Anisotropic Creep Damage and Elastic Damage of Notched Directionally Solidified Materials

Abstract

Drives to improve gas turbines efficiency have lead to an increase in firing temperatures. This increase in exhaust temperature has a negative impact upon turbine blade life. Both engineers and material scientists have produced methods to improve turbine blade life under these conditions. Cooling holes have become commonplace and use relatively cool gas to create a lower temperature barrier around a turbine blade. These cooling holes creating internal and external surfaces; a common sight of crack initiation. Directionally-solidified (DS) turbine blades have also become commonplace. These turbine blades exhibit a transversely-isotropic grain structure that improves creep strength in a desired direction. To model a component under such conditions, anisotropic constitutive models are required. In this paper, an anisotropic tertiary creep damage constitutive model for transversely-isotropic materials is given. The influence of creep-damage on general linear elasticity (elastic damage) is described by a modified Hooke’s compliance tensor. Finite element simulations of a V-notched tensile specimen are conducted to replicate a crack initiation site. A discussion on stress triaxiality, stress redistribution, and damage distribution due to anisotropy is provided.