Non-Destructive Measurement of the Modulus of Elasticity of Wood Using Acoustical Stress Waves

Abstract

Many biomechanical models include modulus of elasticity (E) but it is not always available in the literature. It would be useful to directly measure E for species, and one of the standard techniques for doing so is to utilize a universal testing machine (UTM). While laboratory testing can determine static flexural modulus of elasticity using a UTM, it requires destructive sampling and therefore is only useful after a tree or limb has been removed. Acoustic testing can be used to estimate the dynamic modulus of elasticity (DMOE) of wood, by measuring the speed of sound through a sample of wood without the need to remove any wood samples. This research investigated if acoustic testing can be used to accurately estimate the modulus of elasticity of green wood. Stump sprouts arising after a shelterwood harvest were cut and left at room temperature (21.1°C, warm) or conditioned to -6.7°C (frozen). The modulus of elasticity was measured using a stress-wave timer (DMOE) and a UTM (ES). The DMOE was higher in the frozen samples, but temperature did not affect ES. While the stress-wave timer used in the study found a slightly higher E than a UTM, a simple prediction equation was determined for converting the results. Researchers believe tools such as this can be successfully utilized by the arboriculture industry to rapidly assess the modulus of elasticity of standing trees in the field.