High Tangential Stresses Research Articles

A strength-stress coupling criterion for rockburst: Inspirations from 1114 rockburst cases in 197 underground rock projects

Rockburst is a kind of engineering geological disaster induced by artificial engineering excavation. Qualitative and quantitative statistical analysis of rockburst cases is the primary work and research basis for rockburst prediction and discrimination. In this study, 1114 rockburst cases are collected and the qualitative and quantitative characteristics are analyzed. It is found that rockburst is prone to occur in rocks that are hard, complete, dry, and unweathered. Strong rockburst occurs more frequently in rocks with high uniaxial compressive strength (σc), elastic modulus, and elastic energy index, and in rock masses with high initial maximum principal stress (σ1)and tangential stress. Notably, rockburst may occur only when σc≥ 60 MPa and σ1≥ 10 MPa. On this basis, the “Human–Rock–Environment” three-element mechanism of rockburst is presented. Guided by this conception, the rationality and defects of the traditional strength-stress ratio (SSR) criterion are investigated. The SSR criterion does not adequately consider the absolute difference between the rock strength and geostress, as well as their combined effects. Subsequently, a strength-stress coupling (SSC) criterion is proposed from a two-dimensional scale.This criterion is characterized by considering both the absolute boundary conditions of σcand σ1, as well as their coupling interval. Five intervals of weak, weak–moderate, moderate, moderate–strong, and strong rockburst are divided in the two-dimensional chart and their distinguishing conditions are given. The existence of two transition zones for weak–moderate and moderate–strong reflects the coupling effect of rock strength and geostress when rockburst occurs, confirming the rationality and scientificity of the SSC criterion. The verification results show that the SSC criterion features higher accuracy as compared with the SSR criterion.

Numerical study on the effect of in-situ stress on smoothwall blasting in deep tunnelling

In the present study, a numerical model is first calibrated against the crack networks and pressure attenuation data in laboratory blasting test. Then, based on the calibrated numerical model, two-hole plane models are developed and used to perform a series of simulations of smoothwall blasting in deep tunnelling subjected to in-situ stress. The evolutions of rock fracture and excavation damage zone in the roof/floor and sidewalls under different far-field hydrostatic pressure and anisotropic in-situ stress conditions are numerically investigated. The findings in numerical modelling are also analytically interpreted with the stress distributions around the designed tunnel perimeter and perimeter borehole. The numerical and analytical results show that the variations of rock cracking and excavation damaged zone induced by smoothwall blasting with in-situ stress are mainly attributed to the high tangential compressive stress concentration around the remaining rock after inner primary blasts and the tensile stress acting on the wall of perimeter hole, which control the crack propagation and initiation respectively. At last, the implications of findings for practical smoothwall blasting in deep tunnelling are discussed.

Effects of intermediate stress on deep rock strainbursts under true triaxial stresses

The effect of intermediate stress (in situ tunnel axial) on a strainburst is studied with a three-dimensional (3D) bonded block distinct element method (DEM). A series of simulations of strainbursts under true triaxial in situ stress conditions (i.e. high tangential stress, moderate intermediate stress and low radial stress) of near-boundary rock masses are performed. Compared with the experimental results, the DEM model is able to capture the stress-strain response, failure pattern and energy balance of strainbursts. The fracturing processes of strainbursts are also numerically reproduced. Numerical results show that, as the intermediate stress increases: (1) The peak strain of strainbursts increases, the yield stress increases, the rock strength increases linearly, and the ratio of yield stress to rock strength decreases, indicating that the precursory information on strainbursts is enhanced; (2) Tensile and shear cracks increase significantly, and slabbing and bending of rock plates are more pronounced; and (3) The stored elastic strain energy and dissipated energy increase linearly, whereas the kinetic energy of the ejected rock fragments increases approximately exponentially, implying an increase in strainburst intensity. By comparing the experimental and numerical results, the effect of intermediate stress on the rock strength of strainbursts is discussed in order to address three key issues. Then, the Mogi criterion is applied to construct new strength criteria for strainbursts by converting the one-face free true triaxial stress state of a strainburst to its equivalent true triaxial stress state. In summary, the effect of intermediate stress on strainbursts is a double-edged sword that can enhance the rock strength and the precursory information of a strainburst, but also increase its intensity. ©2022 Institute of Rock and Soil Mechanics, Chinese Academy of Sciences. Production and hosting by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

Porosity effect on the linear stability of flow overlying a porous medium.

