SEDL / STP / STP677-EB / STP34918S

A Strain Based Intensity Factor Solution for Short Fatigue Cracks Initiating from Notches

El Haddad, MH
Research engineer, Ontario Hydro, Toronto, Ontario

Smith, KN
Associate professor and professor, University of Waterloo, Waterloo, Ontario

Topper, TH
Associate professor and professor, University of Waterloo, Waterloo, Ontario

Pages: 16    Published: Jan 1979

Download this paper for $25 PDF (236K)          View License Agreement
Abstract

A strain-based intensity factor is introduced which, while becoming equivalent to the linear elastic stress intensity factor for long elastic cracks, admits plasticity by replacing the conventional stress term with a strain term and accounts for the proximity of a short crack to a free surface by the inclusion of a length constant. Crack growth results for short cracks in both elastic and plastic strain fields of unnotched specimens, when interpreted in terms of this intensity factor, show excellent agreement with elastic long crack data. This intensity factor is then extended to plastically strained notches and the solutions obtained are tested in the correlation of short crack growth data for notches of varying severity with elastic long crack data. Constant stress amplitude tests of these notches gave crack growth rate versus crack length curves which varied from monotonically increasing for blunt notches to an initial decrease followed by an increase for sharp notches. However, all of the data fell within the long crack data when correlated by this inelastic intensity factor. Conversely, solutions for the parameter were used successfully to predict elastic and inelastic short crack growth curves for notches of various severities.