The Tensile Strength of Boron Filament.
MIDWEST RESEARCH INST KANSAS CITY MO
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The ultimate tensile strength of two commercial boron filaments, one of 0.0102 cm 0.0040 in. and the other of 0.0142 cm 0.0056 in. diameter, was determined for the as-received condition and after annealing in vacuum 525 C, 1 hr, 0.000001 torr. The distributions in strength were negatively skewed and annealing increased the mean strength of the filaments. Scanning electron microscopy showed that the fracture surfaces were usually cone-shaped and that a characteristic lip occurred near the circumference of the larger filaments. It was concluded that there is no significant difference in the distribution in ultimate tensile strengths between the two filament sizes evaluated, and that tensile fractures initiate in the boride core or at the interface between the boride core and the boron. Vacuum annealing does not degrade boron filaments, and any observed degradation in filament strength as a result of composite fabrication under these conditions must be chemical or mechanical. Author, modified-PL