Measurement of Young's Modulus and Poisson's Ratio of Wood Speciments in Compression Test
Koji MURATA and Hideaki TANAHASHI
Abstract:For the purpose of obtaining shear modulus, axial, transverse and 45 degree off-axis compression test for wood specimen were performed to measure Young's modulus and Poisson's ratio. Strain was measured using a strain gauge and an extensometer, and deformation of specimens was observed using a digital image correlation (DIC) technique. The precision of the test was determined by the finite element method. The following conclusions were made. The nominal Young’s modulus obtained from the distance between compression jigs was estimated to be smaller than that obtained using the strain gauge and extensometer. This was because large compression deformations occurred in the local area in contact with the jigs. The Poisson’s ratio obtained for the off-axis specimen was negative. The Poisson’s ratio obtained by Cauchy’s transformation rule and the finite element method using mechanical properties cited in literature was also negative. Off-axis specimens were observed to undergo arc-shaped or S-shaped deformation by compression. Constraint on the jigs probably affected the deformation and resulted in the generation of improper shear stress in the specimen. This constraint was thought to be related to the compliance component C16 of Cauchy’s transformation. The component of the cited properties has the maximum value under an off-axis compression of approximately 45°, and the value of the component under an off-axis compression of 15° is 22-69% of the maximum value. We propose that the optimum off-axis angle for obtaining the desired shear modulus probably is approximately 15° for the cited three species. Key Words:Wood specimen, Shear modulus, Young's modulus, Negative Poisson's ratio, 45° off-axis compression,