On the Optical Assessment of the Void Content in Composite Materials.
ROYAL AIRCRAFT ESTABLISHMENT FARNBOROUGH (ENGLAND)
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In order to make full use of composite materials in aircraft structures it is necessary to be able to assess the quality of the material simply and quickly both for design purposes and as a means of ensuring the employment of satisfactory manufacturing techniques. One such quality measurement required is the composite void content. Acid digestion techniques give reliable measurements of void content of fibre-resin composites although only if expertly carried out and if the component densities are accurately known. However, the techniques are no applicable to all types of fibre composites and are not simple to execute. In addition, the densities in the manufactured composite may not be accurately known. These difficulties are reflected in the frequent quotation of negative void contents. This document describes two simple techniques for the assessment of the void content in a composite using standard low power optical microscopy. The nature of voids is discussed and a practical classification proposed. On the basis of this it is suggested that the techniques described are more than adequate for the assessment of material quality for both development and production purposes. Notes on the techniques employed to obtain a satisfactory polished section are appended. Additional keywords Great Britain Fiber epoxy composites Volume fraction.
- Laminates and Composite Materials