Effects of Normal Stress and Joint Inclination Angle on Rock Failure Characteristics Under Compression–Shear Conditions

In this study, cement mortar was used to make specimens containing groups of parallel joints with different inclination angles to simulate natural rock mass, and the specimens were subjected to shear tests under different normal stresses. By analyzing the crack propagation path, failure modes, and strength characteristics of these rock specimens, the effects of normal stress and joint inclination angles on the strength and failure characteristics of this type of rock mass were studied. The following conclusions are drawn: 1) when the inclination angles of the joints are 0° and 15°, the changing of the normal stress did not affect the failure mode of the rock mass. The rock mass was mainly in the mode of shear failure, and the increase in the normal stress only increased the spalling area of the rock mass. 2) When the inclination angles of the joints are 30°, 45°, and 60°, with the increasing of the normal stress, the number of those approximately parallel cracks in the specimens increased, the friction marks caused by shearing increased, and the failure mode of the rock mass changed from tension failure to tension–shear composite failure. 3) Under different joint inclination angles, the propagation and penetration paths of cracks generated in the rock mass and the damage mode of the rock mass were different. With an increase in the joint inclination angles, the damage mode of the rock mass gradually changes from shear damage to tensile–shear composite damage and the α and β angles between the through cracks and the vertical direction on the left and right sides of the specimens tended to decrease. 4) The shear resistance of the rock mass was affected by the inclination angle of the joints and the normal pressure. The shear resistance of rock mass was improved due to the increasing of normal stress. Within a certain range, with the increasing of the inclination angles of the joint, the shear resistance of the rock mass tended to decrease first and then to increase

Exfoliated polymeric carbon nitride nanosheets for photocatalytic applications

Exfoliation into a 2D nanosheet structure can lead to enhanced surface activity and unique optical and electronic properties in polymeric carbon nitride (PCN). In this study, four common exfoliation strategies (liquid ultrasonication, thermal oxidation, hydrothermal oxidation, and chemical oxidation) were adopted, and their effects on the structural and electronic changes in PCN were analyzed in detail. This allows us to understand the relationship between the exfoliation mechanism and the structural/optical properties. Here, we demonstrate that the thermal and ultrasonic exfoliation methods can effectively reduce the thickness of PCN while preserving its original structure. In contrast, the chemical and hydrothermal treatments can strongly affect the morphology and structure of PCN, leading to a decreased performance in phenol photodegradation. Therefore, depending on the employed exfoliation method, the surface area, functionalization, band edge positions, charge carrier generation, and mobility are influenced differently up to the point where semiconducting behavior is entirely lost. Our results allow conclusions about the applicability of the different exfoliation methods to obtain distinct material properties for photocatalytic applications

Deformation Response of Tunnel Lining in Geological Area of Coal Seam Group Caused by Explosion Stress Wave

AbstractTo study the influence of drilling and blasting on the deformation of the tunnel lining in a multimedium surrounding rock section, this paper constructs the deformation calculation theory of the explosion stress wave of the tunnel lining. We select single-medium surrounding rock, multimedium surrounding rock, different explosion accelerations, and different surrounding rock grades as research variables and analyse in depth the causes of the deformation response of the tunnel lining. It is found that the stress wave causes more damage to the surrounding rock closer to the explosion point, and the disturbance to the surrounding rock increases with the increase of the acceleration of the explosion stress wave. And the better the surrounding rock grade, the more obvious the creep effect formed by the explosion stress wave, and the more damaging the stress wave propagation is to the tunnel lining. After the stress wave propagation medium changes from soft to hard, the energy will produce a “nest effect” at the interface between the two media, and the energy will accumulate briefly at the interface. When a certain amount of energy has accumulated, it propagates into the hard medium in an excited state, which causes large vibration of the tunnel lining in the soft medium area. The stress wave propagation medium changes from hard to soft, and the excessive energy in the hard medium produces huge vibration only at the junction of the hard–soft media, and there is no “nest effect.

