Model and experimental study of fiber motion in wet filament winding

Abstract

A model for wet filament winding of thermosetting matrix cylinders was developed. The model relates the processing conditions (applied temperature, fiber tension and processing speed) to temperature, degree of cure, fiber volume fraction and stresses and strains within the composite cylinder. In this work, the modeling techniques behind predicting fiber volume fraction are described and validated. Specifically, a fiber motion model was developed which describes the motion of each layer of the cylinder during winding. This fiber motion model includes the effects of the fiber bed compacting as each new layer is wound and the resin flow through the porous fiber bed. In addition, several unique features were incorporated into the fiber motion model: fiber bed stiffness is evaluated as a function of both the fiber volume fraction and the resin cure state and a rule for the mixing of high-viscosity resin with lower viscosity resin to simulate bleeding through the resin from previously wound layers. Both effects must be included if the fiber position is to be accurately predicted. Model predictions for fiber volume fraction are compared with several full-scale (1 m diameter) commercially wound cylinders. Tow tension, winding time and fiber sizing were varied. There is good agreement between model predictions and experimental data. Several important trends in both the data and model were observed: (1) low fiber volume fraction layers occur when the time between winding one layer and the next is long enough for the resin to each gelation; (2) even when the layer has not completely gelled, high-viscosity resin can bleed through to the next layer wound and cause a low fiber volume fraction; and (3) fiber sizing can increase the overall fiber volume fraction by improving the fiber bed compaction characteristics.