Designing Interfaces in Inorganic Matrix Composites
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missible bond strength limit for the interfacial toughening mechanism to operate will détermine the maximum transverse strength one may expect. 2. Development of methods to measure interfacial micromechanical properties. 3. Modification of interfaces through reinforcement surface treatment. This article treats the conditions for engineering interfaces for the model sys-
OiCr
Al Matrix
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Figure 1. Hexagonal packing of aligned P-55 fibers in an Al matrix. The transverse plastic résistance in the y direction differs from that in the x direction.
tem P-55 (10 fim diameter graphite fiber) in a pure aluminum métal matrix. Similar approaches can be developed for other fibers and matrices. Transverse Behavior and Lower Bound to the Interface Strength Interface strength is probed directly when the composite is stressed in the transverse direction. Hence, the interface strength should be high enough that the transverse stresses can be transferred to the fiber. The complexity of the stress field at the interfaces in a bundle of fibers has required approaching the transverse loading problem with numerical techniques, as in the work of Zywicz.1'2 Figure 1 shows the geometry of a typical close-packed array of pitch-55 fibers in an Al matrix. The relevant results of Zywicz's analysis are given in Table I, where the stress concentrations in purely elastic and elastic-plastic behavior of the Al matrix are summarized as a function of volume fraction, Vf, of fibers for two différent modes of tensile loading in the transverse direction, i.e.,a^ x in the close-packed direction and
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