Influence of Large Deflection on the Measurement of Bending Properties of Veneer by Three-Point Static Bending Tests

Hiroshi Yoshihara, Atsushi Itoh

Abstract


We conducted three-point bending tests of specimens with span/depth ratios larger than those used in the major standards, and examined the influence of deflection on the measurement of bending properties. The specimens were taken from Western hemlock (Tsuga heterophylla Sarg.) and buna (Japanese beech, Fagus crenata Endl.). Bending tests were conducted with the specimens whose span/depth ratios varied from 20 to 140. Bending stress was calculated by the equation based on elementary bending theory and that in which the influence of deflection is taken into account, whereas the strain at the center of the bottom plane was obtained from the deflection and strain gage output. The bending stress-strain relations obtained from the different procedures were compared with each other, and the influence of deflection on the measurement of bending properties—Young's modulus, proportional limit stress, and bending strength—were examined. In addition to the bending tests, simple numerical analyses considering the material nonlinearity were conducted, and the results were compared with those obtained from the bending tests. We found that the deflection had a small influence on the measurement of Young's modulus and proportional limit stress. In contrast, the bending strength obtained by elementary bending theory decreased when the span/depth ratio exceeded 100, whereas that given by the equation considering the deflection was stable throughout the span/depth ratio range examined here. The stress-strain relation given by the numerical analysis showed a rather good approximation of the one obtained from the bending test.

Keywords


Bending test;deflection;span/depth ratio;elementary bending theory;numerical analysis

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