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M R Ayatollahi - One of the best experts on this subject based on the ideXlab platform.
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crack tip asymptotic field and k dominant region for anisotropic semi circular Bend Specimen
Theoretical and Applied Fracture Mechanics, 2020Co-Authors: Morteza Nejati, Saeid Ghouli, M R AyatollahiAbstract:Abstract This study reports the coefficients of the crack tip asymptotic field for the semi-circular Bend (SCB) Specimen made of anisotropic rocks when subjected to pure mode I loading. The finite element over-deterministic method is employed to determine the singular and higher order terms of the crack tip asymptotic field for a wide range of geometry and anisotropy parameters associated with the Mode I SCB test. These parameters are helpful when analysing the fracture path and failure mechanism of anisotropic rocks in cases where the process zone is large compared to the crack length. We also apply an energy-based criterion on the crack tip fields to evaluate the size of the K-dominant region as a function of geometry configuration and anisotropy. It is concluded that the ISRM-suggested size requirement for the SCB samples of rock can yield underestimated values of fracture toughness due to the constraints applied to the FPZ development.
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Stress Intensity Factors of Semi-Circular Bend Specimens with Straight-Through and Chevron Notches
Rock Mechanics and Rock Engineering, 2016Co-Authors: M R Ayatollahi, E. Mahdavi, M. J. Alborzi, Y. ObaraAbstract:Semi-circular Bend Specimen is one of the useful test Specimens for determining fracture toughness of rock and geo-materials. Generally, in rock test Specimens, initial cracks are produced in two shapes: straight-edge cracks and chevron notches. In this study, the minimum dimensionless stress intensity factors of semi-circular Bend Specimen (SCB) with straight-through and chevron notches are calculated. First, using finite element analysis, a suitable relation for the dimensionless stress intensity factor of SCB with straight-through crack is presented based on the normalized crack length and half-distance between supports. For evaluating the validity and accuracy of this relation, the obtained results are then compared with numerical and experimental results reported in the literature. Subsequently, by performing some experiments and also finite element analysis of the SCB Specimen with chevron notch, the minimum dimensionless stress intensity factor of this Specimen is obtained. Using the new equation for the dimensionless stress intensity factor of SCB with straight-through crack and an analytical method, i.e., Bluhm’s slice synthesis method, the minimum (critical) dimensionless stress intensity factor of chevron notched semi-circular Bend Specimens is calculated. Good agreement is observed between the results of two mentioned methods.
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numerical investigation of stress intensity factor for semi circular Bend Specimen with chevron notch
Engineering Solid Mechanics, 2015Co-Authors: E. Mahdavi, Yuzo Obara, M R AyatollahiAbstract:Article history: Received 6 April, 2015 Accepted 12 July 2015 Available online 15 July 2015 One of the Specimens to investigate the mode-I fracture toughness of rock and geo-materials is semi-circular Bend (SCB) Specimen. In general, initial cracks in rock test Specimens are produced in two shapes: straight-edge cracks and chevron notches. The ISRM suggested SCB Specimen has straight shaped notch. However, use of V-shaped (or chevron) notch in the SCB Specimen is preferred because of some technical difficulties associated with making a sharp crack or creating pre-crack to conduct the experimental tests. In this paper, the minimum dimensionless stress intensity factor of cracked chevron notched semi-circular Bend (CCNSCB) Specimen is determined using finite element analysis with ABAQUS software. An analytical method, (i.e. Bluhm’s slice synthesis method) is used to verify the results. It is shown that a good agreement exists between the numerical data and theoretical results. © 2015 Growing Science Ltd. All rights reserved.
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isrm suggested method for determining the mode i static fracture toughness using semi circular Bend Specimen
Rock Mechanics and Rock Engineering, 2014Co-Authors: Mahinda Kuruppu, Yuzo Obara, M R Ayatollahi, Ken P Chong, Takahiro FunatsuAbstract:The International Society for Rock Mechanics has so far developed two standard methods for the determination of static fracture toughness of rock. They used three different core-based Specimens and tests were to be performed on a typical laboratory compression or tension load frame. Another method to determine the mode I fracture toughness of rock using semi-circular Bend Specimen is herein presented. The Specimen is semi-circular in shape and made from typical cores taken from the rock with any relative material directions noted. The Specimens are tested in three-point Bending using a laboratory compression test instrument. The failure load along with its dimensions is used to determine the fracture toughness. Most sedimentary rocks which are layered in structure may exhibit fracture properties that depend on the orientation and therefore measurements in more than one material direction may be necessary. The fracture toughness measurements are expected to yield a size-independent material property if certain minimum Specimen size requirements are satisfied.
