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M R M Aliha - One of the best experts on this subject based on the ideXlab platform.
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on the applicability of ased criterion for predicting mixed mode i ii fracture toughness results of a Rock Material
Theoretical and Applied Fracture Mechanics, 2017Co-Authors: M R M Aliha, Filippo Berto, Ashraf Sadat Mousavi, Seyed Mohammad Javad RazaviAbstract:Abstract A mixed mode fracture criterion based on the strain energy density averaged over a control volume has been successfully used earlier for evaluating the brittle fracture behavior of notched or cracked components made of engineering Materials like metals, polymers and graphite. However, the applicability of the average strain energy density (ASED) criterion has never been investigated till now for Rock Materials. To fill this lack, a set of mixed mode I+II Rock fracture toughness data provided experimentally by the authors are recalled and then predicted theoretically using the ASED criterion. The investigated fracture results have been obtained for a brittle white marble by testing an inclined edge crack triangular shape specimen subjected to symmetric three point bend loading. It is shown that very good ASED predictions are obtained for the fracture loads of the tested Rock Material in the entire range of mode mixities from pure mode I to pure mode II.
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application of an average strain energy density criterion to obtain the mixed mode fracture load of granite Rock tested with the cracked asymmetric four point bend specimens
Theoretical and Applied Fracture Mechanics, 2017Co-Authors: Seyed Mohammad Javad Razavi, M R M Aliha, Filippo BertoAbstract:Abstract Mixed mode brittle fracture behaviour of granite Rock is studied experimentally and theoretically using Asymmetric Four Point Bend (AFPB) specimens containing pre-cracks subjected to different mixed mode loading conditions, ranging from pure mode I to pure mode II. The main aim of this paper is twofold. First, to present a complete set of experimental results on fracture of pre-cracked granite samples under various in-plane loading mixities, and second, to predict the fracture loads of the tested Rock samples under mixed mode I/II conditions using an energy-based criterion, namely the Average Strain Energy Density (ASED) criterion. Good agreement is found between the experimentally obtained fracture loads and the theoretical predictions based on the constancy of the mean strain energy density over the Material volume. It is shown that the ASED criterion is able to provide well predictions for the fracture loads of the investigated Rock Material containing a pre-crack.
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the influence of specimen type on tensile fracture toughness of Rock Materials
Pure and Applied Geophysics, 2017Co-Authors: M R M Aliha, Eqlima Mahdavi, M R AyatollahiAbstract:Up to now, several methods have been proposed to determine the mode I fracture toughness of Rocks. In this research, different cylindrical and disc shape samples, namely: chevron bend (CB), short rod (SR), cracked chevron notched Brazilian disc (CCNBD), and semi-circular bend (SCB) specimens were considered for investigating mode I fracture behavior of a marble Rock. It is shown experimentally that the fracture toughness values of the tested Rock Material obtained from different test specimens are not consistent. Indeed, depending on the geometry and loading type of the specimen, noticeable discrepancies can be observed for the fracture toughness of a same Rock Material. The difference between the experimental mode I fracture resistance results is related to the magnitude and sign of T-stress that is dependent on the geometry and loading configuration of the specimen. For the chevron-notched samples, the critical value of T-stress corresponding to the critical crack length was determined using the finite element method. The CCNBD and SR specimens had the most negative and positive T-stress values, respectively. The dependency of mode I fracture resistance to the T-stress was shown using the extended maximum tangential strain (EMTSN) criterion and the obtained experimental Rock fracture toughness data were predicted successfully with this criterion.
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typical upper bound lower bound mixed mode fracture resistance envelopes for Rock Material
Rock Mechanics and Rock Engineering, 2012Co-Authors: M R M Aliha, M R Ayatollahi, J AkbardoostAbstract:Mixed mode fracture experiments were conducted on Harsin marble using two disc-shape samples namely the Brazilian disc (BD) and the semi-circular bend (SCB) specimens. For each specimen, a complete fracture toughness envelope ranging from pure mode I to pure mode II was obtained. The experimental results indicate that the mixed mode fracture toughness depends on the geometry and loading conditions such that for any similar mode mixture, the BD test data were significantly greater than the SCB fracture toughness results. Therefore, the conventional fracture criteria which present a unique mixed mode fracture curve, fail to predict the test results. It is shown that a generalized criterion, which takes into account the effects of geometry and loading conditions, is able to provide individual fracture curves for theses specimens with very good estimates for the test results obtained from both BD and SCB specimens. The BD and SCB specimens can be suggested as appropriate specimens for obtaining typical upper bound and lower bound envelopes for mixed mode fracture toughness of Rocks.
