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

脉冲全息显微镜对快速扩展裂纹尖端附近三维应力场的实验研究

基本信息

批准号：
01550071
负责人：
SUZUKI Shinichi
金额：
$ 1.34万
依托单位：
Toyohashi University of Technology
依托单位国家：
日本
项目类别：
Grant-in-Aid for General Scientific Research (C)
财政年份：
1989
资助国家：
日本
起止时间：
1989 至 1990
项目状态：
已结题

项目摘要

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

当一盘脆性材料被外部拉伸力打破时，通常会出现快速传播的裂纹。裂缝是开口模式的，并以几百m/s的速度传播。裂纹尖端周围的应力场满足了距尖端一定距离的区域的平面应力条件。也就是说，那里的应力场是二维的。但是，应力场在裂纹尖端附近显示出三维（3-D）的性质。脆性材料的断裂实际上发生在3-D应力场中，因此，使3-D场的结构清除很重要。彼此之间，我们进行了实验研究，该研究集中在下面所述的三个点上。（1）3-D场与快速传播裂纹尖端之间的差距有多远？（2）3-D场的表面奇异性与快速繁殖裂纹的裂纹前边缘角度之间的关系是什么关系？ 3-D应力场从裂纹尖端延伸到标本厚度的一半，沿裂纹的传播方向为72度。结果与Shimizu和Shimada（1978），Shimada和Sasaki（1983），Shimizu等人所显示的固定裂纹相同。（1985）以及Rosakis and Ravi-Chandar（1986）。因此，可以说3-D应力场的程度独立于裂纹速度。还表明，3-D场的范围与样品厚度无关。（2）在试样表面上，即使在3-D应力场中，快速传播裂纹的裂纹开口位移（COD）与距离裂纹尖端的距离R的平方根成正比。这意味着3-D场的表面奇异性为1/<square root> r。结果与Bazant和Estenssoro（1979）给出的缓慢传播裂纹的理论结果一致。 1/<quare root> r的奇异性与裂纹速度无关。裂纹前边缘角度不是直角，而是钝角。如果裂纹速度相对较低，则裂纹前边缘角度不是直角，而是钝角。裂纹速度相对较低，裂纹前边缘角与Bazant和Estenssoro（1979）缓慢传播裂纹的数值结果一致。但是，随着裂纹速度的增加，裂纹前边缘角度降低并接近直角。因此，可以说，当裂纹速度变化时，裂纹前边缘角度变化是为了将表面奇点保持在1/<square root> r。（3）裂纹打开位移与距裂纹前边缘距离的平方根成正比，不仅在样品表面上，而且在板标本中的中平面上。并且动态应力强度因子在中平面上的值几乎与样品表面上的值相同。较少的