Table 4 Crack propagation process of rock specimens with different prefabricated fissure dips.
Fissure dip/° | Impact process | Stress (percentage of peak stress)/MPa | Loading time/ms | Crack propagation process description |
|---|---|---|---|---|
30 | 1 | 4.39 (47.8%) Elastic limit | 0.18 | Longitudinal splitting cracks occur from prefabricated fissures |
2 | 7.12 (77.6%) Stable development of cracks | 0.28 | Longitudinal cracks continue to propagate along the loading direction, the upper part has extended to the loading surface, the lower part has appeared transverse cracks, and the transverse cracks continue to propagate | |
3 | 9.18 (100%) Peak stress | 0.48 | Load reaches its peak value, the crack widens gradually and the transverse crack extends to the side of the specimen | |
4 | 5.57 (60.7%) Post-peak | 0.72 | Longitudinal cracks penetrate, cracks become wider and the number increases, a large number of rock powder appears | |
45 | 1 | 7.61 (62.5%) Elastic limit | 0.19 | A longitudinal splitting crack starts at the prefabricated fissure and extends upward |
2 | 11.65 (95.6%) Stable development of cracks | 0.27 | A new longitudinal splitting crack initiates from the prefabricated fissure and continues to propagate along the loading direction, while the original crack continues to propagate | |
3 | 12.18 (100%) Peak stress | 0.52 | When the peak load is reached, many longitudinal cracks have appeared and are developing steadily. The bottom corner of the specimen has been sheared by shear cracks | |
4 | 7.14 (58.6%) Post-peak | 0.71 | Cracks are becoming more and more dense, wider and longer | |
60 | 1 | 7.39 (57.3%) Elastic limit | 0.19 | A longitudinal splitting crack begins at the end of prefabricated fissures and continues to propagate along the loading direction |
2 | 11.27 (87.4%) Stable development of cracks | 0.50 | Longitudinal cracks continue to propagate and no new cracks are found | |
3 | 12.90 (100%) Peak stress | 0.61 | Cracks continue to extend along the loading direction, and no new cracks are found | |
4 | 9.11 (70.6%) Post-peak | 0.72 | Cracks penetrate and widen, and a new longitudinal short crack appears | |
90 | 1 | 5.51 (43.0%) Elastic limit | 0.13 | A longitudinal splitting crack initiates along the end of prefabricated fissures and continues to extend along the loading direction |
2 | 12.82 (100%) Peak stress | 0.47 | The original crack continues to extend along the loading direction, and no new crack is found | |
3 | 7.88 (61.5%) Post-peak | 0.58 | The original longitudinal crack gradually widen and lengthen, and no new crack is found |
