Equipment for Measuring Complex Moduli of Thin Coatings at Elevated Temperatures

Porcelain enamels are thin, inorganic, glassy coatings, extensively used to protect metal surfaces exposed to the corrosive and erosive effects of hot gases. They are known to increase the fatigue life and vibratory damping of the coated member in some cases but the amount of improvement and the governing parameters are not known. Three pieces of equipment for measuring the damping and complex moduli of porcelain enamel coatings as a function of temperature, strain level and state of stress have been developed as part of a program now underway to determine these properties. All three are designed to cover the temperature range from room temperature to 2000 deg F. The first is an adaptation of the low frequency torsional pendulum equipment useful from about 1 to 20 Hz. The second uses a flat beam in bending to cover the frequency range from 10 Hz to 200 Hz and the third uses a hollow torsional specimen to cover the range from 150 Hz to 600 Hz. This paper describes the design details, advantages and disadvantages and error analysis of each of the three pieces of equipment.