Non destructive evaluation of mechanical properties by vibration

通过模态分析、振动强度分析和声强分析对木材的力学性能进行了研究。从木材的自振模态和振动/声能流的形态考察木材材料评价的可能性。得到了以下结果：(1)当木材中存在结时，木材的自振模态形状发生了很大的变化。(2)振动能量从冲击力位置沿逆时针方向向周边扩散。在低振型情况下，振动能量矢量的流动呈旋流状并沿振动节线行进。另一方面，在振动模态较高的情况下，振动强度主要发生在振型的腹部。据此，可以得到与某一特征振动模态相对应的振动能量的流动，从而显示振动能量的发生、传播和消耗情况。振动强度分析表明，有可能进行材料评价。(3)声强与固有振动模态的对应性较好。木材的材料评价可以用声强法进行评价。在高振型下，辐射的声能跨越节点线，声能从宽辐射区向窄辐射区流动。据推测，它可以通过声强法来评估乐器的辐射、效率、指向性等声音特性。

The mechanical properties of wood were investigated by mode analysis, vibration intensity analysis and sound intensity analysis. The possibility of material evaluation of lumber examined from the shape of natural vibration mode and vibration/sound energy flow. The following results were obtained.(1) With the existence of a knot in a lumber, the shape of natural vibration mode changed largely.(2) Vibration energy spread toward periphery in the counterclockwise direction from a impacting force position. In the case of lower vibration modes, the flows of vibration energy vector draw the swirl shape and traveled cross the vibration nodal lines. On the other hand, in the case of higher vibration modes, vibration intensity mainly occurred in the abdomen of vibration mode. Accordingly, the flow of vibration energy corresponded to a characteristic vibration mode and a situation of occurrence and spread and consumption of vibration energy might be shown. A vibration intensity analysis could be suggested that there was the possibility of material evaluation.(3) The sound intensity corresponded to the natural vibration mode very well. The material evaluation of wood could be evaluated by the sound intensity method. The sound energy radiated cross the nodal lines and the flows of sound energy from wide radiation area to narrow radiation area in the case of higher vibration mode. It was guessed to be the one that is able to evaluate a sound characteristic such as the radiation the efficiency, the directivity of a musical instrument by the sound intensity method.