Crystal plasticity modeling of polycrystalline Ni-base superalloy honeycombs under combined thermo-mechanical loading

Abstract

To meet the ever-growing demands for the efficient operation of turbomachinery, a minimum clearance between the rotating and the stationary components is of great importance. A lack of controlling this clearance often leads to interface rubbing. As a result, thermo-mechanical loads arise that can critically damage both components. Maintaining operational reliability and high efficiency requires seal systems that can tolerate rubbing. Honeycomb labyrinth seals can fulfill this task. In this contribution, we present a three-dimensional microstructure-based simulation approach considering the periodic unit cell of a polycrystalline Ni-base superalloy (Hastelloy X) honeycomb structure. Different honeycomb geometries are investigated, and various loading conditions are applied to simulate the thermo-mechanical behavior of the honeycomb structure during rubbing. The problem is solved in a finite element framework, and the deformation behavior is described by a crystal plasticity model accounting for microstructure attributes of the material. To calibrate the material model, numerical simulations on a representative volume element discretized with a realistic three-dimensional periodic mesh are carried out. The overall thermo-mechanical response of the honeycomb structure as well as the development of local field quantities is investigated. The study reveals that large contact areas seem to be very critical for the initiation of premature damage of the honeycomb structure.