Modelling of the filament-winding fabrication process
A stress model of the filament-winding fabrication process, previously implemented in a finite element program, was improved. Pre- and post-processing codes were developed to make the program easier and more efficient to use. A program which is used to design filament wound composite rocket motor cases was modified to write a model file for the fabrication stress code in the pre-processing stage. The same code was altered to provide post-processing output in the form of graphic displays. Also, a new code was written to provide additional post-processing capability for the fabrication stress model.
Verification of the model of the filament-winding process was performed by comparing experimental pressure and strain data, for the fabrication of a filament wound bottle, with results of an analytical model. The final analytical results using consecutive models of the filament wound bottle show reasonable agreement with experimental pressure and hoop strain data. The maximum difference in the analytical and experimental values in the pressure data was about 25% for the final winding stage. The difference was smaller during the winding progression. These results also show that the accuracy of the model depends heavily on the assumptions made for input parameters during modelling. The stiffness of the segmented steel mandrel, simulated by an effective modulus (degraded by segmentation), and the instantaneous laydown tension loss parameters significantly affected the results of the model. Including the effective modulus for the segmented mandrel in the model reduced the difference in the experimental and analytical pressure results by about 150%. The inclusion of instantaneous laydown tension loss in the model reduced the analytical-experimental difference by roughly 225%. These two parameters reduced the largest difference in the predicted pressure values from about 400% for the first model to around 25% for the final model.
The fabrication stress model was coupled with the thermo-kinetic cure model to provide more accurate fiber motion tension loss analysis capability. The stress model was modified to use the thermo-kinetic model as a subroutine to calculate fiber motion tension loss using a two-dimensional analysis. The results of the qualitative verification show that fiber motion tension loss is more important in the later stages of winding than in the beginning stages which indicates that it may provide the needed accuracy in the final winding stages.