Elastic stiffness analysis of a thermo-formed plain-weave fabric composite - part III: experimental verification

The effects of thermo-forming-induced deformations on the membrane stiffness of plain-weave reinforced thermoplastic laminates are investigated experimentally. Tensile tests on plain-weave glass and carbon reinforced laminates are presented. Stretched and sheared reinforcement configurations are considered. In order to investigate the effects of these deformation modes individually, laminates are heated above the melting temperature of the thermoplastic matrix and subjected to nearly pure stretching and shear deformations. After re-consolidation, tensile test specimens are cut out in, predominantly, the yarn and bias directions. Furthermore, test specimens are obtained from an actual thermo-formed product, which was used for geometric analyses in part I [Compos. Sci. Technol. (2000) 1041]. Simple shear leads to drastic changes in mechanical properties. Fabric stretching leads to a significant difference in stiffness between the straightened and the crimped yarn directions. With results obtained, three classical laminate theory based stiffness models are validated. These models have been reported in part II [Compos. Sci. Technol. (2000) 1249]. In-plane Young's modulus is predicted reasonably well. Poisson's ratio and shear coupling ratio are generally underestimated by the models. (C) 2002 Elsevier Science Ltd. All rights reserved.