PIEZORESISTIVITY AND FAILURE OF CARBON FILAMENTS IN AXIAL-COMPRESSION

A novel technique for axial compression of single carbon filaments is introduced. Single filaments were bonded to the surface of polymer compression specimens in a manner analogous to the mounting of metal-foil strain gages. By measuring the fiber piezoresistive behavior, filament compression could be monitored. In compression, the resistance of the filaments decreased nonlinearly and reached a minimum value just prior to failure. This nonlinear decrease in resistance with compression was found to be reversible up to strains of -3%. Filament failure was marked by an abrupt increase in resistance, and average ultimate compressive strains were -3% or greater for all fiber types. Because these failure strains are approximately double those measured for high-fiber-content composites in longitudinal compression, it was concluded that the compressive strength of composites fabricated from the fiber examined is not limited by the strength of the fiber and that a large potential exists to improve composite strength.