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on determination of mode ii fracture toughness using semi circular bend specimen
International Journal of Solids and Structures, 2006Co-Authors: M R Ayatollahi, M R M AlihaAbstract:The cracked semi-circular specimen subjected to three-point bending has been recognized as an appropriate test specimen for conducting mode I, mode II and mixed mode I/II fracture tests in brittle Materials. The manufacturing and pre-cracking of the specimen are simple. No complicated loading fixture is also required for a fracture test. However, almost all of the theoretical criteria available for mixed mode brittle fracture fail to predict the experimentally determined mode II fracture toughness obtained from the semi-circular bend (SCB) specimen. In this paper, a modified maximum tangential stress criterion is used for calculating mode II fracture toughness KIIc in terms of mode I fracture toughness KIc. The modified criterion is used for predicting the reported values of mode II fracture toughness for two brittle Materials: a Rock Material (Johnstone) and a brittle polymer (PMMA). It is shown that the modified criterion provides very good predictions for experimental results. 2005 Elsevier Ltd. All rights reserved.
Xiao Ping Zhou - One of the best experts on this subject based on the ideXlab platform.
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micromechanical modelling of the complete stress strain relationship for crack weakened Rock subjected to compressive loading
Rock Mechanics and Rock Engineering, 2008Co-Authors: Xiao Ping Zhou, Yunhuai Zhang, Keshan ZhuAbstract:A micromechanics-based model, able to quantify the effect of various parameters on the complete stress–strain relationship, is described. The closed-form explicit expression for the complete stress–strain relationship of a Rock Material containing an echelon cracks arrangement subjected to compressive loading is obtained. The complete stress–strain relationship including the stages of linear elasticity, non-linear hardening and strain softening is established. The results show that the complete stress–strain relationship and the strength of Rock with echelon cracks depend on the crack interface friction coefficient, the sliding crack spacing, the perpendicular distance between the two adjacent rows, the fracture toughness of Rock Material and orientation of the cracks. The present model is used to evaluate the complete stress–strain relationship and strength for crack-weakened Rock at the underground cavern complex of the Ertan Hydroelectric Project. The predicted strength is in agreement with that obtained by the Hoek–Brown criterion. The numerical results obtained with the complete stress–strain relationship seem to be in good agreement with the measured values.
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localization of deformation and stress strain relation for mesoscopic heterogeneous brittle Rock Materials under unloading
Theoretical and Applied Fracture Mechanics, 2005Co-Authors: Xiao Ping ZhouAbstract:Abstract Stress redistribution induced by excavation of underground engineering and slope engineering results in the unloading zone in parts of surrounding Rock masses. The mechanical behaviors of crack-weakened Rock masses under unloading are different from those of crack-weakened Rock masses under loading. A micromechanics-based model has been proposed for brittle Rock Material undergoing irreversible changes of their microscopic structures due to microcrack growth when axial stress is held constant while lateral confinement is reduced. The basic idea of the present model is to classify the constitution relation of Rock Material into four stages including some of the stages of linear elasticity, pre-peak nonlinear hardening, rapid stress drop, and strain softening, and to investigate their corresponding micromechanical damage mechanisms individually. Special attention is paid to the transition from structure rearrangements on microscale to the macroscopic inelastic strain, to the transition from distribution damage to localization of damage and the transition from homogeneous deformation to localization of deformation. The closed-form explicit expression for the complete stress–strain relation of Rock Materials containing cracks under unloading is obtained. The results show that the complete stress–strain relation and the strength of Rock Materials under unloading depend on the crack spacing, the fracture toughness of Rock Materials, orientation of the cracks, the crack half-length and the crack density parameter.
Yingxin Zhou - One of the best experts on this subject based on the ideXlab platform.
