To evaluate the strength of the composites under fixture and analyse the crack growth resistance at room temperature and at high temperature in air at up to 1400 C, special equipment was set up. A 3-point bending/loading system was made from polycrystalline alumina including pushrods, rollers and bearing plates operating in a furnace. Similar equipment was also designed and built with graphite 3 and 4 point bend fixture, for fixture testing in vacuum (1E-5 torr) up to 2000 C.
To evaluated the cyclic stress-strain behaviour, a hydraulic fixture was built. For temperatures up to 1000 C in air, the clamping of flat specimen induced by a hydraulic cylinder enabled a transition from tension to compression.
For creep experiments, a device working up to 1800 C was set up for compression and 3-point bending tests under vacuum.
A special test device was developed to measure thermal diffusion for main directions with a single specimen. Based on the traditional flash method, the technique involves a pulsed source of laser radiating power. It uses 2 pyricon detectors to measure tempratures changes occurring in the front and rear specimen, when subjected to the thermal flux.
In the 2-dimensional silicon carbide/silicon carbide composite, the reinforcement in an arrangement of 2-dimensional laminates. The weaves were made with silicon carbide fibres. The different layers were stacked in a warp on weft combination to obtain the desirable thickness, and a fibre volume fraction of about 40%. The silicon carbide matrix deposited during a chemical vapour infiltration (CVI) process, and a final density of about 2.5 was achieved. The residual porosity was about 10%. The anisotropic material can be considered as orthotropic.
In the 3-dimensional carbon/silicon carbide composite, the reinforcement is a 3-dimensional structure, named NovoltexR made with PAN precursor fibres. The total fibre volume is about 25 to 30% with less than 10% in the third direction. In the main plane, a special arrangement gives the material a quasi isotropic behaviour.
A silicon carbide matrix was deposited by the same CVI process as for the 2-dimensional silicon carbide/silicon carbide composite, and a final density of about 2.2 was reached. The residual porosity volume fraction was approximately in the same range.
FOR MANY THERMO-MECHANICAL APPLICATIONS, SPECIALLY EARTH AND AEROSPACE ENGINES, THE CERAMIC MATRIX COMPOSITE (CMC) MATERIALS REPRESENT A GOOD OPPOTUNITY.
THESE NEW MATERIALS NEED CONSIDERABLE STUDY IN ORDER TO:
- ACHIEVE A BETTER UNDERSTANDING OF THE HIGH TEMPERATURE BEHAVIOUR, UNDER THERMOMECHANICAL LOADS;
- STUDY THE FRACTURE MECHANISMS BY MICROSCOPIC EXAMINATION;
- DEVELOP NEW CONCEPTS OF FRACTURE MECHANISMS MORE SUITABLE TO THESE MATERIALS.
Funding SchemeCSC - Cost-sharing contracts
M13 9PL Manchester
M60 1QD Manchester