ELASTIC CONSTANTS AND INTERNAL FRICTION OF AN SiC-FIBER-REINFORCED Ti-ALLOY-MATRIX CROSSPLY COMPOSITE: MEASUREMENT AND THEORY

摘要

The complete elastic-constant tensor Cij and thecorresponding internal friction Qij-1 for a cross-ply compositeare measured. It consists of silicon-carbide fibers in a Ti-6A1-4V matrix; it contained 35 vol.% fibers. With tetragonalsymmetry, this composite possesses six independent Cij and Qij-1.Principally, two measurement methods were used noncontacting andpoint-contact resonance-ultrasound spectroscopy. Specimens wererectangular parallelepipeds measuring a few to severalmillimeters. By changing the magnetic-field direction, which isneeded for the Lorentz-force coupling, a particularmacroscopic-vibration-mode group among the eight groups for freevibration of a rectangular parallelepiped could be independentlyexcited and detected. This provides a big advantage inidentifying the vibration modes of the observed resonance peaks,whose frequencies yield the Cij by solving an inverse problem.Contactless coupling allowed the measurement of intrinsicinternal friction, avoiding the energy loss associated withcontact coupling. The internal-friction tensor was determined bya free-decay method. Theoretical calculations were made using anextended Mori-Tanaka mean-field theory and good theory-measurement agreement was found.