Moisture dependent elastic constants of particleboard layers by ultrasound and compression tests

Elastic constants of particleboard layers were investigated using by means of ultrasonic waves and compression tests under different humidity regimes. Three Young’s modulus, three shear modulus and six Poisson ratios were determined. Three longitudinal and six shear wave velocities propagating along the principal axes of anisotropy, and additionally, three quasi-shear wave velocities at 45° angle with respect to the main axes of anisotropy were measured. Compression tests were also conducted in order to measure the accuracy of ultrasonic method. Comparing with calculated values, the predicted Young’s modulus values in the principle directions are acceptable. The shear values calculated using ultrasonic method are higher than those determined from compression tests, particularly in the perpendicular directions. Some of the Poisson’s ratios predicted by ultrasound seem to be extreme. The influence of moisture content on Poisson’s ratios is variable. It can be concluded that ultrasonic method can be used as alternative in determination of elastic modulus for particleboard layers at different moisture conditions. The accuracy of ultrasound for determining the Poisson’s ratios of particleboard layers is questionable.

Experimental and numerical studies on mechanical behaviors of beech wood under compressive and tensile states

Effect of loading type (compression and tension) on mechanical properties, including elastic constants, yield strength and ultimate strength of beech (Fagus orientalis) wood were studied based on experimental and numerical methods. The mechanical behaviors of beech wood in compressive and tensile states were simulated by finite element method (FEM) using mechanical parameters measured in an experiment. The results showed that the effect of loading types on mechanical properties of beech was statistically significant. The elastic moduli measured in tension were all bigger than those in compression, but the Poisson’s ratios determined in compression were bigger than those in tension. In compressive state, the yield and ultimate strengths of beech in longitudinal grain orientation were all smaller than those measured in tensile state, while the yield and ultimate strengths of beech in radial and tangential directions were higher than those of longitudinal direction. The results of the FEM in compression and tension were all well consistent with those measured by experiments respectively, and the average errors were all within 13.69%. As a result, the finite element models proposed in this study can predict the mechanical behaviors of wood in tensile and compressive states.