J. Me&. Phys. Solids, 1973, Vol. 21, pp. 395 to 410. Pergamon Press. Printed in Great Britain. ON THE RELATIONSHIP BETWEEN CRITICAL TENSILE STRESS AND FRACTURE TOUGHNESS IN MILD STEEL By R. 0. RITCHIE, J. F. KNOB Department of Metallurgy and Materials Science, Cambridge University and J. R. RICE Division of Engineering, Brown University, Providence, R.I. (Received 5th April 1973) SUMMARY AN ANALYSIS is presented which relates the critical value of tensile stress (a,) for unstable cleavage fracture to the fracture toughness (K,,) for a high-nitrogen mild steel under plane strain conditions. The correlation is based on (i) the model for cleavage cracking developed by E. Smith and (ii) accurate plastic*lastic solutions for the stress distributions ahead of a sharp crack derived by J. R. Rice and co-workers. Unstable fracture is found to be consistent with the attainment of a stress intensification close to the tip such that the maximum principal stress a,, exceeds a, over a characteristic distance, determined as twice the grain size. The model is seen to predict the experimentally determined variation of K,, with temperature over the range -150 to -75°C from a knowledge of the yield stress and hardening properties. It is further shown that the onset of fibrous fracture ahead of the tip can be deduced from the position of the maximum achievable stress intensiiication. The relationship between the model for fracture ahead of a sharp crack, and that ahead of a rounded notch, is discussed in detail. E CO UY 2 uYY u max YY Of ~T7yy,Uo R max = max bYY Ia0 K 42 KR KI, G,(P) a NOMENCLATURE Young’s modulus flow stress uniaxial yield stress in tension ultimate tensile stress yield stress in pure shear longitudinal tensile stress at notch tip (maximum principal stress) maximum value of byy critical tensile stress for unstable cleavage nominal bending stress stress intensification maximum value of R linear elastic stress intensity factor (mode I opening) experimental value of critical K KQ corrected for size of plastic zone plane strain fracture toughness value of K,, for fracture ahead of notch of root radius p crack length 395
ON THE RELATIONSHIP BETWEEN CRITICAL TENSILE STRESS AND FRACTURE TOUGHNESS IN MILD STEEL
May 23, 2023
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