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

The present paper investigates experimentally the influence of thermo-formi ng on the geometry of a plain-weave carbon-fibre thermoplastic laminate. Sp ecifically, effects of the fabric stretching and simple shear deformation m odes on yarn crimp and cross-section geometry are examined. For that purpos e, 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 th at both deformation modes significantly influence yarn crimp and cross-sect ion geometry. The observed deformations are schematised in order to enable stiffness modelling in Part II of this paper. To verify the proposed schema tisations, additional laminate cross-sections are cut from thermo-formed pr oducts which contain several areas with nearly constant shear deformation. Fabric stretching and simple shear occur simultaneously in the products. Ob served yam deformations correspond well with the proposed schematisations. (C) 2000 Elsevier Science Ltd. All rights reserved.