Study on Mesoscale Damage Evolution Characteristics of Irregular Sandstone Particles Based on Digital Images and Fractal Theory

To study the mesoscale damage evolution law of irregular sandstone particles, based on RFPA2D and digital image processing technology, a real mesostructure numerical model of irregular sandstone particles is established to simulate the breakage process of particles, the effects of loading conditions and mesoscale heterogeneity on irregular sandstone particle damage are studied, and the calculation method of fractal dimension of irregular rock particles mesoscale fracture is proposed. The results show that the fracture damage degree (ω) and fractal dimension (D) maximum values of the constrained particles are 0.733 and 1.466, respectively, and the unconstrained particles are 0.577 and 1.153, respectively. The final failure mode of constrained particles is more complicated than unconstrained particles, the damage is more serious, and the fracture is more complete. Thus, the larger values of D yield a more complicated final failure mode of the particles. Consequently, with the larger ω, the final damage is more serious, and the breakage effect is comparatively better. The study is of great significance for exploring the laws of rock particle breakage and energy consumption, rock breakage mechanism, and searching for efficient and energy-saving rock-breaking methods.

Mechanism and Control of Cable Breakage in a Roadway with Thick Top Coal in a Rockburst Mine

Because top coal is not stable, a roadway with thick top coal often appears to mine pressure problems, such as bolt failure, cable breakage, and roof caving. In particular, these problems are more serious in rockburst mines. Based on a cable breakage case of No. 3 roadway in Xingcun coal mine, the paper analyzed the stress and elastic energy evolution law of surrounding rock and stress state of cable in the 3# roadway by means of the numerical simulation method. Thus, the cable breakage mechanism of the roadway with thick top coal in rockburst mine was revealed. Then, because surrounding rock grouting can reduce the stress concentration of surrounding rock and cable, surrounding rock grouting technology was proposed as control technology of cable breakage. Finally, parameters of surrounding rock grouting were designed and applied in the No. 3 roadway. The field results showed that surrounding rock grouting technology can be one of the solutions for cable breakage of roadway with thick top coal in rockburst mine. The research results of this paper can provide certain theoretical and practical value for mine pressure control of roadway.

Breakage Mechanism of Layered Sandstone Penetrated by TBM Disc Cutter

In this paper, the breakage mechanism of layered sandstone subjected to the TBM disc cutter was investigated. A series of typical layered sandstone specimens were prepared for true triaxial compression tests in the laboratory to simulate the disc cutter action at the tunnel face, and an acoustic emission (AE) system was used to monitor the breaking process during the penetration tests. Furthermore, a DV recorder was employed to capture the surface deformation. Then, the failure specimens were scanned by high resolution X-ray micro-CT. The results show that the failure mode of layered sandstone in terms of cracking transforms into local crushing with increasing confining stress. The propagation pattern of the cracks varies with the bedding inclination, which is distinctly different from intact rock. The results also indicate that the peak force presents linear variation with the confining stress and an increasing trend with the bedding inclination at the first penetration, and the failure mode of the second penetration is mainly related to the broken status from the first penetration.

Breakage Mechanism Study of Overhead Ground Wire Under Lighting Stroke Based On Finite Element Analysis

Breakage of overhead transmission lines and distribution lines will lead to severe power outage problems, and clarifying the breakage mechanism of the overhead lines is of great importance and value for the reliability and stability of the power system. Taking overhead ground wire for example, this paper presents its breakage mechanism study under lighting stoke based on finite element analysis. A multi-physics analysis model is built first, which includes the model of contact points. The current density distribution and the temperature rise under the impact of short circuit current are analysed, and contact resistance effect is proved the primary cause for the breakage. Then some major factors that influence the contact resistance which in turn influence the temperature rise are discussed. Based on the discussions, some valuable suggestions are given for the protection of overhead lines.

