Journal of Materials Science and Engineering with Advanced TechnologyAuthor's: Oliver Easterday, Anthony Palazotto, Richard Branam, William Baker and Tommy George
Pages: [69] - [107]
Received Date: April 30, 2014
Submitted by:
Coatings have been assessed for their complex modulus in a non-contact excitation, suspension, and semi-numerical extrapolated strain field technique using a free-free beam suspended in a vacuum. Mechanical characterization of the non-linear thermal barrier coatings beyond room temperature is desirable to expand their design-space from hot- to cold-sections of turbo machinery using the TBC process techniques for HCF suppression. Modern high bypass turbo-machinery achieves around service temperatures up to about 500degC (40:1 pressure ratio) in the “cold sections”. The adoption of a free-free rig to elevated temperature testing while preserving its advantageous features is highly desirable in order to characterize the coatings across the range of service temperatures. This involved some lengthy thermal validation as maintenance of a near-isothermal specimen was critical. Thermal validation was critical as the non-contacting semi-numerical extrapolation of the strain field is from an assumed free-free mode shape; titanium undergoes about a 25% reduction in modulus variation when heated from 20 to 565degC, the design maximum. These elementary thermal issues were thought to be well-covered in the literature, but surprisingly there is little on handling of finite difference radiation boundary conditions, the Stark number lumped capacitance model, and associated FEA modelling.
finite element, thermal barriers coatings, heat transfer.
