A Technique to Measure Strain Distributions in Single Wood Pulp Fibers
Keywords:Fibers, micromechanics, strain, digital image correlation, tensile testing, environmental scanning electron microscopy
AbstractEnvironmental scanning electron microscopy (ESEM) and digital image correlation (DIC) were used to measure microstrain distributions on the surface of wood pulp fibers. A loading stage incorporating a fiber gripping system was designed and built by the authors. Fitted to the tensile substage of an ESEM or a Polymer Laboratories MINIMAT tester, it provided a reliable fiber straining mechanism. Black spruce latewood fibers (Picea mariana (Mill) B.S.P.) of a near-zero microfibril angle displayed a characteristically linear load elongation form. ESEM was able to provide real-time, high magnification images of straining fibers, crack growth, and complex single fiber failure mechanisms. Digital images of single fibers were also captured and used for subsequent DIC-based strain analysis. Surface displacement and strain maps revealed nonuniform strain distributions in seemingly defect-free fiber regions. Applied tensile displacements resulted in a strain band phenomenon. Peak strain (concentration) values within the bands ranged from 0.9% to 8.8%. It is hypothesized that this common pattern is due to a combination of factors including the action of microcompressive defects and straining of amorphous cell-wall polymeric components. Strain concentrations also corresponded well to locations of obvious strain risers such as visible cell-wall defects. Results suggest that the ESEM-based DIC system is a useful and accurate method to assess and, for the first time, measure fiber micro-mechanical properties.
Cameron, R. E., and A. M. Donald. 1994. Minimizing sample evaporation in the environmental scanning electron microscope. J. Microscopy 173(3):227-237.nChu, T. C., W. F. Ranson, M. A. Sutton, and W. H. Peters. 1985. Applications of digital image conrrelation, techniques to experimental mechanics. Exp. Mech. Sept. 1995: 232-244.nFung, Y. C. 1965. Foundation of solid mechanics. Prentice-Hall, Englewood Cliffs, NJ. P. 525.nGroom, L. H., S. M. Shaler, and L. Mott. 1995. Characterizing micro- and macromechanical properties of single wood fibers. Pages 13-22 in Proc. 1995 International Paper Physics Conference. Sept. 11-14, Ontario, Canada.nIllston, J. M., J. M. Dinwoodie, and A. A. Smith. 1987. Concrete, timber, and metals. The nature and behavior of structural materials. Van Nostrand Reinhold, London, UK. P. 378.nJames, M. R., W. L. Morris, B. N. Cox, and M. S. Dadkhah. 1989. Description and application of displacement measurements based on digital image processing. Micromechanics: Experimental Techniques. ASMR-AMD 102:89-99.nKoran, Z. 1974. Intertracheid pitting in the radial cell walls of black spruce tracheids. Wood Sci. 7(2): 111-115.nLif, J. O., C. Fellers, C. Soremark, and M. Sjodahl. 1995. Characterizing the in-plane hygroexpansivity of paper by electronic speckle photography. J. Pulp Paper Sci. 21(9): 302-309.nMott, L. 1995. Micromechanical properties and fracture mechanisms of single wood pulp fibers. Ph.D. dissertation, University of Maine Dept. of Forest Management, Orono, ME. P. 198.nMott, L., S. M. Shaler, L. H. Groom, and B. H. Liang. 1995. The tensile testing of individual wood fibers using environmental scanning electron microscopy and video image analysis. Tappi 78(5): 143-148.nPage, D. H., and F. El-Hosseiny. 1976. The mechanical properties of single wood pulp fibres. Pt. 4: The influence of defects. Sven. Papperstid. 14: 471-474.nPage, D. H., and F. El-Hosseiny. 1976. The mechanical properties of single wood pulp fibres. Pt. 4: The influence of defects. Sven. Papperstid. 14: 471-474.nPage, D. H., and R. S. Seth. 1980. The elastic modulus of paper. 3. The effects of dislocations, microcompressions, curl, crimps, and kinks. Tappi 63(10): 99-102.nPage, D. H., F. El-Hosseiny, K. Winkler, and A. P. Lancaster. 1977. Elastic modulus of single wood pulp fibres. Tappi 60(4): 114-117.nPress, W. H., B. P. Flannery, S. A. Teukolsky, and W. T. Vetterling. 1990. Numerical recipes in C. The art of scientific computing. Cambridge University Press, Cambridge, UK. P. 735.nSheehan, G. S., and L. E. Scriven. 1991. Assessment of environmental scanning electron microscopy for coating research. Pages 377-383 in Proc. Tappi 1991 Coating Conference.nSiau, J. F. 1984. Transport processes in wood. Springer Verlag, Berlin, Germany. P. 245.nWu, E. M., and R. L. Thomas. 1968. Off-axis test of a composite. J. Composite Mater. 2(4):523-526.nWuu, F., R. E. Mark, and R. W. Perkins. 1991. Mechanical properties of cut-out fibers in recycling. Pages 663-680, vol. 2 in Proc. International Paper Physics Conf. Tappi Press, Atlanta, GA.n
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