The asperity wear of rock joints significantly affects their shear behaviour.This study discusses the wear damage of the asperities on the joint surface,highlighting the roughness degradation characteristics during th...The asperity wear of rock joints significantly affects their shear behaviour.This study discusses the wear damage of the asperities on the joint surface,highlighting the roughness degradation characteristics during the shear process.The direct shear experiment of artificial specimens containing rock joints was conducted under different normal stresses based on three-dimensional scanning technology.These experimental results showed the contribution of joint wear to roughness degeneration,such as the height,zone,and volume of asperity degeneration.The wear coefficient of the rock joint was obtained based on the volume wear of asperities in the laboratory experiment.The functional relationship between the friction coefficient and wear coefficient is subsequently determined.To quantitatively analyse the wear damage of a joint surface,a calculation method for determining the wear depth of the rock joint after shearing was proposed based on wear theory.The relationship between the ultimate dilation and wear depth was analysed.A coefficient m,which can describe the damage degree of the joint surface,and a prediction method of joint surface roughness after shearing are established.Good agreement between analytical predictions and measured values demonstrates the capability of the developed model.Lastly,the sensitivity factors on the wear depth are explored.展开更多
The influence of shear deformation on the behaviour of Mg and Zn impurities as well as self-interstitial atoms in Al was studied using molecular dynamics method.The profilies of potential relief were calculated in dir...The influence of shear deformation on the behaviour of Mg and Zn impurities as well as self-interstitial atoms in Al was studied using molecular dynamics method.The profilies of potential relief were calculated in directions of possible migration of interstitials.It was found that under load- ing the location of interstitial atoms may be undefined.It means that the system of determined parti- cles may go into stochastic regime of behaviour.展开更多
The main objective of this research is to study the mechanical behaviour of tropical soils using elasto-plastic constitutive equations in the so-called limit and critical states. Indeed, researchers of the Cambridge U...The main objective of this research is to study the mechanical behaviour of tropical soils using elasto-plastic constitutive equations in the so-called limit and critical states. Indeed, researchers of the Cambridge University had noticed that during their various experiments, the rate of volumetric deformation ( ) of the sample tending to zero every time the rupture of the specimen is reached during a test performed on a clay specimen Roscoe et al., 1958. To better understand and clarify this mechanical behaviour, a description has been proposed in the (e, p, q) representation that means void ratio, volumetric stress (spherical pressure) and deviatoric stress. This frame of theoretical study and apprehension is called: the theory of the Critical State. One of the major problems met at the time of our present research is the non-availability of triaxial apparatus allowing us to achieve some tests on tropical soils (samples from Senegal in West Africa) and to describe the behaviour of these materials easily like the researchers of the university of Cambridge in the theory of the critical state. To by-pass this difficulty, we decided to consider two very classical and simple mechanical tests: shear-box and the oedometer test as well as the interrelationship of the results given by the tests and some theoretical calculations. This is a way to identify an elasto-plastic model (the modified Cam Clay model) without any triaxial experiment. Indeed it supposes the model to be suitable to describe the mechanical behaviour of the considered clays.展开更多
The definition of the thixotropy is a decrease in viscosity with time in shear and a subsequent recovery of viscosity after the shear deformation is removed.We used therefore start-up experiments with constant shear r...The definition of the thixotropy is a decrease in viscosity with time in shear and a subsequent recovery of viscosity after the shear deformation is removed.We used therefore start-up experiments with constant shear rates and can speak consequently of shear stress instead of viscosity.The shear stress increases sharply at the beginning of the stress growth experiment,passes an overshoot and begins to decrease up to the steady state shear stress.We can assume that a stress growth curve with an overshoot points out to thixotropic behavior.After the steady state shear stress is reached,the shear deformation is stopped,and the stress relaxation begins.It is to be expected that the shear stress will recover after the stress relaxation.Systems with shear thinning and plastic flow behavior were examined.The thixotropy is discussed in relation to the flow behavior.Stress growth experiments were performed with shear rates from the first Newtonian region and from the shear thinning region of the systems with shear thinning flow behavior.Stress start-up experiments were carrying out with shear rates from the first and second yield stress regions and from the transition section of a system with plastic flow behavior.展开更多
The microstructure of x-Ti/ mild steel composite fabricated by using constant stand-off cladding technique was observed with optical microscopy, SEM and TEM analyses. Very fine equiaxed grains (<0.1um) with a low d...The microstructure of x-Ti/ mild steel composite fabricated by using constant stand-off cladding technique was observed with optical microscopy, SEM and TEM analyses. Very fine equiaxed grains (<0.1um) with a low dislocation density were observed in the adiabatic shear bands (ASB) this enables a thermomechanical response that may lead to a super plastic de formation.展开更多