We study how the stability of a homogeneous incompressible fluid flow over a saturated Brinkman porous medium is affected by a change in porosity. We produce neutral curves using the shooting method in the area of bimodality. When the porosity decreases, the topology of these curves changes because of the interplay between two instability modes. The long-wave instability is dominant if the medium is highly porous. In contrast, the short-wave instability is the most significant at low porosity because of high tangential stress at the fluid-medium interface. We identify a stability gap between the neutral curve branches within a narrow range of porosity values. The calculated results show the development and disappearance of this gap when the porosity changes.

Molecular Dynamics Simulation of the Edge Dislocation Glide in Nickel and Silver in the Presence of Interstitial Light Element Atoms

The edge dislocation glide velocity in fcc metals (nickel, silver) is studied at various temperatures, tangential stresses, and contents of interstitial atoms of light elements (carbon, nitrogen, oxygen) by molecular dynamics simulation. The glide velocity of partial dislocations in pure metals decreases with increasing temperature at low tangential stresses (~10 MPa) and increases at relatively high tangential stresses (~102 MPa or higher). The introduction of interstitial atoms retards dislocation glide. This effect is more pronounced in nickel than in silver, which is mainly due to the difference in the lattice parameters: the lattice parameter of nickel is smaller than that of silver.

Determination of Forming Behaviour of EN AW-6060 by Different Testing Methods under Cold Bulk Forming Conditions

The description and modelling of the forming behaviour is essential for the numerical prediction of material flow and the applied forming force. A representative stress state as well as comparable strain rate and temperatures should be considered during material characterization. In the presented investigations, an extruded aluminium alloy (EN AW-6060 T6) was formed for different compression tests with diverse specimen geometries (cylinders, discs, flat rings, cuboids) and compared with the tensile and torsion tests under the same forming conditions and with one and the same initial microstructure with an average grain size of 50 µm. To ensure that no microstructural changes during the deformation process (recrystallization) affect the measurement results due to load-related material anomalies, all tests for the material characterization were started at room temperature. The comparison is based on the cylindrical compression test, because this is standardised for room temperature (DIN 50106) and, due to the compressive stress, is the most suitable material description for bulk forming processes. However, in the stacked compression tests without additional guide elements, a much higher friction between the layers is required than between the workpiece and the tool, so that the deformation is not concentrated on the centre of the specimen (with regard to height) and the middle layers won’t get out due to high tangential stresses. By consideration of these conditions the stacked tests are comparable to the cylindrical compression test. However, the friction between material and die must be taken into account for compression tests as well as the resulting forming heat when calculating the flow curve. Based on this, the forming behaviour can be modelled according to various flow curve approaches for cold forming processes. In general, it was found that all flow curves of the tensile tests, torsion tests and the compression test were in the range of ± 7.5 % based on the cylinder compression test.

