MODE-II FREE-EDGE DELAMINATION IN LAMINATED COMPOSITES UNDER UNIAXIAL COMPRESSION

The influence of interlaminar shear stress on mode II free-edge delamination at the free-edge in composite laminate is studied experimentally and analytically. Delamination tests are conducted under uniaxial compressive load to eliminate transverse cracking. Test laminates are designed to have compressive interlaminar normal stress and various ratios of interlaminar shear stresses at the interfaces of interest. The laminates treated in this paper are [(theta4/ - theta4/90(4)]s, [(+/- theta2)2/90(4)]s and [(+/- theta)4/90(4)]s, where theta is 30 and 45 degrees. The experimental results are discussed with the analyzed results obtained by the finite element method. The fracture surface of delamination is further examined for the determination of the predominant mode of delamination using a scanning electron microscope. It is found that some laminates can be delaminated only by the effect of mode II interlaminar shear stress even though it is zero at the free-edge.