Hi-Nicalon fiber-reinforced celsian matrix composites: Influence of interface modification
N.P. Bansal, J.I. Eldridge
(NASA-Lewis Research Center)
Unidirectional celsian matrix composites having 42Ð45 volume percent of uncoated or BN-SiC coated Hi-Nicalon fibers were tested in three-point bend at room temperature. The uncoated fiber-reinforced composites showed catastrophic failure with strength of 210 <>± 35 MPa and a flat fracture surface. In contrast, composites reinforced with coated fibers exhibited graceful failure with extensive fiber pullout. Values of first matrix cracking stress and strain were 435 <>± 35 MPa and 0.27 <>± 0.01%, respectively, with ultimate strength as high as 960 MPa. The elastic Young's modulus of the uncoated and coated fiber-reinforced composites were 184 <>± 4 GPa and 165 <>± 5 GPa, respectively. Fiber push-through tests and microscopic examination indicated no chemical reaction at the uncoated or coated fiber-matrix interface. The low strength of composite with uncoated fibers is due to degradation of the fiber strength from mechanical damage during processing. Because both the coated- and uncoated-fiber reinforced composites exhibited weak interfaces, the beneficial effect of the BN-SiC dual layer is primarily the protection of fibers from mechanical damage during processing.
Keywords: composites; mechanical properties
Order No.: JA806-015 © 1998 MRS

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