Model of Short Fatigue Crack Growth Rate and Fatigue Life Estimation of Carbon Steel Specimens

This study proposed a model describing the kinetics of short fatigue crack growth from a smooth surface and from the top of a blunt notch. The driving force of the fatigue crack is the effective stress intensity factor (SIF), which is defined as the difference between the applied "external" and "internal" SIFs, characterizing the material resistance to crack growth. The model makes it possible to calculate the kinetic diagram of the growth rate of a short fatigue crack from the notch and estimate the fatigue life (number of load cycles) from the moment of crack initiation until it reaches a certain size at a constant range of applied nominal stresses. The total fatigue life is divided into the crack initiation stage (stage 1) and crack growth stage (stage 2). In addition to the load parameters and notch's geometric dimensions, the input data for the calculation are the static strength characteristics (elastic modulus, Poisson's ratio, and macroyield initiation stress) determined via short-term tensile tests of standard specimens of this material, and microstructural characteristics (grain size, grain misorientation angle, Taylor's factor, and Burgers vector) determined from the microstructural analysis of the initial material. The calculations based on the proposed model of the kinetic curve of the crack growth rate and total fatigue life of the tested specimens made of steel 45 show good agreement with the experimental ones.