Computational Model for Durability Analysis of Structure Elements with Defects

A methodology for the determination of number of cycles before the destruction of structure elements exposed to cyclic loading (tension-compression) has been developed. The analysis of the structure element static and dynamic stress-strain state with a usage of numerical methods of finite and boundary elements in order to determine the stress concentration zones is carried out. Model cracks that are placed in the highest stress concentration zones are selected. A database of model cracks is proposed. The initial length at which crack development begins is determined with a usage of the stress intensity factor threshold value. For each crack from the database, a critical number of cycles during which the crack grows to unacceptable sizes, is found based on the Paris criterion. A method for determining stress intensity factors for a structure element with cracks is proposed. The problem is reduced to solving singular integral equations. To obtain a numerical solution of these equations, the boundary element method is used. Densities, which appear as unknown functions in the considered integral equations, are used to calculate stress intensity factors. The analytical and numerical solutions of singular equations are compared. The critical number of cycles for plates with isolated cracks and cracks chains, cracks located at the elements holes and boundaries is determined. It was established that at the same loading level, a smaller critical number of cycles corresponds to a structure element with cracks that are in close proximity to the technological hole. An analysis of the fatigue crack development at holes in an elastic-plastic statement in order to determine the number of cycles before destruction is made, estimated number of cycles before the fatigue crack appearance is given.