Msd Structural Stress Intensity Factor Of Semi-analytical Numerical Algorithms

Multiple sites damage (MSD) is one of the important characters of aging aircraft subjected to long-term fatigue, and its existence and growth would be a fatal threat to the integrity of the aircraft structure. When a structure with MSD evaluated through damage tolerance technique, the first important step is to calculate the stress intensity factors (SIF) at its crack tips, then the characters of crack propagation, crack linkup law and the residual strength of the structure can be assessed successively. With single finite element method, the computational effort is insurmountable to perform SIFs calculation when a little more complex MSD configuration is considered. The use of weighting function method is often restricted by the complexity of crack damage configuration. And also the compounding method is difficult to conduct varieties of complicated SIFs computation in computer programming. In this thesis, finite element method, weighting function and alternating iteration technique are combined and developed into a new semi- analytical numerical method to apply for the computation of the SIFs in the MSD structure. The primary thought of the thesis work is as follows: The compounding method is used to solve such the problems of eccentric single crack in a rectangular plate with a co-linear hole spaced differently from the crack, and the results serve as the reference SLF in the expression of weight function. The distribution of stress on the crack surface is calculated through finite element method, and then is used in the single crack's weight function of complex configuration, through alternating iteration, the SIFs of MSD configuration can be solved. Through the polynomial parametric fittings of non-dimensional SIF modifying factors, the computational process of compounding method is standardized and facilitates the implementation of computer programming. Combined with the method of this thesis, the SIFs of complex MSD configuration can be carried out. Compared with single finite element method, the new method of this thesis does not only save the time but also keeps a high accuracy. The semi-analytical numerical method is a standardized process and can be widely used for the SJFs calculation of MSD configurations with complex force and geometrical boundaries. The whole ideas and detailed work have been introduced in this thesis. A comparison of the SIF analytical solution of single crack in complex configuration with the result of this new method shows a very good agreement with numerical accuracy. In this thesis, four models of MSD configurations have been taken as case studies, and all the solved SIFs have been compared with some references and good accuracy coincidence can be found. Finally the factors affecting on the accuracy in the new method have been studied qualitatively, and the future work is envisaged confidently.