ABSTRACT
The tensile properties of carbon fibers are usually determined by one of two methods: the single filament tensile test [2] and the composite strand tensile test [3]. In the single fiber test, a filament is carefully separated from a yarn or tow of carbon fiber, then mounted on a cardboard form as shown in Figure 1. Care must be taken to ensure that the filament is aligned axially with the tensile direction. Prior to test, the sides of the cardboard mount are cut, leaving only the filament between the grips. As it is not reasonable to attach an extensometer to the filaments, the compliance of the testing instrument must be known to obtain accurate strain measurements. This test is labor intensive, requiring many samples for statistical analysis. The composite strand tensile test is more suitable for rapid and accurate measures of filament tensile properties. A yarn or tow of fiber is impregnated with a resin, usually an epoxy, to produce a rigid test specimen capable of sustaining uniform loading of the individual filaments. The elongation-to-break of the cured resin must be larger than that of the fiber. Depending on the breaking stress of the composite, end tabs of a thermoplastic resin may be required to prevent slippage within the grips. An extensometer is used to accurately determine the amount of strain. Information on the tensile and compressive properties of commercial carbon fibers are provided in Table 1. Table 2 provides additional information on the mechanical properties of some commercial fibers.
