A Numerical Strip-Yield Model for the Creep Crack Incubation in Steels

Abstract

A numerical strip-yield model was developed to simulate creep crack incubation in heat-resistant steels. The model is based on a formulation proposed by Newman (Newman, J. C., Jr., “A Crack-Closure Model for Predicting Fatigue Crack Growth under Aircraft Spectrum Loading,” Methods and Models for Predicting Fatigue Crack Growth under Random Loading, ASTM STP 748, J. B. Chang and C. M. Hudson, Eds., ASTM International, West Conshohocken, PA, 1981, pp. 53–84) for fatigue crack growth under variable amplitude loading. The time evolution of the plastic deformation ahead of a crack loaded in tension is modeled using the Norton law for secondary creep stage, and the primary and tertiary creep stages are neglected. The model assumes a pre-existing crack in a specimen and models the behavior of the material prior to the beginning of crack propagation due to creep loading. The evolution with time of the crack-tip plastic zone, crack-tip opening displacement, and yield strength in the plastic zone are computed at constant temperature for center crack panels. Comparison with two previous strip-yield models and experimental data is performed, and good correlation is obtained for several Cr-Mo-V steels. This approach to modeling creep crack incubation has the potential to be applied to other types of cracked specimens under constant or variable amplitude loading.