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首页> 外文会议>International Symposium on Nondestructive Testing of Wood; 20000913-20000915; Sopron; HU >Evaluation of tools to measure sound velocity and stiffness of green radiata pine logs-Wood NDT 2000
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Evaluation of tools to measure sound velocity and stiffness of green radiata pine logs-Wood NDT 2000

机译：评估辐射松原木声速和刚度的工具的评估-Wood NDT 2000

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This paper describes a series of experiments to evaluate the characteristics of sound waves in green radiata pine logs and to compare sound wave prediction of timber grade recovery with predictions based on visual log measurements. First the radial variation of green density, dry density, modulus of elasticity and sound velocity were determined, using samples taken from three logs. The log density and modulus of elasticity for each series showed a large variation with radial position, while the sound velocity had a much smaller variation, although still substantial. Secondly, the type of wave propagation was established. When the endface of the logs was hit, the amplitude of the bulk wave was so small that it could not be detected at the opposite face. Instead, a single Young's modulus wave of large amplitude is generated and detected, and the velocity of this wave is governed by the average properties of sapwood, heartwood, juvenile wood and mature wood. The velocity is independent of the position of the transducers on the endfaces. The next step was to determine the variation of sound velocity along the length of the logs. A Fakopp was used to measure the variation of sound velocity with length along the tree by driving the transducers through the bark at distances of 1, 2, 3, 4 and 5 m apart. The sound velocity along each of three radiata pine logs was constant, which indicates there is little variation in stiffness along each log. Then the most suitable equipment and technique for determining the sound velocity along radiata pine logs was evaluated. The first technique measures the sound -velocity directly by measuring the transit time between two transducers at opposite ends of the log. The most suitable system consisted of a hybrid system consisting of a Metriguard hammer, a Fakopp timer and Fakopp receiving transducer. An alternative technique was also evaluated, the resonance technique, whereby the resonance frequencies of a log are determined and the sound velocity calculated indirectly. It is intrinsically more accurate. The sound velocity along the stems of 84 radiata pine logs has been measured with a Metriguard and the hybrid system. In addition, each log was excited into longitudinal vibration by impacting one endface with a hammer. The resulting waveform at the same endface was recorded. This was analysed by Fast Fourier Transformation. This yielded the first four longitudinal resonance frequencies. The sound wave velocity was calculated from the first three resonance frequencies. The logs were assessed for quality by measurement of the small and large end diameters, Pilodyn penetration, sound velocity and branch index (BIX). The logs were sawn into boards whose modulus of elasticity (MOE) was determined, and the average MOE of each log was calculated. The highest correlation between sound velocity and log MOE occurred for the hybrid system, with R~2 = 0.65. The vibration technique with FFT analysis yielded velocity values for the first three resonances that correlated to the log MOE with similar R~2 values of 0.62, 0.70 and 0.66 respectively. This technique is superior to the others in that excitation and detection occur at the same endface, so that only one operator is required. In addition it gives additional information and eliminates a systematic error associated with the rise time of the waveforms used for transit time measurement.
机译：本文介绍了一系列实验，以评估绿色辐射松树原木中的声波特性，并将木材品位恢复的声波预测与基于视觉测井测量的预测进行比较。首先，使用取自三个测井的样本确定绿色密度，干密度，弹性模量和声速的径向变化。每个系列的对数密度和弹性模量显示出随径向位置的较大变化，而声速的变化较小，尽管仍然很大。其次，建立了波传播类型。当碰到圆木的端面时，体波的振幅是如此之小，以至于在相对的面都无法检测到。取而代之的是，生成并检测到一个大振幅的杨氏模量波，该波的速度由边材，心材，少年木材和成熟木材的平均特性决定。速度与换能器在端面上的位置无关。下一步是确定声速沿原木长度的变化。 Fakopp通过驱动换能器以1、2、3、4和5 m的距离穿过树皮来测量沿树的声速随长度的变化。沿三个辐射松原木的声速是恒定的，这表明沿每个松木的刚度变化很小。然后评估了确定沿辐射松原木声速的最合适的设备和技术。第一种技术是通过测量在对数两端的两个换能器之间的传播时间直接测量声速。最合适的系统由混合系统组成，该混合系统由Metriguard锤，Fakopp计时器和Fakopp接收传感器组成。还评估了另一种技术，即共振技术，从而确定了对数的共振频率并间接计算了声速。从本质上讲，它更准确。使用Metriguard和混合系统测量了84幅辐射松原木茎上的声速。另外，通过用锤子冲击一个端面，将每个圆木激发成纵向振动。记录在相同端面上的结果波形。通过快速傅立叶变换对此进行了分析。这产生了前四个纵向共振频率。根据前三个共振频率计算声波速度。通过测量小直径和大直径，Pilodyn针入度，声速和分支指数（BIX）来评估原木的质量。将原木锯成板，确定弹性模量（MOE），然后计算每个原木的平均MOE。混合系统的声速与log MOE之间的相关性最高，R〜2 = 0.65。带有FFT分析的振动技术产生的前三个共振速度值与log MOE相关，R〜2值分别相似，分别为0.62、0.70和0.66。该技术优于其他技术，因为励磁和检测都在同一端面进行，因此只需要一名操作员。此外，它还提供了更多信息，并消除了与用于渡越时间测量的波形的上升时间相关的系统误差。

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