Influence of the Free Edge upon the Strength of Angle-Ply Laminates

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Abstract
Strength characterization of the fiber-reinforced laminated composite materials is quite often accomplished through the utilization of the finite-width tension coupon specimen. Recent analytical studies have shown that the state of stress in the vicinity of the free edge of such a laminate is fully three dimensional in nature and may not be predicted by laminated plate theory. Furthermore, experimental results have revealed that while the strength of angle-ply tensile coupons of certain fiber orientations are predicted adequately by laminate strength theories, coupons of other fiber orientations are not. As an explanation of this result, it is argued that large, nonlinear shear strains occur at the interfaces for fiber orientations leading to near maximum shear coupling compliances. Further, these strains allow the initiation of matrix cracks at the free edge, which are ultimately responsible for the premature rupture of the coupon. Experimental evidence which supports these arguments is presented.