Experimental and numerical study on dynamic mechanical behaviors of low-silver lead-free solder under combined compression-shear loadings

In this paper, the behaviors of low-silver lead-free solder Sn0.3Ag0.7Cu were studied by quasi-static and dynamic compression-shear tests and finite-element analysis. The quasi-static tests were performed on MTS-809 material tester, while the dynamic tests were carried out on a modified split Hopkinson pressure bar (SHPB) system that uses inclined cropped cylinders as incident and transmitter bars. The inclination angle, which is formed between the ends of the incident and transmitter bar, allows dynamic combined compression-shear loadings. Inclination angles from 0° to 45° were tested under the same strain rate of 2157 s−1. Experimental results show that a larger inclination angle results in lower normal stress amplitude but higher tangential stress, given the same strain rate. The effect of strain rate was further studied by fixing the inclination angle as 30°. When the strain rate is below 2445 s−1, the strain rate effect is limited. However, from 2445 to 2875 s−1, the strain rate effect becomes significant, not only in normal direction but also in tangential direction. The experimental findings on both inclination angle and strain rate were then simulated by finite element method using the Cowper–Symonds material model. It was found that the adopted material model is able to predict the same trending as experimental data, but an accurate prediction requires a more sophisticated material model.

Influence of truck tires exploid on the level of professional risk in servicing truck wheel

The article deals with a problem of minimization of levels of professional risks while servicing truck tires and wheels. In the process of removal of a truck wheel a worker can sustain a serious or fatal injury caused by the explosion of an inflated truck tire. The explosion of an inflated truck tire can result in affecting of complementary offloading’s on clamps cast spoke wheel. The mathematical model description of move of a disk wheel and values of reactive forces arising from the explosion of an inflated truck tire are presented. The equations of move of a disk wheel at its removal under the influence of reactive forces are solved. Results of numerical modelling of stresses arising on clamps cast spoke wheel during the explosion of the inflated truck tire are presented. The maximum normal stress arises in the stub basis can lead to free move of wheel and in a place of contact of a disk of a wheel high tangential stresses to destruction of a nut is positioned.

Molecular dynamics simulation of silicon carbide nanoscale material removal behavior

The scratching processes of monocrystalline and polycrystalline silicon carbide (SiC) with diamond grit were studied by molecular dynamics simulation to investigate the nanoscale material removal behavior. The results showed that, for both monocrystalline and polycrystalline SiC, the material removal processes were achieved by the phase transition to the amorphous structure. Large depth of cut and low scratching speed induced the large scratching forces, stress, and surface damage layer thickness. Less amorphous structure phase transition, smaller normal scratching force, and higher tangential stress were found in polycrystalline SiC, comparing to the monocrystalline SiC, due to the material soften caused by the microstructure, under all scratching conditions. Furthermore, the tangential stress showed highly dependent on the grain geometry and grain boundary (GB) location in polycrystalline. The subsurface damage layer in polycrystalline was little thinner than that in monocrystalline before the new GB generation at a low depth of cut and deteriorated at large depth of cut. In addition to the plastic deformation, which occurred in the monocrystalline SiC nanoscale scratching, the intergranular fracture and transgranular fracture were also observed through the GB generation and connection in polycrystalline SiC.

Analytical Solution to Study Depletion/Injection Rate on Induced Wellbore Stresses in an Anisotropic Stress Field

During production or injection, the state of stresses within the reservoir as well as around the wellbore changes. It is therefore important to evaluate the impact of the induced stresses on stability of wellbores. This study proposes an analytical solution to estimate the influence of production or injection rate on stresses around a wellbore in an anisotropic stress field. For considering the effect of production/injection rate, pseudo steady state flow was assumed within the reservoir that occurs more frequently than transient or steady state flow in a reservoir with an expanding drainage radius. Until now stress equations have not been developed in which the effect of production/injection rate being included. The results showed that the impact of the depletion and injection rate on induced stresses around the wellbore is significant and should be considered in the geomechanical analysis especially in low permeability reservoirs. Application of the proposed solution on a typical sandstone reservoir showed that in relatively high production rate, the radial and tangential stresses near wellbore decrease whereas the vertical and pore pressure increase. An opposite trend was observed for the effect of injection rate on near wellbore stresses. This results are consistent with field observation and means that in rapid production, the vertical stress will increase and horizontal stresses will decrease leading to surface subsidence.

