Senior engineerMember of ASTM, Northrop Corporation, Aircraft Division, Hawthorne, Calif.
The general characteristics of steady-state fatigue crack growth rates are discussed. An empirical formulation is described where two constants form a basic crack growth rate versus maximum stress intensity Kmax curve, which is a straight line on a log-log graph. The constants that form the base curves for various materials are correlated to Young's modulus. A third parameter that is sensitive to material alloy and environment is described and methods for obtaining this value are presented. Crack growth rate data for several stress ratios can then be projected to the basic modulus-dependent curve, where straight line scatter bands and statistical information pertaining to the overall accuracy of the formulations can be determined.
Paper ID: JTE10541J