Characterization of Mode I Delamination Growth in Glass/Epoxy Composite Cylinders

Mode I delamination growth in filament wound composite cylinders has been examined analytically and experimentally. Beam specimens with the axis parallel to the cylinder axis were machined from the cylinders. The specimen contained an aluminum film at one end to define a starter delamination. A beam model incorporating elastic foundation effects and curved cross sections of the sub-beams of the delamination region was developed for the beam specimens configured for a DCB test from laminated beam theory derived from a shallow shell formulation. An experimental study on [±016 and [±0112, glass/epoxy DCB specimens employing contoured loading tabs accommodated to the curved cross-section was conducted. The delaminations were initially at the mid-surface, and the angles 0 were 300, 550 and 850. Analytical predictions of the compliance were in agreement with experimental data over the range of crack lengths, beam thicknesses, and ply angles examined. The fracture toughness corresponding to propagation straight from the insert increased slightly with increased angle 0 at the ±0 interface. The propagation fracture toughness increased steeply with crack length and then dropped. The increasing resistance, i.e., R-curve behavior, is attributed to the work associated with bridging and fracture of angle-ply fiber bundles, and the drop is attributed to crack jumping to another interface. For all laminates, the crack propagated in a non-uniform manner across the width of the specimen.