This study proposes an algorithm of embedding cohesive elements in Abaqus and develops the computer code to model 3D complex cragk propagation in quasi-brittle materials in a relatively easy and efficient manner. The ...This study proposes an algorithm of embedding cohesive elements in Abaqus and develops the computer code to model 3D complex cragk propagation in quasi-brittle materials in a relatively easy and efficient manner. The cohesive elements with softening traction-separation relations and damage initiation and evolution laws are embedded between solid elements in regions of interest in the initial mesh to model potential cracks. The initial mesh can consist of tetrahedrons, wedges, bricks or a mixture of these elements. Neither remeshing nor objective crack propagation criteria are needed. Four examples of concrete specimens, including a wedgesplitting test, a notched beam under torsion, a pull-out test of an anchored cylinder and a notched beam under impact, were modelled and analysed. The simulated crack propagation processes and load-displacement curves agreed well with test results or other numerical simulations for all the examples using initial meshes with reasonable densities. Making use of Abaqus's rich pre/post- processing functionalities and powerful standard/explicit solvers, the developed method offers a practical tool for engineering analysts to model complex 3D fracture problems.展开更多
The gradual increase in shipping and drilling activities in the Arctic regions has resulted in the increased importance of studying the structural safety of polar ships in various ice conditions.Rafted ice refers to a...The gradual increase in shipping and drilling activities in the Arctic regions has resulted in the increased importance of studying the structural safety of polar ships in various ice conditions.Rafted ice refers to a type of accumulated and overlapped sea ice;it is driven by external forces,such as wind and waves,and may exert high loads on ships and threaten their structural safety.Therefore,the properties of rafted ice and the construction of numerical models should be studied before exploring the interaction and collision between ships and rafted ice.Based on the nonlinear finite-element method,this paper introduces the cohesive element model for the simulation of rafted ice.The interaction between ships and rafted ice is studied,and the ice force of the hull is obtained.Numerical simulation results are compared with model test findings,and the effectiveness of the cohesive element method in the construction of the model of rafted ice materials is verified.On this basis,a multilayer rafted ice model is constructed,and its interaction with the ship is studied.The research unveils that rafted ice parts impede crack generation and slow down crack propagation to a certain extent.展开更多
An appropriate coupled cohesive law for predicting the mixed mode failure is established by combining normal separation and tangential separation of surfaces in the cohesive zone model (CZM) and the cohesive element...An appropriate coupled cohesive law for predicting the mixed mode failure is established by combining normal separation and tangential separation of surfaces in the cohesive zone model (CZM) and the cohesive element method. The Xu-Needleman exponential cohesive law with the fully shear failure mechanism is one of the most popular models. Based on the proposed consistently coupled rule/principle, the Xu-Needleman law with the fully shear failure mechanism is proved to be a non-consistently coupled cohesive law by analyzing the surface separation work. It is shown that the Xu-Needleman law is only valid in the mixed mode fracture when the normal separation work equals the tangential separation work. Based on the consistently coupled principle and the modification of the Xu-Needleman law, a consistently coupled cohesive (CCC) law is given. It is shown that the proposed CCC law has already overcome the non-consistency defect of the Xu-Needleman law with great promise in mixed mode analyses.展开更多
Cohesive element is developed from the Dugdal-Barenblatt model in the field of fracture mechanics. The mechanical constitutive relation of cohesive element can be artificially assumed depending on the specific applica...Cohesive element is developed from the Dugdal-Barenblatt model in the field of fracture mechanics. The mechanical constitutive relation of cohesive element can be artificially assumed depending on the specific applications. It has been successfully applied in the study of crystal plasticity/brittle fracture process and decohesion between delaminations. In this paper, tensile experiments of large steel plate with different length of pre-existing cracks are conducted. Based on commercial software ABAQUS, cohesive element is adopted to simulate the tensile tests, and appropriate parameter values are obtained by fitting displacement-force curves. Using these parameters, a numerical method is presented by applying cohesive element to thermo-elastic-plastic finite element method (TEP-FEM) to simulate plate rigid restraint cracking (PRRC) tests. By changing constitutive relation of cohesive element, dimensions of the model and welding conditions, the influence of welding restraint intensity and welding conditions on the crack propagation are discussed, respectively. Three types of welding cold cracking are simulated. Significant influence of welding cold cracking on resistant stress in welding line is captured by this numerical method.展开更多
