Determination of Ramberg-Osgood approximation for estimation of low-temperature fracture toughness

This article presents a new method for determination of parameters of the Ramberg-Osgood (R-O) approximation of the tensile diagram based on the loading-frame displacement. This procedure was successfully verified on the samples of the high strength steel OCHN3MFA tested at various temperatures with records of both the extensometer elongation and the load-frame displacement. The method can be used in the model for prediction of the KIc-value based on the critical strain local approach. The parameters of the R-O approximation obtained from the extensometer-controlled and the load-frame controlled tests are in a very good agreement. Moreover, the experimental KIc-value at the cryogenic temperature of 77 K and the theoretical one predicted using the loading-frame displacement data are practically identical.