不同应力状态下榉木弹性常数的研究

Study on elastic constants of beech in different stress states

采用电测法,对榉木在不同应力状态下的弹性常数进行了研究。分别对榉木在压缩、拉伸以及弯曲3种应力状态下的弹性常数进行了测量,并对其进行了对比分析。结果表明:在拉伸状态下,木材各主轴方向的弹性模量EL、ER和ET均大于压缩状态下的弹性模量,分别为12%,9%和36%,但泊松比均小于压缩状态,并且泊松比URL和UTL大致相同,但ULR与ULT却存在较大差异。而在弯曲状态下,抗弯弹性模量随着跨距的增大而增大,且呈幂函数变化关系,径向、弦向的抗弯弹性模量与跨距拟合方程的相关性系数均达到0.99以上。同时,通过抗弯弹性模量计算得到的剪切模量GLR、GLT与压缩状态下通过电测法测得的结果存在较大差异,误差分别为212%和167%。因此可得出,通过抗弯弹性模量间接计算得到的剪切模量并不准确。在不同应力状态下木材的弹性常数存在较大差异,故在对木制品及木结构进行设计及数值计算时,应充分考虑木材在不同受力状态下弹性力学特性的差异。

The aim of this paper was to study the influence of different stress states on elastic constants. The elastic con- stants of beech （Zelkova serrata （Thunb.） Makino ） in compress, tensile and bending states were measured by electric resistance strain gauges method, and then the results were compared each other in details. All specimens were processed by Yuli WPC CNC machine with 0.01 mm accuracy. The strain was tested by the static data acquisition in- strument TDS530 with the strain gauge BFH120-3AAOD100 （ 120- 1 ） -. Besides, the size of specimens and tested methods were all in accordance with the national standards. Finally, the experimental data were collected and analyzed by using the Origin software. The results showed that, in tensile state the elastic modulus in three principle directions of wood EL, ER and ET were higher than those in compression state by the percentage of 12%, 9% and 36%, respec- tively. Inaddition, the Poisson＇s ratio URL was nearly consistent with UrL, but the ULR and ULT were distinctly different in two stress states. In addition, the bending modulus of elasticity increased with the increase of the span length with a relationship of power function, and the correlation coefficient was all higher than 0.99 in radical and tan- gential directions of wood. Besides, the shear modulus GLR and GLT worked out by bending modulus of elasticity were much lower than that measured by the electric resistance strain gauges in compression state, and the errors were 212% and 167% respectively. In conclusion, the shear modulus figured out by bending elastic modulus was not accurate, and the elastic modulus of wood were not in agreement in different stress states, which should be well considered when wood products and wooden structure were designed and numerically analyzed.