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A large, comprehensive program is being conducted at Virginia Tech to study the effect of laminate thickness on the fracture strength of notched laminated composites. Part of this program has been the study of the characteristics and development of subcritical crack-tip damage prior to failure. The study has concentrated on the centercracked tension specimen geometry. Subcritical crack-tip damage has been studied using enhanced X-ray radiography and the laminate deply technique.
This paper examines the role that delamination plays in affecting the fracture of [0/±45/90]ns and [0/±45]ns laminates at various values of n. The study has found that delaminations do occur in thin laminates (n = 1) and affect the strength of the laminate. However, in thick laminates such as [0/±45/90]15s and [0/±45]20s, there is sufficient constraint to prevent delaminations from occurring in the interior region of the specimen. The final fracture surface is uniform in the interior and self-similar (collinear with the original starter notch), with “shear-lip” type damage in the form of delaminations and matrix cracking in the first several plies at the surface. These differences in the type of fracture of the thin and thick laminates greatly affect the fracture strength.
delamination, notched strength, thick laminate, composite, fracture, graphite/epoxy
Assistant Professor, Aerospace Engineering, Texas A&M University, College Station, TX
Professor, Virginia Polytechnic Institute and State University, Blacksburg, VA