This study presents a numerical multi-scale simulation framework which is extended to accommodate hybrid simulation （numerical-experimental integration）. The framework is enhanced with a standardized data exchange f...This study presents a numerical multi-scale simulation framework which is extended to accommodate hybrid simulation （numerical-experimental integration）. The framework is enhanced with a standardized data exchange format and connected to a generalized controller interface program which facilitates communication with various types of laboratory equipment and testing configurations. A small-scale experimental program was conducted using a six degree-of-freedom hydraulic testing equipment to verify the proposed framework and provide additional data for small-scale testing of shear- critical reinforced concrete structures. The specimens were tested in a multi-axial hybrid simulation manner under a reversed cyclic loading condition simulating earthquake forces. The physical models were 1/3.23-scale representations of a beam and two columns. A mixed-type modelling technique was employed to analyze the remainder of the structures. The hybrid simulation results were compared against those obtained from a large-scale test and finite element analyses. The study found that if precautions are taken in preparing model materials and if the shear-related mechanisms are accurately considered in the numerical model, small-scale hybrid simulations can adequately simulate the behaviour of shear-critical structures. Although the findings of the study are promising, to draw general conclusions additional test data are required.展开更多
A formulation for the coupled analysis of thermo-hydro-mechanical （THM） problems in joints is first presented. The work involves the establishment of equilibrium and mass and energy balance equations. Balance equati...A formulation for the coupled analysis of thermo-hydro-mechanical （THM） problems in joints is first presented. The work involves the establishment of equilibrium and mass and energy balance equations. Balance equations were formulated taking into account two phases： water and air. The joint element developed was implemented in a general purpose finite element computer code for THM analysis of porous media （Code_Bright）. The program was then used to study a number of cases ranging from laboratory tests to large scale in situ tests. A numerical simulation of coupled hydraulic shear tests of rough granite joints is first presented. The tests as well as the model show the coupling between permeability and the deformation of thejoints. The experimental investigation was focused on the effects of suction on the mechanical behaviour of rock joints. Laboratory tests were performed in a direct shear cell equipped with suction control. Suction was imposed using a vapour forced convection circuit connected to the cell and controlled by an air pump. Artificial joints of Lilla claystone were prepared.Joint roughness of varying intensity was created by carving the surfaces in contact in such a manner that rock ridges of different tip angles were formed. These angles ranged from 0° （smooth joint） to 45° （very rough joint profile）. The geometric profiles of the two surfaces in contact were initially positioned in a ＂matching＂ situation. Several tests were performed for different values of suctions （200, 100, and 20 MPa） and for different values of vertical stresses （30, 60, and 150 kPa）. A constitutive model including the effects of suction and joint roughness is proposed to simulate the unsaturated behaviour of rock joints. The new constitutive law was incorporated in the code and experimental results were numerically simulated.展开更多
With the increased application of High Strength Concrete(HSC)in construction and lack of proper guidelines for structural design in India,behavioral study of high strength concrete is an important aspect of research.R...With the increased application of High Strength Concrete(HSC)in construction and lack of proper guidelines for structural design in India,behavioral study of high strength concrete is an important aspect of research.Research on the behavior of HSC reinforced beams with concrete strength more than 60 MPa has been carried out in the past and is still continuing to understand the structural behavior of HSC beams.Along with the many benefits of the high strength concrete,the more brittle behavior is of concern which leads to sudden failure.This paper presents the behavior of reinforced HSC beams in shear with considering the effects of various factors like shear reinforcement ratio,longitudinal reinforcement ratio,l/d ratio(length to depth ratio),etc.Ten numbers Reinforced Concrete Beams of various sizes using concrete mix with three different w/c ratios(0.46,0.26 and 0.21)were cast for shear strength assessment.The beams were tested in simply supported condition over two fixed steel pedestals with load rate of 0.2 mm/minute in displacement control.Mid-point deflection was measured using LVDT.A comparative analysis of theoretical approaches of Euro code,extension of current IS code up to M90 and the experimental data was done to understand the behavior of beams.Shear capacities of beams without any factors of safety were used to assess the actual capacities and then was compared with the experimental capacity obtained.Results of this study can be used in the design of high strength concrete and will be more reliable in Indian continent as the regional materials and exposure conditions were considered.展开更多
In this work the possibility of identifying two important aspects in the process of adopting soil parameters for calculating stability analysis models in tailing dams is discussed. The use of commercial computer progr...In this work the possibility of identifying two important aspects in the process of adopting soil parameters for calculating stability analysis models in tailing dams is discussed. The use of commercial computer programs for stability calculations allows obtaining numerically exact results. Its representativeness, however, will be linked to the correct definition of the phreatic regime and to the prediction of volumetric soil behavior during shearing (contractile vs. dilating materials). The theoretical principles for the selection of soils parameters for different failure models are briefly presented. Also, how the incorrect assumptions regarding material behavior can significantly affect the estimation of tailing dams’ stability. The results of CPTu tests for the diagnosis of the phreatic and mechanical condition of the materials are discussed and two examples are presented to remark on the care that should be taken to avoid incorrect soils parameters adoption.展开更多
基金the financial support from the National Natural Science Foundation of China(Nos.52079077 and 52209141)the Natural Science Foundation of Shandong Province,China(No.ZR2021QE069).
