THE RELATION OF DYNAMIC ELASTIC-MODULI, MECHANICAL DAMPING AND MASS DENSITY TO THE MICROSTRUCTURE OF SOME GLASS-MATRIX COMPOSITES

Dynamic elastic moduli and mechanical damping were measured with the P UCOT (piezoelectric ultrasonic composite oscillator) technique at room temperature for ceramic-matrix composites (CMCs) of the following com positions: PRD-166 (fibres)/N51A glass (matrix), PRD-166 fibres coated with SnO2/glass, Nextel 480 fibres/glass, Nextel 480 fibres coated wi th SnO2/glass, and Nextel 480 fibres coated with BN/glass. The fibres were continuous, and the volume fractions varied from 0.24 to 0.43. So me of the mechanical-property measurements correlated with the thickne ss of one of the coating materials, and with microstructural observati ons of the misorientation angle of the fibres and normalized fibre len gth. With increasing volume fractions of fibres, the fraction of broke n fibres increased. For the PRD-166/glass and PRD-166/SnO2/glass, a su bstantial fraction of the fibres were misoriented by angles of up to 1 5 degrees. Assessments were made of the measured properties in terms o f the rule of mixtures and other theoretical estimations.