Creep and creep-rupture strength of gas turbine components in view of nonuniform temperature distribution

Abstract

The conventional model of Kachanov-Rabotnov-Hayhurst continuum fracture mechanics is extended to cover the case of variable temperature and strain hardening. The creep and damage rates are assumed to depend on temperature. The resulting model for nonisothermal creep and damageability is implemented in a finite-element code of the general-purpose software package ABAQUS. The mathematical model is tested on an axisymmetric problem for a gas turbine body.Keywords: creep and damage rates, model for nonisothermal creep and damageability.Structural parts of gas turbines have to operate under elevated temperatures and complex stresses over a long a period of time. A study of creep in the structures including the damage accumulation is required for a reliable assessment of their creep rupture strength. Many elements of power-generating plants -high-and low-pressure turbine stages, exhaust manifolds, diffusers -run in a nonunifom temperature field; therefore, a problem on nonisothermal creep and damageability should be stated. This is especially important for thick-walled elements of turbine bodies, where internal pressure is combined with large temperature gradients.Metallographic studies of heat-resistant steels suggest a significant complexity and diversity of physical processes that occur at various creep stages. It may be inferred that the diffusion-controlled migration of dislocations prevails at the second stage of creep. Various mechanisms of the interaction between particles and dislocations as well as the time-dependent alterations in the material microstructure can take place during the thirst stage of creep, leading to the strength degradation and thus to fracture. The activation energies for the diffusion and dislocation processes differently depend on temperature; this fact was taken into account during the development of a creep model including damageability at variable temperature.Thus, the nonisothermal creep model allowing for damageability, which is put forward here, is based on Kachanov-Rabotnov-Hayhurst model [1-3] and physical mechanisms of creep for typical heat-resistant steels. For adequate description of the primary creep stage we introduce a strain hardening function in the formTo specify the different temperature effects on the diffusion creep and cross sliding of dislocations, we use two different functional relations: the first one is entered into the constitutive equation for creep strain rate and the second one into the evolution equation that determines the damage rate. The temperature dependence of these relations is described by the Arrhenius function [4]:For uniaxial stress, the equations for creep and damageability including strain hardening for variable temperature fields are written as 0039-2316/08/4005-0525

Lifetime Prediction with Combined Hygro‐Thermo‐Mechanical Influences on Thick Layer Adhesives

“…[12] and e.g. [13]: B ref , l and c ∞,ref are parameters to be identified for isothermal hygrodamage. The temperature influence is determined by identifying of the parameter p a .…”

Finite Element Analysis of Influence of Non-homogenous Temperature Field on Designed Lifetime of Spatial Structural Elements under Creep Conditions

“…A DP value description under long-term static loading condition (under a creep process presence) can be conducted using the follow general expression [9]:…”

“…This approach is developed and implemented for different loading conditions in the publications of Ukrainian scientists M. Bobyr, V. Golub, G. L'vov, Yu. Shevchenko [5,6,9,14] and foreign ones (Chen G., Hayhurst D., Lemaitre J., Murakami S., Otevrel I., etc. ), particularly in [10-12, 15, 16].…”