SCOPE

The Hoffman theory and the Tensor Polynomial (Tsai-Wu) theory with F12 set equal to zero have been found to be preferred alternatives to the general Tensor Polynomial theory for predicting strength of filamentary composite laminae. These theories were used to predict failure of off-axis boron/epoxy and E-glass/epoxy test specimens and gave excellent agree-ment with available experimental results. In lieu of additional experimental data on other materials and loading conditions, a numerical experiment was performed to estimate the errors for ten different composite systems under six different loadings. The maximum error in predicted failure loads among all cases was below 10 percent. These results suggest that the Hoff-man failure theory and the Tensor Polynomial theory with F12 = 0 can predict failure of practical filamentary composite materials under general biaxial loading with sufficient accuracy for engineering applications. Thus, use of either theory is recommended as a preferred alternative to the experimental determination of F12 in the general Tensor Polynomial theory for orthotropic laminae