Measurement of Mechanical Properties and Constitutive Modeling of Woods

목재 물성 측정 및 변형 예측 모델 개발

Abstract

This study measured the mechanical properties of an ash wood under various temperature and humidity conditions and a finite element model was developed to predict the behavior of the wood. A humidity-controlled chamber was developed and used for measuring the dimensional changes of woods under various humidity conditions. The thermal expansion coefficient and the elastic stiffness constants were measured by using a thermal chamber and the three-point bending test along the three principal axes of the wood. A constitutive model was proposed to describe the moisture content and temperature dependent behavior of wood. The proposed model was validated for the warping test of a wood plate. The warping of the plate was calculated using the finite element method. The calculated amount of warping was in consistence with the measurements.

Fig. 1 The principal axes of wood

Fig. 2 Wood specimens

Fig. 4 Humidity in outer and inner chambers at the target humidity of 80%

Fig. 6 Evolution of strain with respect to the moisture content

Fig. 5 Weight during the drying test

Fig. 7 Strains at various temperatures along the three directions

Fig. 8 3-point bending test of wood specimens

Fig. 9 Warped wood specimen and the amount of warping

Fig. 10 Amounts of warping at various humidity conditions

Fig. 11 Finite element model

Fig. 12 Predicted equilibrium moisture content

Fig. 13 Annual zones and local orientations of the wood specimen

Fig. 14 Moisture content distribution of the deformed wood specimen at the humidity of 75, 85, and 95 % after 11 days

Fig. 3 Setup of the humidity chamber

Table 1 Hygroscopic expansion coefficients

Table 2 Thermal expansion coefficients

Table 3 Conditions for 3-point bending test

Table 4 Orthotropic elastic constants (MPa if apply)