Paper number 326

THE EFFECT OF SIMPLE SHEAR ON STIFFNESS AND STRENGTH OF FABRIC LAMINATES

J. Hofstee and F. van Keulen DLR

Institute of Structures and Design, Postfach 800320, D-70503 Stuttgart, Germany Laboratory for Engineering Mechanics, Delft University of Technology, P.O. Box 5033, NL-2600 GA Delft, the Netherlands

Summary

The effect of thermoforming induced simple shear on stiffness and strength of carbon plain weave reinforced laminates is investigated experimentally. Tensile tests are carried out in yarn direction, bias direction and an off-axis direction in which maximum shear coupling is expected. Obtained results are used to validate three classical laminate theory based stiffness models. The models take shear into account by defining equivalent uni-directional reinforced layers with identical properties and in-plane orientations as the yarns. Yarn crimp is either neglected or included with an isostrain or an isostress assumption. In yarn direction good agreement is found when crimp is included. In other directions agreement is less because the influence of resin pockets is neglected for all models. Strength is approximately constant in yarn direction and highly increases in bias direction for sheared laminates.

Keywords

sheared fabric, yarn crimp, laminate stiffness, thermoforming, tensile test, anisotropy, plain weave.