Based on the Hamiltonian governing equations of plane elasticity for sectorial domain, the variable separation and eigenfunction expansion techniques were employed to develop a novel analytical finite element for the ...Based on the Hamiltonian governing equations of plane elasticity for sectorial domain, the variable separation and eigenfunction expansion techniques were employed to develop a novel analytical finite element for the fictitious crack model in fracture mechanics of concrete. The new analytical element can be implemented into FEM program systems to solve fictitious crack propagation problems for concrete cracked plates with arbitrary shapes and loads. Numerical results indicate that the method is more efficient and accurate than ordinary finite element method.展开更多
An extended dielectric crack model is proposed to capture the effects of the physical properties of crack interior on crack-tip thermoelectroelastic fields.The typical crack-face boundary conditions can be retrieved b...An extended dielectric crack model is proposed to capture the effects of the physical properties of crack interior on crack-tip thermoelectroelastic fields.The typical crack-face boundary conditions can be retrieved by considering the limiting cases of electrical permeability and thermal conductivity inside a crack.Making use of the Fourier transform technique,the problem of a thermopiezoelectric strip weakened by a Griffith crack is investigated and transformed to solve the system of the second kind Fredholm integral equations with Cauchy kernel.The Lobatto-Chebyshev collocation method is used to form a nonlinear system of algebraic equations,which is solved by elaborating on an algorithm.The crack-tip thermoelectroelastic fields are determined by using the approximate solutions.Numerical simulations are carried out to show the variations of the fracture parameters of concern under applied thermoelectromechanical loads,the physical properties of the dielectric medium inside the crack and the geometry of the cracked thermopiezoelectric strip.Some comparisons with the experimental results are reported to reveal the effectiveness of the extended dielectric crack model.展开更多
An elastic analysis of an internal central crack with bridging fibers parallel to the free surface in an infinite orthotropic anisotropic elastic plane was performed. A dynamic model of bridging fiber pull-out of comp...An elastic analysis of an internal central crack with bridging fibers parallel to the free surface in an infinite orthotropic anisotropic elastic plane was performed. A dynamic model of bridging fiber pull-out of composite materials was presented. Resultingly the fiber failure is governed by maximum tensile stress, the fiber breaks and hence the crack extension should occur in self-similar fashion. By the methods of complex functions, the problem studied can be transformed into the dynamic model to the Reimann-Hilbert mixed boundary value problem, and a straightforward and easy analytical solution is presented. Analytical study on the crack propagation subjected to a ladder load and an instantaneous pulse loading is obtained respectively for orthotropic anisotropic body. By utilizing the solution, the concrete solutions of this model are attained by ways of superposition.展开更多
Peridynamics(PD)is an effective method for simulating the spontaneous initiation and propagation of tensile cracks in materials.However,it faces great challenges in simulating compression-shear cracking of geomaterial...Peridynamics(PD)is an effective method for simulating the spontaneous initiation and propagation of tensile cracks in materials.However,it faces great challenges in simulating compression-shear cracking of geomaterials due to the lack of efficient contact-friction models.This paper introduces an original contact-friction model that leverages twin mesh and potential function principles within PD to model rock cracking under tensile and compressive stresses.The contact detection algorithm,based on space segmentation axis-aligned bounding box(AABB)tree data structure,is used to address the significant challenge of highly efficient contact detection in compression and shear problems.In this method,the twin mesh and potential function are utilized to quantify contact detection and contact degree,as well as friction behavior.This is in contrast to the distance and circular contact area model,which lacks physical significance in the classical PD method.As demonstrated by the tests on specimens containing cracks,the proposed model can capture 8 types of secondary fractures,reduce the contact detection error by about 29%e56%,and increase the contact retrieval efficiency by over 1600 times compared to the classic PD models.This significantly enhances the capability of PD to simulate the initiation,expansion,and coalescence of intricate compression-shear cracks.展开更多
