by the equation of type of ΔΦt(200)=A(ΔJ)q. In general, the power exponents, q are smaller than the value of 1/(n'+1) or 1/(n+1) estimated by assuming the HRR singular field around the fatigue crack tip where n' and n are the cyclic and monotonic strain hardening exponents of materials.
