Microscopic investigation of tow geometry changes in a woven prepreg material during draping and consolidation

Changes in tow geometry are measured during draping and consolidation of a helmet component with 5-harness satin weave carbon fibre reinforced plastic (CFRP) prepreg. The tow microstructure is found by sectioning specimens cut from the helmet. Various tow geometry parameters are extracted using image analysis. Results are compared with similar measurements on dry fabric specimens sheared using the bias extension and biaxial test methods [Compos. Sci. Technol. 63 (2003) 99], and on unsheared specimens cured under light pressure or in an autoclave. Results suggest that, for this particular material and process route, the significant differences observed in tow geometry over the surface of the helmet are mainly due to differences in contact pressure between the prepreg and the mould, with the effect of shear deformation less significant. Differences between tows running longitudinal and transverse to the axis of the helmet are ascribed to differences in contact conditions between these sets of tows and the mould surface.