An Experimental Characterization of Damping Properties of Thermal Barrier Coatings at Elevated Temperatures
AIR FORCE INST OF TECH WRIGHT-PATTERSON AFB OH GRADUATE SCHOOL OF ENGINEERING AND MANAGEMENT
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This research program developed the apparatus and associated techniques to mechanically characterize the complex modulus of hard coatings across a temperature range from about 70 deg F to 900 deg F. Major effort in designing, analyzing, and experimentally validating the chamber were performed to establish that it isothermally heated a beam specimen, accomplished modal detuning, and achieved a near free-free boundary condition, and that the chamber was characterized for its forcing excitation. Novel aspects of the chamber include non-contact for the excitation, nearly non-contacted boundary conditions, and measurement of the field variables within the specimen using a hybrid experimental-numerical approach. This allowed for very low damping values to be measured. A common thermal barrier coating material, 8YSZ, was characterized in the chamber to determine its loss-factor damping and storage modulus stiffness, at both a system-level, and well as, extracted bulk material properties-sense at temperatures from 70 to 900 deg F. The use of the free-decay technique using logarithmic decrement was the primary means used to characterize the coating, although some forced response was also performed and showed agreement. Some specimens that were bare titanium and bond-coat-only were studied as well. The former resulted in the discovery that the chamber is a very sensitive to slight modulus changes in classical engineering materials and the latter was shown to have fairly minimal influence on the coated beam system dynamics.
- Test Facilities, Equipment and Methods