Simplified analysis of residual stresses in in-situ cured hoop-wound rings

A simple theoretical empirical hybrid method for the prediction of residual stresses in in-situ cured, thick, hoop-wound, thermosetting composite rings is presented. The method avoids the need for complicated characterizations of resin and fiber properties that affectresidual stress development during the manufacturing process. New results from a series of experiments with in-situ cured hoop-wound glass and carbon reinforced epoxy composites show that residual stresses due to non-thermal sources such as winding tension and resin shrinkage during cure are essentially constant for fixed manufacturing process parameters and resin system, regardless of ring geometry and fiber type. Also, the combined effect of winding tension and resin shrinkage becomes progressively less important in comparison to thermal effects as the ID/OD ratio of a ring decreases. The analysis method is demonstrated by using the data acquired with a single ring to predict the residual stress in another ring with different fiber, ID, and OD. Equations for the thermal expansion of hoop-wound composite rings were corrected from the published version and verified for a range of ring geometries, two different types of fibers, and two resin systems. The analysis tools outlined in this paper aid the design and fabrication of multiple-concentric-ring structures subjected to varying temperatures, such as composite fly wheels for energy storage.