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 study has analyzed the relationship between the water-drainage sluice process of reservoir, stress triggers and shadows of earthquake and porosity variability of fault slip zone. First, the pore pressure, pressure...The study has analyzed the relationship between the water-drainage sluice process of reservoir, stress triggers and shadows of earthquake and porosity variability of fault slip zone. First, the pore pressure, pressure gradient, viscous stress and Reynolds stress to reservoir-earthquake fault slip problem are analyzed, and these are un-negligible factors of the extended coulomb failure stress under ultra-high temperature and pressure condition. Second, the porosity tensor and permeability tensor are studied, the relationship between Zipingpu reservoir and Longmenshan slip has been analyzed, and the extended viscous stress and Reynolds stress as function of time and infiltration process are obtained. Last, some primary conclusions about the flow-solid coupled facture mechanism to the Zipingpu reservoir and Longmenshan slip problem are presented, which can help understand the flow-solid coupled facture mechanism of reservoir-coseismic fault slip problem.展开更多
Experimental study is performed on the probabilistic models for the long fatigue crack growth rates (da/dN) of LZ50 axle steel. An equation for crack growth rate was derived to consider the trend of stress intensity f...Experimental study is performed on the probabilistic models for the long fatigue crack growth rates (da/dN) of LZ50 axle steel. An equation for crack growth rate was derived to consider the trend of stress intensity factor range going down to the threshold and the average stress effect. The probabilistic models were presented on the equation. They consist of the probabilistic da/dN-ΔK relations, the confidence-based da/dN-ΔK relations, and the probabilistic- and confidence-based da/dN-ΔK relations. Efforts were made respectively to characterize the effects of probabilistic assessments due to the scattering regularity of test data, the number of sampling, and both of them. These relations can provide wide selections for practice. Analysis on the test data of LZ50 steel indicates that the present models are available and feasible.展开更多
The understanding of crack propagation characteristics and law of rocks during the loading process is of great significance for the exploitation and support of rock engineering.In this study,the crack propagation beha...The understanding of crack propagation characteristics and law of rocks during the loading process is of great significance for the exploitation and support of rock engineering.In this study,the crack propagation behavior of rocks in triaxial compression tests was investigated in detail.The main conclusions were as follows:1)According to the evolution characteristics of crack axial strain,the differential stress?strain curve of rocks under triaxial compressive condition can be divided into three phases which are linear elastic phase,crack propagation phase,post peak phase,respectively;2)The proposed models are applied to comparison with the test data of rocks under triaxial compressive condition and different temperatures.The theoretical data calculated by the models are in good agreement with the laboratory data,indicating that the proposed model can be applied to describing the crack propagation behavior and the nonlinear properties of rocks under triaxial compressive condition;3)The inelastic compliance and crack initiation strain in the proposed model have a decrease trend with the increase of confining pressure and temperature.Peak crack axial strain increases nonlinearly with the inelastic compliance and the increase rate increases gradually.Crack initiation strain has a linear relation with peak crack axial strain.展开更多
This paper investigates the influence of crack orientation on damage quantification using Lamb wave in plate structures. Finite element simulation is performed to acquire Lamb wave signal responses for different confi...This paper investigates the influence of crack orientation on damage quantification using Lamb wave in plate structures. Finite element simulation is performed to acquire Lamb wave signal responses for different configurations of crack orientations and crack lengths. Two Lamb wave features, namely the normalized amplitude and the phase change, are used as damage sensitive features to develop a crack size quantification model. A hypothesis based on the geometrical influence on signal features is proposed, and the crack size quantification model incorporating the orientation angle is established using the hypothesis. An index of Probability of Reliable Quantification(PRQ) is proposed to evaluate the performance of the model. The index can be used to determine the sizing risk in terms of probabilities. A realistic aluminum plate is used to obtain the experimental data using piezoelectric(PZT) wafer-type sensors around a center through crack. The experimental data are used to validate the overall method. Results indicate that the proposed model can yield reliable results for size quantification of inclined cracks.展开更多
