Fatigue Damage Evolution Model Research On Ti Alloy Welded Joint

With the rapid development of aero science, it requires the aero engine ratio of traction to weight is higher and higher. Since last century, whole welded blisc has been applied in aero engine new developed. Nowadays, it is still one of the problems of welded structure life forecasting in aero engine whole welded blisc application. Taking Ti alloy TC11 electron beam welded work-piece as research object, which is the conventional material of aero engine compressor blisc, the fatigue damage evolution law of fatigue damage action in the area of welded joint based on damage mechanics theory is analysed, and fatigue damage model, which macro-parameter and micro-damage characteristics are related, with fractal geometry-a new conception of modern mathematics is set up in this paper. It tries to research the measuring method of fatigue fracture fractal dimension and the relationship of fractal damage variable with fatigue life. It also sets up the welded joint fatigue damage fractal evolution equation. For weld structure fatigue life forecasting, it has important theory meanings and practical applying value. The innovations are following aspects:1. According to fractal propagation characteristics of fatigue crack, it defines structure fatigue fractal damage variables and sets up the structure fatigue damage fractal evolution mode which macro and micro are consistent. The mode not only reflects damage microstructure traits, but also makes it easy to analyze and research macro parameters.2. According to the result of fatigue experiment, it gets fatigue traits of Ti alloy TC11, which is the relationship curve of the maximum loading strain range with fatigue life. According to the measuring result of fatigue fracture fractal dimension, it gets the relationship curve of Ti alloy TC11 welded joint fracture fractal dimension with loading strain range, and the method of fatigue life forecasting fatherly.3. According to the model of structure fatigue damage fractal evolution, the relation between macro-damage variable, fractal damage variable and fatigue life can be found, and the fatigue damage evolution equation of Ti alloy TC11 welded joint can be built, and the method of more forecast fatigue damage is given.4. The research of metal fatigue fractal dimension measuring is in the study of materialcharacteristic analyzing. It demonstrates: the selection of magnifying multiple and measuring size are different to material structure, and the measured result is greatly influenced. The selections of electron microscope magnifying multiple and measuring size in fatigue fracture fractal measure are studied in this paper, and the improved treatment of secondary electron lines scanning fractal dimension, is applied successfully to the measuring of Ti alloy welded joint fracture fractal dimension and the valuable selective range of fractal dimension measuring parameter is got, which is very important to further research.Using fractal dimension defining damage variable and building macro and micro-fatigue damage evolution model of structure are suggested in this paper. The variety of damage which is not easy macro-measured to Ti alloy TC11 whose material structure is high intensity can reflect fatigue damage process effectively by studying the relation between fracture and structure life. So, it is the new method of researching welded structure fatigue damage process. The obtained result is very important to the life forecasting of welded blisc of aero engine, and has appliance reference to the future.