Characterization Methods for Elastic Properties of Wood Fibers from Mats for Composite Materials
Keywords:Wood fiber, stiffness, fiber mat, test methods, composites
AbstractWood fibers offer excellent specific properties at low cost and are of interest as reinforcement in composites. This work compares two alternative test methods to determine the stiffness of wood fibers from simple macroscopic tests on fiber mats. One method is compression of the fiber mat in the thickness direction, which uses a statistical micromechanical model based on first-order beam theory to describe the deformation. The other method is tensile testing of fiber mats and back calculation of the fiber stiffness with a laminate model. Experiments include compression tests and tensile stiffness index tests as well as determination of fiber content, orientation, and dimensional distribution. For mats with unbleached softwood kraft fibers, an effective value of the Young's modulus of 20.1 GPa determined by the compression method can be compared with values of 17.4-19.0 GPa obtained from tensile tests. These are in agreement with values for similar cellulosic fibers found in literature. The compression method is more appropriate for low-density fiber mats, while the tensile test works better for well-consolidated high-density fiber mats. The two methods have different ranges of applicability and are complementary to one another. Limitations of the methods are also discussed. The main advantage of the methods is that they are quantitative. The potential as stiffening reinforcement of various types of fibers can be systematically investigated, even if the fiber mat microstructures are different.
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