As the first safety barrier of nuclear reactors,zirconium alloy cladding tubes have attracted extensive attention because of its good mechanical properties.The strength and ductility of zirconium alloy are of great si...As the first safety barrier of nuclear reactors,zirconium alloy cladding tubes have attracted extensive attention because of its good mechanical properties.The strength and ductility of zirconium alloy are of great significance to the service process of cladding tubes,while brittle hydrides precipitate and thus deteriorate the overall performance.Based on the cohesive finite element method,the effects of cohesive strength,interfacial characteristics,and hydrides geometric characteristics on the strength and ductility of two-phase material(zirconium alloy with hydrides)are numerically simulated.The results show that the fracture behavior is significantly affected by the cohesive strength and that the overall strength and ductility are sensitive to the cohesive strength of the zirconium alloy.Furthermore,the interface is revealed to have prominent effects on the overall fracture behavior.When the cohesive strength and fracture energy of the interface are higher than those of the hydride phase,fracture initiates in the hydrides,which is consistent with the experimental phenomena.In addition,it is found that the number density and arrangement of hydrides play important roles in the overall strength and ductility.Our simulation provides theoretical support for the performance analysis of hydrogenated zirconium alloys during nuclear reactor operation.展开更多
Effective elastic properties of porous media are known to be significantly influenced by porosity.In this paper,we investigated the influence of another critical factor,the inter-grain cementation stiffness,on the eff...Effective elastic properties of porous media are known to be significantly influenced by porosity.In this paper,we investigated the influence of another critical factor,the inter-grain cementation stiffness,on the effective elastic properties of a granular porous rock(Bentheim sandstone)using an advanced numerical workflow with realistic rock microstructure and a theoretical model.First,the disparity between the experimentally tested elastic properties of Bentheim sandstone and the effective elastic properties predicted by empirical equations was analysed.Then,a micro-computed tomography(CT)-scan based approach was implemented with digital imaging software AVIZO to construct the 3D(three-dimensional)realistic microstructure of Bentheim sandstone.The microstructural model was imported to a mechanics solver based on the 3D finite element model with inter-grain boundaries modelled by cohesive elements.Loading simulations were run to test the effective elastic properties for different shear and normal intergrain cementation stiffness.Finally,a relation between the macroscale Young’s modulus and inter-grain cementation stiffness was derived with a theoretical model which can also account for porosity explicitly.Both the numerical and theoretical results indicate the influence of the inter-grain cementation stiffness,on the effective elastic properties is significant for porous sandstone.The calibrated normal and shear stiffnesses at the inter-grain boundaries are 1.2×10^(5) and 4×10^(4) GPa/m,respectively.展开更多
A micromechanical model is presented to study the initiation and propagation of microcracks of intermetallic compounds(IMCs)in solder joints.The effects of the grain aggregate morphology,the grain boundary defects and...A micromechanical model is presented to study the initiation and propagation of microcracks of intermetallic compounds(IMCs)in solder joints.The effects of the grain aggregate morphology,the grain boundary defects and the sensitivity of the various cohesive zone parameters in predicting the overall mechanical response are investigated.The overall strength is predominantly determined by the weak grain interfaces;both the grain aggregate morphology and the weak grain interfaces control the crack configuration;the different normal and tangential strengths of grain interfaces result in different intergranular cracking behaviors and play a critical role in determining the macroscopic mechanical response of the system.展开更多
Triaxial fracturing modeling experiments were carried out on whole diameter shale cores from different layers of Shahejie Formation in the Dongpu sag,Bohai Bay Basin to find out the vertical propagation shapes of hydr...Triaxial fracturing modeling experiments were carried out on whole diameter shale cores from different layers of Shahejie Formation in the Dongpu sag,Bohai Bay Basin to find out the vertical propagation shapes of hydraulic fractures in different reservoirs.A numerical simulation method of inserting global cohesive elements was adopted to build a pseudo-three-dimension fracture propagation model for multiple shale oil reservoirs considering interface strength,perforation location,and pump rate to research the features of hydraulic fracture(HF)penetrating through layers.The hydraulic fracture propagates in a cross pattern in tight sandstone layers,in a straight line in sandstone layers with natural fractures,forms ladder fracture in shale layers with beddings.The hydraulic fracture propagates in a stripe shape vertically in both sandstone and shale layers,but it spreads in the plane in shale layers after connecting beddings.Restricted by beddings,the hydraulic fractures in shale layers are smaller in height than those in sandstone layers.When a sandstone layer and a shale layer are fractured at the same time,the fracture extends the most in height after the two layers are connected.Perforating at positions where the sandstone-shale interface is higher in strength and increasing the pumping rate can enhance the fracture height,thus achieving the goal of increasing the production by cross-layer fracturing in multiple shale oil layers.展开更多
Interface debonding between particle and matrix in composite propellant influences its macroscopic mechanical properties greatly. For this, the laws of interface cohesive damage and failure were analyzed. Then, its mi...Interface debonding between particle and matrix in composite propellant influences its macroscopic mechanical properties greatly. For this, the laws of interface cohesive damage and failure were analyzed. Then, its microscopic computational model was established. The interface mechanical response was modeled by the bilinear cohesive zone model. The effects of interface properties and particle sizes on the macroscopic mechanical behavior were investigated. Numerical simulation of debonding damage evolution of composite propellant under finite deformation was carried out. The debonding damage nucleation, propagation mechanism and non-uniform distribution of microscopic stress-strain fields were discussed. The results show that the finite element simulation method based on microstructure model can effectively predict the trend of macroscopic mechanical behavior and particle/matrix debonding evolution process. It can be used for damage simulation and failure assessment of composite propellants.展开更多
