Investigation On The Damage Tolerance Of Turbine Disk Based On Three-dimensional Crack Growth Simulation Method

The damage tolerance method has been more and more used in the design,optimization,life assessment and maintenance of the gas turbine and aeroengine.In this method,the crack in the structure is regarded as the research object to quantify the crack growth life,and to fully utilize the potential residual life on the premise of fulfilling the requirements of reliability.It is a potential technology to solve the bottleneck problem of gas turbine and aeroengine development.In this dissertation,the existing problems of three-dimensional crack growth simulation and theoretical methods are analyzed by using the analytical method and the numerical simulation method.The stress intensity factor estimation expressions are derived based on the theoretical model of the kinked crack.The parametric modeling and growth simulation method of three-dimensional crack are developed,then the crack growth behavior of a turbine disk is analyzed and the relationship between the crack size and the remaining life is explored based on the above research results.It has important theoretical significance and engineering application value for damage tolerance design and life extension of aeroengine disk.The main contents of this dissertation are:(1)Based on the ANSYS platform and its APDL parameterized design language,combining with the Matlab platform,a three-dimensional crack parametric automatic modeling and crack growth simulation technique based on finite element method is developed.The crack is inserted in the structure model by inlaying the cracked block.The crack growth process is simulated by automatically updating the cracked block.The parametric modeling of crack according to the crack growth parameters and automatical analysis of the crack growth process are achieved.This technique provides a platform for the damage tolerance analysis of complex structures.(2)In the simulation of crack growth,the local position of the crack front can be regarded as two dimensional kinked crack,so the variation of stress intensity factor of three-dimensional crack can be analyzed through the theoretical study of the two-dimensional kinked crack.Based on the theoretical model of the two dimensional kinked crack and performing the analysis for the planar and anti-planar problem by considering the influence of high order term coefficients in the stress field series of the crack tip,the estimation expressions for estimating the stress intensity factors of kinked crack are modified.Compared to the conventional expressions,the new ones are more accurate and applicable.(3)Based on the theoretical research results of kinked crack,the technique in the conventional method for calculating the crack growth parameter without considering the influence of the crack growth length and kinked angle is improved by using the stress intensity factors calculated by the kinked crack instead of directly using the result of the last step.Besides,the treatment for the simulation results of crack shape near the free surface is also develpoed.Combining these two aspects,the modified crack growth simulation method is built.The increased accuracy compared with the conventional method is proven by simulating the planar and non-planar crack growth and comparing the results with the experimental results.(4)According to the results of the static strength analysis of a turbine disk,the high stress area of bolt hole and central hole are investigated as the region of crack growth.The crack growth behavior and crack growth life of the turbine disk are analyzed by the three-dimensional crack growth simulation method developed in this dissertation.The relationship between the crack size of the key parts and the remaining life of the turbine disk is analyzed and the damage tolerance is obtained.It shows that the research results in this dissertation can provide a feasible solution for the damage tolerance analysis of complex structures such as turbine discs.