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The problems of establishing design allowables and factors of safety for filamentary composites are considered. A method is recommended for determining design data when small sample sizes are employed to establish basic laminate properties. It is advocated that the traditional factor of safety of 1.5 should not be employed without some reference to the coefficient of variation of the strength data. The concept of reliability is introduced. Methods for predicting design allowables under multiaxial stress are discussed in general terms. The influence of lamina failure is considered together with means for predicting this. Results presented indicate that a linear analysis, based on the distortional energy criterion, can predict progressive lamina failure adequately for design purposes. A description of the phenomenon of crazing is included, and it is suggested that this is generally due to initial lamina failures. The paper concludes with some comments on the effects of testing and processing variables.
design allowables, safety factor, fiber composites, reliability, laminates, failure, evaluation, tests
Jones, B. H.
senior engineer/scientist, McDonnell Douglas Corp.Aeronautical Research Associates of Princeton Inc., Long BeachPrinceton, Calif.N.J.