This paper performed flexural test and numerical simulation of clay-beams with different water contents to study the tensile fracture of clay soil and the relevant mechanisms.The crack initiation and propagation proce...This paper performed flexural test and numerical simulation of clay-beams with different water contents to study the tensile fracture of clay soil and the relevant mechanisms.The crack initiation and propagation process and the accompanied strain localization behaviors were all clearly observed and analyzed.The exponential cohesive zone model was proposed to simulate the crack interface behavior of the cohesive-frictional materials.The experimental results show that the bending capacity of clay-beams decrease with the water content,while those of the crack mouth opening displacement,crack-tip strain and the strain localization range increase.The numerical predictions successfully reproduce the evolving tensile cracks and the strain localization phenomenon of the clay beams with different fracture ductility,which demonstrates the validity of the proposed cohesive zone model in modelling clay fractures.展开更多
Reduced graphene oxide(rGO)enhanced B_(4)C ceramics was prepared by SPS sintering,the enhancement effect of rGO on the microstructure and mechanical properties of composites was studied through experiments and numeric...Reduced graphene oxide(rGO)enhanced B_(4)C ceramics was prepared by SPS sintering,the enhancement effect of rGO on the microstructure and mechanical properties of composites was studied through experiments and numerical simulation.The results show that the composite with 2wt%rGO has the best comprehensive mechanical properties.Compared with pure boron carbide,vickers hardness and bending strength are increased by 4.8%and 21.96%,respectively.The fracture toughness is improved by 25.71%.The microstructure observation shows that the improvement of mechanical properties is mainly attributed to the pullout and bridge mechanism of rGO and the crack deflection.Based on the cohesive force finite element method,the dynamic crack growth process of composites was simulated.The energy dissipation of B_(4)C/rGO multiphase ceramics during crack propagation was calculated and compared with that of pure boron carbide ceramics.The results show that the fracture energy dissipation can be effectively increased by adding graphene.展开更多
This paper presents a novel approach for simulating the localized leakage behavior of segmentally lined tunnels based on a cohesive zone model.The proposed approach not only simulates localized leakage at the lining s...This paper presents a novel approach for simulating the localized leakage behavior of segmentally lined tunnels based on a cohesive zone model.The proposed approach not only simulates localized leakage at the lining segment,but also captures the hydromechanically coupled seepage behavior at the segmental joints.It is first verified via a tunnel drainage experiment,which reveals its merits over the existing local hydraulic conductivity method.Subsequently,a parametric study is conducted to investigate the effects of the aperture size,stratum permeability,and spatial distribution of drainage holes on the leakage behavior,stratum seepage field,and leakage-induced mechanical response of the tunnel lining.The proposed approach yields more accurate results than the classical local hydraulic conductivity method.Moreover,it is both computationally efficient and stable.Localized leakage leads to reduced local ground pressure,which further induces outward deformation near the leakage point and slight inward deformation at its diametrically opposite side.A localized stress arch spanning across the leakage point is observed,which manifests as the rotation of the principal stresses in the adjacent area.The seepage field depends on both the number and location of the leakage zones.Pseudostatic seepage zones,in which the seepage rate is significantly lower than that of the adjacent area,appear when multiple seepage zones are considered.Finally,the importance of employing the hydromechanical coupled mechanism at the segment joints is highlighted by cases of shallowly buried tunnels subjected to surface loading and pressure tunnels while considering internal water pressure.展开更多
Finite element analysis is developed to simulate the breakage of capsule in capsule-based self-healing concrete.A 2D circular capsule with different core-shell thickness ratios embedded in the mortar matrix is analyze...Finite element analysis is developed to simulate the breakage of capsule in capsule-based self-healing concrete.A 2D circular capsule with different core-shell thickness ratios embedded in the mortar matrix is analyzed numerically along with their interfacial transition zone.Zero-thickness cohesive elements are pre-inserted into solid elements to represent potential cracks.This study focuses on the effects of mismatch fracture properties,namely fracture strength and energy,between capsule and mortar matrix into the breakage likelihood of the capsule.The extensive simulations of 2D specimens under uniaxial tension were carried out to investigate the key features on the fracture patterns of the capsule and produce the fracture maps as the results.The developed fracture maps of capsules present a simple but valuable tool to assist the experimentalists in designing appropriate capsule materials for self-healing concrete.展开更多
