Characteristic features of local breakdown near a crack-tip in the transition zone from nucleation to unstable rupture during stick-slip shear failure

1991 ◽  
Vol 28 (2-3) ◽  
pp. A75
Keyword(s):  
Transition Zone ◽  
Shear Failure ◽  
Crack Tip ◽  
Stick Slip ◽  
Characteristic Features ◽  
Local Breakdown

scholarly journals Investigations of Coal-Rock Parting-Coal Structure (CRCS) Slip and Instability by Excavation

2021 ◽  
Vol 2021 ◽  
pp. 1-15
Author(s):  
Guang-Jian Liu ◽  
Heng Zhang ◽  
Ya-Wei Zhu ◽  
Wen-Hao Cao ◽  
Xian-Jun Ji ◽  
...  
Keyword(s):  
Shear Failure ◽  
P Wave ◽  
Shear Behaviour ◽  
Failure Zone ◽  
Stick Slip ◽  
Coal Structure ◽  
P Wave Velocity ◽  
Splitting Failure ◽  
Shear And Tensile Cracks ◽  
Coal Rock

Slip and instability of coal-rock parting-coal structure (CRCS) subjected to excavation disturbance can easily induce coal-rock dynamic phenomena in deep coal mines. In this paper, the failure characteristics and influencing factors of CRCS slip and instability were investigated by theoretical analysis, numerical simulations, and field observations. The following main results are addressed: (1) the slip and instability of CRCS induced by excavation are due to stress release, and the damage of the rock parting is partitioned into three parts: shear failure zone, slipping zone, and splitting failure zone from inside to outside with slip; (2) the slip and instability process of CRCS is accompanied by initiation, expansion, and intersection of shear and tensile cracks. The development of the cracks is dominated by shear behaviour, while the tensile crack is the main factor affecting fracture and instability of CRCS; and (3) slip and instability of CRCS are characterized by stick-slip first and then stable slip, accompanied with high P-wave velocity and rockburst danger coefficient based on microseismic tomography.

Tests and Calculations of Thermomechanical Shocks in the Brittle/Ductile Transition Zone of a Pressure Vessel Steel

2003 ◽  
Author(s):  
M. Reytier ◽  
S. Chapuliot ◽  
M. Ne´de´lec
Keyword(s):  
Transition Zone ◽  
Mouth Opening ◽  
Crack Tip ◽  
Compact Tension ◽  
Compact Tension Specimen ◽  
Crack Mouth Opening Displacement ◽  
Pressure Vessel Steel ◽  
Opening Displacement ◽  
Vessel Steel ◽  
Brittle Ductile Transition

In order to study the effects of a sudden cooling in a thick hot structure, such as the vessel of a pressurised water reactor, a specially-adapted compact tension specimen has been developed. It consists of a CT50 (2T-CT specimen) with holes through the specimen to cool the crack tip locally by liquid nitrogen. Therefore, this new test allows to study in details different loading-temperature histories near the brittle/ductile transition zone which may put the classical crack intiation criteria in the wrong. First, this article describes in details two tests for which a cleavage rupture has been obtained during the thermal shock on this 16MND5 steel. Either the Crack Mouth Opening Displacement was maintained during the test or the applied load. Then, numerical calculations have been realised in order to estimate the local mechanical fields at the crack tip and to evaluate the global fracture mechanics parameters. Thanks to these tests and these thermal and mechanical simulations, a work is done on rupture criteria under thermal shocks by using either the “Master Curve” approach or the Beremin model.

Mechanisms of Microstructural Rearrangement on Two-Dimensional Aggregates under Compressive Stress

2011 ◽  
Vol 312-315 ◽  
pp. 682-687 ◽  
Author(s):  
Sarunya Promkotra
Keyword(s):  
Large Scale ◽  
Shear Failure ◽  
Elastic Stress ◽  
Tensile Failure ◽  
Small Scale ◽  
Two Dimensional ◽  
Stick Slip ◽  
Elastic And Plastic Deformations ◽  
Elastic Loading ◽  
Air Liquid Interface

