Yadzhak N. Development of the models for short crack growth in metallic materials under long-term loading and operating environments

Modelling of short crack propagation is important for a wide range of scientific and industrial processes, since short cracks are present in structural elements already on early stages of their exploitation. This thesis presents research findings on mathematical modeling of short and small fatigue crack propagation in metallic structural elements subjected to fatigue loading and corrosive environments. The study considers the following problems of short and small crack propagation: mode I fatigue and corrosion-fatigue cracks in thin plates; mode II, mode III and mixed mode II+III cracks in thick plates, as well as mode I, mode II and mode III flat surface cracks in three-dimensional bodies. The mathematical models proposed in this study are built in strain parameters of crack tip opening displacements and are based on the energy approach, harmonic functions and the generalized equivalent area method. Application of the equivalent stressed state method helped to derive the formulas for determination of the crack tip opening displacements for the mentioned combinations of geometry and loading conditions and take into account the relative load level of a plate. The research has demonstrated that the deformational parameter of crack tip opening displacement, contrary to stress intensity factor, is an invariant characteristic for determination of short fatigue and corrosion fatigue crack growth rate. The solutions of the considered problems obtained by the proposed models were compared to the numerical results and the published experimental data. The comparison indicates high accuracy of the developed mathematical models to describe crack propagation starting from short cracks up to the final fracture of structural elements.