中文摘要：

【目的】研究应力波在不同树木径切面内传播速度的变化情况,建立传播速度模型,以期进一步认识应力波在树木径切面内的传播规律及其影响因素,为树木内部缺陷的三维成像技术提供理论依据。【方法】首先通过理论分析,建立应力波在树木径切面内的传播速度模型;然后以浙江农林大学植物园内8类有代表性的树种（香樟、枫香、乐昌含笑、鹅掌楸、响叶杨、悬铃木、松树、白杨）为试验材料,在样本径切面上,采用Arbotom应力波木材无损检测仪测量与径向成不同角度方向的应力波传播时间,计算不同角度方向上的应力波传播速度,并对健康样本径切面内沿方向角θ的应力波速度vθ和径向应力波速度v0的比值vθ/v0与方向角θ之间的关系进行回归分析。【结果】应力波在健康香樟样本径切面内的传播速度随方向角的增大而增大,径向传播速度最小,其原因是当应力波在树木内部沿径向传播时,传播方向与树木纤维方向垂直,受到细胞壁边界的阻碍较多,传播速度较慢;而随着方向角的增大,应力波传播方向与树木纤维方向逐渐平行,受到细胞壁边界的阻碍变少,传播速度逐渐增加。枫香、乐昌含笑、鹅掌楸、响叶杨4种树种的健康样本在相同方向角上的应力波传播速度大小不同,但其变化规律与香樟活力木相同。对健康样本试验数据的拟合结果为vθ/v0≈kθ^21（0≤k≤1）,k值取决于被测树木的物理力学参数。在所建立的回归模型中,决定系数R2均大于0.92,表明模型具有较高的拟合优度。在有缺陷的悬铃木样本试验中,径切面上方向角为-20°~-50°的应力波传播路径经过缺陷区域,其余传播路径均位于健康区域内。当应力波传播路径位于径切面的健康区域时,传播速度随方向角的变化趋势满足一元二次函数模型;但当应力波经过径切面的缺陷区域时,传播速度明显降低,不?

英文摘要：

【Objective】Standing trees of different species were selected as samples to study the stress wave propagation velocity pattern in the RL（ radial and longitudinal） plane of wood so that the rule of stress wave propagation can be understood well,and the theoretical basis of three dimensional imaging of wood internal structure can be improved.【Method】Firstly,an analytical stress wave velocity model in RL plane of wood was derived. Then eight standing trees of different species（ Cinnamomum camphora,Liquidambar formosana,Michelia chapensis,Liriodendron chinensis,Populus adenopoda,Platanus sp.,Pinus sp.,and Populus alba） at the university arboretum in Zhejiang Agricultural and Forestry University were selected as samples for nondestructive evaluation experiments. Arbotom detector was used to measure the stress wave velocity at different grain angles in the RL plane of specimens. For the healthy samples of standing tree,theregression analysis about the ratio of the velocity vθalong the direction angle θ and the radial velocity v0 was finished.【Result】In the RL plane of healthy trees,stress wave velocity increased with direction angle θ becoming larger,and the wave velocity along the radial direction was the smallest. The radial direction angle θ = 0. When θ increased gradually,the stress wave velocity became faster and propagated parallel to the grain gradually. For the same direction angle θ,the stress wave velocity vθwere different in different standing trees. Generally,the relationship between the direction angle θand the ratio vθ/ v0 approximated to a quadratic function vθ/ v0≈ kθ^2 1（ 0≤ k ≤1）,and k depended on the physical and mechanical properties of wood. For all the regression models of different samples of standing trees,the coefficient of determination R2 was higher than 0. 92. The regression results demonstrated the effectiveness of the analytical stress wave velocity model. In order to evaluate the effectiveness of above mentioned model,two other experiments on Platan