Unlike monocrystalline cubic boron nitride(CBN), polycrystalline CBN(PCBN) shows not only higher fracture resistance induced by tool-workpiece interaction but also better selfsharpening capability;therefore, efforts h...Unlike monocrystalline cubic boron nitride(CBN), polycrystalline CBN(PCBN) shows not only higher fracture resistance induced by tool-workpiece interaction but also better selfsharpening capability;therefore, efforts have been devoted to the study of PCBN applications in manufacturing engineering. Most of the studies, however, remain qualitative due to difficulties in experimental observations and theoretical modeling and provide limited in-depth understanding of the self-sharpening behavior/mechanism. To fill this research gap, the present study investigates the self-sharpening process of PCBN abrasives in grinding and analyzes the macro-scale fracture behavior and highly localized micro-scale crack propagation in detail. The widely employed finite element(FE) method, together with the classic Voronoi diagram and cohesive element technique,is used considering the pronounced success of FE applications in polycrystalline material modeling.Grinding trials with careful observation of the PCBN abrasive morphologies are performed to validate the proposed method. The self-sharpening details, including fracture morphology, grinding force, strain energy, and damage dissipation energy, are studied. The effects of maximum grain cut depths(MGCDs) and grinding speeds on the PCBN fracture behavior are discussed, and their optimum ranges for preferable PCBN self-sharpening performance are suggested.展开更多
We present a three-dimensional(3D)numerical model to investigate complex fracture behavior using cohesive elements.An efficient packing algorithm is employed to create the mesoscale model of heterogeneous capsulebased...We present a three-dimensional(3D)numerical model to investigate complex fracture behavior using cohesive elements.An efficient packing algorithm is employed to create the mesoscale model of heterogeneous capsulebased self-healing concrete.Spherical aggregates are used and directly generated from specified size distributions with different volume fractions.Spherical capsules are also used and created based on a particular diameter,and wall thickness.Bilinear traction-separation laws of cohesive elements along the boundaries of the mortar matrix,aggregates,capsules,and their interfaces are pre-inserted to simulate crack initiation and propagation.These pre-inserted cohesive elements are also applied into the initial meshes of solid elements to account for fracture in the mortar matrix.Different realizations are carried out and statistically analyzed.The proposed model provides an effective tool for predicting the complex fracture response of capsule-based self-healing concrete at the meso-scale.展开更多
This paper investigates the fracture process of a capsule when subjected to uniaxial tension in encapsulation-based self-healing concrete.A circular capsule embedded in the mortar matrix is considered along with diffe...This paper investigates the fracture process of a capsule when subjected to uniaxial tension in encapsulation-based self-healing concrete.A circular capsule embedded in the mortar matrix is considered along with different ratios of core-shell thickness.To represent potential cracks,zero thickness cohesive elements are pre-inserted throughout element boundaries.The effects of fracture strength around the interfacial transition zone of the capsule are analyzed.The crack nucleation,propagation,and fracture mode of capsule are also discussed.The numerical results indicate that increasing the strength of the interfacial transition zone around the capsule can increase the load-carrying capacity of self-healing concrete.Moreover,given a similar fracture strength around the interface of the capsule,the fracture probability of capsule in encapsulation-based self-healing concrete is strongly dependent on the core-shell thickness ratio..展开更多
Mimicking the natural design motifs of structural biological materials is a promising approach to achieve a unique combination of strength and toughness for engineering materials.In this study,we proposed a 2D computa...Mimicking the natural design motifs of structural biological materials is a promising approach to achieve a unique combination of strength and toughness for engineering materials.In this study,we proposed a 2D computational model,which is a two-hierarchy hybrid composite inspired by the ultrastructural features of bone.The model is composed of alternating parallel array of two subunits(A&B)mimicking‘mineralized collagen fibril’and‘extrafibrillar matrix’of bone at ultrastructural level.The subunit-A is formed by short stiff platelets embedded within a soft matrix.The subunit-B consists of randomly distributed stiff grains bonded by a thin layer of tough adhesive phase.To assess the performance of the bioinspired design,a conventional unidirectional long-fiber composite made with the same amount of hard and soft phases was studied.The finite element simulation results indicated that the toughness,strength and elastic modulus of the bioinspired composite was 312%,83%,and 55%of that of the conventional composite,respectively.The toughness improvement was attributed to the prevalent energy-dissipating damage of adhesive phase in subunit-B and crack-bridging by subunit-A,the two major toughening mechanisms in the model.This study exemplifies some insights into natural design of materials to gain better material performance.展开更多
Two grades of Dyneema composite laminates with the commercial designations of HB26 and HB50 were cut into blocks with or without an edge crack and compressed in the lon- gitudinal fiber direction. The cracked and uncr...Two grades of Dyneema composite laminates with the commercial designations of HB26 and HB50 were cut into blocks with or without an edge crack and compressed in the lon- gitudinal fiber direction. The cracked and uncracked specimens show similar compressive responses including failure pattern and failure load. The two grades of Dyneema composites exhibits different failure modes: a diffuse, sinusoidal buckling pattern for Dyneema HB50 due to its weak matrix constituent and a kink band for Dyneema~ HB26 due to its relatively stronger matrix constituent. An effective finite element model is used to simulate the collapse of Dyneema composites, and the sensitivity of laminate compressive responses to the overall effective shear modulus, interlaminar shear strength, thickness and imperfection angle are investigated. The change of failure mode from kink band to sinusoidal buckling pattern by decreasing the interlaminar shear strength is validated by the finite element analyses.展开更多
基金supported by EPSRC UK(No.EP/F00656X/1)Xiangting Su's one-year visit to the University of Liverpoosupported by the China Scholarship Council and the National Natural Science Foundation of China(No.50579081).
