Testing of individual fiber-fiber joints under biaxial load and simultaneous analysis of deformation

Abstract In this paper a novel direct method for mechanical testing of single fibers and fiber joints is presented. Additional to the measurement of joint strength it is also possible to investigate loading geometry, deformation during testing, bending stiffness of fibers as well as bonding energy. Furthermore biaxial loading of fiber-fiber joints is possible. Initial experiments have shown that mode II and III shear strength of fiber-fiber joints can be measured with this setup. Initial results for fibers and fiber joints of unbleached softwood kraft pulp are presented. The resulting values are 1.1724·10^-9to 3.8798·10^-11Nm² for bending stiffness, 3.9180·10^-10to 2.8793·10^-11kJ/bond for bonding energy, 6.54 mN for mode II and 1.057 mN for mode III mean shear strength. Mode II mean shear strength under biaxial load with a preload of 20 mN perpendicular to the loading direction of the fiber-fiber joint was found to be 2.52 mN. These values are compared to results of other measurement techniques and discussed.