Kinetic Theory of the Fracture of the Coal (Rock) Edge by the Gas-Filled Cracks. Instantaneous Loading-Out

The kinetic theory of the fracture of brittle materials is applied to the study of undercritical and critical growths of cracks in gas-filled rocks. In this type of the materials, the gas filtration from the environment to the cavity of a growing crack plays an important role. The proper account for this factor combined with the dynamics of the stressed state of the bed allows the estimation of the rate of growth of the main crack on the assumption of the Griffith criterion validity. It is found that, immediately after the instantaneous loading-out of the bed in the course of excavation, the cracks of certain size and orientation are exploded with the succeeding growth dependent on the gas entry into the cracks. The time of the filtration growth of the cracks has been estimated. The intervals of the control parameters (formational gas pressure, crack size, overburden pressure, surface energy of coal/rock, modulus of elasticity), where the spontaneous fracture of the bed becomes possible, have been found. The results open a way to the forecast of instantaneous outbursts of coal, rock, and gas.

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Experimental Observations of Dominant Effective Short Fatigue Crack Behavior for Railway LZ50 Axle Steel

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.118-120.54 ◽

2010 ◽

Vol 118-120 ◽

pp. 54-58 ◽

Cited By ~ 2

Author(s):

Bing Yang ◽

Yong Xiang Zhao

Keyword(s):

Crack Initiation ◽

Evolutionary Process ◽

Crack Size ◽

Short Crack ◽

Structural Barriers ◽

Banded Structure ◽

Crack Behavior ◽

Growing Crack ◽

Two Stages ◽

Hardness Values

, was experimentally investigated by a replica technique to seven smooth hourglass shaped specimens for railway LZ50 axle steel. Character of two-stages, i.e. the micro-structural short crack (MSC) stage and the physical short crack (PSC) stage, was revealed for the crack initiation and growth. Most importantly, the crack growth rate exhibited decelerations twice in MSC stage. This behavior was corresponding to the ferrite grain boundary firstly and then to the pearlite banded structure. The boundary appeared a barrier because there were pearlites around with significant higher micro-hardness values. The banded structure appeared a barrier because each band was rich in hard layered pearlites for the crack to cross. In PSC stage, the crack propagated with a decreasing resistance of micro-structural barriers as the crack length increased. The two barriers are inherent in the material and the crack initiation and growth are subjected to an evolutionary process under competition between the inherent resistances from the barriers and the increasing driving force from the growing crack size. This provides a prehensive understanding of the crack initiation and growth.

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On transient relativistic thermodynamics and kinetic theory

Proceedings of the Royal Society of London Series A - Mathematical and Physical Sciences ◽

10.1098/rspa.1977.0155 ◽

1977 ◽

Vol 357 (1688) ◽

pp. 59-75 ◽

Cited By ~ 116

Keyword(s):

Heat Conduction ◽

Kinetic Theory ◽

Relativistic Theory ◽

Speed Of Light ◽

Equilibrium Thermodynamics ◽

Dilute Gas ◽

Fourier Heat Conduction ◽

Relativistic Thermodynamics ◽

Proper Account ◽

Propagation Velocities

In the conventional Onsager formulation of non-equilibrium thermodynamics the Fourier heat conduction law is parabolic, and permits arbitrarily large propagation velocities for temperature discontinuities. While embarassing in a non-relativistic theory, this is unacceptable in a relativistic one. This paper presents a detailed discussion of the thermodynamics and (in the dilute gas limit) kinetic theory of such transients. When proper account of the two length scales involved is taken into account, the theory becomes hyperbolic; propagation velocities for a dilute gas never exceed √3/5 c = 0.775 c , where c is the speed of light.

