Visualization and analysis of stress waves in blasting processes by a laser-shadowgraph method

爆破动态断裂控制在地下工程开挖和混凝土结构拆除中具有重要意义。为了实现高程度的断裂控制，有必要研究爆破过程中应力波、气体和裂纹的动力学机理。本文介绍了激光阴影法显示爆破应力波的实验结果，提出了断裂控制爆破的新方法。建立了以调Q红宝石激光器为光源的阴影照相系统。利用该系统可以在任意时刻获得强脉冲束流，并获得高空间和时间分辨率的瞬态可视化图像。对应力波与圆孔、圆弧形自由表面和90 °角自由表面的相互作用进行了实验研究。以20 mm厚的PMMA板为透明材料进行了模型试验。从这些实验中，获得了以下结果。阴影图显示了反射波的行为、圆孔的变形以及入射波与孔的相互作用在孔中产生的会聚冲击波。对于沿入射波传播方向沿着有两个缺口的孔，可以看出在缺口附近产生了著名的阴影斑。根据事实，可以预期，利用带切口的圆孔作为实现断裂控制的导孔技术是有效的。

Dynamic fracture control in blasting is very important in underground excavation and demolition of concrete structures. It is necessary to examine the dynamic mechanism of stress waves, gases and cracks in blasting process for achieving high degree of fracture control. In this research, experimental results on visualization of stress waves in blasting by a laser-shadowgraph method are presented and a new method for fracture controlled blasting is suggested. The shadowgraph system using a Q switched ruby laser as a light source is set up. The system enables us to get a giant pulse beam at a desired time and to obtain the high spatial and time resolved instantaneous visualization photographs.Experiments are made on stress waves interacting with a circular hole, a circular arc-shaped free surface and a free surface with 90ﾟ corner. Model experiments are casrried out with the PMMA plate of 20 mm in thickness as a transparent material. From these experiments, the following results are obtained. The shadowgraphs show the behavior of reflected waves, deformations of the circular hole and the generation of converging shock waves in the hole by interaction of incident waves with the hole. In the case of the hole with two notches along the prpagation direction of the incident waves, it can be seen that the well-known shadow spots are produced in the vicinity of the notches. From the fact, it might be expected that utilization of the circular hole with notches is effective as the guide hole technique for achieving fracture control.