Stress distribution around Fe5Si3 and its effect on interface status and mechanical properties of Si3N4 ceramics

AbstractSi3N4 ceramics with different amount of Fe5Si3 were prepared by adding FeSi2. Residual thermal stress distribution and elastic energy around Fe5Si3 particles in various depths were calculated. The interface status between second phase particles and matrix was analyzed in terms of stress and energy. High tangential compressive stresses and low radial tensile stresses were generated along the surface of the ceramics. Elastic strain energy caused by unit interface was high around big particles in deep area of the ceramics. Microcracks are observed around the big Fe5Si3 particles. Furthermore, accord to our calculation, microcracks are easily generated around particles in superficial layer of matrix when second phase particles have lower thermal expansion coefficient than the matrix, while microcracks tend to be generated in deep layer of matrix preferentially when the thermal expansion coefficient of second phase particles is higher than matrix. Residual stresses and microcracks around Fe5Si3 particles greatly influenced mechanical properties. Fracture toughness of Si3N4 ceramics with similar Si3N4 particle size distribution increased with the amount of Fe5Si3, and fine Fe5Si3 particles could enhance the strength of Si3N4 ceramics. Si3N4 ceramics exceeding 1.2 GPa strength were prepared.

Failure Mechanisms and Evolution Assessment of the Excavation Damaged Zones in a Large-Scale and Deeply Buried Underground Powerhouse

The Jinping I underground powerhouse is deeply buried and is one of the largest underground powerhouses in China. As a result of high levels of in situ stress, complex geological conditions and the effects of excavation in adjacent caverns, the surrounding rock mass has been severely deformed and broken, and excavation damaged zones (EDZs) have become major obstacles to the design of cavern excavation and support. Field investigations and monitoring data indicated that there are two main modes of failure: high tangential stress induced failure and progressive failure, which have occurred on the mountain side and the river valley side of the Jinping I underground powerhouse. These two main modes of failure were due to strong secondary principal stress forces in the sub-parallel directions and sub-vertical directions, acting on the axes of the main powerhouse on the mountain side and on the river valley side, respectively. Deformations and EDZs on the river valley side were generally larger than those found along the mountain side, and the distribution of deformations was consistent with the distribution of EDZs. The evolution of the EDZ on the river valley side has clearly been time dependent, especially along the downstream arch abutment, and the EDZ was considerably enlarged with further excavation. Additionally, the deformation of the surrounding rock mass was first initiated from the edge of the excavation area and gradually extended to deeper areas away from the opening. However, the EDZ on the mountain side was enlarged only during the first two phases of excavation. The extension of pre-existing cracks and the creation of new fractures has mainly occurred in the oldest EDZ section, and the HDZ has been visibly enlarged, whereas the EDZ has shown little change in other excavation phases.

Investigation of the Effect of Radiation-Induced Shape Change of Fuel Assemblies on the Temperature Regime and Stress-Strain State of Fuel-Element Cladding

Methods of calculating the temperature regime and stress-strain state of fuel elements in a sodium-cooled BN-600 are presented. Deformation effects and the local azimuthal temperature distribution of fuel elements with wire winding spacing in fuel assemblies are taken into account. The influence of radiation effects on the temperature regime and stress-state of the fuel elements is shown. The maximum stresses are observed in the section with maximum shape change. At run completion, as a result of nonuniform swelling of the cladding material, on the inner fiber of the cladding the compression stresses transform into tensile stresses and repeat the character of the temperature distribution along the cladding perimeter. The maximum inelastic accumulated strains (ec = 1.5%) occur at the point of greatest swelling and high tangential stress.

