Observation of crack propagation in non-metals and fracture mechanism

利用光学系统可以高分辨率地测量裂纹的传播速度，因为当光束斜入射到透明固体中非常平坦的裂纹面上时，它可以在裂纹面上完全反射。本研究的目的是了解固体中的断裂机制。高速响应的光学方法已经建立，然后我们计划用补助金一起观察裂纹尖端的形状。该仪器主要测量了NaCl单晶中的裂纹扩展，并以0.1 μ c的分辨率观察了裂纹尖端形状的变化。第一年，我们将平行激光束分成长激光束和窄激光束，并利用多通道波存储器构建光学系统，同时测量每束光强的变化。在去年，通道的数量从4个增加到8个，但由于高频率和幅值的光传感器相互设置在狭窄的空间中，通道之间的干扰很难消除。通过对NaCl单晶中裂纹扩展的观察，我们明确了以下几点：裂纹扩展在空间和时间上都不均匀。那就是；裂纹扩展的起裂发生在局部，并通过其扩展进行。在某些情况下，裂纹的一部分可能很晚才开始扩展。裂纹扩展速度往往在裂纹扩展开始后立即达到最大值（约1000m/sec），裂纹扩展也有开始时速度较低，后期速度较高的现象。对于作为本计划目标之一的半导体裂纹扩展的观察实验，由于激光束的不均匀性，测量不能以足够的分辨率运行。

The propagation velocity of crack can be measured with high resolution with a optical system because when a light beam incidents obliquely on a very flat crack plane in a transparent solid, it can be totally reflected at the crack plane. The objective of this study is to understand the fracture mechanism in solid. The optical method with high-speed response has already been established, then by using the grant we planed to observe the shape of the crack tip together, too. With this apparatus the crack propagation mainly in NaCl single crystals was measured and the change of the shape of the crack tip was observed with 0.1 musec resolution.In the first year, we divided the parallel laser beam into several long and narrow ones and constructed the optical system by using a multi-channel wave memory to measure the change of the intensity of every light beam at the same time. In the last year, the number of the channels was improved from 4 to 8, although it was very difficult to eliminate the interference among the channels because the photo sensors with high frequency and the amplitudes are set up in narrow space each other. By the observation of crack extension in NaCl single crystals, we made the following clear. Crack extension is not uniformly both spatially and temporally. That is ; the initiation of crack propagation occurs locally and proceeds through its expansion. In some cases, one part of the crack may begin to propagate very late.The crack velocity often reaches the maximum value (about 1000m/sec) immediately after its initiation of propagation and crack can also propagate, on the other hand, at the lower speed at the beginning and at the upper later. For the experiment of the observation of the crack propagation in semi-conductor that is one of the objective of this plan, the measurements could not be run with adequate resolution because of lack of uniformity of the laser beam.