Temperature Dependence of Mode II Fracture Toughness

Abstract

This paper is concerned with the ductile-brittle transition behavior of steels under mode II loading. Mode II fracture tests were carried out on center-cracked thin-sheet specimens of HT 50 and S 20 C. Test temperature was changed from room temperature to -196°C. From mode II tests, it was found that the fracture appearance changed with temperature as follows : (i) in the region T < T_B, a cleavage crack initiates and extends, (ii) in the region T > T_D, a ductile crack initiates and extends, and (iii) in the region T_B ≤ T ≤ T_D, a ductile crack initiates and then extends as a brittle cleavage crack. The transition curve under mode II loading was shifted to lower temperature than that under the mode I loading condition. The direction of the cleavage crack was about 64°inclined to the precrack. The direction of the ductile crack coincided with that of the precrack.