Error Reduction for the Determination of Transverse Moduli of Single-Strand Carbon Fibers via Atomic Force Microscopy
USMA Research Unit Affiliation
Nuclear Science and Engineering Research Center, Physics and Nuclear Engineering
Date of Award
Master of Science (MS)
PeakForce Atomic Force Microscopy (AFM) Quantitative Nanomechanical Measurement (QNM) is utilized to measure the transverse fiber modulus of single strand carbon fibers to less than 5% error for eleven types of carbon fibers, manufactured by Mitsubishi, Toray, and HEXCEL, with longitudinal moduli between 924-231 GPa, including export-controlled fibers. A positive linear correlation between the longitudinal and transverse modulus with an R^2=0.76 is found. Statistical and physical criterion for outlier removal are studied and established to improve the quality of data to exclude outlier measurement points in an image based on the peak force, adhesion force, and indentation depth. Statistical and physical criterion are also developed to exclude outlier images within the sample set. Three alternative methods for calculating the transverse modulus using the raw instrument data were studied. The first method approximated the indentation force curve using the peak force and adhesion force values. This method calculated moduli lower than that reported by the instrument and with no correlation between the transverse and longitudinal modulus. The second method approximated the indentation force curve using the peak force and net force zero point. This method found values larger than that reported by the instrument and no correlation between the transverse and longitudinal modulus. The final method performs a linear fit to the measured indentation force curves at each indentation point. This method also found values lower than reported by the instrument. Pitch-based fibers are found to exhibit lower measurement error than PAN-based fibers. Additionally, PAN fibers exhibited no apparent modulus correlation when the Pitch fibers are excluded. Underlying reasons for this lack of correlation are explored, with the most likely reasons being the difference in long-range order in the fiber microstructure and aging effects due to the different sourcing and storage methods used for the PAN fibers. Low uncertainty characterization of the transverse modulus supports greater understanding of fiber mechanical behavior, and would allow fiber manufacturers to certify their fibers in both the longitudinal and transverse axes. Additionally, it would improve the confidence in engineering estimates used by industry and defense programs for transverse performance of carbon fiber-reinforced composites.
Defense Threat Reduction Agency
Air Force Institute of Technology
Frey, Josh, "Error Reduction for the Determination of Transverse Moduli of Single-Strand Carbon Fibers via Atomic Force Microscopy" (2021). West Point ETD. 20.