Theoretical and Applied Research on Crack Growth and Damage Evolution
|School||Beijing University of Aeronautics and Astronautics|
|Keywords||Thermodynamics of solids Fracture mechanics Damage mechanics Loading-displacement curve Stress intensity factory Resistance curve Fatigue life Crack initiation Crack growth Monotonic loading Repeated loading|
In the design process of long term structures, the damage-tolerance and durability design are very important design links. The behaviors against fracture of materials and structural members are key indexes of above designs. However, there are no solid theoretical foundations in these aspects. Therefore, the topic of this dissertation have important significance in academic research and engineering application.In this dissertation, comprehensive theoretical studies and necessary experimental works are performed. The relevant achievements can be divided into following three parts.PartⅠ, the closed form analytical solutions of nonlinear load-deflection curves of two dimensional structural members with through thickness cracks under the conditions of crack growth and ligament yielding are provided and verified by experimental results.PartⅡ, an improved closed form solution of stress intensity factors and energy release rates of three dimensional structural members with non-through thickness cracks are carried out on the basis of energy method and checked by finite element computions..Furthermore, the theoretical expressions of fatigue crack growth rates of three dimensional structural members with non-through thickness cracks under repeated loading are established on the foundation of thermodynamics and fatigue crack growth lives are predicted by these expressions with numerical method. Similarly, the system of differential equations of crack growth of three dimensional structural members with non-through thickness cracks under monotonic loading is founded on the basis of themodynamics also and resistance curves can be drawn by this system of differential equations through numerical method.PartⅢ, a closed form solution of probabilistic fatigue crack initiation life prediction based upon the conservative integral principle of damage mechanics, finite element method and theory of plasticity is applied to the pressurized cabin of certain type civil aircraft. The computational result agree with the result given by the full scale fatigue test of the pressurized cabin.