Discussions for the charging efficiency of the resistor–capacitor and resistor–inductor–capacitor series circuits under different excitation sources

Aiming at the resistor–capacitor (RC) series circuit and resistor–inductor–capacitor (RLC) series circuit of capacitor charging, this paper discusses the energy efficiency of the capacitor charging circuit under the four excitation conditions of the step function, slope function, quadratic function, and exponential function. The simulation circuits are built based on MATLAB Simulink, and are compared under the four excitation conditions. It is pointed out that the charging efficiency of the RC series circuit and RLC series circuit under slope function excitation can reach the maximum value. Under the same slope function excitation, the energy efficiency of the RC series circuit is almost the same as that of the RLC series circuit, while the charging time of the second-order RLC series circuit is shorter

Calculation method of HJC constitutive model parameters of natural joint angle slate

Abstract In the course of underground engineering, layered slate is often encountered. Understanding the mechanical characteristics of layered slate is a prerequisite for engineering construction and disaster prevention and mitigation. As a result, at the beginning of a project, a large number of indoor tests are required, which are time-consuming and laborious. In addition, the natural joint angle of the layered slate is random, so it is extremely difficult to establish a database of the mechanical characteristics of layered slate. Hence, it is necessary to find a simple, feasible, and high-precision method to determine the Holmquist–Johnson–Cook (HJC) constitutive model parameters for naturally jointed layered slate with different dip angles. This study first determines the HJC constitutive model parameters of layered slate with five specific joint dip angles (0°, 30°, 45°, 60°, and 90°) through static tests and the split Hopkinson pressure bar (SHPB) test. Furthermore, by employing sensitivity analysis methods, the influence of key parameters of the HJC constitutive model on the dynamic peak stress of slate is determined. Among them, parameters A and B have the most significant impact on stress, exceeding 50%. Thirdly, a nonlinear fitting regression method is used to determine the HJC constitutive model parameters of naturally jointed angular slate. The relationship between the HJC model parameters and the inclination angle of slate joints is derived, and the accuracy of these parameters is verified through numerical simulation methods. The error between the numerical simulation and indoor experiments is within 10%, indicating a high level of simulation accuracy. The research findings provide a highly precise numerical simulation method for similar projects

Analysis of the influence of shear-tensile resistance and rock-breaking effect of cutting holes

Abstract In the process of drilling and blasting construction of large-cross-section tunnels, the layout of wedge-shaped cutting holes has a great influence on the effect of blasting. In this study, theoretical analysis and numerical simulation were used to assess the effect of different forms of cutting hole placement on blasting effectiveness. First, the fissure-inducing angle was proposed, a three-dimensional model of wedge-shaped cutting considering the effect of shear-tensile resistance was established, and theoretical analyses of cutting holes with different cutting angles and fissure-inducing angles were carried out. Second, the parameters of the Riedel–Hiermaier–Thoma model were determined based on the experimental data, and verified. Third, three-dimensional numerical models were established, and analyze the influence of different forms of hole deployment on the blasting effect from the perspective of stress wave propagation and dynamic damage to the surrounding rock. Finally, based on the theoretical analysis and numerical simulation results, the wedge-shaped hollowing holes were re-designed, and 20 tunnel blasting tests were carried out using this deployment method for large-section tunnel blasting, which verified the feasibility of this deployment method. The results of the study show that for level III surrounding rock, the angle of wedge-shaped cutting holes should meet 68° ≤ θ ≤ 70° and 70° ≤ β ≤ 72°. This study provides a kind of refined and efficient blasting for the drilling and blasting excavation process of large section tunnels

sEMG-Based Gain-Tuned Compliance Control for the Lower Limb Rehabilitation Robot during Passive Training

