Two related criteria based on stress distribution are presented for predicting the uniaxial tensile strength of laminated composites containing through the thickness discontinuities of a general shape. The criteria result in two parameter (unnotched tensile strength and a characteristic dimension) models which are capable of predicting observed discontinuity size effects without resorting to classical concepts of linear elastic fracture mechanics. As a direct consequence of the stress criteria, however, a relationship between Mode I fracture toughness and unnotched laminate tensile strength is determined. Limited comparison of theory to experimental data for circular holes and straight cracks yields good results. The simplicity of the analytical approach coupled with its generality make it of practical value to the designer.

A bending theory for anisotropic laminated plates developed by Yang, Norris, and Stavsky is investigated. The theory includes shear deformation and rotary inertia in the same manner as Mindlin’s theory for isotropic homogeneous plates. The governing equations reveal that unsymmetrically laminated plates display the same bending-extensional coupling phenomenon found in classical laminated plate theory based on the Kirchhoff assumptions. Solutions are presented for bending under transverse load and for flexural vibration frequencies of symmetric and nonsymmetric lamninates. Good agreement is observed in numerical results for plate bending as compared to exact solutions obtained from classical elasticity theory. For certain fiber-reinforced composite materials, radical departure from classical laminated plate theory is indicated.

Two previously developed failure criteria for predicting the uniaxial tensile strength of a laminated composite containing through-the-thickness material discontinuities (notches) are subjected to further experimental scrutinization. In particular, the two-parameter (unnotched tensile strength of the laminate and a characteristic length) models, which are capable of predicting observed discontinuity size effects without resorting to the concepts of linear elastic fracture mechanics, are based on limited experimental verification. In the present paper, and experimental program is presented which examines the effect of changes in the material system, the laminate fiber orientations, and the notch shape and size (stress gradient), on the model predictions. This is accomplished by obtaining experimental data on two material systems, glass/epoxy and graphite/epoxy, in conjunction with two orientations of fiber-dominated laminates containing through-the-thickness circular holes and sharp tipped cracks of several sizes. In addition to the test results, two observations based on the models are presented. First, the statistical failure distribution for a composite containing a circular hole is predicted using the models and shown to agree well with experimental observations. Second, an Irwin type correction factor applied to the stress intensity factor is shown to result in nearly constant values of the critical stress intensity factor for all values of crack length. The correction factor is shown to be related to the characteristic length of the present models.

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A bending theory which includes transverse shear deformations is presented for laminated plates. Closed form solutions are obtained for bending deflections, flexural vibration frequencies, and buckling loads of simply-supported rectangular plates of special construction. Results show that shear deformation can significantly effect gross plate response for highly anisotropic laminates. Comparison to exact elasticity solutions show excellent agreement for gross behavior of laminates.