Study On The Creep-Fatigue Crack Propagation Mechanism Of Steam Turbine Blades

The largest proportion of the forms of power generation is thermal power generation.One of the main components of the thermal power generating is the steam turbine.One of the most prone failure modes of turbine blades is creep-fatigue fracture.In this paper,the creep-fatigue crack mechanism of steam turbine blade is studied,which has important engineering application value for life prediction and safety evaluation of steam turbine blade.The main research contents are as follows:(1)This paper firstly establishes the solid model and flow field model of the steam turbine blade in ABAQUS and Fluent respectively,and gets the surface temperature and stress distribution of the steam turbine blade under the thermal-fluid-solid coupling through MPCCI,and determines the position of the dangerous section of the blade.The analysis results show that the maximum stress value of the turbine blade occurs at the junction of blade profile and blade root which is called the dangerous area.(2)Basing on the result,it is showed that the material of the dangerous section of the blade has entered the plastic stage,and the material will undergo fatigue-creep coupling damage.So this paper establishes a material creep-fatigue coupling damage model,develops the linear follow-up hardening elastoplasticity constitutive model subroutine and the fatigue-creep non-linear coupling damage evolution subroutine of the blade material in ABAQUS.(3)The paper establishes the Voronoi microscopic calculation model of the dangerous position of the steam turbine blade in ABAQUS,and uses the elastoplasticity constitutive model subroutine and the fatigue-creep non-linear coupling damage evolution subroutine to simulate the crack behavior of steam turbine blades.Then,the effects of different loading frequencies and steam inlet temperatures on the crack propagation mode are studied.The results found that:1.As the frequency of the load cycle increases,the cracks inside the material expand in the form of intergranular cracks,firstly.Then the transgranular cracks appear and their proportion gradually increases.Finally they expand in a mixed way,and the rate of initiation and expansion gradually accelerates.2.With the increase of steam inlet temperature,the blades are dominated by intergranular cracks,and the growth rate of the cracks gradually increases.