FEM Analysis On Fretting Fatigue Of The Dovetail Construction

Fretting fatigue phenomenon will accelerate fatigue crack initiation and propagation of parts, causes a significant reduce of the service life of components, which is the main reason of damage to the turbine blade failure. Due to the complex the loading effect on dovetail which connects turbine blade with the wheel, the contact area located in the tenon and mortise is prone to get fretting damaged. Therefore the research on dovetail fretting fatigue phenomenon has important engineering application value. Contact strength and crack growth analysis are the two key points in the study of the dovetail structure fretting phenomenon. Contact strength calculations can be achieved by FEM; As XFEM method has a discontinuous expansive shape functions to describe the nature of the discontinuity of the crack tip, it could make the crack be independent of the grid boundaries, which are widely used in the study of crack problem.Work done as follows:(1) A brief introduction of the extended finite element method(XFEM) and other associated fracture theory. XFEM aspects mainly include: XFEM basic principle, the level set function crack tracking method and a description of the crack tip enrichment functions. Fracture theory describes a method for solving the stress intensity factor, the position determination criteria of crack initiation and crack propagation direction.(2) A finite element model of the dovetail contact structure was established, the structure of the high stress dovetail contact zone gradient was solved,the stress distribution on the contact surface was analyzed. Based on this, the fatigue crack initiation location, and the prediction method of extending direction of crack initiation angle were put forward, further the XFEM method was used to simulate crack propagation of dovetail in the contact area. The theoretical value of the location of crack initiation, crack initiation angle and propagation angle relative ratio were compared with experimental results or foreign research results. The parallel results gave verification that XFEM could be used to simulate crack propagation in dovetail structure.(3) The relevant parameters affected on fretting fatigue: coefficient of friction, cyclic loading stress ratio and the length of contact were analyzed. The results showed that reducing the friction coefficient and increasing the size of the contact area is a reliable method of improving the fatigue strength of dovetail deconstruction. In addition, fretting fatigue contact stress parameter increased with the increasing of cyclic stress ratio.