Error Reduction for the Determination of Transverse Moduli of Single-Strand Carbon Fibers via Atomic Force Microscopy
AIR FORCE INSTITUTE OF TECHNOLOGY
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 R2=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.
Theses or dissertations
PeakForce Atomic Force Microscopy (AFM), Quantitative Nanomechanical Measurement (QNM)
Frey, Josh, "Error Reduction for the Determination of Transverse Moduli of Single-Strand Carbon Fibers via Atomic Force Microscopy" (2021).