Research on the Impact of Different Force Directions on the Mechanical Properties and Damage Evolution Law of Sandstone with Different Hole Diameters

In this research, a uniaxial acoustic emission experiment was conducted on rock samples with different positions and diameters of the hole, and an analysis was made on the impact of different hole positions and diameters on the mechanical properties, failure, energy conversion, and acoustic emission-caused damage characteristics and laws of the rock samples. The results reveal as follows: first, due to the existence of holes in rocks, the stress-strain curve changes at each stage, accompanied by multiple stress drops. And the peak strength gradually reduces with the increase in hole diameter. At different hole positions, the duration that the rock sample passes through at each stage of the stress-strain curve varies, and the peak strength of the rock with the vertical hole is greater than that of the rock with the horizontal hole. This indicates that the bearing capacity and stability of the rock sample with the vertical hole are greater than those of the rock sample with the horizontal hole of the same diameter. Second, by making a comparison on the failure characteristics of rock samples, it is found that the intact rock shows brittle failure. For the rock sample with the horizontal hole, symmetrical tensile cracks initially appear in the upper and lower parts of the hole and finally form shear failure. As for the rock sample with the vertical hole, Y-shape failure originally presents and eventually forms N-shape failure with the increase in hole diameter. Over a comparison with the failure pattern of an intact rock sample, it is demonstrated that the final failure pattern and crack expansion trend on the rock sample vary with the change in the hole position and diameter. Third, as obtained by comparing and analyzing the energy conversion of the rock with different diameters of the hole, the energy conversion in the rock is changed due to the existence of holes, and the increase in hole diameter causes a gradual decrease in the elastic energy stored in the rock and gradual increase in the dissipated energy. And by comparing the energy conversion of the rock with different positions of the hole, it is acquired that the elastic energy conversion ratio of the rock with the vertical hole is higher than that of the rock with the horizontal hole. Furthermore, an explanation was made on the difference in the failure processes of the two types of rocks from the perspective of energy conversion.

Analysis of the Damage Characteristics and Energy Dissipation of Rocks with a Vertical Hole under Cyclic Impact Loads

This study systematically investigates the failure patterns, energy dissipation, and fracture behavior of rock specimens containing a vertical hole under impact loads. First, an improved damage calculation equation suitable for the analysis of rock specimens with a vertical hole is obtained based on the one-dimensional stress wave theory and the interface continuity condition. After that, the Hopkinson pressure bar (SHPB) device was used to conduct cyclic impact tests with different impact pressures and impact modes (impact pressures with equal amplitude and unequal amplitude). The experimental results suggest that, under the equal-amplitude high pressure and unequal-amplitude pressure, the degree of damage of the rock significantly increased, the bearing capacity greatly reduced, and the rock gradually transitions from having good ductility to experiencing brittle failure. The cumulative specific energy absorption value gradually increases with the increase in the cyclic impact. Compared to that of the equal impact condition, the degree of damage to the rock is more severe for the case of equal-amplitude high pressure and unequal impact, and the failure mode undergoes a transformation from transverse tensile failure to transverse tensile failure-axial splitting failure combination and axial splitting failure. Through the analysis of rock energy changes and rock failure patterns during cyclic impact, it will be helpful to predict and control the fracture caused by local stress concentration during excavation, thus can reduce the cost of support and reinforcement in excavation and improve the stability of surrounding rocks.

A Restoration Study of Bokchundong-34's Armor and Helmet

Bokchundong-Tombs, from which various Armors of the fourth and fifth centuries were excavated, is a critical site for Three-Kingdom era Armor research. Despite the excavation of various types of Armor, including Scale Armor, Neck Aromor, Vertical Plate Helmet, and Bard(Horse Sacale Armor), Bokchundong-34 has not captured scholastic attention due to the lack of detailed information. This report examined the significance of Bokchundong-34 through the examination of recently reported restoration and production methods of Bokchundong-34 Armors. First of all, the research found Scale Armor to be Dong-hwan Scale Armor, comprised of Body-Lameller, Waist-Lameller, and Skirt-Lameller depending on the form of Lameller and arrangement of Hole. Also, Scale Armor has an S-shaped Waist- Lameller and 2-Line Vertical Binding. Furthermore, the connection method through Body-Lameller s Third Vertical Hole and the Vertical Binding method of the last hem Skirt-Lameller is a new method that has never been introduced. The report estimates Brachial Armors to have connected Lamellers through Fan shape and had the overall form of Upside-down Trapezoid style. Hyeok-po that covers Lameller s edge and Inner side with a layer of leather were confirmed from Neck Aromor and Vertical Plate Helmet, and the 1 Hole Which is placed in Neck Lameller center is thought to have bonded the Layer of leather with Lameller. Lastly, Bard, although very similar in overall form to Jjokssaem-C10 with Rectangular Lameller and Hoof-shaped Lameller, was decided to be an arrangement only with Neck and Chest Armor. In conclusion, Bokchundong-34 embodies transitional aspects of Armor of Yeongnam area characterized by Heavy Cavalry through Armor-Combine typical of the first quarter of the fifth century. Also, the excavation of Heavy Cavalry s Armor from Bokchundong-34, despite its relatively small scale, implies the advanced military might of Bokchundong-Tombs at the time.