Strain method for synchronous dynamic measurement of elastic, shear modulus and Poisson’s ratio of wood and wood composites

Abstract

In this work, the principle and method for synchronous dynamic measurement of elasticity, shear modulus and Poisson’s ratio of wood and wood composite with two strain gauges were studied and discussed. The experimental scheme, named 0°–75° scheme, was developed for synchronous dynamic measurement of elasticity (E), shear modulus (G) and Poisson’s ratio (μ) with two strain gauges of 0° and 75°. The 75° strain gauge was not only used to measure Poisson’s ratio together with the 0° strain gauge, but also to measure the first-order torsional frequency of cantilever plate. In addition, the principle of measuring elasticity and shear modulus by the 0°–75° scheme was described. Based on the stress and strain analysis of first-order bending and torsional modes of cantilever plates, the pasting position and orientation of strain gauges in the 0°–75° scheme were decided. Comparing the results of using two combinations of strain gauges, 0°–75° and 0°–90° schemes, the correspondence indicates that the 0°–75° scheme is feasible for dynamic measurement of Poisson’s ratio. By transient excitation, the strain spectrums under 0° and 75° of Poplar’s tangential section, Sitka spruce’s radial section and medium density fiberboard (MDF) cantilever plate were measured. Thus, one-hammer-excitation synchronous measurement of elasticity, shear modulus and Poisson’s ratio of materials was achieved. Its correctness was verified by axial tension and static square-plate torsion tests.