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In this paper, the tensile failure behaviour of transversally bedding layers was numerically simulated by using particle flow code in two dimensions. Firstly, numerical model was calibrated by uniaxial, Brazilian and triaxial experimental... more
In this paper, the tensile failure behaviour of transversally bedding layers was numerically simulated by using particle flow code in two dimensions. Firstly, numerical model was calibrated by uniaxial, Brazilian and triaxial experimental results to ensure the conformity of the simulated numerical model\'s response. Secondly, 21 circular models with diameter of 54 mm were built. Each model contains two transversely bedding layers. The first bedding layer has low mechanical properties, less than mechanical properties of intact material, and second bedding layer has high mechanical properties, more than mechanical properties of intact material. The angle of first bedding layer, with weak mechanical properties, related to loading direction was 0o, 15o, 30o, 45o, 60o, 75o and 90o while the angle of second layer, with high mechanical properties, related to loading direction was 90o, 105o, 120o, 135o, 150o,160o and 180o. Is to be note that the angle between bedding layer was 90o in all bedding configurations. Also, three different pairs of the thickness was chosen in models; i.e., 5 mm/10 mm, 10 mm/10 mm and 20 mm/10 mm. The result shows that In all configurations, shear cracks develop between the weaker bedding layers. Shear cracks angel related to normal load change from 0o to 90o with increment of 15o. Numbers of shear cracks are constant by increasing the bedding thickness. It\'s to be note that in some configuration, tensile cracks develop through the intact area of material model. There is not any failure in direction of bedding plane interface with higher strength.
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In this paper, the effect of cable indent shape on the shear behavior of concrete-cable attachment surface has been investigated using PFC2D. Firstly, calibration of PFC was performed using the Brazilian experimental test and uniaxial... more
In this paper, the effect of cable indent shape on the shear behavior of concrete-cable attachment surface has been investigated using PFC2D. Firstly, calibration of PFC was performed using the Brazilian experimental test and uniaxial compression test to reproduce the concrete sample. After calibration of PFC2D, punch shear tests were simulated by creating a rectangular concrete model in PFC2D. Numerical models with a dimension of 100mm *100 mm were prepared. cable with different indent shape was inserted within the model. The punch shear test condition was added to the model. The normal load was fixed at 3.7 MPa (σc/10) and shear load was applied to the model till failure occurred. The results show that tensile cracks are the dominant mode of failure that occurs in the attachment surface. Also, the shape of the attachment surface has an important effect on the failure mechanism of concrete. The shear strength increased by increasing both of the bolt indent width and length.
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The effects of dip angles and thicknesses of bedding layers at the interaction line in between the planes of a normal fault and bedding layers are numerically studied by a discrete element modelling technics. The calibration of the... more
The effects of dip angles and thicknesses of bedding layers at the interaction line in between the planes of a normal fault and bedding layers are numerically studied by a discrete element modelling technics. The calibration of the numerical method is accomplished by using an inverse-modelling approach. The laboratory results of Brazilian tensile tests may be used to measure the micro-mechanical parameters of the intact rocks. The shear test results are also performed on the rock joints to determine the micro-mechanical parameters of the bedding interfaces in the present simulation work. The numerical simulation of the shear behaviour of normal fault is performed by making box models with dimensions of 100 mm × 72 mm to represent the bedding layers with different dips and thicknesses. The bedding plane dip angles change from 0° to 165° with an increment of 15° and the thicknesses of these layers change from 6 mm to 12 mm with an increment of 6 mm. The shear testing conditions are exposed to these models to form the normal faults for the numerical modelling of the physical problem under a lateral pressure of 2 MPa. The numerical modelling results show that the shear cracks initiate from all of the bedding interfaces. In this numerical modelling, three major oriented parallel tensile bands are developed and one vertical tensile fracture also propagates through the shear band so that the model is failed. As the bedding layers’ dips are increased, the angle in between the shear bands and the bedding layers is decreased, and as the bedding thickness is decreased, the lengths of shear bands are increased. However, when the bedding angles are 120° and 135° the minimum shear strength of the model is occurred.
