Experimental Studies on Bifurcation Process of Fast Propagating Cracks in Araldite B and Homallite 100

对方沸石B和Homallite 100中快速扩展裂纹的分叉进行了实验研究，得到了以下结果：[1]快速：用高速全息显微镜拍摄了方沸石B和Homallite 100中快速扩展裂纹的分叉。(1)裂纹张开位移Cods与分叉前距裂纹尖端的距离r成正比，分叉后母裂纹的Cods与距母裂纹名义尖端的距离r成正比。(2)从Cods得到的能量释放率在裂纹分岔点上逐渐且持续增加。能量释放率在分叉时没有出现间断变化。(3)在裂纹分叉时刻，流向裂纹尖端的能量通量也逐渐连续增加，没有出现间断变化。这是由于裂纹分叉后裂纹不连续减速所致。[2]用脉冲全息显微镜的两个光学系统同时拍摄了平板试件两侧的Homallite 100和Araldite B的快速分叉裂纹的照片：(1)分叉裂纹在试件两侧具有不同的裂纹形状。由此可见，裂纹分叉不是二维现象，而是三维现象。(2)两条裂纹分支张开位移不同。这意味着分叉相对于沿母裂纹的线是不对称的。[3]上述结果与PMMA裂纹上的结果相同。因此，这三种材料(方沸石B、Homallite 100和PMMA)具有以下两个共性：(1)由COD测量得到的能量释放率在分叉点上是连续的。(2)裂纹分叉不是二维现象，而是三维现象。

Experimental studies were carried out to figure out the bifurcation of fast propagating cracks in Araldite B and Homallite 100, and the following results were obtained.[1]Fast : Propagating cracks in Araldite B and Homallite 100 were photographed by high-speed holographic microscopy at bifurcation. Crack speed was more than 400m/s.(1)Crack opening displacements, CODs, are proportional to the distance r from the crack tip before bifurcation : After bifurcation CODs of mother cracks are proportional to r from the nominal tip of the mother cracks.(2)The energy release rate obtained from the CODs increases gradually and continuously across the bifurcation point of the cracks. Discontinuous change of the energy release rate doesn't occur at the bifurcation.(3)The energy flux toward the crack tips also increases gradually and continuously at the moment of crack bifurcation, and doesn't show discontinuous change. This is caused by the fact that the crack doesn't decelerate discontinuously after crack bifurcation.[2]Two optical systems of pulsed holographic microscopy were applied to take photographs of rapidly bifurcating cracks in Homallite 100 and Araldite B on the both sides of plate specimens simultaneously.(1)Bifurcating cracks have different crack shapes on the both side of a specimen. Thus it can be said that the crack bifurcation is not two-dimensional phenomenon, but three-dimensional one.(2)Two crack branches have different opening displacement. This means that bifurcation is not symmetric with respect to the line along the mother crack.[3]The above mentioned results are the same as those on cracks in PMMA. Consequently the following two can be said to be common to the three materials, Araldite B, Homallite 100 and PMMA.(1)The energy release rate obtained form COD measurement is continuous across the bifurcation point.(2)Crack bifurcation is not two-dimensional but three-dimensional phenomenon.