Interlaminar Stresses around Circular Cutouts in Composite Plates under Tension

Abstract

1~5 From these results, the static failure strengths are obtained with good quantitative prediction compared to experiments. Delamination at free edges is another failure mode of laminated composites, especially under fatigue loadings. Extensive delamination at free edges is reported on static strength as well as fatigue strength, with and without notches.610 Hence, the determination of interlaminar shear stresses and the normal or peel stress is a current research topic. However, all the previous studies are restricted to straight boundaries1127 except for finite element solutions in Refs. 14 and 28-30. There is no analytical closed-form solution available to predict interlaminar stresses for curvilinear boundaries. Therefore, the present paper attempts to study the interlaminar stresses at a circular cutout in an infinite composite laminate under uniform tensile load. The boundary-layer theory for composite laminates in Ref. 20 is extended here to the formulation of polar coordinates, and the title problem is investigated for the case of orthotropic composite plates. The laminate considered here is under inplane loading symmetric about the midplane. The construction of the laminate is also midplane symmetric so that there is no stretching/bending coupling of the plate due to external load. The force resultants around the hole of an orthotropic or anisotropic plate are given by Refs. 31 and 32. The radial and shear force resultants at the edge of the hole are zero. From the plane stress solution, the strains at the edge of the hole can be calculated by the force resultant-strain relation. Due to the compatibility of deformation, the strains of individual layers are the same as the laminate. Therefore, the stresses of each layer may then be computed from the layer stress-strain law. However, the computed radial and shear stresses of each layer along the contour of the hole are in general not zero. Because there exists a three-dimensio nal state of stresses at the free edge of each layer where the plane stress solution cannot predict. The region of the plate adjacent to and including the edge, where the plane stress solution may not be adequate, is called the boundary layer. To obtain the governing equations in this