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در این مقاله با استفاده از مطالعات آزمایشگاهی و شبیه سازی عددی، تاثیر زاویهداری سرمته PDC بر مکانیزم شکست نمونههای شبه سنگی بررسی شده است. به این منظور، سه جفت سرمته PDC با زاویه برنده صفر ، 30 و 60 درجه ساخته شد. 9 نمونه شبه سنگی گچ با... more
در این مقاله با استفاده از مطالعات آزمایشگاهی و شبیه سازی عددی، تاثیر زاویهداری سرمته PDC بر مکانیزم شکست نمونههای شبه سنگی بررسی شده است. به این منظور، سه جفت سرمته PDC با زاویه برنده صفر ، 30 و 60 درجه ساخته شد. 9 نمونه شبه سنگی گچ با ابعاد cm5* cm11 *cm14 آماده سازی شد. نسبت گچ به آب، 2 است. برای هر زاویه داری سرمته، 3 نمونه گچ تحت آزمایش قرار گرفت. نمونه گچ بالای سرمته ها نصب شده و مجموعه ها تحت آزمایش تک محوره قرار گرفتند. نرخ بارگذاری mm/min 05/0 است. همزمان با تست های آزمایشگاهی، شبیه سازی عددی توسط نرم افزار کد جریان ذره انجام شد. به این ترتیب که ابتدا نرم افزار PFC برای گچ کالیبره شد. در مرحله دوم، مدل عددی با ابعاد cm11 *cm14 آماده شد. سپس هفت جفت سرمته با زاویه داری، 0، 15، 30، 45 و 60 درجه شبیه سازی شد و در قسمت تحتانی مدل عددی قرار گرفت. سرمته ها با نرخ mm/sec 01/0 به سمت مدل حرکت کرده و باعث شکست مدل می شود. نتایج نشان می دهد که الگوی شکست نمونه ها تابع زاویه داری سرمته است همچنین مقاومت نمونه ها توسط الگوی شکست نمونه ها کنترل می شود. با افزایش زاویه داری نمونه، نیرو...
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DOI:10.22044/jme.2021.10601.2013 The tensile strength of the anisotropic rock-like material specimens is meastred directly in the laboratory using a new device converting the compressive loading to that of the tensile before the rock... more
DOI:10.22044/jme.2021.10601.2013 The tensile strength of the anisotropic rock-like material specimens is meastred directly in the laboratory using a new device converting the compressive loading to that of the tensile before the rock breakage. The specially prepared concrete slabs of dimensions 19 cm * 15 cm * 15 cm with a central hole of 7.5 cm in diameter are tested experimentaly. The specimens are located in the compressive-to-tensile load converting device, and tested under a compressive loading rate of 0.02 MPa/s by the universal testing machine. The cubic slab samples are made in three different configurations to have the directions of 0°, 45°, and -45° with respect to the applied loading direction. In order to compare the direct tensile strength of the concrete samples with that of the indirect measuring tests, some Brazilian tests are also carried out on the concrete disc specimens prepared in the laboratory. By comparing the direct and indirect testing results of the concre...
In this paper, interaction between semi-circular space and neighboring joint with and without Presence of Rock Bolt is investigated using Particle Flow Code. For this purpose, firstly calibration of PFC was performed using both of the... more
In this paper, interaction between semi-circular space and neighboring joint with and without Presence of Rock Bolt is investigated using Particle Flow Code. For this purpose, firstly calibration of PFC was performed using both of the Brazilian experimental test and uniaxial compression test. Secondly, numerical model with dimension of 100mm *100 mm was prepared. A semi-circular space with radius of 25 mm was situated below the model. A joint with length of 40 mm was situated above the space. Joint opening was 2mm. Joint angle related to horizontal direction was 0°, 15°, 30°, 45°, 60° and 75°. Totally, 6 different configurations of semi-circular space and neighboring joint were prepared. These models tested with and without presence of vertical rock bolts by biaxial test. The Rock bolt length was 50 mm. The value of lateral force was fixed at 2 MPa. Axial force was applied to the model till final failure was occurred. The results shows that presence of rock bolts change the failure ...
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Two blade samples from the first and second stages of a gas turbine were investigated to understand the reason of fracture. All samples suffered excessive heat superficially. Using a TBC layer on top of Diffusion coating will be a... more
Two blade samples from the first and second stages of a gas turbine were investigated to understand the reason of fracture. All samples suffered excessive heat superficially. Using a TBC layer on top of Diffusion coating will be a reasonable solution for protecting the blades. Although in case of the first stage blades cracking was postponed, the thermomechanical fatigue cracks still originated from the blade surface. It was observed that the damage of the thermal barrier coating layer would lead to the overheating of the blades, promoting the rate of creep and rafting of precipitates. This phenomenon was more severe in the second stage samples with more damaged protective layers. It was found that the chemical composition of the fuel gas may increase the potential and rate of corrosion and damage to the blades. Concurrent with physical investigation, numerical simulation was performed to study the effect of particle impact into the blade. By changing the particle radii and its p...
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In this paper, a compression-to-tensile load converter device is developed to determine the anisotropic tensile strength of brittle material. A cubic sample with an internal pore was used as the test specimen, and a series of finite... more
In this paper, a compression-to-tensile load converter device is developed to determine the anisotropic tensile strength of brittle material. A cubic sample with an internal pore was used as the test specimen, and a series of finite element analysis and DDM simulations were performed thereafter to analyse the effect of pore dimensions on the stress concentration, as well as to render a suitable criterion for determining the anisotropic tensile strength of concrete. The results obtained by this device show that the tensile strength of concrete is similar in different directions because of the homogeneity of bonding between the materials.