文摘The asperity wear of rock joints significantly affects their shear behaviour.This study discusses the wear damage of the asperities on the joint surface,highlighting the roughness degradation characteristics during the shear process.The direct shear experiment of artificial specimens containing rock joints was conducted under different normal stresses based on three-dimensional scanning technology.These experimental results showed the contribution of joint wear to roughness degeneration,such as the height,zone,and volume of asperity degeneration.The wear coefficient of the rock joint was obtained based on the volume wear of asperities in the laboratory experiment.The functional relationship between the friction coefficient and wear coefficient is subsequently determined.To quantitatively analyse the wear damage of a joint surface,a calculation method for determining the wear depth of the rock joint after shearing was proposed based on wear theory.The relationship between the ultimate dilation and wear depth was analysed.A coefficient m,which can describe the damage degree of the joint surface,and a prediction method of joint surface roughness after shearing are established.Good agreement between analytical predictions and measured values demonstrates the capability of the developed model.Lastly,the sensitivity factors on the wear depth are explored.
文摘The influence of shear deformation on the behaviour of Mg and Zn impurities as well as self-interstitial atoms in Al was studied using molecular dynamics method.The profilies of potential relief were calculated in directions of possible migration of interstitials.It was found that under load- ing the location of interstitial atoms may be undefined.It means that the system of determined parti- cles may go into stochastic regime of behaviour.
文摘The main objective of this research is to study the mechanical behaviour of tropical soils using elasto-plastic constitutive equations in the so-called limit and critical states. Indeed, researchers of the Cambridge University had noticed that during their various experiments, the rate of volumetric deformation ( ) of the sample tending to zero every time the rupture of the specimen is reached during a test performed on a clay specimen Roscoe et al., 1958. To better understand and clarify this mechanical behaviour, a description has been proposed in the (e, p, q) representation that means void ratio, volumetric stress (spherical pressure) and deviatoric stress. This frame of theoretical study and apprehension is called: the theory of the Critical State. One of the major problems met at the time of our present research is the non-availability of triaxial apparatus allowing us to achieve some tests on tropical soils (samples from Senegal in West Africa) and to describe the behaviour of these materials easily like the researchers of the university of Cambridge in the theory of the critical state. To by-pass this difficulty, we decided to consider two very classical and simple mechanical tests: shear-box and the oedometer test as well as the interrelationship of the results given by the tests and some theoretical calculations. This is a way to identify an elasto-plastic model (the modified Cam Clay model) without any triaxial experiment. Indeed it supposes the model to be suitable to describe the mechanical behaviour of the considered clays.
文摘The definition of the thixotropy is a decrease in viscosity with time in shear and a subsequent recovery of viscosity after the shear deformation is removed.We used therefore start-up experiments with constant shear rates and can speak consequently of shear stress instead of viscosity.The shear stress increases sharply at the beginning of the stress growth experiment,passes an overshoot and begins to decrease up to the steady state shear stress.We can assume that a stress growth curve with an overshoot points out to thixotropic behavior.After the steady state shear stress is reached,the shear deformation is stopped,and the stress relaxation begins.It is to be expected that the shear stress will recover after the stress relaxation.Systems with shear thinning and plastic flow behavior were examined.The thixotropy is discussed in relation to the flow behavior.Stress growth experiments were performed with shear rates from the first Newtonian region and from the shear thinning region of the systems with shear thinning flow behavior.Stress start-up experiments were carrying out with shear rates from the first and second yield stress regions and from the transition section of a system with plastic flow behavior.
文摘The microstructure of x-Ti/ mild steel composite fabricated by using constant stand-off cladding technique was observed with optical microscopy, SEM and TEM analyses. Very fine equiaxed grains (<0.1um) with a low dislocation density were observed in the adiabatic shear bands (ASB) this enables a thermomechanical response that may lead to a super plastic de formation.
