ON MEASURING THE ELASTIC AND DAMPING CONSTANTS OF ORTHOTROPIC SHEET MATERIALS

Many common sheet materials, ranging from natural materials such as wood to modern composites, possess approximately orthotropic symmetry. Within the approximations of thin-plate bending theory, the linear vibrational properties of such sheets are governed by four elastic constants and four damping constants (at any given frequency). A simple procedure is presented whereby all four elastic constants may be determined from measurements of the resonant frequencies of low-frequency modes of thin rectangular plates with free edges. Also, at least three of the four damping constants may be determined by measuring the damping factors of the same modes. The procedure is illustrated with measurements on wooden plates cut at different angles from the solid timber, plywood, and two different fiber-reinforced composites. The procedure could form a part of any program of quality control, material selection or non-destructive testing involving orthotropic sheet materials.