Reliability-based first-ply failure envelopes of composite tubes subjected to combined axial and torsional loadings

Abstract

In the present work, the response and first-ply failure of composite tubes subjected to axial and torsional loadings are studied. Both uniform-diameter and tapered composite tubes are considered. The random spatial variations of in-situ material properties that are caused during the manufacturing of the ply material and the laminated tube are considered. The in-situ stiffness and strength properties of the composite ply are represented as random variables. The first-ply failure envelopes of the tubes are determined based on the finite element modeling and the Tsai-Wu failure criterion. Existing works are used to validate the finite element models. In addition, a new analytical solution for the response of the tapered composite tube is developed and is used for validation. The reliability of the composite tube is quantified based on the probability density functions of the response and failure parameters. The reliability-based failure envelopes are developed based on the Monte Carlo simulation and the variabilities in the failure envelopes are characterized. It is shown that the change in the first-ply failure loading with the reliability is not linear and that when conventional design methodology is used in conjunction with the mean values of the material properties, only 50% reliability is achieved. Considering these aspects and limitations, a new reliability-based design methodology for the composite tubes is developed. Using this new methodology, composite tubes can be designed for the reliability desired in the specific application, considering the uncertainties in the in-situ material properties that are induced during the manufacturing of the tube.