Some Mechanical Properties of Wood Fibers in Tension

Using an electrical-mechanical system for measuring force and deformation, it was possible to determine the load-deformation properties of single fibers of wood. The data from tests of fibers of ten species of coniferous trees demonstrated not only vast differences between fibers of different species but also frequently between early and latewood fibers of a single species. Air-dried stock of the ten species, each exhibiting 10 to 20 growth rings per radial inch, were pulped using a technique developed by Spearin and Isenberg. The technique produces a fiber virtually free of lignin while maintaining the essential structure of the cellulosic portion of the cell wall. Using jeweler’s tweezers, unbroken fibers, free of cell wall damage, were picked from a dilute slurry by grasping one end. Common sythentic adhesives which set by polymerization were found suitable for bonding the ends of fibers to small wires. Subsequently the fiber and wires were placed in a testing machine, and a tensile force was applied to the fiber through the wires bonded to each end. Using the load-deformation relationship, tensile strength, Young’s modulus, proportional limit stress, deformation at failure, and work to failure were computed for each fiber. For the most part, stress-strain curves were linear to stresses in the range of 50 to 70 percent of maximum. At this point proportionality between force and deformation ceased and deformation increased at an increasing rate.

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