Stress Wave Propagation Velocity Model In RL Plane Of Standing Trees

How to protect and make use of existing forest resources, improve the utilization of wood has become the focus of foresters, therefore, stress wave nondestructive testing technology has been rapid development. The theory research of stress wave propagation is the premise of stress wave nondestructive testing technology. In this paper, Standing trees of different species were selected as samples for studying the stress wave 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. The main contributions of this paper are given as follows.1. An analytical stress wave velocity model in RL plane of wood was derived. Then standing trees of different species 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 on the RL plane of specimens, then the regression analysis about the ratio of the velocity V? along the direction angle ? and the radial velocity V0 was finished. Generally, the relationship between the direction angle ? and the ratio V?/V0 approximated to a quadratic function V?/V0 ? k?2+1(0? k ?1), and k depends on the 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.2. At different heights of healthy trees, different knocking forces were applied for experiments. The experiment result showed that the model proposed was not influenced by height and knocking force. In the RL plane of defective samples, some stress wave propagation paths traversed through the decay area, and the wave velocities didn’t accord with above mentioned mode for these paths.3. Finally, based on the proposed longitudinal wave velocity model, a four direction cross-testing method was presented, which can detect the location of internal defect of wood, which showed that the proposed wave model can help detect the internal defects of trees.