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.