文摘This study proposes an algorithm of embedding cohesive elements in Abaqus and develops the computer code to model 3D complex cragk propagation in quasi-brittle materials in a relatively easy and efficient manner. The cohesive elements with softening traction-separation relations and damage initiation and evolution laws are embedded between solid elements in regions of interest in the initial mesh to model potential cracks. The initial mesh can consist of tetrahedrons, wedges, bricks or a mixture of these elements. Neither remeshing nor objective crack propagation criteria are needed. Four examples of concrete specimens, including a wedgesplitting test, a notched beam under torsion, a pull-out test of an anchored cylinder and a notched beam under impact, were modelled and analysed. The simulated crack propagation processes and load-displacement curves agreed well with test results or other numerical simulations for all the examples using initial meshes with reasonable densities. Making use of Abaqus's rich pre/post- processing functionalities and powerful standard/explicit solvers, the developed method offers a practical tool for engineering analysts to model complex 3D fracture problems.
基金The National Natural Science Foundation of China(Grant Nos.52192693,52192690,51979051,51979056 and U20A20327)the National Key Research and Development Program of China(Grant No.2021YFC2803400)。
文摘The gradual increase in shipping and drilling activities in the Arctic regions has resulted in the increased importance of studying the structural safety of polar ships in various ice conditions.Rafted ice refers to a type of accumulated and overlapped sea ice;it is driven by external forces,such as wind and waves,and may exert high loads on ships and threaten their structural safety.Therefore,the properties of rafted ice and the construction of numerical models should be studied before exploring the interaction and collision between ships and rafted ice.Based on the nonlinear finite-element method,this paper introduces the cohesive element model for the simulation of rafted ice.The interaction between ships and rafted ice is studied,and the ice force of the hull is obtained.Numerical simulation results are compared with model test findings,and the effectiveness of the cohesive element method in the construction of the model of rafted ice materials is verified.On this basis,a multilayer rafted ice model is constructed,and its interaction with the ship is studied.The research unveils that rafted ice parts impede crack generation and slow down crack propagation to a certain extent.
基金Project supported by the National Natural Science Foundation of China(Nos.50878117 and 51038006)the China Scholarship Council Project(No.M.H.HE-2009621076)the Tsinghua University Initiative Scientific Research Program(No.20101081766)
文摘An appropriate coupled cohesive law for predicting the mixed mode failure is established by combining normal separation and tangential separation of surfaces in the cohesive zone model (CZM) and the cohesive element method. The Xu-Needleman exponential cohesive law with the fully shear failure mechanism is one of the most popular models. Based on the proposed consistently coupled rule/principle, the Xu-Needleman law with the fully shear failure mechanism is proved to be a non-consistently coupled cohesive law by analyzing the surface separation work. It is shown that the Xu-Needleman law is only valid in the mixed mode fracture when the normal separation work equals the tangential separation work. Based on the consistently coupled principle and the modification of the Xu-Needleman law, a consistently coupled cohesive (CCC) law is given. It is shown that the proposed CCC law has already overcome the non-consistency defect of the Xu-Needleman law with great promise in mixed mode analyses.
文摘Cohesive element is developed from the Dugdal-Barenblatt model in the field of fracture mechanics. The mechanical constitutive relation of cohesive element can be artificially assumed depending on the specific applications. It has been successfully applied in the study of crystal plasticity/brittle fracture process and decohesion between delaminations. In this paper, tensile experiments of large steel plate with different length of pre-existing cracks are conducted. Based on commercial software ABAQUS, cohesive element is adopted to simulate the tensile tests, and appropriate parameter values are obtained by fitting displacement-force curves. Using these parameters, a numerical method is presented by applying cohesive element to thermo-elastic-plastic finite element method (TEP-FEM) to simulate plate rigid restraint cracking (PRRC) tests. By changing constitutive relation of cohesive element, dimensions of the model and welding conditions, the influence of welding restraint intensity and welding conditions on the crack propagation are discussed, respectively. Three types of welding cold cracking are simulated. Significant influence of welding cold cracking on resistant stress in welding line is captured by this numerical method.
基金Supported by National Key Research and Development Plan of China(Grant No.2018YFC0808800)National Natural Science Foundation of China(Grant No.51875398)China Postdoctoral Science Foundation(Grant No.2021M693240).
文摘As the first safety barrier of nuclear reactors,zirconium alloy cladding tubes have attracted extensive attention because of its good mechanical properties.The strength and ductility of zirconium alloy are of great significance to the service process of cladding tubes,while brittle hydrides precipitate and thus deteriorate the overall performance.Based on the cohesive finite element method,the effects of cohesive strength,interfacial characteristics,and hydrides geometric characteristics on the strength and ductility of two-phase material(zirconium alloy with hydrides)are numerically simulated.The results show that the fracture behavior is significantly affected by the cohesive strength and that the overall strength and ductility are sensitive to the cohesive strength of the zirconium alloy.Furthermore,the interface is revealed to have prominent effects on the overall fracture behavior.When the cohesive strength and fracture energy of the interface are higher than those of the hydride phase,fracture initiates in the hydrides,which is consistent with the experimental phenomena.In addition,it is found that the number density and arrangement of hydrides play important roles in the overall strength and ductility.Our simulation provides theoretical support for the performance analysis of hydrogenated zirconium alloys during nuclear reactor operation.
