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Kevlar KM2, 600 denier, was Instron tested in quasi-static, uniaxial tension to determine its strength. Specimens included both single yarns and 68-yarn-wide, single-ply strips of plainwoven fabric (Style 706). Never-woven single-yarn specimens were tested with varying degrees of initial twist. Strength of the untwisted, never-woven yarn was 2.66 ± 0.04 GPa. The twist multiplier was 1.2. Single warp-oriented and fill-oriented yarns were extracted from Style 706 fabric, tested, and found to have strengths of 2.06 ± 0.01 and 2.20 ± 0.05 GPa, respectively. The single-ply fabric specimens of both warp and fill orientations were tested and found to have strengths of 2.23 ± 0.04 and 2.67 ± 0.04 GPa, respectively. The strength effects of weaving, finishing, yarn extraction, and inter-yarn contact are discussed.n Acknowledgments

Approved for public release; distribution is unlimited. AbstractThe necessity for epoxies in new technologies is overwhelming. For these epoxies to perform at their maximum capabilities, both high strength and toughness must be in the list of mechanical properties. This is where bi-modal networks become important. Their combinations of both long-and short-chain cross linkers vary the cross-link density of the epoxy and thus improve the toughness. Here, a study was done to see if these bi-modal networks increase toughness without loss in modulus. Through the use of the differential scanning calorimeter to find the glass transition temperature, the dynamic mechanical analyzer to find the storage modulus, and the Izod impact machine to find the impact strength, we can make a conclusion whether these networks really work. In the beginning, the results seemed to be what we had hoped for, that is, the decrease in cross-link density did improve the impact strength; however, the storage modulus also decreased with a decrease in cross-link density. Finally, the conclusion can be stated that the bi-modal network does increase the toughness of this system but with a loss in modulus.u ACKNOWLEDGMENTS This work was partially funded through a summer student fellowship for Stephen MacKenzie from the Center for

This report reviews various test techniques published in the literature for evaluating carbon fiber via the single-filament tensile test, the dry bundle test, the resin-impregnated strand test, and the single-fiber fragmentation test (optical microscopy and acoustic emission). Experimental procedures, data analysis, and statistical tensile strength theory are also described. Each technique is followed by a discussion of the advantages and limitations. Furthermore, a materials property database has been developed that includes mechanical properties for several commercially available carbon fibers.n Acknowledgments