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This paper treats the development of pertinent theories that establish the properties of the fiber-matrix interface needed to achieve efficient composites and the development of a test technique to measure these properties. An equation is derived that relates the externally applied load to the failure mode, fiber tensile strength, and interface shear strength. This equation makes it possible to establish the interface strength that is required to obtain overall composite failure instead of interface failure. The effect of interface on the bending stiffness and Young's modulus of filamentary composites is investigated. A technique, based on shear-lag theory, that will measure the properties of the interface is presented. This technique involves pullout tests on fibers that are imbedded in a matrix. An approximate solution also is presented for the shear-stress distribution around a discontinuous fiber that is surrounded by six continuous fibers. The seven fibers are a part of a composite of infinite extent that is subjected to a remotely applied tensile stress. It is shown that there is a significant variation in the shear-stress distribution along the fiber length as well as around its circumference.
interfaces, required strength, properties, measurement, interfaces, shear, fibers, composite materials, fracture properties, evaluation, tests
Greszczuk, L B
Staff engineer, Douglas Aircraft Co., Santa Monica, Calif.