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Computation of V-notch shape factors in four-point Bend Specimen for fracture tests on brittle materials
Archive of Applied Mechanics, 2013Co-Authors: M R Ayatollahi, M. Dehghany, Z. KavehAbstract:Four-point Bend (FPB) Specimen is an important test sample in mixed mode fracture study of notched components made from brittle materials like rocks, brittle polymers, ceramics, etc. On the other hand, the notch stress intensity factors (NSIFs) are vital parameters in brittle fracture assessment of V-notched structures. Therefore, computation of NSIFs in FPB Specimens is of practical interest to engineers and researchers. Since the available methods for calculating the NSIFs are often cumbersome and need complicated calculations, it is preferred to show them as a set of dimensionless parameters for the FPB Specimen. In this research, the finite element method coupled with a recently developed algorithm called FEOD is employed to calculate the NSIFs of a FPB Specimen for several V-shape notches and for different combinations of mode I and mode II. The obtained NSIFs are then converted to dimensionless parameters called notch shape factors and are illustrated in a number of figures. It is shown that depending on the notch depth and the location of loading points, full mode mixity from pure mode I to pure mode II can be provided in the FPB Specimen. The numerical results obtained in this research are verified by using very limited results reported earlier in literature.
E. Mahdavi - One of the best experts on this subject based on the ideXlab platform.
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Stress Intensity Factors of Semi-Circular Bend Specimens with Straight-Through and Chevron Notches
Rock Mechanics and Rock Engineering, 2016Co-Authors: M R Ayatollahi, E. Mahdavi, M. J. Alborzi, Y. ObaraAbstract:Semi-circular Bend Specimen is one of the useful test Specimens for determining fracture toughness of rock and geo-materials. Generally, in rock test Specimens, initial cracks are produced in two shapes: straight-edge cracks and chevron notches. In this study, the minimum dimensionless stress intensity factors of semi-circular Bend Specimen (SCB) with straight-through and chevron notches are calculated. First, using finite element analysis, a suitable relation for the dimensionless stress intensity factor of SCB with straight-through crack is presented based on the normalized crack length and half-distance between supports. For evaluating the validity and accuracy of this relation, the obtained results are then compared with numerical and experimental results reported in the literature. Subsequently, by performing some experiments and also finite element analysis of the SCB Specimen with chevron notch, the minimum dimensionless stress intensity factor of this Specimen is obtained. Using the new equation for the dimensionless stress intensity factor of SCB with straight-through crack and an analytical method, i.e., Bluhm’s slice synthesis method, the minimum (critical) dimensionless stress intensity factor of chevron notched semi-circular Bend Specimens is calculated. Good agreement is observed between the results of two mentioned methods.
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numerical investigation of stress intensity factor for semi circular Bend Specimen with chevron notch
Engineering Solid Mechanics, 2015Co-Authors: E. Mahdavi, Yuzo Obara, M R AyatollahiAbstract:Article history: Received 6 April, 2015 Accepted 12 July 2015 Available online 15 July 2015 One of the Specimens to investigate the mode-I fracture toughness of rock and geo-materials is semi-circular Bend (SCB) Specimen. In general, initial cracks in rock test Specimens are produced in two shapes: straight-edge cracks and chevron notches. The ISRM suggested SCB Specimen has straight shaped notch. However, use of V-shaped (or chevron) notch in the SCB Specimen is preferred because of some technical difficulties associated with making a sharp crack or creating pre-crack to conduct the experimental tests. In this paper, the minimum dimensionless stress intensity factor of cracked chevron notched semi-circular Bend (CCNSCB) Specimen is determined using finite element analysis with ABAQUS software. An analytical method, (i.e. Bluhm’s slice synthesis method) is used to verify the results. It is shown that a good agreement exists between the numerical data and theoretical results. © 2015 Growing Science Ltd. All rights reserved.
Y. Obara - One of the best experts on this subject based on the ideXlab platform.
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Stress Intensity Factors of Semi-Circular Bend Specimens with Straight-Through and Chevron Notches
Rock Mechanics and Rock Engineering, 2016Co-Authors: M R Ayatollahi, E. Mahdavi, M. J. Alborzi, Y. ObaraAbstract:Semi-circular Bend Specimen is one of the useful test Specimens for determining fracture toughness of rock and geo-materials. Generally, in rock test Specimens, initial cracks are produced in two shapes: straight-edge cracks and chevron notches. In this study, the minimum dimensionless stress intensity factors of semi-circular Bend Specimen (SCB) with straight-through and chevron notches are calculated. First, using finite element analysis, a suitable relation for the dimensionless stress intensity factor of SCB with straight-through crack is presented based on the normalized crack length and half-distance between supports. For evaluating the validity and accuracy of this relation, the obtained results are then compared with numerical and experimental results reported in the literature. Subsequently, by performing some experiments and also finite element analysis of the SCB Specimen with chevron notch, the minimum dimensionless stress intensity factor of this Specimen is obtained. Using the new equation for the dimensionless stress intensity factor of SCB with straight-through crack and an analytical method, i.e., Bluhm’s slice synthesis method, the minimum (critical) dimensionless stress intensity factor of chevron notched semi-circular Bend Specimens is calculated. Good agreement is observed between the results of two mentioned methods.