基金The authors would like to acknowledge the support of the EC project‘SURE-Novel Productivity Enhancement Concept for a Sustainable Utilization of a Geothermal Resource-RIA’(CEC 654662,H2020).
文摘Effective elastic properties of porous media are known to be significantly influenced by porosity.In this paper,we investigated the influence of another critical factor,the inter-grain cementation stiffness,on the effective elastic properties of a granular porous rock(Bentheim sandstone)using an advanced numerical workflow with realistic rock microstructure and a theoretical model.First,the disparity between the experimentally tested elastic properties of Bentheim sandstone and the effective elastic properties predicted by empirical equations was analysed.Then,a micro-computed tomography(CT)-scan based approach was implemented with digital imaging software AVIZO to construct the 3D(three-dimensional)realistic microstructure of Bentheim sandstone.The microstructural model was imported to a mechanics solver based on the 3D finite element model with inter-grain boundaries modelled by cohesive elements.Loading simulations were run to test the effective elastic properties for different shear and normal intergrain cementation stiffness.Finally,a relation between the macroscale Young’s modulus and inter-grain cementation stiffness was derived with a theoretical model which can also account for porosity explicitly.Both the numerical and theoretical results indicate the influence of the inter-grain cementation stiffness,on the effective elastic properties is significant for porous sandstone.The calibrated normal and shear stiffnesses at the inter-grain boundaries are 1.2×10^(5) and 4×10^(4) GPa/m,respectively.
基金supported by the NationalNatural Science Foundation of China (NSFC) under Grant 11872078,and Beijing Natural Science Foundation No.3222005.
文摘A micromechanical model is presented to study the initiation and propagation of microcracks of intermetallic compounds(IMCs)in solder joints.The effects of the grain aggregate morphology,the grain boundary defects and the sensitivity of the various cohesive zone parameters in predicting the overall mechanical response are investigated.The overall strength is predominantly determined by the weak grain interfaces;both the grain aggregate morphology and the weak grain interfaces control the crack configuration;the different normal and tangential strengths of grain interfaces result in different intergranular cracking behaviors and play a critical role in determining the macroscopic mechanical response of the system.
基金Supported by the National Natural Science Foundation of China(51874328,52074311,U1762215,U19B6003-05)China National Petroleum Corporation-China University of Petroleum(Beijing)Strategic Cooperation Science and Technology Project(ZLZX2020-02)。
文摘Triaxial fracturing modeling experiments were carried out on whole diameter shale cores from different layers of Shahejie Formation in the Dongpu sag,Bohai Bay Basin to find out the vertical propagation shapes of hydraulic fractures in different reservoirs.A numerical simulation method of inserting global cohesive elements was adopted to build a pseudo-three-dimension fracture propagation model for multiple shale oil reservoirs considering interface strength,perforation location,and pump rate to research the features of hydraulic fracture(HF)penetrating through layers.The hydraulic fracture propagates in a cross pattern in tight sandstone layers,in a straight line in sandstone layers with natural fractures,forms ladder fracture in shale layers with beddings.The hydraulic fracture propagates in a stripe shape vertically in both sandstone and shale layers,but it spreads in the plane in shale layers after connecting beddings.Restricted by beddings,the hydraulic fractures in shale layers are smaller in height than those in sandstone layers.When a sandstone layer and a shale layer are fractured at the same time,the fracture extends the most in height after the two layers are connected.Perforating at positions where the sandstone-shale interface is higher in strength and increasing the pumping rate can enhance the fracture height,thus achieving the goal of increasing the production by cross-layer fracturing in multiple shale oil layers.
基金Sponsored by the General Armament Department Advanced Research Project (20101019)
文摘Interface debonding between particle and matrix in composite propellant influences its macroscopic mechanical properties greatly. For this, the laws of interface cohesive damage and failure were analyzed. Then, its microscopic computational model was established. The interface mechanical response was modeled by the bilinear cohesive zone model. The effects of interface properties and particle sizes on the macroscopic mechanical behavior were investigated. Numerical simulation of debonding damage evolution of composite propellant under finite deformation was carried out. The debonding damage nucleation, propagation mechanism and non-uniform distribution of microscopic stress-strain fields were discussed. The results show that the finite element simulation method based on microstructure model can effectively predict the trend of macroscopic mechanical behavior and particle/matrix debonding evolution process. It can be used for damage simulation and failure assessment of composite propellants.
基金sponsored by the National Key Research and Development Program of China(No.2016YFC0800200)the National Basic Research Program of China(No.2014CB047000),and the NSFC(Grant No.51578502).
