The effect of material behaviour on the analysis of single crystal turbine blades: Part I – Material model

Abstract

This paper describes a slip system model developed for the analysis of modern single crystal superalloys – specifically, the first generation alloys RR2000 and SRR99, and the second generation alloy CMSX‐4. The single crystal model is implemented as an ABAQUS User MATerial (UMAT) subroutine, the framework is based on the classical theory of single crystal plasticity. The constitutive equations used have different formulations based on the micromechanisms of deformation and experimental measurements. The emphasis is on the effect of incorporating the micromechanisms of material behaviour on predicted macroscopic results. Several important phenomena and mechanisms, which are required for explaining creep properties as a function of stress, temperature and orientation are identified and included in the model. These include: activation of < 101 > {111} and < 112 > {111} slip systems, rigid body rotation, continuum damage, slip system softening, dislocation interaction, threshold behaviour and rafting. Model simulations are compared with experimental data in various deformation regimes. In a later part of the paper, the model is used to analyse the performance of a single crystal turbine blade. This enables the effect of the micromechanisms of deformation on overall component behaviour to be quantified.

An Investigation Into the Mechanics of Single Crystal Turbine Blades With a View Towards Enhancing Gas Turbine Efficiency

“…Recently Maclachlan and Knowles [30] have proposed a model based on single crystal plasticity wherein they incorporate the damage induced due to creep through a fourth order damage operator. Most of the models for creep of single crystal superalloys fail to take into account the symmetry of single crystals and the fact that the symmetry does not change as the single crystal undergoes inelastic deformation.…”

“…Although models based on single crystal plasticity are three dimensional and they incorporate the symmetry of single crystals, such models require extensive details of slip systems which are operating. Also, the model requires information about self and latent hardening of slip systems that are active which lead to a overwhelming number of material parameters (The model developed by Maclachlan and Knowles [30] has 42 material parameters). The effect of high temperature rafting on creep was incorporated in models developed by Reed et al [64] and Maclachlan and Knowles [30] who used a dislocation hardening mechanism first proposed by Gilman [17].…”

“…Also, the model requires information about self and latent hardening of slip systems that are active which lead to a overwhelming number of material parameters (The model developed by Maclachlan and Knowles [30] has 42 material parameters). The effect of high temperature rafting on creep was incorporated in models developed by Reed et al [64] and Maclachlan and Knowles [30] who used a dislocation hardening mechanism first proposed by Gilman [17]. Apart from including the effect of rafting on creep in a macroscopic way, there have been several works devoted to describe the kinetics of the rafting behavior itself but most of them are limited to the elastic regime (see for example [63,34,35,24,25,15,54]).…”

Mitigation of Turbine Vane Shock Waves Through Trailing Edge Cooling

“…Impingement of trailing-edge shocks generated at nozzle vanes causes heat transfer oscillations over the surface of rotor blades [4], which leads to stress variations originated by inhomogeneous and transient temperature distributions over the blade geometries referred as airfoil load shakedown [5]. Also, mechanical fatigue caused by unsteady flow structures is a dominant factor determining the life time of turbomachinery parts [6].…”

Film Cooling Modelling for Gas Turbine Nozzles and Blades: Validation and Application

“…Further development of turbine airfoil manufacturing techniques, such directionally-solidification castings and single-crystal castings led to higher metal temperature capability. More recently, numerous testing evaluations have been conducted to characterize new hot-gas path material super-alloys in terms of tensile, rupture, fatigue, creep, Introduction toughness, corrosion and oxidation resistances, producibility, processing, and other thermophysical properties [2,3,4,5,6]. Following extensive laboratory testing, actual operating experience is gained with engine testing subject to real operational environments culminating in mature levels of technology readiness levels for production.…”