Yuzo Obara - One of the best experts on this subject based on the ideXlab platform.
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numerical investigation of stress intensity factor for semi circular Bend Specimen with chevron notch
Engineering Solid Mechanics, 2015Co-Authors: E. Mahdavi, Yuzo Obara, M R AyatollahiAbstract:Article history: Received 6 April, 2015 Accepted 12 July 2015 Available online 15 July 2015 One of the Specimens to investigate the mode-I fracture toughness of rock and geo-materials is semi-circular Bend (SCB) Specimen. In general, initial cracks in rock test Specimens are produced in two shapes: straight-edge cracks and chevron notches. The ISRM suggested SCB Specimen has straight shaped notch. However, use of V-shaped (or chevron) notch in the SCB Specimen is preferred because of some technical difficulties associated with making a sharp crack or creating pre-crack to conduct the experimental tests. In this paper, the minimum dimensionless stress intensity factor of cracked chevron notched semi-circular Bend (CCNSCB) Specimen is determined using finite element analysis with ABAQUS software. An analytical method, (i.e. Bluhm’s slice synthesis method) is used to verify the results. It is shown that a good agreement exists between the numerical data and theoretical results. © 2015 Growing Science Ltd. All rights reserved.
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isrm suggested method for determining the mode i static fracture toughness using semi circular Bend Specimen
Rock Mechanics and Rock Engineering, 2014Co-Authors: Mahinda Kuruppu, Yuzo Obara, M R Ayatollahi, Ken P Chong, Takahiro FunatsuAbstract:The International Society for Rock Mechanics has so far developed two standard methods for the determination of static fracture toughness of rock. They used three different core-based Specimens and tests were to be performed on a typical laboratory compression or tension load frame. Another method to determine the mode I fracture toughness of rock using semi-circular Bend Specimen is herein presented. The Specimen is semi-circular in shape and made from typical cores taken from the rock with any relative material directions noted. The Specimens are tested in three-point Bending using a laboratory compression test instrument. The failure load along with its dimensions is used to determine the fracture toughness. Most sedimentary rocks which are layered in structure may exhibit fracture properties that depend on the orientation and therefore measurements in more than one material direction may be necessary. The fracture toughness measurements are expected to yield a size-independent material property if certain minimum Specimen size requirements are satisfied.
D. H. Tong - One of the best experts on this subject based on the ideXlab platform.
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stress intensity factors for surface cracks in single edge notch Bend Specimen by a three dimensional weight function method
Fatigue & Fracture of Engineering Materials & Structures, 2016Co-Authors: X. C. Zhao, James C. Newman, D. H. TongAbstract:A three-dimensional (3D) weight function method is employed to calculate stress intensity factors of quarter-elliptical corner cracks at a semi-circular notch in the newly developed single-edge notch Bend Specimen. Corner cracks covering a wide range of geometrical parameters under pin-loading and remote tension conditions are analysed. Stress intensity factors from the 3D weight function analysis agree well with ABAQUS-Franc3D finite element results. An engineering similitude approach previously developed for the half-elliptical surface crack in single-edge notch Bend Specimen is also applied to the present corner crack configuration. The results compare well with those from the present weight function analysis.
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Stress intensity factors for surface cracks in single‐edge notch Bend Specimen by a three‐dimensional weight function method
Fatigue & Fracture of Engineering Materials & Structures, 2016Co-Authors: X. C. Zhao, James C. Newman, D. H. TongAbstract:A three-dimensional (3D) weight function method is employed to calculate stress intensity factors of quarter-elliptical corner cracks at a semi-circular notch in the newly developed single-edge notch Bend Specimen. Corner cracks covering a wide range of geometrical parameters under pin-loading and remote tension conditions are analysed. Stress intensity factors from the 3D weight function analysis agree well with ABAQUS-Franc3D finite element results. An engineering similitude approach previously developed for the half-elliptical surface crack in single-edge notch Bend Specimen is also applied to the present corner crack configuration. The results compare well with those from the present weight function analysis.
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Weight functions and stress intensity factors for pin-loaded single-edge notch Bend Specimen: WEIGHT FUNCTIONS AND STRESS INTENSITY FACTORS FOR PSENB Specimen
Fatigue & Fracture of Engineering Materials & Structures, 2015Co-Authors: X. C. Zhao, D. H. TongAbstract:A recently developed pin-loaded single-edge notch Bend Specimen provides an alternative to the single-edge notch tension Specimen commonly used for small-crack growth testing. In this paper, weight functions for pin-loaded single-edge notch Bend Specimen are derived by using two methods, the classical analytical weight function method and the newly developed numerical weight function complex variable Taylor series expansion method. Excellent agreement between the two methods is achieved. Based on these weight functions, accurate stress intensity factors for two load cases, that is, pin-loading and Dugdale loading, which is required for plasticity-induced crack-closure analysis based on the strip-yield model, are determined.