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Content archived on 2024-04-19



Plasma deposits on flat substrates have been characterised using nanoindentation and chemical surface analysis. The chemistry was found to change from organic to inorganic with the addition of oxygen to the plasma. A corresponding increase in the modulus of 3-3.5 GPa was found from nanoindentation tests. Equivalent coatings were deposited on to untreated, unsized carbon fibres. These fibres were than impregnated with resin to form single filament fragmentation test (SFFT) specimens, and in bundles to form composite rods. An adhesion promoting oxygen pre-treatment was applied and optimised using the SFFT in combination with SEM fractography. The influence of a high modulus coating upon micro and macro-mechanical properties was measured using SFFT, tensile and torsional testing of the composite rods. Using models of these 3-phase systems, the properties of the coating within the composite were found to agree with estimates predicted from the coating chemistry, via its correlation with the values determined separately by nanoindentation. Estimates of the fracture toughness (GC) of the interface between fibre and matrix in a 2 phase composite have been made. The models are being applied to the estimation of the fracture toughness of an HMDSO/02 plasma interphase.
The proposed research is directed towards the development of a fibre coating technology and related microchemical and micro and macromechanical understanding for the improvement of the reliability and damage assistant of composite materials. These objectives can be achieved by molecular engineering of the coating for the optimisation of the interphase between fibre and matrix to provide improved off-axis properties.

These polymer films with controlled modulus and thickness will be deposited onto the carbon fibre surface by microwave plasma polymerisation, which enables extremes of coating properties, from elastomeric to glassy to be examined. The microchemistry and surface chemistry can be varied through the plasma parameters. The major research tasks are :

1. Correlation of the mechanical properties of supported and unsupported films with chemistry for calibration purposes.

2. Synthesis of coatings on fibres with different properties.

3. Conditions for synthesis of controlled coatings of defined modulus, thickness and with good adhesion to fibres and matrix.

4. Characterisation of model composites and laminates.

5. Modelling of micro and macromechanical tests to establish effect of coating properties and dimensions on composite properties.

6. Verification of improvements in damage resistance.

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University of Sheffield
EU contribution
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Mappin Street
S1 3JD Sheffield
United Kingdom

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Participants (3)