Measuring elastic constants of wood through static bending using a strain gauge

Wood has important engineering applications. However, some important parameters required in numerical simulations or engineering calculations, including the true longitudinal bending elasticity E-L and shear modulus G(LT) and G(LR), remain difficult to measure accurately. According to Timoshenko's beam theory, the total deflection of a beam under conventional center loading is affected by both bending moment and shear force. Therefore, E calculated from the total deflection is an apparent value. In addition, the measurement of G is difficult, and previously used methods may be insufficient. This study proposed a method that can measure E and G directly and accurately using a strain gauge and dial gauge simultaneously under a fixed span/depth ratio. The measured E and G values were compared with those obtained indirectly by adjusting the span/depth ratio and those measured using a four-point loading test. As a result, this method could be used to measure E and G accurately for wood in a standard bending test with standard specimens with span/depth ratio equal to 14. Other factors such as local indentation caused by the loading point, regression deviation caused by a change in span range, and influence of the selection of strain levels were also discussed.

Automated summary

Wood is widely used in engineering, but accurately measuring parameters such as longitudinal bending elasticity and shear modulus remains challenging. This study proposes a method using strain gauges and dial gauges to directly and accurately measure these parameters, providing a reliable way to assess the elastic and shear properties of wood.