Two-dimensional (2D) colloidal aggregates of polystyrene microspheres 4 μm were experimentally modeled to study the rearranged mechanisms and compression behaviors at the air-liquid interface. The aggregated models occurred due to the interaction forces between particles. The combination of mechanical testing technique and the digital video microscopy had been developed to quantitatively analyze the compressive deformation of 2D aggregates. When the compressive forces were applied to the cluster, these forces were transmitted trough the aggregated network during compression. Solid-like mechanical properties of 2D aggregated cluster were examined. Deformation mechanisms occurred within the aggregated network which presented the particle rearrangements during yield. Elastic deformation had undergone the compressive elastic stress of the elastic loading. Rearrangement mechanisms found generally were rolling-hinge, sliding mechanisms and tensile failure for a small-scale deformation. Shear failure and stick-slip mechanisms caused a large-scale plastic deformation. However, across the yield point, the tensile failures were dominated. Rearrangement mechanisms of particles affected both elastic and plastic deformations.

scholarly journals Study of Dynamics of Block-Media in the Framework of Minimalistic Numerical Models

2020 ◽  
pp. 143-168
Author(s):  
Alexander E. Filippov ◽  
Valentin L. Popov
Keyword(s):  
Numerical Models ◽  
Seismic Energy ◽  
Static Friction ◽  
Stability Diagram ◽  
Friction Model ◽  
Low Energy ◽  
Stick Slip ◽  
State Dependent ◽  
Proposed Model ◽  
Characteristic Features

AbstractOne of the principal methods of preventing large earthquakes is stimulation of a large series of small events. The result is a transfer of the rapid tectonic dynamics in a creep mode. In this chapter, we discuss possibilities for such a transfer in the framework of simplified models of a subduction zone. The proposed model describes well the basic characteristic features of geo-medium behavior, in particular, statistics of earthquakes (Gutenberg Richter and Omori laws). Its analysis shows that local relatively low-energy impacts can switch block dynamics from stick–slip to creep mode. Thus, it is possible to change the statistics of seismic energy release by means of a series of local, periodic, and relatively low energy impacts. This means a principal possibility of “suppressing” strong earthquakes. Additionally, a modified version of the Burridge-Knopoff model including a simple model for state dependent friction force is derived and studied. The friction model describes a velocity weakening of friction between moving blocks and an increase of static friction during stick periods. It provides a simplified but qualitatively correct stability diagram for the transition from smooth sliding to a stick–slip behavior as observed in various tribological systems. Attractor properties of the model dynamic equations were studied under a broad range of parameters for one- and two-dimensional systems.

Stick-slip unstable shear failure as a source of high frequency elastic radiation

1989 ◽  
Vol 33 (4) ◽  
pp. 322-337
Author(s):  
J. Kozák ◽  
T. Lokajíček ◽  
J. Šílený ◽  
V. Rudajev
Keyword(s):  
High Frequency ◽  
Shear Failure ◽  
Stick Slip

scholarly journals Flare-Like Ultraviolet Spectra of Active Regions

1975 ◽  
Vol 68 ◽  
pp. 105-107 ◽  
Author(s):  
G. E. Brueckner
Keyword(s):  
Transition Zone ◽  
Broad Band ◽  
Active Regions ◽  
Uv Spectra ◽  
Strong Line ◽  
Time Intervals ◽  
Small Areas ◽  
Characteristic Features ◽  
Short Time ◽  
Selection Of

SummarySome characteristic features of UV spectra which can be seen in flares (Brueckner, this Symposium, p. 135) can also be detected in active regions without the presence of typical other flare phenomena like X-ray enhancement. Another distinct difference between these ‘flare-like’ spectra and flare spectra is the absence of very high temperature ions like Fe XXI in the ‘flare-like’ spectra. They occur in small areas and can be detected as ‘fluctuating Hα bright points’ in broad band Hα. Simultaneously, a strong UV brightening can be seen. As reported by the Skylab crews, these brightenings occur more frequently and quasi-periodic prior to flares. Their spectra show the very broad transition zone lines and often strong line shifts toward the blue or red. Figure 1 shows a selection of typical spectra. One notices a very asymmetric Lα profile in one case. Spectra prior to, during, and after a flare are reproduced in Figure 2. One recognizes that the transition zone instability started intermittently prior to the flare and could be seen during short time intervals long after the flare had ceased.

Sign in / Sign up

Export Citation Format

Share Document