94 research outputs found
Origin of abnormal glass transition behavior in metallic glasses
No full textIn this paper, the phenomenon of two glass-transition-like appearance in the supercooled liquid region of metallic glasses was investigated. It is confirmed that this abnormal behavior is attributed to the transition process of an amorphous state from higher energy to lower energy. The amorphous state with higher energy comes from the uneven distribution of compositions in glasses, which is mainly caused by the component with significant differences in atomic size and nonnegative values of enthalpy of mixing. The results were verified by high resolution transmission electron microscopy and energy-dispersive spectrometry. (C) 2014 Elsevier Ltd. All rights reserved
A correlation radius estimate between in-panel faults and high-stress areas using Monte Carlo simulation and point process statistics
No full textResearch on Prevention of Rock Burst with Relieving Shot in Roof
No full textAbstractDuring hard roof rupture or slip instability with the sudden release of large amount of elastic energy, rock burst will be caused by violent shock easily. Based on the geological conditions of 6303 working face in Jisan Colliery, numerical simulation was carried out systematically of relieving shot in roof, then the reasonable parameters of relieving shot was provided. The results of danger-breaking measures of relieving shot in roof on-site shows that the danger of rock burst is reduced with fractured circle connected and values of electromagnetic emission and drillings decreased
Coal Burst Induced by Horizontal Section Mining of a Steeply Inclined, Extra-Thick Coal Seam and Its Prevention: A Case Study from Yaojie No. 3 Coal Mine, China
No full textAt present, coal bursts in working faces of steeply inclined coal seams (SICSs) have rarely been investigated, and current research focuses on the influences of roof breaking and instability of overlying structures in goaf on coal bursts; however, the stress state of coal masses in working faces being subjected to coal bursts is rarely researched. To overcome the above defects, a model for analysing stresses on coal masses in horizontal section of SICSs was established based on the coal burst that occurred in LW5521-20, Yaojie No. 3 Coal Mine, Lanzhou, Gansu Province, China. Moreover, the mechanism underpinning such a coal burst in SICSs was analysed based on the superposition mechanism of dynamic and static loads. The results show that the side abutment pressure near the roof and floor under the horizontal sections of SICSs is asymmetrically distributed in the vertical direction in which the peak of side abutment pressure near the roof is closer to the working face and therefore is taken as the source of static loads for coal bursts in working faces. When the superimposed dynamic load caused by hanging roof breaking and high static load borne in the coal masses is larger than the critical load for coal burst inception, a coal burst will occur. Furthermore, the superimposed dynamic load induced by coal bursts on the support and the initial static load on the supports are larger than their limiting load, which leads to support collapse and eventually causes dynamic failure of the working face. The coal burst in working faces in horizontal sections of SICSs can be prevented by using deep-hole presplit blasting in a hard roof, destress blasting in coal masses, and support optimisation of working faces, showing a favourable preventative effect
Effects of Crystallization on Boson Peak of ZrCuNiAlTi Bulk Metallic Glass
No full textThe low-temperature specific heats of ZrCuNiAlTi metallic glass and its corresponding crystallized alloy are studied from 3 to 53 K. The effects of crystallization on the specific heat and boson peak of these alloys are discussed. In analyzing the experimental data, in addition to the contribution of the Debye mode and Einstein modes, the origin of the boson peak is interpreted using the harmonic localized modes based on the vibrations of loose "rattler" atoms in the oversized cage structures. The results are useful to understand the structure-property relationship of metallic glasses at low temperature
Numerical Investigation into the Mechanical Behaviours and Energy Characteristics of Hard Coal Subjected to Coupled Static-Dynamic Loads
No full textIn practical engineering, coal burst is usually caused by the combination of high geo-stress and dynamic loading. To study the dynamic response of coal in geo-stress conditions, numerical models of a coupled static–dynamic split Hopkinson pressure bar (SHPB) test system were established, based on which impact tests for coal specimens at different impact speeds and static pre-stress levels were conducted. The mechanical properties, energy characteristics and failure patterns of coal specimens under coupled static and dynamic loads were analyzed. The results show that when the pre-stress is constant, peak stress, the maximum strain energy and the maximum kinetic energy increase significantly with impact speed. Nevertheless, they are less affected by the static pre-stress, increasing linearly with a pre-stress level under lower impact speeds but becoming stable under higher impact speeds. In addition, weak dynamic loads may trigger the instability of the coal specimen in a high pre-stress condition. Overall, both the impact speed and static pre-stress have influence on the mechanical behavior and energy characteristics of coal specimens under coupled static and dynamic loads, but the influence of the impact speed outweighs that of the static pre-stress
Dynamic and static load effect of non-uniformly “bow-shaped” super-thick key strata
No full textThe rupture of super-thick key strata is a crucial factor in triggering mine dynamic disasters. Investigating the impact of their non-uniform thickness on mining-induced stress environments and rupture dynamic loads, and further revealing the mechanism of dynamic and static loading on rock burst pressure, is the theoretical foundation for predicting rock burst risks and disaster prevention and control. This paper investigates the non-uniformly thick “bow-shaped” super-thick key strata in the Binchang mining area of Shaanxi. Through comprehensive theoretical analysis and numerical simulation, it analyzes the mechanical principle of abnormal stress concentration in the coal rock mass beneath the “bow-shaped” super-thick key strata, clarifies the influence of the “bow-shaped” morphology on the rupture characteristics of the super-thick key strata and reveals the mechanism of dynamic and static load superposition in the area beneath the “bow-shaped” formation, leading to rock bursts. Based on the study above, a method for predicting the disaster risks caused by the rupture of “bow-shaped” super-thick key strata is proposed. The results show that in the convex area under the “bow-shaped” formation of the super-thick key strata, the high stress is exceptionally concentrated, increasing the coal rock body stress by an additional 22.1 MPa, with an increase rate of up to 56%, which is the fundamental reason for the high static load formation in the underlying coal-rock body. At the same time, the principal stress in the concave area of the “bow-shaped” formation concentrates and undergoes significant deformation, increasing the risk of strong dynamic loads due to rupture. Under the combined action of dynamic and static loads in the non-uniformly thick “bow-shaped” super-thick key strata, the rock bursts are likely to occur in the pillar and roadway areas. The proposed method for predicting the disaster risks due to the rupture of “bow-shaped” super-thick key strata effectively guides the disaster prevention and control in high-risk mining areas prone to rock bursts. Additionally, the distributed fiber optic field measurement results validate the intrinsic connection between the rupture of super-thick key strata and the generation of dynamic loads
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