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To investigate the dynamic mechanical properties of water-saturated fissure rock at different strain rates, prefabricated sandstone specimens with a 45° dip angle were treated with water saturation and the impact compression test was performed with a Split Hopkinson Pressure Bar (SHPB) test device at different impact pressures. The results show that the clusters of dynamic stress–strain curves of water-saturated and natural sandstone specimens with a 45° dip angle of prefabricated fissures are basically similar under different impact air pressures. A distinct strain rate effect was observed for dynamic strain and dynamic compressive strength, both of which increased with increasing strain rate. From the failure pattern of the specimen, it can be seen that cracks appeared from the tip of the prefabricated fissure under axial stress, spreading to both ends and forming wing cracks and anti-wing cracks associated with shear cracks. As the strain rate increased, the energy dissipation density of the specimen gradually increased, and the macroscopic cracks cross-expanded with each other. The fracture form of the specimen showed a small block distribution, and the average particle size of the specimen gradually decreased. The specimen crushing energy dissipation density was negatively correlated with fracture size, reflecting a certain rate correlation. The sandstone fragments' fractal dimension increases with the increase in crushing energy dissipation density, and the fractal dimension may be applied as a quantitative index to characterize sandstone crushing. [ABSTRACT FROM AUTHOR]

To investigate the dynamic mechanical properties of water-saturated fissure rock at different strain rates, prefabricated sandstone specimens with a 45° dip angle were treated with water saturation and the impact compression test was performed with a Split Hopkinson Pressure Bar (SHPB) test device at different impact pressures. The results show that the clusters of dynamic stress–strain curves of water-saturated and natural sandstone specimens with a 45° dip angle of prefabricated fissures are basically similar under different impact air pressures. A distinct strain rate effect was observed for dynamic strain and dynamic compressive strength, both of which increased with increasing strain rate. From the failure pattern of the specimen, it can be seen that cracks appeared from the tip of the prefabricated fissure under axial stress, spreading to both ends and forming wing cracks and anti-wing cracks associated with shear cracks. As the strain rate increased, the energy dissipation density of the specimen gradually increased, and the macroscopic cracks cross-expanded with each other. The fracture form of the specimen showed a small block distribution, and the average particle size of the specimen gradually decreased. The specimen crushing energy dissipation density was negatively correlated with fracture size, reflecting a certain rate correlation. The sandstone fragments’ fractal dimension increases with the increase in crushing energy dissipation density, and the fractal dimension may be applied as a quantitative index to characterize sandstone crushing.

The new three-dimensional angle-interlock woven UHMWPEF/epoxy composite was prepared by the VARIM method, and its mechanical properties were studied. Specifically, quasi-static and dynamic compression tests were carried out by universal testing machine and split Hopkinson pressure bar (SHPB) apparatus. Stress-strain curves under the quasi-static and high strain rates (800, 1000, 1400, and 1600 s−1) reveal the destructive characteristics of the composite material. The results indicate that the UHWMPEF/epoxy composite is a strain rate sensitive material and shows different levels of sensitivity at various strain rates. In the quasi-static compression test, when the strain rate was increased from 4.2 × 10−4 to 1.4 × 10−3 s−1, the failure load and ultimate strength increased by about 19.1% and 20.1%, respectively, and the failure strain and specific energy absorption decreased by about 1.53% and 6.1%, respectively. In the dynamic compression test, when the strain rate increased from 800 to 1600 s−1, the failure load and ultimate strength increased by about 16% and 15.9%, respectively, and the failure strain and specific energy absorption decreased by about 64.7% and 60.3%, respectively. The failure fracture surface of the specimen under quasi-static compression was at an angle of 40°–45° with the load direction. The matrix fragmentation at the fracture was obvious, and the warp fiber bundle was broken and peeled off from the matrix. The damage of specimen under dynamic compression develops quickly and the deformation process is short, which shows a relatively symmetrical shear fracture failure morphology. [ABSTRACT FROM AUTHOR]