Expanding the capabilities of the Ten-Percent Rule for predicting the strength of fibre–polymer composites

The Ten-Percent Rule, for predicting the strength and stiffness of fibre–polymer composites on the basis of simple rule-of mixtures formulae, is here extended beyond its prior restriction to only fibre patterns in the 0°,±45°,90° family of balanced laminates. This has been accomplished by characterizing the implicit, but previously unused, lamina failure envelope associated with the model, and increasing the transverse strains-to-failure in the fibres to prevent prematurely predicted matrix failures undercutting fibre-dominated strengths. The use and validity of such an extension is demonstrated for the composite materials and fibre patterns involved in an international exercise (organized by Hinton, Soden and Kaddour). The theory is applied also to a ±55° glass-epoxy laminate, and a 30°,±90° glass-epoxy laminate. The simplifications remain valid only for highly orthotropic materials, like fibre–polymer composites.