A coupled system simulating both firebox and reactor is established to study the naphtha pyrolysis in an industrial tubular furnace.The firebox model is based on zone method including combustion,radiation,and convecti...A coupled system simulating both firebox and reactor is established to study the naphtha pyrolysis in an industrial tubular furnace.The firebox model is based on zone method including combustion,radiation,and convection to simulate heat transfer in the furnace.A two-dimensional recirculation model is proposed to estimate the flow field in furnace.The reactor model integrates the feedstock reconstruction model,an auto-generator of detail kinetic schemes,and the reactor simulation model to simulate the reaction process in the tubular coil.The coupled simulation result is compared with industrial process and shows agreement within short computation time.展开更多
Jujube fruit cracking has become a major concern in jujube production. It can affect fruit quality and yield and crop productivity, resulting in significant economic loss. Recent advances in jujube fruit cracking rese...Jujube fruit cracking has become a major concern in jujube production. It can affect fruit quality and yield and crop productivity, resulting in significant economic loss. Recent advances in jujube fruit cracking research provide opportunities to improve our understanding of the impacts of environmental factors and plant physiological metabolism on jujube fruit cracking. In this article, we have developed a novel systemic modeling software for jujube fruit cracking. The potential function and value of this modeling software are presented. Current issues and future research directions in the modeling of jujube fruit cracking system are also discussed. To our knowledge, this is the first functional and/or integrated modeling software developed for the management of jujube fruit cracking.展开更多
Single-event microkinetic(SEMK) model of the catalytic cracking of methylcyclohexane admixed with 1-octene over REUSY zeolites at 693 K—753 K in the absence of coke formation is enhanced. To keep consistency with the...Single-event microkinetic(SEMK) model of the catalytic cracking of methylcyclohexane admixed with 1-octene over REUSY zeolites at 693 K—753 K in the absence of coke formation is enhanced. To keep consistency with the wellknown carbenium ion chemistry, hydride transfer forming and consuming allylic carbenium ions in the aromatization of cycloparaffins are further investigated and differentiated. The reversibility of endocyclic β-scission and cyclization reactions is refined by accounting explicitly for the reacting olefins and resulting cycloparaffins in the corresponding thermodynamics. 24 activation energies for the reactions involved in the cracking of cycloparaffins are obtained by the regression of 15 sets of experimental data upon taking the resulting 37 main cracking products, i. e., responses into account. The enhanced SEMK model can adequately describe the catalytic behavior of 37 main products with conversion and temperature.展开更多
Here,the stress corrosion crack growth behaviour of a high-strength low-alloy steel under anodic poten-tial was investigated in artificial seawater.As applied potential shifts positively,the crack growth rate first in...Here,the stress corrosion crack growth behaviour of a high-strength low-alloy steel under anodic poten-tial was investigated in artificial seawater.As applied potential shifts positively,the crack growth rate first increases and then decreases.The crack growth behaviour is controlled by the mechano-electrochemical effect at the crack tip.Even under anodic potential,hydrogen embrittlement(HE)occurs at the crack tip,and HE is the main factor of crack growth.A model of mechano-electrochemical effect at the crack tip is developed to study the phenomenon.It was found that applied potentials change the crack growth behaviour via involvement in HE and anodic dissolution at the crack tip.The critical value of applied potential affecting crack growth is the crack tip potential of-0.0591 pH.展开更多
This paper proposes a case study in the control of a heavy oil pyrolysis/cracking furnace with a newly extended U-model based pole placement controller(U-PPC). The major work of the paper includes: 1) establishing a c...This paper proposes a case study in the control of a heavy oil pyrolysis/cracking furnace with a newly extended U-model based pole placement controller(U-PPC). The major work of the paper includes: 1) establishing a control oriented nonlinear dynamic model with Naphtha cracking and thermal dynamics; 2) analysing a U-model(i.e., control oriented prototype) representation of various popular process model sets; 3)designing the new U-PPC to enhance the control performance in pole placement and stabilisation; 4) taking computational bench tests to demonstrate the control system design and performance with a user-friendly step by step procedure.展开更多
