Determination of Fracture Stress and Effective Crack Tip Radius from Toughness (KIc) and Yield Strength (Y).

摘要

This is the last of several reports in which KIc toughness is not considered basic, but dependent on two metallurgically controllable parameters, the tensile nil-ductility fracture stress and an effective crack tip radius formed by straining at the sharp crack tip which is shown by examples not to be uniquely dependent on load as would the mathematical increase in radius of a rounded tip no matter how small, in a homogeneous material but also dependent metallurgically on micromechanical structure. The reports describe how to determine the fracture stress and the radius from KIc tests with the aid of a postulated fracture criterion characteristic of the material and a curve derived from the solution for the state of stress in the yielded region of a short elliptically shaped flat crack lying across the center of a plate under uniform tensile loading. Here a more exact solution by Colin E. Freese and Dennis M. Tracey supplants the approximate ones used previously and it is shown that dependent on tempering or test temperature, radius determinations remain unchanged to 20% larger although fracture stress determinations are 75% to 85% as large. Fracture mechanics.