Quantitative Detection Of Log And Plate Cavity Defect Based On Ultrasonic Propagation Field

In order to give a deep analysis of ultrasonic wave propagation in wood and enrich the propagation theory, which can provide theoretical basis and relevant guidance for applying ultrasonic wave in wood physical properties testing and deficiency detecting, the strain, stress, velocity and displacement equations of ultrasonic wave propagation in wood were theoretically derived. The concept of propagation field was put forward. Then, taking cross-section of log, with diameter of38cm, and thickness of10cm, and radial section of plate with length of34cm, width of28cm and thickness of7cm as test material, based on grid points test method and MATLAB software programming, the transmission of ultrasonic wave was simulated using RSM-SY5non-metallic ultrasonic detector. Thus, the ultrasonic wave propagation field was verified. Then the influence of different size cavity defect on the propagation field of both log and plate was discussed. And finally, based on the propagation field figures of different directions and MATLAB software programming, the cavity defect was quantitatively detected. Research results show that:The propagation of ultrasonic wave in non-defect wood is in the type of field. When the ultrasonic wave transmits in the cross section of log, the wave velocity is faster in radial direction. And the propagation field curves is symmetrically distributed with x=0(which is the emitting direction of ultrasonic wave) as axis. When it transmits in radial section of the plate, the propagation curve is sharp and narrow in grain direction. But in stripe direction it is more flat and smooth. The ultrasonic wave velocity in grain direction is about1.8times of that in stripe direction.Cavity defect has significant influence on ultrasonic wave propagation field in wood. In cross-section of log, as the diameter of cavity increases, the propagation field curves that are passing the defect show an inward contraction tendency; as to the one that has already passed through, the curves present the shape of high in the two ends and low in the middle. To observe the propagation field as a whole, it shows a "lagging behind" phenomenon led by the cavity. In radial direction of plate, when the wave passes through defect, two "vortex" circular areas will appear in grain direction; and in stripe direction, the curves behind cavity present an arc shape bend to the reverse direction of launch point.The overlying of ultrasonic propagation field figures can be used to detect internal defect of wood quantitatively. The detection accuracy of cavity diameter of4cm,8cm,12cm,16cm and20cm is respectively83.2%,84.8%,94.0%,95.8%and96.2%. And the accuracy of cavity defect area of64cm2,128cm2and192cm2in plate is88.9%,89.4%and92.6%.The overlying of ultrasonic wave propagation field figures from different directions can not only judge the size and position of log internal defect, but identify the shape as well.