Paper number 697

MECHANICAL PROPERTIES AND INTERFACIAL CHARACTERIZATION OF NEXTEL 312(TM) FIBER/BN/BLACKGLAS(TM) COMPOSITES

Richard L. Schalek^*, John Helmuth^**, and Lawrence T. Drzal#^*

*Composite Materials and Structures Center, Michigan State University
2100 Engineering Bldg., East Lansing, MI 48824
**Department of Materials Science and Mechanics, Michigan State University
2100 Engineering Bldg., East Lansing, MI 48824
#Department of Chemical Engineering and Materials Science and Mechanics,
Michigan State University, 2100 Engineering Bldg., East Lansing, MI 48824-1226

Summary

Boron nitride (BN)-coated Nextel(tm) 312 fibers, produced via ammonia nitridation, along with 'as-received' and 'desized' fibers, were composited in a Blackglas(tm) matrix. The composite mechanical properties, failure properties, and fiber-matrix interfacial chemistry was investigated. BN treated fiber composites show a 90% improvement in flexural strength and substantial increases in shear strength (short beam shear and Iosipescu) over the 'as-received' fiber composite. The composite fabricated with 'desized' underwent spontaneous delamination and therefore mechanical testing was impossible. X-ray photoelectron spectroscopy of the starting materials and of composite fracture surfaces combined with environmental scanning electron microscopy provided data on surface and interfacial chemistry and helped identify the locus of failure for the composites. Examination of the fracture surfaces identified boron and nitrogen on the fiber surface suggesting that the locus of failure for the BN- coated fiber composites occurs at the matrix/BN coating interface.

Keywords

Blackglas, pyrolization, adhesion, boron nitride coating, alumina fiber, fractography, interface characterization.