Development of Explosively Driven High-Speed Loading Apparatus and Its Applications to Dynamic Fracture Experiments of Rock-Like Materials

岩石类材料的强度、刚度和脆性受加载速率的影响。然而，在高速加载时缺少数据。本文研制了一种新型的炸药驱动高速加载装置。使用电雷管作为装药，并将其置于装满水的装药筒中。装置的加载活塞由水下激波和爆炸气体的动态作用驱动。对舔岩材料进行了压缩和劈裂拉伸的动态断裂实验。用石英负载传感器测量动载荷，用应变片测量动应变。采用高速摄像技术观察了试样的动态断裂过程。得到如下结果：(1)高速加载装置可重复使用，适用于类岩材料的动态断裂实验。结果表明，以加载持续时间表示的加载速率约为200 ~ 220 MN/s。(2)观察到类岩石材料的强度增加。动态抗压强度比静态强度大85% ~ 100%。(3)高速视频图像显示了试样在压缩状态下的断裂过程，如裂纹扩展和末端边界条件产生的剪切断裂。在劈裂拉伸实验中，裂纹是在圆柱形圆盘试样的中心附近产生的。(4)采用带两个楔形空腔的装药座，观察了类岩材料在拉伸作用下的断裂扩展。高速视频图像显示，从装药座向自由面传播的裂缝与自由面传播的裂缝发生碰撞，产生裂缝面。

Strength, stiffness and brittleness of rock-like materials are affected by the rate of loading. However, there is a lack of date at high rates loading. In this research, a new high-speed loading apparatus driven by explosives was developed. An electric detonator was used as a charge and set in a charge cylinder filled with water. A loading piston of the apparatus was driven by dynamic actions of underwater shock waves and explosion gases. The dynamic fracture experiments were made for rock-lick materials in compression and/or splitting tension. The dynamic load was measured by a quartz load sensor and the dynamic strains were measured by strain gauges. The dynamic fracture processes of the specimens were observed by high-speed videography. The following results are obtained.(1)The presented high-speed loading apparatus is reusable and applicable to dynamic fracture experiments of rock-like materials. Results show that the loading rate indicated by the loading duration to the maximum load is about 200〜220 MN/s.(2)Increases in strength of rock-like materials are observed. The dynamic compressive strength is found to be as much as about 85 to 100% greater than the static strength.(3)High-speed video images show fracture processes of the specimens in compression, such as crack propagation and shearing fracture produced by end boundary conditions. In splitting tension experiments, cracks are initiated near the center of the cylindrical disk specimen.(4)Fracture propagation of rock-like materials in tension is observed by using the charge holders with two wedge-shaped air cavities. It is obtained from high-speed video images that the fracture propagating from the charge holder towards the free surface collides with the fracture from the free surface and the fracture plane is produced.