SEDL / STP / STP893-EB / STP35348S

Effect of Laminate Thickness and Specimen Configuration on the Fracture of Laminated Composites

Harris, CE
Assistant professor, Texas A&M University, College Station, TX

Morris, DH
Professor, Virginia Polytechnic Institute and State University, Blacksburg, VA

Pages: 19    Published: Jan 1986

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Abstract

The effect of laminate thickness on the fracture behavior of laminated graphite/epoxy (T300/5208) composites has been studied. The predominantly experimental research program included the study of the [0/±45/90]^ns and [0/90]^ns laminates with thicknesses of 8, 32, 64, 96, and 120 plies and the [0/±45]^ns laminate with thickness of 6, 30, 60, 90, and 120 plies. The research concentrated on the measurement of fracture toughness utilizing the center-cracked tension, compact tension, and three-point bend specimens. The development of crack-tip damage prior to fracture was also studied.

Test results showed fracture toughness to be a function of laminate thickness. The fracture toughness of the [0/±45/90]^ns and [0/90]^ns centercracked laminates decreased with increasing thickness and asymptotically approached lower bound values of 1043 MPa √mm (30 ksi √in.) and 869 MPa √mm (25 ksi √in.), respectively. The fracture toughness of the [0/±45]^ns center-cracked laminate increased with increasing thickness but reached an upper plateau value of 1390 MPa √mm (40 ksi √in.). The fracture toughness of all laminates was independent of crack size except the [0/90]^2s laminate that split extensively. The fracture surface of all thick laminates was uniform in the interior and self-similar with the starter notch. With the exception of the [0/±45]^ns laminate, the fracture toughness of the thicker laminates was relatively independent of specimen configuration.