Structural and dynamic performance of an asphalt slab track in a sharp curve

The increasing preoccupation about railway externalities, such as train-induced vibrations, has prompted the incorporation of bituminous materials as a part of the railway infrastructure. In this paper, the structural and dynamic behavior of a real asphalt slab track, made of a mixture SMA-16 with a 0.5% of recycled plastomers is studied with a FEM model of the vehicle and the track considering both vertical and lateral dynamics. The FEM model is used to study the different dynamic behavior on the track surroundings due to the effect of the trains passing at different speeds. The paper has two main purposes. One is to provide the differences in dynamic response for straight and curved sections at three different speeds. The other aim of the paper is to obtain high tangential stresses in the interfaces between the different layers of the infrastructure. The results reveal how the structural behavior of the track is checked and demonstrate the important role of horizontal accelerations induced in the infrastructure.

A new approach to DEM simulation of sand production

This paper presents a model for the investigation of sandstone degradation and sand production mechanisms coupled with fluid flow analysis using the Discrete Element Method (DEM). The model was used to investigate the effects of in-situ stresses and flow rate on sand production.We developed a linked DEM-fluid flow model for sanding analysis. The model calculates seepage forces and applies them on solid particles in the DEM model. The model accounts for permeability and porosity changes due to sandstone deformation and sand production. The DEM model was verified against poro-elastoplastic analytical solutions. Subsequently, the model was used for sanding simulation from a block-shaped sample under different far-field stress and pressure conditions. The boundary stresses and fluid pressures were varied to study their influence on sandstone degradation and sand production.The creation of a borehole in a solid block resulted in the development of uniform or V-shape breakouts around the borehole. The failure zone around the borehole expanded after the application of fluid flow and sand grain detachments. Fluid flow was observed to influence the size and mode of failure in the breakout zone and sand production. Boundary stress dominated the sanding response at higher boundary stress conditions. However, much lower sanding occurred under higher boundary stresses but low boundary fluid pressures. High tangential stresses around the borehole caused by high confining stress resulted in strong frictional interlocking that alleviated sand production. Massive sanding was observed at lower far-field stress but higher boundary pore pressure.

Coupled thermal-hydrological-mechanical behavior of rock mass surrounding a high-temperature thermal energy storage cavern at shallow depth

We numerically model the thermal-hydrological-mechanical (THM) processes within the rock mass surrounding a cavern used for thermal energy storage (TES). We consider a cylindrical rock cavern with a height of 50m and a radius of 10m storing thermal energy of 350°C as a conceptual TES model, and simulate its operation for thirty years. At first, the insulator performance are not considered for the purpose of investigating the possible coupled THM behavior of the surrounding rock mass; then, the effects of an insulator are examined for different insulator thicknesses. The key concerns are hydro-thermal multiphase flow and heat transport in the rock mass around the thermal storage cavern, the effect of evaporation of rock mass, thermal impact on near the ground surface and the mechanical behavior of the surrounding rock mass. It is shown that the rock temperature around the cavern rapidly increases in the early stage and, consequently, evaporation of groundwater occurs, raising the fluid pressure. However, evaporation and multiphase flow does not have a significant effect on the heat transfer and mechanical behavior in spite of the high-temperature (350°C) heat source. The simulations showed that large-scale heat flow around a cavern is expected to be conduction-dominated for a reasonable value of rock mass permeability. Thermal expansion as a result of the heating of the rock mass from the storage cavern leads to a ground surface uplift on the order of a few centimeters, and to the development of tensile stress above the storage cavern, increasing the potentials for shear and tensile failures after a few years of the operation. Finally, the analysis shows that high tangential stress in proximity of the storage cavern can some shear failure and local damage, although large rock wall failure could likely be controlled with appropriate insulators and reinforcement.

Fretting fatigue behavior of SUS304 stainless steel under pressurized hot water

Fretting fatigue behavior of the sensitized SUS304 stainless steel under a pressurized hot water at 7.3MPa and 288°C was investigated. The tests were carried out under a contact pressure of 100MPa and a frequency of 20Hz. From the experimental result, combined effect of pressurized hot water and localized high tangential stress due to fretting resulted in nucleation of intergranular crack along the outer edge of contact region at lower stress amplitudes, while a fretting fatigue crack was nucleated at the highest tangential force point independently from these intergranular cracks at higher stress amplitudes. No intergranular crack nucleation was observed for fretting fatigue at the same temperature in air. The higher stress ratio reduced the fatigue strength, where the crack tip was exposed more in corrosive environment due to the high mean stress compared to the lower stress ratio.