文摘This study presents a numerical multi-scale simulation framework which is extended to accommodate hybrid simulation （numerical-experimental integration）. The framework is enhanced with a standardized data exchange format and connected to a generalized controller interface program which facilitates communication with various types of laboratory equipment and testing configurations. A small-scale experimental program was conducted using a six degree-of-freedom hydraulic testing equipment to verify the proposed framework and provide additional data for small-scale testing of shear- critical reinforced concrete structures. The specimens were tested in a multi-axial hybrid simulation manner under a reversed cyclic loading condition simulating earthquake forces. The physical models were 1/3.23-scale representations of a beam and two columns. A mixed-type modelling technique was employed to analyze the remainder of the structures. The hybrid simulation results were compared against those obtained from a large-scale test and finite element analyses. The study found that if precautions are taken in preparing model materials and if the shear-related mechanisms are accurately considered in the numerical model, small-scale hybrid simulations can adequately simulate the behaviour of shear-critical structures. Although the findings of the study are promising, to draw general conclusions additional test data are required.
文摘A formulation for the coupled analysis of thermo-hydro-mechanical （THM） problems in joints is first presented. The work involves the establishment of equilibrium and mass and energy balance equations. Balance equations were formulated taking into account two phases： water and air. The joint element developed was implemented in a general purpose finite element computer code for THM analysis of porous media （Code_Bright）. The program was then used to study a number of cases ranging from laboratory tests to large scale in situ tests. A numerical simulation of coupled hydraulic shear tests of rough granite joints is first presented. The tests as well as the model show the coupling between permeability and the deformation of thejoints. The experimental investigation was focused on the effects of suction on the mechanical behaviour of rock joints. Laboratory tests were performed in a direct shear cell equipped with suction control. Suction was imposed using a vapour forced convection circuit connected to the cell and controlled by an air pump. Artificial joints of Lilla claystone were prepared.Joint roughness of varying intensity was created by carving the surfaces in contact in such a manner that rock ridges of different tip angles were formed. These angles ranged from 0° （smooth joint） to 45° （very rough joint profile）. The geometric profiles of the two surfaces in contact were initially positioned in a ＂matching＂ situation. Several tests were performed for different values of suctions （200, 100, and 20 MPa） and for different values of vertical stresses （30, 60, and 150 kPa）. A constitutive model including the effects of suction and joint roughness is proposed to simulate the unsaturated behaviour of rock joints. The new constitutive law was incorporated in the code and experimental results were numerically simulated.
文摘With the increased application of High Strength Concrete(HSC)in construction and lack of proper guidelines for structural design in India,behavioral study of high strength concrete is an important aspect of research.Research on the behavior of HSC reinforced beams with concrete strength more than 60 MPa has been carried out in the past and is still continuing to understand the structural behavior of HSC beams.Along with the many benefits of the high strength concrete,the more brittle behavior is of concern which leads to sudden failure.This paper presents the behavior of reinforced HSC beams in shear with considering the effects of various factors like shear reinforcement ratio,longitudinal reinforcement ratio,l/d ratio(length to depth ratio),etc.Ten numbers Reinforced Concrete Beams of various sizes using concrete mix with three different w/c ratios(0.46,0.26 and 0.21)were cast for shear strength assessment.The beams were tested in simply supported condition over two fixed steel pedestals with load rate of 0.2 mm/minute in displacement control.Mid-point deflection was measured using LVDT.A comparative analysis of theoretical approaches of Euro code,extension of current IS code up to M90 and the experimental data was done to understand the behavior of beams.Shear capacities of beams without any factors of safety were used to assess the actual capacities and then was compared with the experimental capacity obtained.Results of this study can be used in the design of high strength concrete and will be more reliable in Indian continent as the regional materials and exposure conditions were considered.
文摘In this work the possibility of identifying two important aspects in the process of adopting soil parameters for calculating stability analysis models in tailing dams is discussed. The use of commercial computer programs for stability calculations allows obtaining numerically exact results. Its representativeness, however, will be linked to the correct definition of the phreatic regime and to the prediction of volumetric soil behavior during shearing (contractile vs. dilating materials). The theoretical principles for the selection of soils parameters for different failure models are briefly presented. Also, how the incorrect assumptions regarding material behavior can significantly affect the estimation of tailing dams’ stability. The results of CPTu tests for the diagnosis of the phreatic and mechanical condition of the materials are discussed and two examples are presented to remark on the care that should be taken to avoid incorrect soils parameters adoption.
