Measurement and Prediction of Process-induced Residual Strains in Thick Wound Composite Rings

Abstract

Analytical and experimental studies are performed to investigate the process-induced residual strains within a thick wound composite ring for the flywheel energy storage system. First, an effective temperature change that equivalently describes the distribution of the residual strains is implemented into a two-dimensional stress analysis. The locations and magnitudes of the maximum radial stress and strains are then derived and the delamination indices are accordingly defined in terms of the inner and outer radius ratio and the material properties. The present method is numerically validated using the results from the cure-simulation program WINDTHICK. Thick rings are made of T300/epoxy, and the residual strains in the radial and hoop directions are measured using a split-ring method, i.e., cutting the ring in the radial direction and releasing the residual stresses. The measured residual stains are in good agreement with the analytical results. It is shown that the effective temperature change remains the same over a wide range of the ring thickness. Delaminations observed in the tests are successfully predicted using the present method, and the rings of the geometric similarity experience a delamination at the same temperature drop.