Determination of shear modulus of some wood species using ultrasonic and static test methods

In this study, shear modulus of Calabria pine, Black pine and Scots pine wood, one of the elastic constants of wood material, were determined using static and dynamic test methods. Tress species are native to Turkey and in the top tree according to area coverage. Also they are commonly used in woodworking industry. Because of these reasons these species were chosen. Calabria pine and Black pine logs were obtained from Isparta while Scots pine logs were obtained from Bolu. All logs were sawn into timber in Isparta and dried till the EMC. Destructive and non-destructive test samples were prepared using dried timber. All the samples were acclimatized at constant temperature at 20±1°C and 45%, 65%, 75% and 85% relative humidity (RH) conditions in a climate chamber to determine the effect of moisture content (MC) on shear modulus. Densities of the samples were determined according to TS2472 standard. Non-destructive measurements performed using Olympus EPOCH 650 ultrasonic flaw detector and shear transducer that propagates 1MHz frequency. Dynamic shear moduli were calculated by related formulas using obtained time of flight values. 26 surface polyhedral samples used to perform non-destructive tests. All terms of elasticity matrix can be obtained on only one sample which has this type of geometry and shear moduli which are the diagonal terms of this matrix obtained in this study. Destructive test were conducted by off-axis compression test. Universal test machine with 5 tons load cell was used to perform compression test. Stress-strain values were obtained using bi-axial extensometer while performing compression test. Static shear moduli were calculated using these stess-strian values using related formulas. Obtained values that used to predict and calculate the dynamic and static shear moduli were statistically analyzed using IBM SPPP v20 and MS Office software used to create tables and graps that present the results. Maximum 15.18% difference between static and dynamic shear values obtained at the end of study. Maximum difference was calculated for LT plane shear modulus of Scots pine wood which acclimatized at 85% RH. According to the literature, dynamic shear modulus values are generally higher than static ones and difference between dynamic and static shear modulus is generally about 20% but this difference can reach up to 40% in some cases. According to results, moisture dependent shear moduli of Calabria pine, Black pine and Scots pine wood, which were not in the literature, determined and it is proved that ultrasonic measurement is applicable to predict these values by reasonable differences. Consequently, it can be said that, ultrasonic measurements provide some contributions to predict shear behaviour of structures or structural designs without any destruction to ensure whether they are safe of not. Furthermore, FEA of off-axis compression samples performed using density and shear moduli values of Black pine, Calabria pine and Scots pine that determined by static method. And then load-deformation behavior of models proved. Other elastic constants, Young's moduli and Poisson ratios, required for FEA were obtained from the literature. Load-deformation curves that obtained by static tests transformed into stress-strain curves and they compared with the stress-strain lines that obtained by FEA. And, it's determined that FEA results fairly agreed with the static test results.