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Fracture expansion in rock masses can be observed by monitoring the break of contacts between the bounding particles via the discrete element method. The latter's realization in this study via the PFC2D program tracked the evolution process of the zonal disintegration in an exemplary roadway-surrounding rock affected by mining. Besides, the damage evolution pattern in a high-stress soft rock roadway was simulated by the FLAC2D program using a strain-softening plastic model, revealing the effects of rock mass strength, stress state, and anchor support on the zonal disintegration of the roadway. Numerical simulation results show that in a roadway with high-level stress, the obvious fractures spread from the roadway surface to the depth of the surrounding rock along a series of geometric planes and cut the surrounding rock into rock mass blocks. Under high crustal stress, conjugate shear fractures occur near the roadway surfaces and form a closed-loop fractured zone after intersecting the conjugate fracture faces. The closed fractured zone becomes a free face, from which conjugate shear fractures develop, forming new closed fractured zones in the deep surrounding rock. By repeatedly generating the closed fracture zones, a fracture network appears in the roadway-surrounding rock. The development of zonal disintegration of roadway-surrounding rock mainly depends on the rock mass strength and its stress state. Zonal disintegration only occurs when the crustal stress of the roadway-surrounding rock exceeds its strength. When the horizontal stress is low and the vertical stress exceeds the rock mass strength, zonal disintegration only occurs on two sides of the roadway. When the vertical stress is low and the horizontal stress exceeds the rock's mass strength, it only appears on the roof and floor. When the values of cohesion, internal friction angle, and tensile strength are reduced in the same proportion, cohesion has the greatest impact on the expansion of the zonal disintegration zone, followed by the internal friction angle, while the tensile strength effect is the least. In anchor-supported roadways undergoing zonal disintegration processes, the intact zone blocks slide relatively along the fracture surface during the process of loosening and deformation of the surrounding rock, making the anchor rods susceptible to tensile, shear, and bending actions. [ABSTRACT FROM AUTHOR]

Fracture expansion in rock masses can be observed by monitoring the break of contacts between the bounding particles via the discrete element method. The latter’s realization in this study via the PFC2D program tracked the evolution process of the zonal disintegration in an exemplary roadway-surrounding rock affected by mining. Besides, the damage evolution pattern in a high-stress soft rock roadway was simulated by the FLAC2D program using a strain-softening plastic model, revealing the effects of rock mass strength, stress state, and anchor support on the zonal disintegration of the roadway. Numerical simulation results show that in a roadway with high-level stress, the obvious fractures spread from the roadway surface to the depth of the surrounding rock along a series of geometric planes and cut the surrounding rock into rock mass blocks. Under high crustal stress, conjugate shear fractures occur near the roadway surfaces and form a closed-loop fractured zone after intersecting the conjugate fracture faces. The closed fractured zone becomes a free face, from which conjugate shear fractures develop, forming new closed fractured zones in the deep surrounding rock. By repeatedly generating the closed fracture zones, a fracture network appears in the roadway-surrounding rock. The development of zonal disintegration of roadway-surrounding rock mainly depends on the rock mass strength and its stress state. Zonal disintegration only occurs when the crustal stress of the roadway-surrounding rock exceeds its strength. When the horizontal stress is low and the vertical stress exceeds the rock mass strength, zonal disintegration only occurs on two sides of the roadway. When the vertical stress is low and the horizontal stress exceeds the rock’s mass strength, it only appears on the roof and floor. When the values of cohesion, internal friction angle, and tensile strength are reduced in the same proportion, cohesion has the greatest impact on the expansion of the zonal disintegration zone, followed by the internal friction angle, while the tensile strength effect is the least. In anchor-supported roadways undergoing zonal disintegration processes, the intact zone blocks slide relatively along the fracture surface during the process of loosening and deformation of the surrounding rock, making the anchor rods susceptible to tensile, shear, and bending actions.

The objective of this study is to apply the finite difference method (FDM) scheme to generate profiles of velocity, vorticity, pressure, temperature, and density of the flow field inside the chamber of a rotating detonation engine. In addition, this study discusses the Kuo's algorithm used in the computation of Chapman-Jouguet (CJ) variables. A new computational algorithm is introduced to compute the CJ variables, the shock, and the post-shock conditions. Five different fuels are tested, H 2 –O 2 , H 2 -air, CH 4 -air, C 2 H 6 -air, and C 2 H 2 -air. The results show good performance for the FDM scheme, and the new algorithm is adopted in this study to perform all CJ calculations. The new algorithm's results are compared with the experimental data available for the tested fuels and show close results. Another important result is that the highest vorticity forms along the slip line of the combustion chamber, then it gradually shrinks along the path of the slip line. • Presenting a new algorithm to compute the Chapman-Jouguet variables. • Each detonation wave can achieve a different Chapman-Jouguet pressure. • CFD test cases fuels used: H 2 –O 2 , H 2 -air, CH 4 -air, C 2 H 6 -air, and C 2 H 2 -air. • The RDE detonation reactants mixture height varies with fuel type. • Vorticity is highest at the slip line and shrinks downstream the slip line. [ABSTRACT FROM AUTHOR]