The lower limb rehabilitation robot is a typical man-machine coupling system. Aiming at the problems of insufficient physiological information and unsatisfactory safety performance in the compliance control strategy for the lower limb rehabilitation robot during passive training, this study developed a surface electromyography-based gain-tuned compliance control (EGCC) strategy for the lower limb rehabilitation robot. First, the mapping function relationship between the normalized surface electromyography (sEMG) signal and the gain parameter was established and an overall EGCC strategy proposed. Next, the EGCC strategy without sEMG information was simulated and analyzed. The effects of the impedance control parameters on the position correction amount were studied, and the change rules of the robot end trajectory, man-machine contact force, and position correction amount analyzed in different training modes. Then, the sEMG signal acquisition and feature analysis of target muscle groups under different training modes were carried out. Finally, based on the lower limb rehabilitation robot control system, the influence of normalized sEMG threshold on the robot end trajectory and gain parameters under different training modes was experimentally studied. The simulation and experimental results show that the adoption of the EGCC strategy can significantly enhance the compliance of the robot end-effector by detecting the sEMG signal and improve the safety of the robot in different training modes, indicating the EGCC strategy has good application prospects in the rehabilitation robot field

A new large area MCP-PMT for high energy detection

Abstract 20-inch Large area photomultiplier tube based on microchannel plate (MCP-PMT) is newly developed in China. It is widely used in high energy detection experiments such as Jiangmen Underground Neutrino Observatory (JUNO), China JinPing underground Laboratory (CJPL) and Large High Altitude Air Shower Observatory (LHAASO). To overcome the poor time performance of the existing MCP-PMT, a new design of large area MCP-PMT is proposed in this paper. Three-dimensional models are developed in CST Studio Suite to validate its feasibility. Effects of the size and bias voltage of the focusing electrodes and MCP configuration on the collection efficiency (CE) and time performance are studied in detail using the finite integral technique and Monte Carlo method. Based on the simulation results, the optimized operating and geometry parameters are chosen. Results show that the mean ratio of photoelectrons landing on the MCP active area is 97.5%. The acceptance fraction of the impinging photoelectrons is close to 100% due to the emission of multiple secondary electrons when hitting the MCP top surface. The mean transit time spread (TTS) of the photoelectrons from the photocathode is 1.48 ns

Responses of soil nutrients, enzyme activities, and maize yield to straw and plastic film mulching in coastal saline-alkaline

To address the issue of low soil nutrients and low crop yields in coastal alkaline salines, a field experiment of straw combined with plastic film mulching in coastal alkaline salines was conducted in this study to explore the effects of different treatments on soil nutrients, enzyme activities and maize yield. Four treatments, including no mulching (NM), straw mulching (SM), plastic film mulching (PM), and straw mulching combined with plastic film mulching (SP), were set up during 2019-2020. In the 0-20 cm soil layer, compared with NM, the soil organic carbon (SOC) and soil catalase activity (SCA) of SM significantly increased by 23.4% and 46.2%, respectively (P < 0.05). The soil total nitrogen (STN), soil available phosphorus (SAP), available potassium (SAK), sucrase activity, urease activity, alkaline phosphatase activity, and maize yield (MY) of SP significantly increased by 40.7, 26.8, 13.9, 34.6, 73.8, 36.2 and 19.0%, respectively (P < 0.05). SOC, STN, SAP, SAK and SCA were significantly correlated with MY. Therefore, straw mulching combined with plastic film mulching has the best effect on increasing soil nutrients, soil enzyme activity, and maize yield and is suitable for promotion and application in coastal alkaline salines

The R&D of the 20 in. MCP-PMTs for JUNO

<p> A new concept of large area photomultiplier based on MCPs was conceived for JUNO by the scientists in IHEP, and with the collaborative work of the MCP-PMT collaboration in China, 8 in. and 20 in. prototypes were produced. Test results show that this type of MCP-PMT can have good SPE performance as the traditional dynode type PMTs. (C) 2015 Elsevier B.V. All rights reserved.</p