Experimental Studies on Three-dimensional Stress Fields near Fast Propagating Crack Tips by means of Pulses Holographic Microscopy

快速传播裂缝经常出现当一个小材料板被外部张力力破坏时。裂缝是以各种百米/秒的速度传播的开放模式和传播的。压力场周围的裂缝尖端满意度是该地区的平面压力状况，与尖端有一定的距离。无名氏，压力场有两个--尺寸的。压力场， However，Show Three-dimensional （3-d） Nature in the Crack Tip小材料的断裂实际上在三维压力场中出现，因此，它对使三维压力场结构清晰很重要。确切地说，我们已经开始研究实验性的研究，这些研究集中在下面的三点上。（1）三维场从快速传播裂缝尖端传播到多远？（2）三维场的表面单一性和快速传播裂缝的裂缝前边缘角之间的关系是什么？（3）快速传播裂缝在三维领域和在三维领域是什么形状的 ... More 那个特别的人？作为一个结果，我们得到了以下的合并。（1）三维压力场扩散到目前为止，大约是特殊物质从裂缝尖端的一半厚度，在从裂缝传播方向的72度的方向上。Shimizu和Shimada （1978年）、Shimada和Sasaki （1983年）、Shimizu等人（1985年）和Rosakis和Ravi-Chandar （1986年）的《固定裂缝》的结果是一样的。可以，顺便说一下，可以说，在三维压力场的范围内，它是独立于裂缝速度的。而且这也是显而易见的，因为三维场的面积是特殊厚度的独立性。（2）在一个特殊的表面上，快速传播裂缝的裂缝打开置换（COD）可能是从裂缝尖端到方形根的距离r，甚至在三维压力领域。这意味着三维场的表面单一性是1/<square root>r。结果与Bazant和Estensoro的理论结果达成一致，缓慢传播裂缝（1979年）。1/ r的单一性是<square root>Hence，是crack speed的独立性。裂缝的前边缘角不是一个正确的角度，而是一个缺点。在这种情况下，裂缝速度相对较低，裂缝前边缘角度不是正确的角度，而是使用。在这种情况下，破解速度相对较低，破解前边缘角与Bazant和Estensoro的数字结果达成了一致，以缓慢传播破解（1979年）。但是，裂缝的前端边缘的退化和方法是正确的角度，因为裂缝的速度增加。它可以，所以，可以说，在命令保持表面的单一性成为1/<square root>r时，当裂缝速度变化时。（3）裂缝打开的置换是从裂缝前缘距离的正方形根，不仅仅是在一个特定的表面上，但也是在一个特定的平面上。而中间平面上的动态压力强度因素的价值几乎是相同的，因为它在一个特殊的表面上。Less（低）

A fast propagating crack often appears when a plate of brittle material is broken by external tensile force. The crack is of the opening mode and propagates at a speed of several hundred m/s. The stress field around the crack tip satisfies the plane stress condition in the region a certain distance away from the tip. Namely, the stress field is twoーdimensional there. The stress field, however, shows threeーdimensional (3-d) nature in the vicinity of the crack tip. Fracture of brittle materials actually occurs in the 3-d stress field, therefore, it is important to make the structure of the 3-d field clear. Accordingly, we carried out the experimental studies which were focused on the three point described below.(1) How far does the 3-d field spread from the fast propagating crack tip?(2) What relation is between the surface singularity of the 3-d field and the crack front edge angle of the fast propagating crack?(3) What shape does the fast propagating crack have in the 3-d field and in … More the specimen?As a result, we obtained the following conclusions.(1) The 3-d stress field spreads as far as about half of the specimen thickness from the crack tip, in the direction of 72 degrees from the propagation direction of the crack. The result is same as that on a stationary crack which was shown by Shimizu and Shimada (1978), Shimada and Sasaki (1983), Shimizu et al. (1985) and Rosakis and Ravi-Chandar (1986). It can, consequently, be said that the extent of the 3-d stress field is independent of crack speed. And it was also shown that the extent of the 3-d field is independent of specimen thickness.(2) On a specimen surface, the crack opening displacement (COD) of the fast propagating crack is proportional to square root of the distance r from the crack tip, even in the 3-d stress field. It means that the surface singularity of the 3-d field is 1/<square root>r. The result is in agreement with the theoretical result on a slowly propagating crack given by Bazant and Estenssoro (1979). The singularity of 1/<square root>r is, hence, independent of crack speed. The crack front edge angle is not a right angle but obtuse. In case that crack speed is relatively lower, the crack front edge angle is not at right angle but obtuse. In case that crack speed is relatively lower, the crack front edge angle is in agreement with the numerical result on a slowly propagating crack given by Bazant and Estenssoro (1979). But the crack front edge angle decreases and approaches a right angle, as the crack speed increases. It can, thus, be said that the crack front edge angle varies in order to preserve the surface singularity to be 1/<square root>r, when the crack speed changes.(3) Crack opening displacement is proportional to the square root of the distance from the crack front edge, not only on a specimen surface but also on the mid-plane in a plate specimen. And the value of the dynamic stress intensity factor on the mid-plane is nearly same as that on a specimen surface. Less