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suggested methods for determining the dynamic strength parameters and mode i fracture toughness of Rock Materials
International Journal of Rock Mechanics and Mining Sciences, 2012Co-Authors: Yingxin Zhou, Kaiwen Xia, Jian Zhao, Zilong Zhou, F DaiAbstract:The properties of Rocks under dynamic loading are important for the study of a whole range of Rock mechanics and Rock engineering problems, including blasting, protective design, explosives storage, Rock bursts and seismic events. The propagation of dynamic stress waves in the ground, response of Rock tunnels to dynamic load, dynamic support design and damage assessment all require a good understanding of the behavior of Rocks under dynamic loading. Due to the transient nature of dynamic loading, the dynamic tests of Rock Material are very different from static tests.
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numerical analysis of blast induced stress waves in a Rock mass with anisotropic continuum damage models part 1 equivalent Material property approach
Rock Mechanics and Rock Engineering, 2002Co-Authors: Hong Hao, Yingxin ZhouAbstract:This paper uses the concept of anisotropic damage mechanics to analyze dynamic responses of a granite site under blasting loads. An anisotropic continuum damage model is suggested to model Rock mass behavior under blasting loads. The effects of existing cracks and joints in the Rock mass are considered by using equivalent Rock Material properties obtained from both field and laboratory test data. The anisotropic damage accumulations are simulated by continuous degradation of equivalent Material stiffness and strength during loading process and are calculated using the exponential function with respect to the principal tensile strain in three directions. The suggested models are programmed and linked to an available computer program Autodyn3D through its user's subroutine capability. Stress wave propagation and damage zone in the Rock mass induced by underground explosions are simulated. Numerical results of damaged area, peak particle velocity and acceleration attenuation as well as acceleration time histories and Fourier spectra are compared with those from independent field tests.
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Rock dynamics research related to cavern development for ammunition storage
Tunnelling and Underground Space Technology, 1999Co-Authors: Jian Zhao, Yingxin Zhou, A M Hefny, S G Chen, Huanqing Li, M Jain, C C SeahAbstract:Abstract Researches on Rock dynamics related to a cavern development project for ammunition storage in Singapore have been carried out. The researches include the study of dynamic properties of Rock Material (strength, modulus, constitutive relations), dynamic normal and shear properties of Rock joints, shock wave propagation across joints and through the Rock mass, and dynamic response of the Rock mass and structures in Rock using the discrete element method. The results obtained from the research works provide the necessary input to the design and construction of the cavern project.
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numerical simulation of underground explosions
Fragblast, 1998Co-Authors: Yingxin ZhouAbstract:Abstract This paper presents a numerical method to calculate stress wave propagation in Rock mass and to estimate damage zone around an underground borehole generated by explosion. Numerical calculations are carried out by using a commercial software AUTODYN2D, which is a finite difference code with Lagrange, Euler and combined Lagrange-Euler processors, and is especially suitable for modelling high velocity nonlinear dynamic problems. The Material models in AUTODYN2D, however, are mainly those applicable to metals. They are not exactly suitable for geoMaterials such as Rock and soil. In this paper, a modified linear equation of state which includes the effects of bulk modulus degradation due to Rock Material damage, a piecewise linear strength model to reflect the pressure sensitive properties of Rock mass, and a damage based failure model to simulate the strain rate effect, are developed. The developed models are implemented into the AUTODYN2D code through its user subroutine capability. Numerical resul...
M R Ayatollahi - One of the best experts on this subject based on the ideXlab platform.
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the influence of specimen type on tensile fracture toughness of Rock Materials
Pure and Applied Geophysics, 2017Co-Authors: M R M Aliha, Eqlima Mahdavi, M R AyatollahiAbstract:Up to now, several methods have been proposed to determine the mode I fracture toughness of Rocks. In this research, different cylindrical and disc shape samples, namely: chevron bend (CB), short rod (SR), cracked chevron notched Brazilian disc (CCNBD), and semi-circular bend (SCB) specimens were considered for investigating mode I fracture behavior of a marble Rock. It is shown experimentally that the fracture toughness values of the tested Rock Material obtained from different test specimens are not consistent. Indeed, depending on the geometry and loading type of the specimen, noticeable discrepancies can be observed for the fracture toughness of a same Rock Material. The difference between the experimental mode I fracture resistance results is related to the magnitude and sign of T-stress that is dependent on the geometry and loading configuration of the specimen. For the chevron-notched samples, the critical value of T-stress corresponding to the critical crack length was determined using the finite element method. The CCNBD and SR specimens had the most negative and positive T-stress values, respectively. The dependency of mode I fracture resistance to the T-stress was shown using the extended maximum tangential strain (EMTSN) criterion and the obtained experimental Rock fracture toughness data were predicted successfully with this criterion.
