Elastic stiffness analysis of a thermo-formed plain-weave fabric compositePart II: analytical models

Two models are developed for stiffness analysis of plain-weave-fabric-reinf orced thermoplastic laminates after thermo-forming. A repeating element of every fabric-reinforced lamina is modelled such that yam reorientations in the fabric plane and changes in yarn crimp are reflected. These deformation s were schematised in Part I of this paper for two in-plane thermo-forming deformation modes, simple shear and fabric stretching. To account for crimp , effective yam stiffnesses are calculated with either an isostress or an i sostrain assumption. Subsequently, the yarns and neat resin material are re placed by substitute layers, and overall laminate stiffnesses are calculate d by using classical laminate theory. For weaves with moderate crimp, close d form solutions are obtained for both isostress and isostrain models. Para metric studies are carried out to establish the effect of very large thermo -forming deformations on laminate stiffnesses. It is found that fabric stre tching and simple shear significantly affect predictions. (C) 2000 Elsevier Science Ltd. All rights reserved.