Spreadsheet-based method for predicting temperature dependence of fracture toughness in ductile-to-brittle temperature region

Abstract

A spreadsheet-based simplified and direct toughness scaling method to predict the temperature dependence of fracture toughness Jc in the ductile-to-brittle transition temperature region is proposed. This method uses fracture toughness test data and the Ramberg–Osgood exponent and yield stress at the reference temperature, and yield stress at the temperature in interest to predict Jc. The physical basis of the simplified and direct toughness scaling method is the strong correlation between Jc and yield stress. The simplified and direct toughness scaling method was validated for Cr–Mo steel Japan Industrial Standard SCM440 and 0.55% carbon steel Japan Industrial Standard S55C by comparing the simplified and direct toughness scaling prediction results with the median results of an experiment performed at four temperatures ranging from −55°C to 100°C and at three temperatures ranging from −85°C to 20°C, respectively. The simplified and direct toughness scaling method can predict Jc from both low to high temperatures, and vice versa. Thus, 12 and 6 predictions were made for each material. The prediction discrepancy for these 18 cases ranged from −50.4% to +25.8% and the average absolute discrepancy was 22.1%. These results were acceptable considering the large scatter generally observed with Jc. In particular, in case of predicting Jc at temperatures higher than the lowest temperature of −55°C for SCM440, the simplified and direct toughness scaling method predicted Jc more realistically than the American Society for Testing and Materials E1921 master curve approach. Although the simplified and direct toughness scaling method requires additional tensile test data compared with the master curve approach, the acceptable prediction accuracy at high temperatures seems beneficial because the mass and time required for tensile tests are admissible.