A basic requirement for the design of structures fabricated from composite materials is a knowledge of the design allowables for the materials under consideration. These allowables not only include the fundamental static strength properties such as tension, compression, and shear, but also properties such as bearing strength, flexural strength fatigue characteristics, environmental effects, etc. The requirements on many structures include combined loading necessitating establishing an acceptable failure criteria. Composite materials have many variables which affect their properties. If these variations in properties are not properly recognized, the design allowables are penalized.
This paper discusses statistical factors which influence design allowables, and the importance of recognizing those variables which can effectively reduce scatter in test data.
Methods are discussed which, by narrowing the scatter in test data, will improve the design allowables.