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Constitutive behaviors of granular materials are driven by both particle interactions and geometric arrangements of contact network. To bridge the gap between the grain scale and the sample scale, the mesoscale is of great importance as it corresponds to the smallest scale at which geometrical effect can be accounted for. Meso shear structures (sometimes called microbands) have been observed frequently on incremental strain maps in granular materials under shearing, while the Rudnicki and Rice localization criterion for shear band is not fulfilled yet. These meso structures are thin, quasi-linear and they involve a few grains as well as their surrounding voids. This paper introduces the concept of “incremental shear strain chain” (simply called “shear chain”) to provide a specific quantitative definition of such mesostructures. “Shear chains” are defined based on incremental deviatoric strain fields in 2D biaxial simulations. Particular attention is paid to demonstrate that the shear chain orientation is a material scale property, insensitive to boundary conditions, loading paths and sample densities. Since shear chains are shown to be closely related to sliding mechanisms, they can stand for a mesoscale definition of the concept of slip lines as defined in the standard elasto-plasticity theory. [ABSTRACT FROM AUTHOR]

Copyright of China Mechanical Engineering is the property of Editorial Board of China Mechanical Engineering and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

• shock-driven gas-particle flow under the moderately dense regime is studied • formation mechanism of the primary and secondary vortexes is discussed • inter-particle collisions affect the slip line stability at the upstream cloud edge • particle cloud evolutions after being impacted by the shock are discussed Shock-driven gas-particle flows exist in a wide variety of physical systems, covering the range from dilute to dense regime. There are a lot of fundamental questions remaining to be answered, like the evolutions of flow instability, two-phase interactions, and inter-particle collision effects. In this work, the Eulerian-Lagrangian approach with gas-particle four-way coupling is applied to model two-dimensional shock-driven gas-particle flow under the moderately dense regime. For the gas flow, the formation mechanism of primary and secondary vortexes is discussed. The primary vortex is caused by the roll-up of slip line, while the secondary vortexes are induced by the velocity and density difference between the penetrating flow of particle-laden zone and the outside mainstream. Parametric studies of different Mach numbers, particle diameters and initial volume fractions have been performed to investigate the effects on shock behaviours and slip line instabilities. For the particle phase, a high-volume-fraction compression region forms at the upstream cloud zone, which blocks the penetrating gas, and results in the formation of slip line. The cloud tail is mainly composed of the upstream edge particles. The inter-particle collisions have impact on the particle distributions, and greatly affect the slip line stability at the upstream cloud edge. This work provides valuable insights into the instability mechanism of compressible gas-solid flow and the particle dispersion behaviours. However, it is important to note that our analysis is based on a two-dimensional configuration. In a real three-dimensional context, the generation of vortices is likely to differ, and may affect the particle dynamics to a certain degree. [Display omitted] [ABSTRACT FROM AUTHOR]

Abstract Based on the slip line and limit analysis theories, this paper presents a new 3D collapse mechanism to analyze the face stability of a circular shield-driven tunnel in purely cohesive soil. The new collapse mechanism is a 4-variable multizone mechanism that depends on cover-to-diameter ratios (C/D). The proposed mechanism suggests that failure zones at the tunnel face are primarily formed by shear failure. A comparison of this approach with numerical methods and other kinematic approaches shows that the proposed failure mechanism significantly improves the existing upper-bound solutions for the face stability of circular tunnels in purely cohesive soils. [ABSTRACT FROM AUTHOR]

In studies on instabilities of flowfield in rotating detonation, one of the most common concerns is the instability at the slip line originating from the conjunction of the detonation wave and oblique shock. Using Euler equations associated with the 7-species-and-8-reaction finite-rate chemical reaction model of hydrogen/air mixtures, further studies are performed to simulate the 2-D rotating detonation, and the flow mechanism of instability at the slip line is investigated in depth. The results show that the distinct wake profile exists at the slip line, which is different from the typical mixing layer. Analysis indicates that the generation of wake is caused by the transition shock between the detonation wave and oblique shock. Because of the wake profile, the vorticity distribution therein appears in a double-layer layout, and different evolutions exist in different vorticity layers. Based on the velocity profile across the slip line, the analysis by the linear stability theory is made, and two main unstable modes which have different shape profiles and phase velocities are found. Discrete Fourier transformation is utilised to analyse the numerical results, and similar shape profiles are obtained. A general coincidence in velocity of vortex movement is also attained between the theoretical predictions and simulations. Investigations show that the wake instability is responsible for the unstable mechanism, and corresponding unstable structures differ from the canonical ones in typical mixing layers. [ABSTRACT FROM AUTHOR]

The problem of extension of a plate with symmetric edge notches of different shape is numerically solved on the basis of the theory of plane stress state of an ideally plastic body under the von Mises plasticity condition. The discontinuities of the tangential and normal components of the velocity along the rigid-plastic boundaries, which result in the plastic strain localization in the neck and the material fracture, are calculated. The obtained results are of practical interest for estimating the limit extension force for a plate with edge notches of different shape and the limit strain of a thin sheet in inhomogeneous biaxial extension. [ABSTRACT FROM AUTHOR]

The relationship between acoustic emission (AE) signals and tribological phenomena in the elementary processes of friction and wear is examined. The elementary processes of friction and wear were observed by a frictional surface microscope, which installed a friction system into the view of an optical microscope. In this paper, the elementary processes are focused on the plastic deformation of the friction surface and the formation of wear particles between friction surfaces. In-situ experiments with the frictional surface microscope were performed by a pin-on-block type sliding test for iron and zinc. The friction surface and its side face were also observed by an atomic force microscope. The results show that two types of AE signals—a continuous AE signal of low amplitude and a burst-type AE signal of high amplitude—are detected in the elementary processes of friction and wear. The continuous AE signal of low amplitude is detected by the generation of slip lines and wear elements. The burst-type AE signal of high amplitude is detected by the formation of a transfer particle.