The various methods of self-sensing and self-healing developed within the Composite Systems Innovation Centre, University of Sheffield, are reviewed. Damage sensing using electrical resistance in carbon fibre reinforced composite or using the fibres as optical sensing elements in glass fibre reinforced composite is demonstrated. Amelioration of low level damage is demonstrated in both monolithic composite materials and sandwich structures using direct chemical reactions within the matrix without the use of encapsulants. These reactions can be activated by resistive heating of the material itself. The use of a combination of these techniques could create a truly smart structure able to both sense and repair damage and degradation.
The paper considers the usefulness of ultrasonic measurement for monitoring the properties of commercially processed material. It can be applied nondestructively for quality control; or by taking sections, full measurement of anisotropy can be made. The methods are exemplified by results for moulded and solid-state-formed polypropylene; and a full 5 MHz elastic measurement has been performed in one case. The relationship of the 5 MHz moduli to those obtained by more usual techniques is also considered; and the possibility of correlation with tensile and impact results. It is felt that the technique will have growing commercial importance.
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