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Nanoscale fracture of defective popgraphene monolayer

10.1101/463505 ◽

2018 ◽

Author(s):

Fanchao Meng ◽

Ming Ni ◽

Feng Chen ◽

Jun Song ◽

Dong Wei

Keyword(s):

Point Defect ◽

Point Defects ◽

Fracture Stress ◽

Defect Density ◽

Linear Trend ◽

Crack Size ◽

Carbon Allotrope ◽

Griffith Criterion ◽

Individual Point ◽

Dynamics Simulations

ABSTRACTA new carbon allotrope, namely popgraphene, has been recently demonstrated to possess high potentials for nanodevice applications. Here, the fracture of defective popgraphene was studied using molecular dynamics simulations and continuum modeling. Three scenarios of defects were considered, including an individual point defect, distributed point defects, and nanocracks. It was found that the fracture stress of popgraphene with an individual point defect was governed by both the geometry of the defect and the critical bond where fracture initiates. Moreover, the fracture stress of popgraphene with distributed point defects was discovered to be inversely proportional to the defect density, showing a nice linear trend. Furthermore, for popgraphene with a nanocrack, it failed in a brittle fashion and exhibited a negligible lattice trapping effect. Griffith criterion was subsequently employed with the consideration of crack deflection to accurately predict the dependence of fracture stress on crack size. The present study lays a mechanistic foundation for nanoscale applications of popgraphene and offers a better understanding of the roles of defects in fracture of low-dimensional materials.

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Relativistic Kinetic Theory

10.1017/9781107261365 ◽

2017 ◽

Cited By ~ 14

Author(s):

Gregory V. Vereshchagin ◽

Alexey G. Aksenov

Keyword(s):

Kinetic Theory ◽

Relativistic Kinetic Theory

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Kinetic Theory of Living Pattern

10.1017/cbo9780511529726 ◽

1993 ◽

Cited By ~ 56

Author(s):

Lionel G. Harrison

Keyword(s):

Kinetic Theory

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Tracer diffusion in perfectly aligned liquid crystalline phases Kinetic theory and molecular dynamics simulations

Molecular Physics ◽

10.1080/00268979709482789 ◽

1997 ◽

Vol 91 (6) ◽

pp. 993-1003 ◽

Cited By ~ 1

Author(s):

ANJALI KHARE ◽

DAVID KOFKE ◽

GLENN EVANS

Keyword(s):

Molecular Dynamics ◽

Kinetic Theory ◽

Molecular Dynamics Simulations ◽

Liquid Crystalline ◽

Tracer Diffusion ◽

Crystalline Phases ◽

Liquid Crystalline Phases ◽

Dynamics Simulations

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Methods for Restricting Maximum Exposure Rate in Computerized Adaptative Testing

Methodology ◽

10.1027/1614-2241.3.1.14 ◽

2007 ◽

Vol 3 (1) ◽

pp. 14-23 ◽

Cited By ~ 9

Author(s):

Juan Ramon Barrada ◽

Julio Olea ◽

Vicente Ponsoda

Keyword(s):

Measurement Accuracy ◽

Computerized Adaptive Testing ◽

Computation Time ◽

Adaptive Testing ◽

Exposure Rate ◽

Control Parameters ◽

The Impact ◽

Two Alternatives ◽

Selection Of ◽

Maximum Exposure

Abstract. The Sympson-Hetter (1985) method provides a means of controlling maximum exposure rate of items in Computerized Adaptive Testing. Through a series of simulations, control parameters are set that mark the probability of administration of an item on being selected. This method presents two main problems: it requires a long computation time for calculating the parameters and the maximum exposure rate is slightly above the fixed limit. Van der Linden (2003) presented two alternatives which appear to solve both of the problems. The impact of these methods in the measurement accuracy has not been tested yet. We show how these methods over-restrict the exposure of some highly discriminating items and, thus, the accuracy is decreased. It also shown that, when the desired maximum exposure rate is near the minimum possible value, these methods offer an empirical maximum exposure rate clearly above the goal. A new method, based on the initial estimation of the probability of administration and the probability of selection of the items with the restricted method ( Revuelta & Ponsoda, 1998 ), is presented in this paper. It can be used with the Sympson-Hetter method and with the two van der Linden's methods. This option, when used with Sympson-Hetter, speeds the convergence of the control parameters without decreasing the accuracy.

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