Search

With the explosive growth in demand for lithium (Li) resources, the Mufushan area has been a hotspot for Li deposit exploration in China in recent years. Geochemical maps and geochemical anomaly maps are basic maps in the geochemical exploration of mineral resources. A fixed-value method to contour a Li geochemical map is presented here, in which Li concentrations are divided into 19 levels on 18 fixed values, ranging from 5 μg/g (corresponding to the detection limit) to 1858 μg/g (corresponding to the cut-off grade of Li deposit in hard-rock type) and illustrated in six color tones corresponding to Li areas of low background, high background, low anomaly, high anomaly, mineralization in clay-type, and mineralization in hard-rock type. The geochemical map of Li in the Mufushan area using the new fixed-value method indicates that the study area belongs to the high background area, and the known Li deposits are located in the high anomaly areas. In addition, the geochemical anomaly map of the Mufushan area is drawn using the method of seven levels of classification, and indicates that the known Li deposits are all in the anomaly areas, with anomaly levels not lower than the second level. Furthermore, four other areas are recognized for Li resource potential based on the geochemical map and geochemical anomaly map in the Mufushan area.

Laser direct joining enables non-destructive and lightweight joining of carbon fiber reinforced thermoplastic (CFRTP) composites and aluminum alloys. The interfacial bonding process determines the joint performance and is influenced by the time-varying temperature distribution. However, the interfacial bonding process occurs inside the joint, making it difficult to study the effect of temperature distribution. To resolve this issue, a novel online observation device for the interfacial bonding process between CFRTP composites and aluminum alloys is design, and the polymer melting, flowing, and bonding with metal during laser direct joining are observed. Further, temperature field simulation models for laser direct joining are established, and temperature distribution and gradient are calculated. The results show that the temperature distribution determines the melting of CFRTP composites, and bubbles generated by the thermal decomposition of the polymer hinder the melting. The temperature gradient is related to the movement of the molten matrix and fibers, and the movement towards the aluminum alloy induces cracking and delamination. Once the interface is filled with polymer, the motion changes to along the laser scanning direction and the joining defects are reduced. The study can provide a foundation for promoting interfacial bonding and reducing the defects of laser direct joining.

The shear behavior of the Bolt-Grout interface has a significant effect on the stability of a bolting system. In this paper, a series of shear tests were conducted on Bolt-Grout interfaces, and the effects of rib spacing, rib angles, and normal stress on the shear characteristics and failure modes of the Bolt-Grout interface were investigated. The results showed that the shear strength varied nonlinearly with an increase in rib spacing and angle, and also that it increased linearly with an increase in normal stress. With smaller rib spacings, the effect of rib spacing on peak shear strength was more apparent. The failure modes of the interface can be categorized as shear-slip failure, shear-break failure, and composite failure. The proportion of shear-slip failure and shear-break failure mainly depends on the rib spacing, rib face angle and normal stress.

Coal has played an important role in the economies of many countries worldwide, which has resulted in increased surface and underground mining in countries with large coal reserves, such as China and the United States. However, coal mining is subject to frequent accidents and predictable risks that have, in some instances, led to the loss of lives, disabilities, equipment damage, etc. The assessment of risk factors in underground mines is therefore considered a commendable initiative. Therefore, this research aimed to develop an efficient model for assessing and predicting safety risk factors in underground mines using existing data from the Xiaonan coal mine. A model for evaluating safety risks in underground coal mines was developed based on the optimized particle swarm optimization-backpropagation (PSO-BP) neural network. The results showed that the PSO-BP neural network model for safety risk assessment in underground coal mines was the most reliable and effective, with MSE, MAPE, and R2 values of 2.0 × 10−4, 4.3, and 0.92, respectively. Therefore, the study proposed the neural network model PSO-BP for underground coal mine safety risk assessment. The results of this study can be adopted by decision-makers for evaluating and predicting risk factors in underground coal mines.

