Space Shuttle filament wound case compressive strength study. II - Analysis

In order to explain the results of the testing conducted in Part I and relate the subscale test specimen performance to case performance during prelaunch loading, a comprehensive analysis program was conducted. Finite element models of both full-scale case and subscale test coupons were made. Validated axisymmetric models were used for the case analyses. Modeling of coupons was accomplished using a generalized plane strain finite element model in most cases, although some three-dimensional finite element modeling was used to investigate the importance of three-dimensional effects on the coupon performance. The large number of plies and complexity of the test coupons used limited the finite element grids to a through-the-thickness discretization of one element per ply. Delaminations observed in the helical ply dropoff region were modeled using frictionless sliders. Comparisons of predicted strains and displacements were made with the test data from both cases and coupons to validate the finite element models. Based on observations of the test results and finite element predictions, a failure criterion for both coupons and cases was postulated and then validated by comparing performance predictions to test results. Finally, the validated failure criterion was used to predict the performance of the first two flight cases under prelaunch loads.