A HIGH-TEMPERATURE TORSION APPARATUS FOR THE HIGH-RESOLUTION CHARACTERIZATION OF INTERNAL-FRICTION AND CREEP IN REFRACTORY-METALS AND CERAMICS - APPLICATION TO THE SEISMIC-FREQUENCY, DYNAMIC-RESPONSE OF EARTHSUPPER-MANTLE

The design and performance of a compact apparatus for the characteriza tion of internal friction in simple shear at elevated temperature (les s than or equal to 1400 degrees C) and low frequencies (less than or e qual to 1 Hz) are described. High-temperature components are fabricate d from a refractory molybdenum alloy that is straightforwardly machine d. The apparatus has demonstrated, at high temperature, a torque resol ution of 2x10(-5) Nm and an angular displacement resolution of 4x10(-6 ) rad; for the specimen size we employ, these limits provide a shear s tress and strain resolution of 2 kPa and 5x10(-7), respectively. The a pparatus, while applicable to dynamic and static mechanical analyses o f any engineering material, was developed for the characterization of internal friction (attenuation) in synthetic silicate aggregates repre sentative of Earth's upper mantle; we discuss the constraints inherent in the required tests, as they affect apparatus design (including mat erials selection) and experimental protocol. Static and dynamic data a t 1250 degrees C for a polycrystalline aggregate of ferromagnesian oli vine of controlled, uniform (similar to 3 mu m) grain size are present ed and discussed. (C) 1998 American Institute of Physics.