文摘This paper performed flexural test and numerical simulation of clay-beams with different water contents to study the tensile fracture of clay soil and the relevant mechanisms.The crack initiation and propagation process and the accompanied strain localization behaviors were all clearly observed and analyzed.The exponential cohesive zone model was proposed to simulate the crack interface behavior of the cohesive-frictional materials.The experimental results show that the bending capacity of clay-beams decrease with the water content,while those of the crack mouth opening displacement,crack-tip strain and the strain localization range increase.The numerical predictions successfully reproduce the evolving tensile cracks and the strain localization phenomenon of the clay beams with different fracture ductility,which demonstrates the validity of the proposed cohesive zone model in modelling clay fractures.
基金by the National Natural Science Foundation of China(52002299)。
文摘Reduced graphene oxide(rGO)enhanced B_(4)C ceramics was prepared by SPS sintering,the enhancement effect of rGO on the microstructure and mechanical properties of composites was studied through experiments and numerical simulation.The results show that the composite with 2wt%rGO has the best comprehensive mechanical properties.Compared with pure boron carbide,vickers hardness and bending strength are increased by 4.8%and 21.96%,respectively.The fracture toughness is improved by 25.71%.The microstructure observation shows that the improvement of mechanical properties is mainly attributed to the pullout and bridge mechanism of rGO and the crack deflection.Based on the cohesive force finite element method,the dynamic crack growth process of composites was simulated.The energy dissipation of B_(4)C/rGO multiphase ceramics during crack propagation was calculated and compared with that of pure boron carbide ceramics.The results show that the fracture energy dissipation can be effectively increased by adding graphene.
基金supported by the National Key Research and Development Project of China(No.2019YFC0605105)the National Natural Science Foundation of China(Grant Nos.52278407 and 41877227)the Shanghai Science and Technology Innovation Action Program(No.19DZ1201004).
文摘This paper presents a novel approach for simulating the localized leakage behavior of segmentally lined tunnels based on a cohesive zone model.The proposed approach not only simulates localized leakage at the lining segment,but also captures the hydromechanically coupled seepage behavior at the segmental joints.It is first verified via a tunnel drainage experiment,which reveals its merits over the existing local hydraulic conductivity method.Subsequently,a parametric study is conducted to investigate the effects of the aperture size,stratum permeability,and spatial distribution of drainage holes on the leakage behavior,stratum seepage field,and leakage-induced mechanical response of the tunnel lining.The proposed approach yields more accurate results than the classical local hydraulic conductivity method.Moreover,it is both computationally efficient and stable.Localized leakage leads to reduced local ground pressure,which further induces outward deformation near the leakage point and slight inward deformation at its diametrically opposite side.A localized stress arch spanning across the leakage point is observed,which manifests as the rotation of the principal stresses in the adjacent area.The seepage field depends on both the number and location of the leakage zones.Pseudostatic seepage zones,in which the seepage rate is significantly lower than that of the adjacent area,appear when multiple seepage zones are considered.Finally,the importance of employing the hydromechanical coupled mechanism at the segment joints is highlighted by cases of shallowly buried tunnels subjected to surface loading and pressure tunnels while considering internal water pressure.
基金Supported and financed by RISTEKDIKTI(Directorate General of Resources for Science,Technology and Higher Education.Ministry of Research,Technology and Higher Education of Indonesia)under funding agreement No:153.39/E4.4/2014the German Academic Exchange Program(DAAD).
文摘Finite element analysis is developed to simulate the breakage of capsule in capsule-based self-healing concrete.A 2D circular capsule with different core-shell thickness ratios embedded in the mortar matrix is analyzed numerically along with their interfacial transition zone.Zero-thickness cohesive elements are pre-inserted into solid elements to represent potential cracks.This study focuses on the effects of mismatch fracture properties,namely fracture strength and energy,between capsule and mortar matrix into the breakage likelihood of the capsule.The extensive simulations of 2D specimens under uniaxial tension were carried out to investigate the key features on the fracture patterns of the capsule and produce the fracture maps as the results.The developed fracture maps of capsules present a simple but valuable tool to assist the experimentalists in designing appropriate capsule materials for self-healing concrete.
基金the financial support provided by the National Natural Science Foundation of China (No. 51775275 and No. 51575270)the Fundamental Research Funds for the Central Universities of China (No. NP2018110)+1 种基金Top Six Talents Project in Jiangsu Province of China (No. JXQC-002)the Foundation of Postgraduate Research & Practice Innovation Program of Jiangsu Province of China (KYCX18_0264)
文摘Unlike monocrystalline cubic boron nitride(CBN), polycrystalline CBN(PCBN) shows not only higher fracture resistance induced by tool-workpiece interaction but also better selfsharpening capability;therefore, efforts have been devoted to the study of PCBN applications in manufacturing engineering. Most of the studies, however, remain qualitative due to difficulties in experimental observations and theoretical modeling and provide limited in-depth understanding of the self-sharpening behavior/mechanism. To fill this research gap, the present study investigates the self-sharpening process of PCBN abrasives in grinding and analyzes the macro-scale fracture behavior and highly localized micro-scale crack propagation in detail. The widely employed finite element(FE) method, together with the classic Voronoi diagram and cohesive element technique,is used considering the pronounced success of FE applications in polycrystalline material modeling.Grinding trials with careful observation of the PCBN abrasive morphologies are performed to validate the proposed method. The self-sharpening details, including fracture morphology, grinding force, strain energy, and damage dissipation energy, are studied. The effects of maximum grain cut depths(MGCDs) and grinding speeds on the PCBN fracture behavior are discussed, and their optimum ranges for preferable PCBN self-sharpening performance are suggested.
