Elastic stiffness analysis of a thermo-formed plain-weave fabric composite: Part I: geometry

The present paper investigates experimentally the influence of thermo-forming on the geometry of a plain-weave carbon-fibre thermoplastic laminate. Specifically, effects of the fabric stretching and simple shear deformation modes on yarn crimp and cross-section geometry are examined. For that purpose, specimens are stretched and sheared in a heat chamber above the melting temperature of the resin. Microscopic geometry analyses are carried out on laminate cross-sections prepared along both yarn directions. It is found that both deformation modes significantly influence yarn crimp and cross-section geometry. The observed deformations are schematised in order to enable stiffness modelling in Part II of this paper. To verify the proposed schematisations, additional laminate cross-sections are cut from thermo-formed products which contain several areas with nearly constant shear deformation. Fabric stretching and simple shear occur simultaneously in the products. Observed yarn deformations correspond well with the proposed schematisations.