Real Area of Contact in Carbon Fabric Forming

Abstract

An experimental rig and image analysis method have been developed to measure the real area of contact between carbon fibre fabric and a smooth tool. By using as the tool surface a flat glass slide with an optical coating, and viewing the contact through the slide, the contact area is clearly visible at a fibre scale. Straightforward image analysis is used to estimate the length of fibre contact. A microcontact density is defined, normalising the measured fibre contact length by the value for an idealised packing arrangement of close-packed parallel fibres. The method is applied to a 2×2 twill weave carbon fabric and a 12k carbon fibre single tow. Both for the woven fabric and the single tow, the microcontact density is significantly below the idealised value of 100%. The contact density is sensitive to contact pressure and has a similar value of between 4 and 8 % for the two materials considered at the contact pressure of a few kPa appropriate to dry pre-forming operations