MEAN STIFFNESS OF THERMOPLASTIC COMPOSITES

Composite materials based on thermoplastics are often anisotropic and inhomogeneous to a significant degree. These features complicate the process of material evaluation and the development of design procedures. There are advantages to be gained from the use of a 'mean stiffness' of these materials since that quantity can be defined for orthotropic materials and may be insensitive to the degree of mechanical anisotropy. The mean flexural stiffness of composite plates can be rapidly estimated by the use of flexure tests performed on a single, disc-shaped specimen. This test also provides an indication of the variation of stiffness with direction. Whilst the general problem of design requires a wide appreciation of the material properties, a number of situations can be identified where the substitution of the mean stiffness value into isotropic design equations provides a good approximation to the full solution. © 1979.