Crack velocity, gas ejection, and stress waves play an important role in determining delay time, designing a blast and understanding the mechanism of rock fragmentation by blasting. In this paper, the emerging times of the earliest cracks and gas ejection on the lateral surfaces of cylindrical granite specimens with a diameter of 240 mm and a length of 300 mm were determined by high-speed photography, and the strain waves measured by an instrument of dynamic strain measurement during model blasting. The results showed that: (1) the measured velocity of gas penetration into the radial cracks was in a range of 196–279 m/s; (2) the measured velocity of a radial crack extending from the blasthole to the specimen surface varied from 489 to 652 m/s; (3) the length of strain waves measured was about 2800 µs, which is approximately 1000 times greater than the detonation time. At about 2850 µs after detonation was initiated, gases were still ejected from the surface cracks, and the specimens still stood at their initial places, although surface cracks had opened widely.

中文翻译：

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在模型岩石爆破中在试样表面测量的破裂起始、气体喷射和应变波

裂缝速度、气体喷射和应力波在确定延迟时间、设计爆破和了解爆破岩石破碎机制方面起着重要作用。本文利用高速摄影法测定了直径240 mm、长300 mm的圆柱形花岗岩试样侧面最早裂纹和气体喷射的出现时间，并利用仪器测量了应变波。模型爆破过程中的动态应变测量。结果表明：（1）实测气体渗入径向裂纹的速度在196～279 m/s范围内；(2)从炮眼延伸到试样表面的径向裂纹的实测速度为489～652 m/s；(3) 测得的应变波长度约为 2800 µs，这大约是爆炸时间的 1000 倍。爆炸开始后约 2850 µs，尽管表面裂纹已广泛张开，但仍从表面裂纹中喷出气体，试样仍停留在初始位置。