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

Analysis and experiments on angle-ply laminate MMB fracture specimens with curved cross-section machined from filament-wound composite cylinders are presented. The analysis is based on superposition of compliance and energy release rate expressions previously derived from laminated theory for angle-ply laminate DCB and ENF specimens with curved cross-section. Elastic interactions between the two arms of the specimen, asymmetry in geometry and lay-up, and interlaminar shear deformation are incorporated in the analysis. The analysis predicts global compliance of the specimen and energy release rate components, GI and GI,, obtained from global considerations. It was found that the ratio between GI and GI, is only slightly sensitive to ply angle in the angle-ply laminates. The ratio G/GH, likewise, is only weakly dependent on crack length. An experimental study was conducted on glass/epoxy MMB specimens using contoured loading tabs and supports to accommodate the curved cross-section. Specifically, [±016 and [±0112 laminates with mid-surface delaminations were considered, where 0 = 30°, 550 and 85°. Several mode ratios (G1/G11) were examined. Analytical predictions of the compliance were in good agreement with experimental data over the range of beam thicknesses and ply angles examined. The initiation fracture toughness, GC, increased with decreased ratio G1/G11 and increased ply angle O. For all laminates, the crack propagated in a non-uniform manner across the width of the specimen.