Characterization of mode I delamination growth in glass/epoxy composite cylinders

Mode I delamination growth in filament wound composite cylinders has been e xamined analytically and experimentally. Beam specimens with the axis paral lel to the cylinder axis were machined from the cylinders. The specimen con tained an aluminum film at one end to define a starter delamination. A beam model incorporating elastic foundation effects and curved cross sections o f the sub-beams of the delamination region was developed for the beam speci mens configured for a DCB test from laminated beam theory derived from a sh allow shell formulation. An experimental study on [+/-theta](6) and [+/-the ta](12), glass/epoxy DCB specimens employing contoured loading tabs accommo dated to the curved cross-section was conducted. The delaminations were ini tially at the mid-surface, and the angles theta were 30 degrees, 55 degrees and 85 degrees. 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 propagatio n straight from the insert increased slightly with increased angle theta at the +/-theta interface. The propagation fracture toughness increased steep ly with crack length and then dropped. The increasing resistance, i.e., R-c urve behavior, is attributed to the work associated with bridging and fract ure 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-uni form manner across the width of the specimen.