Progressive failure analysis of [0/+/-60] laminates under bi-axial stress by generalized Yeh-Stratton criterion

The light weight of composite materials has attracted interests to improve fuel economy of aircrafts and to extend flight range. The usage of composite materials is increasing in airframes and other parts of aerospace industry. Although most tests on composites are conducted uniaxially, they are subjected to multi-axial loads in real life applications. Hence, there is a need to better understand the complex failure mechanisms in composite structures. More reliable failure theories and damage progression models should be devised. Also, reliable criteria for predicting failure of fiber composite laminates are necessary for rational analysis and design. In this thesis, the behavior of a symmetric composite material under bi-axial loading is studied and the failure of the composite material is predicted by Yeh-Stratton criterion. A MATLAB program is prepared for the study of failure in tubular specimens composed of AS4/3501-6 carbon/epoxy laminates, which were subjected to internal pressure and axial force simultaneously to vary the states of stress. It is shown that the Yeh-Stratton criterion is in a good agreement with the experimental results. Future work may include collection of more accurate and different kind of experimental data on composite materials and modification of the interaction factor B12 value to evaluate its effect on the theoretical prediction by the Yeh-Stratton criterion.