Cutting blasting is a crucial step in underground blasting driving. To investigate the influences of cutting cavity depth on subsequent rock breaking properties, driving sections with different cutting cavities depths were simplified as sandstone specimens with different depths of cavities. A series of dynamic compression tests were conducted using a 50 mm diameter split Hopkinson pressure bar (SHPB) testing system. Then, the dynamic peak stresses, dynamic peak strains, energy dissipation characteristics, and fracture patterns of the specimens were analyzed as the cavity depth varied, and the field cutting blasting parameters were optimized accordingly. The results demonstrate significant trends for sandstone specimens with cavity diameters of 10 and 20 mm. As the cavity depth increases, the dynamic peak stress decreases by 17.69% and 39.05%, the dynamic peak strain increases by 7.58% and 18.56%, the dissipation energy increases by 22.87% and 45.92%, the dissipation energy density increases by 26.92% and 73.08%, respectively. And the specimens fragmentation size also gradually decreases with the extension of cavity depth. These findings indicate that increasing cutting cavity depth could reduce the rock mass resistance to failure, enhance its deformation capacity and energy utilization efficiency, and improve its fragmentation effects. When the cavity diameter is 20 mm, the dynamic mechanical properties and energy dissipation characteristics of the specimens change at a faster rate with the increase of cavity depth, and the fragmentation size is smaller. This indicates that increasing the cutting cavity diameter is also beneficial for rock breaking. The cutting blasting technique with inner-hole and outer-hole composite delays is adopted, which can increase the cavity depth and diameter to provide sufficient free surfaces for subsequent blasting process. This optimization achieved remarkable filed performance that increasing the cycle advance and hole utilization rate of the full-section blasting into 5.0 m and 96.1%, and ensuring uniform and reasonable rock fragmentation degree. The research findings not only effectively reveal the influences of cutting cavity depth on the full-section rock breaking effects, but also provide theoretical supports and practical references for the design optimization of actual cutting blasting projects.

Ti/steel clad plates are considered as ideal candidate materials for applications such as marine engineering and low-temperature pressure vessels operating at −70 ℃. However, their large-scale production and application are severely restricted by the manufacturing process and the quality of interfacial bonding. To investigate the influence mechanism of vacuum pressure on interfacial morphology and mechanical properties, TC4/09MnNiDR (Ti/steel) clad plates were fabricated using explosive welding under ambient pressures of 20, 60, and 100 kPa, and the fabricated clad plates were named as CP-20, CP-60 and CP-100, respectively. A specially designed vacuum chamber was employed to precisely control the environmental pressure during the explosive process. After welding, all specimens were subjected to a uniform stress-relief annealing treatment at 550 ℃ for 2 h under a vacuum atmosphere to eliminate residual stresses and improve the reliability of subsequent characterization. The interfacial microstructure and chemical characteristics were systematically analyzed using multiple characterization techniques. Scanning electron microscopy (SEM) was used to observe interfacial morphology, including wave formation and defect distribution. Energy dispersive spectroscopy (EDS) was applied to examine elemental distribution across the bonding interface. Electron backscatter diffraction (EBSD) was employed to evaluate grain structure, grain boundary characteristics, recrystallization fraction, and texture evolution near the interface. Electron probe microanalysis (EPMA) was conducted to quantitatively determine the chemical composition of the interfacial melting zone and vortex regions, with both mapping and point analyses performed to identify the constituent phases. Mechanical properties at −70 ℃ were evaluated through tensile tests, Charpy impact tests, and three-point bending tests, all carried out in accordance with relevant national standards, with the results reported as mean values ± standard deviations. Results show that the vacuum environment significantly improves interfacial quality. With increasing vacuum degree, the interfacial wave becomes finer, more continuous, and more uniform, while the thickness of the molten layer decreases, and the presence of defects and brittle intermetallic compounds is reduced. EBSD analysis reveals grain refinement and an increased recrystallization fraction at the interface under vacuum conditions, demonstrating that the interfacial microstructure can be effectively controlled by adjusting the ambient pressure. EPMA further reveals that the vortex regions are mainly composed of Fe and Ti elements, while the weld seam region exhibits a stable chemical composition with Ti-to-Fe atom number ratios close to 1∶1 or 2∶1, indicating that the dominant intermetallic phases formed at the interface are TiFe and TiFe₂. Benefiting from the optimized interfacial structure, the clad plates exhibit excellent mechanical properties at −70 ℃. The tensile strengths of the CP-20, CP-60 and CP-100 are 880, 911, and 867 MPa, respectively. The impact absorbed energies are 17.5, 10.2, and 6.4 J, respectively. And the flexural strengths are 1469, 1350, and 1167 MPa, respectively. This study demonstrates that vacuum explosive welding is a reliable technique for producing high-performance low-temperature metal composites, with 60 kPa identified as the optimal processing window.

Renewable energy is addressing some of the key challenges facing global society today, and zero-carbon energy systems are the fundamental way to achieve carbon neutrality. Therefore, hydrogen and ammonia have gained great attention as zero-carbon energy sources. To further study the combustion characteristics of ammonia-hydrogen-air premixed gas flame inside and outside the duct, the influence of ammonia doped amount (φ) on the flame morphology and the evolution of pressure inside and outside the duct under stoichiometric ratio was explored with the help of high-speed photography and pressure sensor in the 2000-mm-long stainless steel duct with a 400-mm-long and 70-mm-wide observation window. The results show that φ significantly affects the pressure inside and outside the duct, and the time to reach the reverse flow phenomenon caused by the secondary explosion also increases. The pressure measuring point PS1 is set at 400 mm away from the explosion vent in the duct to collect data. The pressure curves in the duct under each working condition are presented as a three-peak structure, named p₁, p₂, and p₃. The three pressure peaks are caused by the rupture of the explosion vent film, the gas venting in the duct, and the gas reverse generated by the secondary explosion outside the duct. The size of p₁ depends on the tensile strength of the explosion venting membrane, and its amplitude is almost independent of the φ. p₂ and p₃ both increase with the increase of φ, and the p₃ increase rate is the largest when φ is in 50%–65%. p₂ changes from a single peak to a fluctuating pressure platform in the pressure curve diagram, and the time of the platform extends with the increase of φ. The pressure measurement point PS2 is set at the horizontal central axis, 500mm away from the explosion vent outside the duct, to collect data. And the peak pressure of the secondary explosion outside the duct (p_out) decreases with the increase of the φ, and the time to reach p_out increases. This study provides a theoretical basis for the utilization of ammonia and hydrogen energy.