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typical upper bound lower bound mixed mode fracture resistance envelopes for Rock Material
Rock Mechanics and Rock Engineering, 2012Co-Authors: M R M Aliha, M R Ayatollahi, J AkbardoostAbstract:Mixed mode fracture experiments were conducted on Harsin marble using two disc-shape samples namely the Brazilian disc (BD) and the semi-circular bend (SCB) specimens. For each specimen, a complete fracture toughness envelope ranging from pure mode I to pure mode II was obtained. The experimental results indicate that the mixed mode fracture toughness depends on the geometry and loading conditions such that for any similar mode mixture, the BD test data were significantly greater than the SCB fracture toughness results. Therefore, the conventional fracture criteria which present a unique mixed mode fracture curve, fail to predict the test results. It is shown that a generalized criterion, which takes into account the effects of geometry and loading conditions, is able to provide individual fracture curves for theses specimens with very good estimates for the test results obtained from both BD and SCB specimens. The BD and SCB specimens can be suggested as appropriate specimens for obtaining typical upper bound and lower bound envelopes for mixed mode fracture toughness of Rocks.
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on determination of mode ii fracture toughness using semi circular bend specimen
International Journal of Solids and Structures, 2006Co-Authors: M R Ayatollahi, M R M AlihaAbstract:The cracked semi-circular specimen subjected to three-point bending has been recognized as an appropriate test specimen for conducting mode I, mode II and mixed mode I/II fracture tests in brittle Materials. The manufacturing and pre-cracking of the specimen are simple. No complicated loading fixture is also required for a fracture test. However, almost all of the theoretical criteria available for mixed mode brittle fracture fail to predict the experimentally determined mode II fracture toughness obtained from the semi-circular bend (SCB) specimen. In this paper, a modified maximum tangential stress criterion is used for calculating mode II fracture toughness KIIc in terms of mode I fracture toughness KIc. The modified criterion is used for predicting the reported values of mode II fracture toughness for two brittle Materials: a Rock Material (Johnstone) and a brittle polymer (PMMA). It is shown that the modified criterion provides very good predictions for experimental results. 2005 Elsevier Ltd. All rights reserved.
Hong Hao - One of the best experts on this subject based on the ideXlab platform.
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anisotropic dynamic damage and fragmentation of Rock Materials under explosive loading
International Journal of Engineering Science, 2003Co-Authors: Yongqiang Zhang, Hong HaoAbstract:This paper describes the development of a constitutive model for predicting dynamic anisotropic damage and fragmentation of Rock Materials under blast loading. In order to take account of the anisotropy of damage, a second rank symmetric damage tensor is introduced in the present model. Based on the mechanics of microcrack nucleation, growth and coalescence, the evolution of damage is formulated. The model provides a quantitative method to estimate the fragment distribution and fragment size generated by crack coalescence in the dynamic fragmentation process. It takes account of the experimental facts that a brittle Rock Material does not fail if the applied stress is lower than its static strength and certain time duration is needed for fracture to take place when it is subjected to a stress higher than its static strength. Numerical results are compared with those from independent field tests.
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numerical analysis of blast induced stress waves in a Rock mass with anisotropic continuum damage models part 1 equivalent Material property approach
Rock Mechanics and Rock Engineering, 2002Co-Authors: Hong Hao, Yingxin ZhouAbstract:This paper uses the concept of anisotropic damage mechanics to analyze dynamic responses of a granite site under blasting loads. An anisotropic continuum damage model is suggested to model Rock mass behavior under blasting loads. The effects of existing cracks and joints in the Rock mass are considered by using equivalent Rock Material properties obtained from both field and laboratory test data. The anisotropic damage accumulations are simulated by continuous degradation of equivalent Material stiffness and strength during loading process and are calculated using the exponential function with respect to the principal tensile strain in three directions. The suggested models are programmed and linked to an available computer program Autodyn3D through its user's subroutine capability. Stress wave propagation and damage zone in the Rock mass induced by underground explosions are simulated. Numerical results of damaged area, peak particle velocity and acceleration attenuation as well as acceleration time histories and Fourier spectra are compared with those from independent field tests.
