Winding and curing stress analysis of filament wound composites by finite elements

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Virginia Polytechnic Institute and State University


Filament wound composite structures are becoming more and more attractive to designers in the aircraft and aerospace industries due to increasing strength- and stiffness-to-weight ratios and falling fabrication costs. However, the interaction of some of the manufacturing process variables such as mandrel stiffness and thickness, winding tension and pattern, and cure cycle characteristics can lead to common defects such as delamination, matrix cracking and fiber buckling.

A model of the filament winding process was developed to better understand the behavior of wound structures during fabrication. Specifically, the residual stress state at the end of winding, heat-up and cool-down was determined. This information is important because adverse stress states are the mechanism through which the process variables cause fabrication defects.

The process model utilized an incremental finite-element analysis to simulate the addition of material during winding. Also, the model was refined and extended to include changes that occur in the material behavior during the cure.

A fabrication analysis was performed for an 18 in. (457 mm) graphite/epoxy filament wound bottle. Two different mandrel models were examined, a rigid steel and a soft sand/rubber mandrel. At the end of winding, the composite layers in the model retained all of their initial winding tension for the steel mandrel but did exhibit significant loss of tension for the sand/rubber mandrel. The composite layers experienced a large increase in tension during heating for the steel mandrel but showed no significant recovery of tension for the sand/rubber system.