Studies On Three-parameter Theory Of Three-dimensional Creep Fracture

Gas turbine is one of the important parts of aviation gas turbine engine. The performance in high temperature of gas turbine represents the level of aviation engine. The high temperature behavior of turbine blade has been valued for scholars and engineers. Creep deformation affects the strength of component which is always under high temperature. The analyses of creep deformation and stress level of component in high temperature is necessary to predict the creep life. It is significant to establish the predicting method of creep life based on crack tip fields for creeping solids. In the present thesis, we focus on theoretical and numerical research in three-dimensional creep fracture. For different types of crack under creep conditions, the distribution of crack tip fields is analyzed. The main contents are as following:1. To study the thickness effect and size effect of crack tip fields under creep condition, finite element analyses for centre-cracked tension specimens with different thicknesses and crack depths are performed. The distributing characteristics of C(t)-integral, out-of-plane constraint factor TZ and Q* item ahead of crack border are analyzed. The single-edge cracked bend specimen and compact tension specimen are discussed in the present thesis. The three-parameter C(t)-TZ-Q* description can characterize the stress fields ahead of crack border of them, and accurately predict the tensile stress and radical stress on the ligament in mid-plane under extensive creep condition.2. The crack tip fields of embedded elliptical crack, semi-elliptical crack and quarter elliptical crack under creep condition are analyzed. The distributing characteristics of C(t)-integral, out-of-plane constraint factor TZ and Q* item ahead of elliptical crack border are discussed. The conception of equivalent thickness in liner elastic theory is developed into the analyses of creep mechanics. For through-thickness crack and elliptical crack, the distribution of out-of-plane factor TZ on the ligament ahead of crack front can be normalized with equivalent thickness. It is concluded in theory that the three-parameter C(t)-TZ-Q* solution of through-thickness crack can be used in the description of crack tip fields of elliptical crack under creep condition for the connection function of equivalent thickness. The finite element results validate that the three-parameter C(t)-TZ-Q* solution is appropriate for the description of crack tip fields of elliptical crack under creep condition.