Interlaminar Stress and Delamination Analysis of Internally-Tapered Composite Laminates

In the present work, the interlaminar fracture behavior of internally-tapered composite laminates that have cracks in the drop-off region is investigated using J-integral and direct calculation methods. The influences of cracks at the resin layer–interleaf interface and at the interface between adjacent plies are studied. The composite laminate is modeled and analyzed using partial hybrid stress finite elements that are formulated based on the Hellinger–Reissner variational principle and the generalized plane deformation theory. In the formulation, only three interlaminar stress components that cause delamination at the interface are independently assumed in addition to displacement interpolation. Both the six-node triangular and eight-node quadrilateral hybrid finite elements (formulated and presented in a companion paper [He, K., Hoa, S.V. and Ganesan, R. “Stress Analysis of Tapered Composite Laminate Using Partial Hybrid Finite Elements”, J. Reinforced Plastics and Composities, 23:6, 2004.]) are used in the fracture analysis. A parametric study is conducted to determine the influences of geometric and material properties on the fracture behavior of the tapered laminate. Experimental work was carried out for the observation of fracture. The analysis results and the experimental observation are compared.