MECHANICS OF GROWTH OF INTERNAL FATIGUE CRACKS

We apply the theory of fatigue cracks based upon the synthesis of fracture mechanics and mechanics of accumulation of dispersed defects to predict the growth of internal tensile cracks of elliptic shape in an elastically deformed medium being damaged. The stability conditions for the system cracked body-load are completed by the equation of damage accumulation near the front of the crack and on its continuation and also by an equation that describes the change of conditions at the front of the growing crack. Numerical analyses are performed for the influence of the material properties, the initial dimensions of the crack, and the initial conditions at the crack front on (i) the number of cycles until the crack starts growing, (ii) the modification of the crack dimensions and relationships between these dimensions, and (iii) the change of the damage measure and of the effective radius of curvature along the perimeter of the front of the crack. The final results are represented in the form of standard diagrams showing the rates of growth of typical sizes of the crack as functions of the ranges of the corresponding stress intensity factors.