基金The authors thank the support of the RISTEK-DIKTI(Directorate General of Resources for Science,Technology and Higher Education.Ministry of Research,Technology and Higher Education of Indonesia)under funding agreement No:153.39/E4.4/2014the project ‘Carl-Zeiss Stiftung’ Durchbriiche—Exzellenz in der Forschung:‘Funktionalisierung 191 smarter Werkstoffe unter Mehrfeldanforderungen fur die Verkehrsinfrastruktur’.
文摘We present a three-dimensional(3D)numerical model to investigate complex fracture behavior using cohesive elements.An efficient packing algorithm is employed to create the mesoscale model of heterogeneous capsulebased self-healing concrete.Spherical aggregates are used and directly generated from specified size distributions with different volume fractions.Spherical capsules are also used and created based on a particular diameter,and wall thickness.Bilinear traction-separation laws of cohesive elements along the boundaries of the mortar matrix,aggregates,capsules,and their interfaces are pre-inserted to simulate crack initiation and propagation.These pre-inserted cohesive elements are also applied into the initial meshes of solid elements to account for fracture in the mortar matrix.Different realizations are carried out and statistically analyzed.The proposed model provides an effective tool for predicting the complex fracture response of capsule-based self-healing concrete at the meso-scale.
基金supported and financed by RISTEKDIKTI(Directorate General of Resources for Science,Technology and Higher Education,Ministry of Research,Technology and Higher Education of Indonesia)under funding agreement No.153.39/E4.4/2014,and the German Academic Exchange Program(DAAD).The supports are gratefully acknowledged.
文摘This paper investigates the fracture process of a capsule when subjected to uniaxial tension in encapsulation-based self-healing concrete.A circular capsule embedded in the mortar matrix is considered along with different ratios of core-shell thickness.To represent potential cracks,zero thickness cohesive elements are pre-inserted throughout element boundaries.The effects of fracture strength around the interfacial transition zone of the capsule are analyzed.The crack nucleation,propagation,and fracture mode of capsule are also discussed.The numerical results indicate that increasing the strength of the interfacial transition zone around the capsule can increase the load-carrying capacity of self-healing concrete.Moreover,given a similar fracture strength around the interface of the capsule,the fracture probability of capsule in encapsulation-based self-healing concrete is strongly dependent on the core-shell thickness ratio..
基金This research was supported by a grant from National Science Foundation(CMMI-1538448)a grant from the University of Texas at San Antonio,Office of the Vice President for Research.
文摘Mimicking the natural design motifs of structural biological materials is a promising approach to achieve a unique combination of strength and toughness for engineering materials.In this study,we proposed a 2D computational model,which is a two-hierarchy hybrid composite inspired by the ultrastructural features of bone.The model is composed of alternating parallel array of two subunits(A&B)mimicking‘mineralized collagen fibril’and‘extrafibrillar matrix’of bone at ultrastructural level.The subunit-A is formed by short stiff platelets embedded within a soft matrix.The subunit-B consists of randomly distributed stiff grains bonded by a thin layer of tough adhesive phase.To assess the performance of the bioinspired design,a conventional unidirectional long-fiber composite made with the same amount of hard and soft phases was studied.The finite element simulation results indicated that the toughness,strength and elastic modulus of the bioinspired composite was 312%,83%,and 55%of that of the conventional composite,respectively.The toughness improvement was attributed to the prevalent energy-dissipating damage of adhesive phase in subunit-B and crack-bridging by subunit-A,the two major toughening mechanisms in the model.This study exemplifies some insights into natural design of materials to gain better material performance.
基金supported by the National Natural Science Foundation of China (11242015,11172071)
文摘Two grades of Dyneema composite laminates with the commercial designations of HB26 and HB50 were cut into blocks with or without an edge crack and compressed in the lon- gitudinal fiber direction. The cracked and uncracked specimens show similar compressive responses including failure pattern and failure load. The two grades of Dyneema composites exhibits different failure modes: a diffuse, sinusoidal buckling pattern for Dyneema HB50 due to its weak matrix constituent and a kink band for Dyneema~ HB26 due to its relatively stronger matrix constituent. An effective finite element model is used to simulate the collapse of Dyneema composites, and the sensitivity of laminate compressive responses to the overall effective shear modulus, interlaminar shear strength, thickness and imperfection angle are investigated. The change of failure mode from kink band to sinusoidal buckling pattern by decreasing the interlaminar shear strength is validated by the finite element analyses.