On Relevant Ramberg-Osgood Fit to Engineering Nonlinear Fracture Mechanics Analysis

The present paper proposes a robust method for the Ramberg-Osgood (R-O) fit to accurately estimate elastic-plastic J from the engineering fracture mechanics analysis based on deformation plasticity. The proposal is based on engineering stress-strain data to determine the R-O parameters, instead of true stress-strain data. Moreover, for practical applications, the method is given not only for the case when full stress-strain data are available but also for the case when only yield and tensile strengths are available. The reliability of the proposed method for the R-O fit is validated against detailed three-dimensional FE analyses for through-wall cracked pipes under global bending using five different materials, three stainless steels and two ferritic steels. Taking the FE J results based on incremental plasticity using actual stress-strain data as the reference, the FE J results based on deformation plasticity using various R-O fits are compared with reference J values. Comparisons show that the proposed R-O fit provides more accurate J values for all cases, compared to existing methods for the R-O fit. Advantages of the proposed R-O fit in practical applications are discussed, together with its accuracy.