Evaluation of First Ply Failure in a Three-Dimensional Load Space

Numerically generated failure envelopes for several three-dimensional failure criteria are presented and compared to experimental data. These envelopes are developed through finite element analysis and are based on first ply failure (FPF). The experimental data are based on ultimate failure of filament wound tubes constructed from Toray 1000/DER332-T403 and loaded in various combinations of axial traction (both tension and compression), internal pressure, and torsion. All tubes have a layup of [± 1.5, ± 45, ± 89] _T . Five three-dimensional failure criteria are considered: max-stress, max-strain, one proposed by Tsai, and two recently proposed by Feng. In addition to the three-dimensional failure criteria evaluated, the finite element results are used in conjunction with classical lamination theory to test the predictive capability of some of the more common two-dimensional failure criteria (max-strain, Tsai-Hill, and Tsai-Wu). None of the predicted envelopes compares well with the experimental data; thereby illustrating the need for progressive failure analysis in structures subjected to complex stress states. It is shown that it is possible to improve the accuracy of at least one of the three-dimensional failure criteria through a very minor modification of the theory.