The Study Of Detection Of Hole Defects In Log Based On Stress Wave Reflection Method

The inner defects of the logs affect the effective utilization directly. So the effective defectdetection for logs has a big significance. In order to detect the holes in log effectively, the stress wavereflection method was used to detection the defects in log’s longitudinal direction. The position and thesize of the holes were analyzed by means of the stress wave signals.First, according to the structure and material property of log, stress wave propagation process inlongitudinal direction in log was analyzed. Treating the log as a one-dimensional bar, stress wavepropagation process in log was simplified. Then, the pine logs were modeled by FEM and the differentposition and size holes in the pine log were detected. Eventually, the stress wave reflection method wasused to detect man-made holes in the pine logs and natural-hole in a camphor log to verify thetheoretical analysis and the simulation results.Major achievements:1. Treating the propagation velocity between the log ends as the reference velocity, the position andsize of holes were analyzed by the frequency domain information of stress wave, and the calculationexpressions of the hole’s position and size were mentioned.2. The orthotropic pine log was modeled by the unit solid185, and the simulation test was performed.The stress wave signals from simulation were same as the experiment’s, which shows FEMsimulation of the stress wave reflection method was successful.3. Simulation and experiment results show the distance between the test end and the hole position formtest is farther than the actual distance. The error increases with the size of the hole, and the errorvalue is within12%. That the size of the hole in log can be estimated by resonant amplitude formedby reflected wave from the hole.