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Experimental Characterization of Progressive Damage in Countersunk Composite Laminates Loaded in Bearing



Composite materials are more widely used in the aerospace industry due to their superior stiffness and weight-savings when compared to metals. Although composites significant reduce the need for fasteners, they are not completely eliminated. The failure of these composite laminates at fastener sites has been a long recognized as a problem and investigated by many researchers. The focus of this work is on countersunk bolted joints in composite laminates. Countersunk fasteners are preferred in aerospace to satisfy aerodynamic smoothness of airframe or wing outer surface. The ASTM D5961 Procedure A is the standard test to obtain bearing strengths of composite laminates. The ASTM D5961 Procedure C is recommended to use in testing countersunk composite joints. For thick laminates and large fastener diameter to laminate thickness (d/t) ratios, Procedure C is not very representative. In this paper we perform bearing tests of laminated composites, using a modified ASTM D5961 fixture designed for testing countersunk bolted joints. The progressive failure behaviour and the damage resulting from the modified test fixture are quantified and compared to laminates tested using the standard ASTM D5961 Procedure A (double shear with straight pin) and Procedure C (countersunk single lap shear).

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