THE CRITICAL TENSILE STRESS CRITERION FOR CLEAVAGE.
STANFORD UNIV CA DEPT OF MATERIALS SCIENCE AND ENGINEERING
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An elastic-plastic analysis was used to accurately measure the microscopic cleavage strength sigma asterisk sub f of notched bars of high nitrogen steel in bending. It was found that sigma asterisk sub f increases as the root radius of the notch rho decreases. For rho 0.010 in., the variation of sigma asterisk sub f with rho, and the difference between sigma asterisk sub f and the cleavage fracture strength of a plane tensile specimen, sigma sub f, is due to a statistical effect, due to differences in the volume of highly stressed material in the plastic zone. For rho .010 in., the primary reason for the apparent increase in sigma asterisk sub f with decreasing rho, is the steep stress gradient at the notch tip, which forces the critical plastic zone size to extend further to insure that unstable microcrack propagation can occur. Both the statistical and stress gradient effects have been quantitatively evaluated and found to be in good agreement with the experimental data. Author