In China, soft rock roof makes up the majority of coal mine roof, yet it is easy to break due to low strength and poor integrity. As such, it is difficult for the traditional pillar-based roadway protection means and pillarless mining techniques to effectively control the roadway roof. In order to solve the problems with pillarless mining under soft rock roof conditions, using the 1510 working face of Xinyi Coal Mine as an example, a gob-side caving roadway forming (GSCRF) technique for broken immediate roof is developed. This paper discusses the adaptability and feasibility of this technology through theoretical modeling and on-site engineering testing. A roadway rock surrounding control scheme based on “cable + steel beams + yielding prop” is further designed, and field tests and monitoring are carried out. Field tests show that, during GSCRF of the 1510 working face, the maximum subsidence of the roof remains within 200 mm. The convergence of the two sides causes stabilization. The tension on the anchor cables is gradually becoming stable. The monitoring results show that the roadway has a good stress environment and the surrounding rock is effectively controlled. Compared with the traditional pillarless mining mode, this technology has the technical advantages of achieving complete elimination of coal pillars, reduced pressure on the roadway roof, and interference-free mining of the working face. The research outcome can provide useful reference for pillarless mining by GSCRF and a solution for pillarless mining under soft rock roof conditions.

To analyze the shear characteristics and mesoscopic failure mechanism of irregular serrated rock discontinuities, a great deal of interview samples of irregular serrated structures were made by 3D printing technology, and laboratory shear tests were carried out on them under different normal stresses. At the same time, PFC numerical simulation software is used to establish relevant models to study the evolution of microcracks and the distribution characteristics of the force chain on the rock discontinuity during the shear process. The results show that the shear mechanical properties of irregular serrated rock discontinuities are affected by normal stress, undulating angle, and undulating height. The shear strength increases with the increase of normal stress and undulating height, and decreases with the increase of undulating angle. The numerical simulation results show that the irregular structural surface cracks under different undulation angles, which first start at the near force end serration root on both sides and further evolve to the adjacent serrations, while the irregular structural surface cracks under different undulation heights, which first start at the serration root with the lowest height and expand to the adjacent serrations. At the same time, the number of cracks increases with the increase of normal stress and the force chain is mainly distributed near the sawtooth surface. The force chain is more concentrated near the near force end sawtooth and at the tip and root of the rest of the sawtooth. At the same time, the direction of the force chain is approximately perpendicular to the force surface of the sawtooth. The research results are helpful in further understanding the shear mechanical properties and differences of irregular serrated rock discontinuities.

The noise control of a compressor has always been a hot spot in the field of industrial application. In this paper, the air inlet structure of the sound insulation hood of an air compressor unit was studied and improved. Acoustic finite element numerical simulation analysis of the sound insulation hood model was carried out using the acoustic software LMS Virtual Lab Acoustics. The simulation results were compared with the experimental data to verify the correctness of the model, and the theoretical results showed a good agreement with the experiment data. The sound insulation performance of the sound insulation hood under different structures was also investigated in this paper. The results show that the main source of unit noise leakage is outward radiation through the air inlet. In addition, the noise at the air inlet of the unit and the overall noise were significantly reduced compared with the traditional sound insulation hood upon installing 120° and 90° diaphragm structures on the inner wall of the air inlet. The optimization results show that the noise reduction effect of the sound insulation hood with a 90° diaphragm structure was better than that with a 120° diaphragm structure.

For truss structures, the question of whether to weld hidden welds or not has been controversial. In the actual construction process of truss structures, the members are usually spot welded in place on the assembly platform, and then welded as a whole, while the hidden welds of the truss are not welded, especially for small pipe diameter trusses. Furthermore, in this study, under hidden weld unwelded conditions, two kinds of reinforcing method (adding a half outer sleeve on each joint and filling concrete into the chord members) are adopted to achieve the purpose of strengthening the truss. Therefore, this paper presents an experimental study on the static behavior of four types of Warren tubular trusses made of CHS members. These four types are (1) T-HW: The truss with hidden welds welded; (2) T-HN: The truss with hidden welds unwelded; (3) TS-AS: The truss strengthened on the basis of T-HN by adding a half outer sleeve on each joint; (4) TS-FC: The truss strengthened on the basis of T-HN by filling concrete into the top and bottom chord members. The mechanical behavior, failure mode, bearing capacity, and load-displacement of all specimens were investigated. The surface plasticity of the bottom chord member, the weld fracture around tubular joints at the bottom chord member, and the bending deformation of the bottom chord member were observed in the tests. Compared with the T-HW specimen, the load carrying capacity of the T-HN specimen decreased by 18%. On the other hand, the T-HN specimen has better deformability than the T-HW specimen. The reinforcing method of adding a half outer sleeve on each joint and filling concrete into the chord members can effectively improve the load carrying capacity and stiffness of the truss, thus reducing the overall deformation of the truss, but the reinforcing method of filling concrete into the chord members is more efficient.