Beam analysis of angle-ply laminate mixed-mode bending specimens

An analysis of angle-ply laminated beam fracture specimens loaded in a mixed-mode bending (MMB) apparatus is presented. The analysis is based on superposition of compliance and strain-energy release rate expressions previously derived from laminated beam theory for DCB and ENF angle-ply laminate specimens. Elastic interactions between the two arms of the specimen, asymmetry in lay-up, and interlaminar shear deformation are incorporated in the analysis. It was found that the ratio between G(I) and G(II) is only slightly sensitive to ply angle in the angle-ply laminates, where G(I) and G(II) denote the mode I and mode II components of the strain energy release rate, G. The ratio G(I)/G(II), likewise, is only weakly dependent on crack length. An experimental study on glass/polyester quasi-unidirectional and angle-ply laminates was conducted. Specifically, [0](6), [+/-30](5) and [+/-45](5) laminates with midplane delaminations were tested at various mode ratios (G(I)/G(II)) Predicted compliance values were in good agreement with experimental data. The fracture toughness, G(c), increased with decreased ratio G(I)/G(II). G(c) increased with increased ply angle theta in the angle-ply laminates except for pure mode I conditions. Nonuniform and skewed crack fronts were observed for the angle-ply laminates as a result of elastic coupling in the laminate beams of the cracked region. (C) 1999 Elsevier Science Ltd. All rights reserved.