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For investigating the effect of the pre-existing joints on the initiation pattern of hydraulic fractures, the numerical simulation of circular holes under internal hydraulic pressure with a different pattern of the joint distributions are... more
For investigating the effect of the pre-existing joints on the initiation pattern of hydraulic fractures, the numerical simulation of circular holes under internal hydraulic pressure with a different pattern of the joint distributions are conducted by using a finite element code, FRANC2D. The pattern of hydraulic fracturing initiation are scrutinized with changing the values of the joint length, joint offset angle. The hydraulic pressures with 70% of the peak value of borehole wall breakout pressure are applied at the similar models. The simulation results suggest that the opening-mode fracture initiated from the joint tip and propagated toward the borehole for critical values of ligament angle and joint offset angle. At these critical values, the crack grow length is influenced by joint ligament length. When the ligament length is less than 3 times the borehole diameter the crack growth length increases monotonically with increasing joint length. The opening-mode fracture disappear...
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In this paper the effect of confining pressure and tunnel depth on the ground vertical settlement has been investigated using particle flow code (PFC2D). For this perpuse firstly calibration of PFC2D was performed using both of tensile... more
In this paper the effect of confining pressure and tunnel depth on the ground vertical settlement has been investigated using particle flow code (PFC2D). For this perpuse firstly calibration of PFC2D was performed using both of tensile test and triaxial test. Then a model with dimention of 100 m × 100 m was built. Acircular tunnel with diameter of 20 m was drillled in the middle of the model. Also, a rectangular tunnel with wide of 10 m and length of 20 m was drilled in the model. The center of tunnel was situated 15 m, 20 m, 25 m, 30 m, 35 m, 40 m, 45 m, 50 m, 55 m and 60 m below the ground surface. these models are under confining pressure of 0.001 GPa, 0.005 GPa, 0.01 GPa, 0.03 GPa, 0.05 GPa and 0.07 GPa. The results show that the volume of colapce zone is constant by increasing the distance between ground surface and tunnel position. Also, the volume of colapce zone was increased by decreasing of confining pressure. The maximum of settlement occurs at the top of the tunnel roof....
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This study presents crack initiation, propagation and coalescenceat or near pre-existing open cracks in a numericalmodel under Brazilian test. Firstly, Particle Flow Code intwo dimensions (PFC2d) was calibrated with respect to thedata... more
This study presents crack initiation, propagation and coalescenceat or near pre-existing open cracks in a numericalmodel under Brazilian test. Firstly, Particle Flow Code intwo dimensions (PFC2d) was calibrated with respect to thedata obtained from experimental laboratory tests to ensurethe conformity of the simulated numerical models response.Brazilian discs contain one, two, three, four, and five parallelcentred cracks (45° to the horizontal) under compressiveline loading. Models containing two and three cracks havedifferent joint spacing and joint configuration. In model consistingone flaws, tensile cracks initiated from notch tip andpropagates in direction of compressive loading till coalescewith model edge. By increasing the number of notch, first typeof tensile crack initiated at the tips of outer flaws and coalescedwith model edge. Also second type of tensile cracksinitiates from middle of inner flaws and coalesce with tip ofthe neighbouring flaws. The results show that joint...
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The present article discusses the effect of the ratio of bridge surface to total shear surface, number of bridge areas and normal stress on the failure behavior of the planar non-persistent open joints. Totally, 38 models were prepared... more
The present article discusses the effect of the ratio of bridge surface to total shear surface, number of bridge areas and normal stress on the failure behavior of the planar non-persistent open joints. Totally, 38 models were prepared using plaster and dimensions of 15 cm
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PurposeDevelop a new three‐dimensional discrete element code (BLOKS3D) for efficient simulation of polyhedral particles of any size. The paper describes efficient algorithms for the most important ingredients of a discrete element... more
PurposeDevelop a new three‐dimensional discrete element code (BLOKS3D) for efficient simulation of polyhedral particles of any size. The paper describes efficient algorithms for the most important ingredients of a discrete element code.Design/methodology/approachNew algorithms are presented for contact resolution and detection (including neighbor search and contact detection sections), contact point and force detection, and contact damping. In contact resolution and detection, a new neighbor search algorithm called TLS is described. Each contact is modeled with multiple contact points. A non‐linear force‐displacement relationship is suggested for contact force calculation and a dual‐criterion is employed for contact damping. The performance of the algorithm is compared to those currently available in the literature.FindingsThe algorithms are proven to significantly improve the analysis speed. A series of examples are presented to demonstrate and evaluate the performance of the propo...