Elastic and Shear Moduli of Poplar Heartwood

The elasticity and shear moduli of Populus canadensis were determined. Furthermore, the influence of annual ring width (ARW) on moduli was figured out. The diffraction between the heartwood and sapwood moduli was presented by comparing the reported data. The moduli were dynamically determined by ultrasonic testing and evaluation. The pressure (2.25 MHz) and shear (1 MHz) waves were propagated to obtain transmission time which was used to calculate ultrasonic wave velocities and then the moduli. The average ARW and density were 2.48 cm and 381 kg/m³, respectively. The average elasticity modulus in longitudinal (EL), radial (ER), and tangential (ET) directions, and shear modulus in LR (GLR), LT (GLT), and RT (GRT) planes were 4728 MPa, 1119 MPa, 407 MPa, 1102 MPa, 579 MPa, and 117 MPa, respectively. Either a good or moderate relationship between ARW and moduli was not observed by linear regression analysis. The literature says that the modulus of elasticity decreases with the increase in ARW. However, based on the comparison of reported sapwood to heartwood results of this study, ER, GLR, and GRT were increased with the increase in ARW. However, it should be noted that due to the absence of ARW-related EL, ET, and GLT values, a common expression is not valid, and a comparison needs to be made.