SIMPLIFIED ANALYSIS OF RESIDUAL-STRESSES IN IN-SITU CURED HOOP-WOUND RINGS

A simple theoretical/empirical hybrid method for the prediction of res idual stresses in in-situ cured, thick, hoop-wound, thermosetting comp osite rings is presented. The method avoids the need for complicated c haracterizations of resin and fiber properties that affect residual st ress development during the manufacturing process. New results from a series of experiments with in-situ cured hoop-wound glass and carbon r einforced epoxy composites show that residual stresses due to non-ther mal sources such as winding tension and resin shrinkage during cure ar e essentially constant for fixed manufacturing process parameters and resin system, regardless of ring geometry and fiber type. Also, the co mbined effect of winding tension and resin shrinkage becomes progressi vely less important in comparison to thermal effects as the ID/OD rati o of a ring decreases. The analysis method is demonstrated by using th e data acquired with a single ring to predict the residual stress in a nother ring with different fiber, ID, and OD. Equations for the therma l expansion of hoop-wound composite rings were corrected from the publ ished version and verified for a range of ring geometries, two differe nt types of fibers, and two resin systems. The analysis tools outlined in this paper aid the design and fabrication of multiple-concentric-r ing structures subjected to varying temperatures, such as composite fl ywheels for energy storage.