Research On Life Evaluation And Optimization When Applying Functionally Graded Materials In Power Machinery

Many parts in energy industry are working under high temperature conditions, the elevation of temperature has great influnce on the metal material properties, which limits some efficient ways of improving economics, e.g., the temperature of super heated steam. The pressure of super heated steam in a power units has already reached super critical pressure. However, the temperature of super heated steam is limited beneath 620℃, it is important to research and develop new materials to elevate super heated steam temperature.Functionally graded materials (FGM), thanks to the spatial continuity and functional flexibility of the volume fraction distribution of constituent particles, provide superior thermomechanical performances, when compared with other composite materials. FGMs can withstand high-temperature environments while maintain their structural integrity, thus the materials have been applied widely for ultimate high-temperature conditions such as spacecrafts, nuclear plants, fusion reactors, etc. In this paper, the estimation of temperature, thermal stress and damage for a FGM structure with complex geometry and load conditions has been researched and analyzed from the requirement of application.Firstly, nonlinear steady heat transfer and thermoelastic stress analyses of a thick-walled FGM cylinder with temperature dependent materials are performed by using analytical method. Secondly, Nonlinear transient heat transfer and thermoelastic stress analyses of a 2-D axis-symmitric FGM object with temperature dependent materials are performed by using the perturbation method. Two cases have been given to compare the results calculated by the models deduced with those calculated by FEM(finite element method). It is shown that the models presented in this work have satisfied accuracy.In order to obtain accuracy boundary conditions, inverse methods have been adapted in solving transient heat transfer problem and determining the heat transfer coefficient. Damage model is also been discussed with the theory of Miner's rule, thus it can be used to online evaluate the damage caused by high temperature low cycle loading.An on-line fatigue and creep monitoring system has been developed based on the models mentioned above. The system is inset into DCS monitoring and control system and can on-line monitor the fatigue and creep degradation of several components in a power plant. The system converts the plant transients to temperature/stress responses, computes the fatigue usage factor and updates the information continuously. This system has already been installed at Henan Jiaozuo power plant in china for monitoring the fatigue and creep degradation, which gives much help for the application of FGM in energy industry.