The Applied model of grinding a spherical solid particle with a direct impact on a non-deformable flat surface

A grinding process using a free impact breakage mechanism is used in industries. In order to make calculations, predict grinding results, and evaluate mills functioning, it is necessary to assess the parameters of the grinding process and interrelations between the process parameters, mills parameters and materials properties, i.e. it is necessary to use an adequate mechanical-mathematical model of the process. However it is difficult to model due to some phenomena occurring in this process. Nowadays, various researchers have established the basis for the structure of the grinding process, but the application of the existing hypotheses and methods to evaluate the grinding process is quite difficult. This paper solves the problem of a spherical shape particle impacting an absolutely rigid half-space. It proposes a refined mechanical and mathematical model describing the process of destruction of the particle using the free direct impact breakage mechanism on an absolutely rigid, stationary, and flat surface. By using the Hertz-Staerman's classical analytical dependencies on the force contact interaction of the spherical bodies and the technical theory of the longitudinal waves’ propagation in the elastic continuous medium, we obtained a new refined solution of the applied dynamic problem related to a direct impact of a ball simulating a particle of a feeding material (an absolutely rigid surface simulating the working body of the mill) taking into account local physically linear deformations, the time parameter and radial particle size. The improved theoretical model of the spherical particle destruction was brought to applicable analytical calculations, tested and illustrated by a numerical example. It made it possible to describe the fracture of the material particles, predict the result and calculate the grinding process depending on its parameters providing the required quality of grinding by regulating and selecting characteristics, designing and selecting the grinding equipment, and modeling the grinding process using the free impact breakage mechanism.

The Eureka Valley Landslide: Evidence of a Dual Failure Mechanism for a Long-Runout Landslide

Long-runout landslides are well-known and notorious geologic hazards in many mountainous parts of the world. Commonly encompassing enormous volumes of debris, these rapid mass movements place populations at risk through both direct impacts and indirect hazards, such as downstream flooding. Despite their evident risks, the mechanics of these large-scale landslides remain both enigmatic and controversial. In this work, we illuminate the inner workings of one exceptionally well-exposed and well-preserved long-runout landslide of late Pleistocene age located in Eureka Valley, east-central California, Death Valley National Park. The landslide originated in the detachment of more than 5 million m3 of Cambrian bedrock from a rugged northwest-facing outcrop in the northern Last Chance Range. Its relatively compact scale, well-preserved morphology, varied lithologic composition, and strategic dissection by erosional processes render it an exceptional laboratory for the study of the long-runout phenomenon in a dry environment. The landslide in Eureka Valley resembles, in miniature, morphologically similar “Blackhawk-like” landslides on Earth, Mars, and minor planet Ceres, including the well-known but much larger Blackhawk landslide of southern California. Like these other landslides, the landslide in Eureka Valley consists of a lobate, distally raised main lobe bounded by raised lateral levees. Like other terrestrial examples, it is principally composed of pervasively fractured, clast-supported breccia. Based on the geologic characteristics of the landslide and its inferred kinematics, a two-part emplacement mechanism is advanced: (1) a clast-breakage mechanism (cataclasis) active in the bedrock canyon areas and (2) sliding on a substrate of saturated sediments encountered and liquefied by the main lobe of the landslide as it exited the main source canyon. Mechanisms previously hypothesized to explain the high-speed runout and morphology of the landslide and its Blackhawk-like analogs are demonstrably inconsistent with the geology, geomorphology, and mineralogy of the subject deposit and its depositional environment.

Automated device for continuous stirring while sampling in liquid chromatography systems

Ultra-performance liquid chromatography is a common analysis tool, and stirring is common in many laboratory setups. Here we show a device which enables continuous stirring of samples whilst inside an ultra-performance liquid chromatography system. Utilizing standard magnetic stirring bars that fit standard vials, the device allows for the automation of experimental setups that require stirring. The device is designed such that it can replace the standard sample holder and fits in its place, while being battery operated. The use of three-dimensional (3D) printing and commercially available parts enables low-effort and low-cost device production, as well as easy modifications. Testing the device was performed by video analysis and by following the kinetics of a dynamic combinatorial library that is known to be exquisitely sensitive to agitation, as a result of involving a fiber growth-breakage mechanism. Design files and schematics are provided.