Tensile Properties of Carbon Fiber: Single Filament Vs Tow Based Testing

摘要

In the work presented here, single filament PAN carbon fibers (~7 microndiameter) are tested using a highly precise MTS Nano UTM tensile test machine.Current practice of ISO or ASTM methods involve testing tensile properties ofcarbon fibers using an infused tow of fibers. It is a current norm that carbon fibercompanies report tensile strength and modulus (normal, intermediate, and high)based on measurements using full tow of fiber impregnated with some resin type,usually an epoxy system. For example, ASTM D4018 standard allows for the fibertow to be collimated, impregnated with resin, and tensioned while keeping a fibervolume fraction in the range of 35% to 60%. This process can be completed twodifferent ways: manually or automated. The manual method allows for the strand ofa certain length and weight to be saturated in a resin bath and pulled through a dieand attached to a tensioning rack. An automated setup for large volume applicationstypically involves passing the fiber tow through a resin bath, through multiplerollers (to help align the fiber) and wound on a tensioned spindle. After the strandsare cured, they are tabbed using a standard gage length of ~150 mm. The presentstudy considered how the mechanical properties measured using single carbonfibers translate to those obtained using a 24k tow based testing. Since tow basedtesting is largely dependent on morphology of the tow, interfacial shear strengthbetween carbon fiber and resin, and the specific type of resin used, and relativetension of filaments within a tow, the motivation of this paper is to develop afundamental understanding of translation of single carbon fiber mechanicalproperties to a resin reinforced composite tow. We are also developing a simple andrepeatable test procedure for tow based properties without resin infusion. Weibullstatistics of single filament based results are considered in the discussion.