Some considerations in the design of engineering materials based on brittle solids

Abstract

In traditional materials the mean elastic bond strain at failure may be between 0.01 and 1.0%, and the tensile strength is therefore about that fraction of the Young’s modulus. Latterly, tensile strengths approaching the theoretical value, which may be rather over 0.20 E , have been realized experimentally with fibres. The highest confirmed results known to me are about 0.20 E for silica glass and about 0.12 E for a crystal, forsterite (Sears 1962). In practice values between 0.03 E and 0.08 E are commonly observed for good ‘production’ whiskers and glass fibres. Even these practical values represent a very great increase as compared with the strength of most conventional materials and it seems important to enquire into the exploitation of such strengths in load carrying structures. It might be urged that the development of any kind of ‘improved’ material can be justified, since engineering design will tend to advance up to the limits of available materials whatever these may be. No doubt uses of a kind can be found for almost any material but experience with reinforced plastics shows that it is possible to develop substances having, for instance, outstanding strength but very little appeal to structural engineers.