A Microstructural Resolved Model for the Stress Analysis of Lithium-Ion Batteries

The stress field in a lithium-ion (Li-ion) battery can have a significant impact on its performance. To better understand the stress distribution in a Li-ion battery cell, a 2D multiphysics microstructural resolved model (MRM) with realistic electrode geometries has been developed. This model considers the species transport, battery kinetics, and the deformations and stresses of the components caused by Li intercalation. The model was used to examine a LixC6|PP|LiyMn2O4 cell. The stress distributions and developments in the active particles and in the binder were discussed in detail. The results show that while the intercalation stress distributions in general agree with the description of the analytical solutions for spherical active particles, a higher tangential stress can arise at the particle surface at locations where the local curvature is concave or when the particle is next to a rigid current collector. The results also indicate that between the two binder systems investigated, the one with a lower modulus and larger elongation appears to be a better choice over the higher modulus, less ductile grade, provided that the two systems have the same ratio of the interfacial adhesion strength to the binder strength. This work demonstrates the potential of the MRM in improving our understanding on the stress and deformation in battery components and in the selection of battery materials.

Analysis of Near-Surface Cracking under Critical Loading Conditions Using Uncracked and Cracked Pavement Models

In this paper, the mechanism of near-surface cracking under critical loading conditions was investigated using mechanistic modeling approaches. These loading conditions were represented by a combination of nonuniform tire contact stresses in three directions generated during vehicle maneuvers (free rolling, acceleration/braking, and cornering) that were predicted from a tire-pavement interaction model. Three-dimensional finite element models of uncracked and cracked pavements were developed to evaluate the critical factors that are responsible for crack initiation and propagation at the near-surface of a typical full-depth pavement structure. It was found that the near-surface cracks in the proximity of tire edges showed strong mixed-mode (tension and shear) fracture potential. The pavement responses from both uncracked and cracked pavement models indicated that shear mode of fracture in the presence of compression appeared to be the dominant mode of damage for near-surface cracking. Compared to the free rolling condition, tire braking/acceleration and cornering induced high tangential contact stresses on the pavement surface, which could significantly accelerate the development of cracks at the pavement near-surface. The near-surface cracking potential was dependent on the variations of localized tire contact stress distributions. The findings presented in this study shed light on the experimental characterization of the near-surface cracking phenomenon, which appears to be driven by different stress conditions than the classical bottom-up fatigue cracking. This study also highlights the impact of vehicle maneuvering on premature pavement damage that is often neglected in the current pavement design process.

Effects of the roller feed ratio on wrinkling failure in conventional spinning of a cylindrical cup

In this study, wrinkling failure in conventional spinning of a cylindrical cup has been investigated by using both finite element (FE) analysis and experimental methods. FE simulation models of a spinning experiment have been developed using the explicit finite element solution method provided by the software Abaqus. The severity of wrinkles is quantified by calculating the standard deviation of the radial coordinates of element nodes on the edge of the workpiece obtained from the FE models. The results show that the severity of wrinkles tends to increase when increasing the roller feed ratio. A forming limit study for wrinkling has been carried out and shows that there is a feed ratio limit beyond which the wrinkling failure will take place. Provided that the feed ratio is kept below this limit, the wrinkling failure can be prevented. It is believed that high compressive tangential stresses in the local forming zone are the causes of the wrinkling failure. Furthermore, the computational performance of the solid and shell elements in simulating the spinning process are examined and the tool forces obtained from wrinkling and wrinkle-free models are compared. Finally, the effects of the feed ratio on variations of the wall thickness of the spun cylindrical cup are investigated.