Validation of Advanced Composite Thermal Stress Analysis Methods

The thermal stress analysis of thermally degrading tape wound phenolic composites in rocket nozzles is complicated by the extreme variation of properties with temperature, combined with steep temperature gradients on the order of 50,000° F/in. This study applied two very different numerical approaches to the same problem of predicting thermal stresses in a moderately thick conical frustum. One method uses a variational theorem derived by Reissner while the other applies the classical finite element method based on minimization of the total potential energy. The good agreement of the two methods appears to validate the results and an extensive convergence study is presented that identifies the magnitude of errors in the finite element method as a function of element density. A modification to the finite element method to account for intra-element material property variation is shown to improve the convergence of the procedure.