This paper proposes a model-based prognostics method that couples the Extended Kalman Filter(EKF) and a new developed linearization method. The proposed prognostics method is developed in the context of fatigue crack ...This paper proposes a model-based prognostics method that couples the Extended Kalman Filter(EKF) and a new developed linearization method. The proposed prognostics method is developed in the context of fatigue crack propagation in fuselage panels where the model parameters are unknown and the crack propagation is affected by different types of uncertainties. The coupled method is composed of two steps. The first step employs EKF to estimate the unknown model parameters and the current damage state. In the second step, the proposed efficient linearization method is applied to compute analytically the statistical distribution of the damage evolution path in some future time. A numerical case study is implemented to evaluate the performance of the proposed method. The results show that the coupled EKF-linearization method provides satisfactory results: the EKF algorithm well identifies the model parameters, and the linearization method gives comparable prediction results to Monte Carlo(MC) method while leading to very significant computational cost saving. The proposed prognostics method for fatigue crack growth can be used for developing predictive maintenance strategy for an aircraft fleet, in which case, the computational cost saving is significantly meaningful.展开更多
The propagation for the model I crack in aluminum single crystal has been directly studied by in-situ TEM observation.The equation of energy barrier of the dislocation building-up and emission at the model I crack tip...The propagation for the model I crack in aluminum single crystal has been directly studied by in-situ TEM observation.The equation of energy barrier of the dislocation building-up and emission at the model I crack tip has been established by means of Peierls-Nabarro dislocation model and starting from angle of energy.By means of calculation,the critical value of spontaneous emission of the dislocations from tip of the model I crack was obtained.展开更多
The internal cracks in continuously cast slabs are attributed to the excessive tensile strain occurring at the solidifying frontduring the continuous casting process. Based on the understanding, a model for diagnosing...The internal cracks in continuously cast slabs are attributed to the excessive tensile strain occurring at the solidifying frontduring the continuous casting process. Based on the understanding, a model for diagnosing the formation of the internal cracks was established, in which the strains at the solidifying front caused by' bulging, straightening or unbending, and roll misalignment were calculated and compared with a critical strain value to estimate whether the internal cracks form. Moreover, the established model was appliedto a real slab caster to reveal the distribution of the strains in casting direction and its effect on the internal cracks. It was proved that themodel was reliable and useful for optimizing the operation of continuous casting.展开更多
The purpose of this study was to develop an analytical model to predict the time required for cracking of concrete due to corrosion of the iron reinforcement. The concrete and cement specimens used for this study were...The purpose of this study was to develop an analytical model to predict the time required for cracking of concrete due to corrosion of the iron reinforcement. The concrete and cement specimens used for this study were batched with cover material ranging from 0.75 to 1.3 in (1.91 to 3.30 cm). The extent of cover material was not formulated into the model under the assumption that crack initiation would tend to produce visible cracking within a relatively short time period. The model was derived using both Hooke’s Law and the volume expansion induced by the corrosion oxides. Correlation achieved with specimen cracking data from the literature was relatively good with a 95% level of confidence. This model presents a key benefit to facility and infrastructure managers by enabling them to plan the time when corrosion mitigating actions are required. It also provides a significant convenience as the condition of the concrete structure or its environment changes over time. The only parameter that needs to be updated over time is the corrosion rate measurement. This single parameter captures the most influential impact that stems from several other parameters which tend to be required in models that are more mechanistically definitive.展开更多
A new generic reaction in the form of PC_i→PC_m+[i,m]→PC_m+λi,m coke+surplusage has been proposed for describing the catalytic cracking behavior of petroleum narrow cuts or pseudo-components(PCs),where the rate con...A new generic reaction in the form of PC_i→PC_m+[i,m]→PC_m+λi,m coke+surplusage has been proposed for describing the catalytic cracking behavior of petroleum narrow cuts or pseudo-components(PCs),where the rate constant formula is derived from the transition state theory and the coking amount is correlated to the properties of the intermediate substance [i,m].In composing the cracking reaction network for feedstock and product oils,only the product PC m of the proposed generic reaction is used,which together with a criterion for excluding exothermic reactions,distinctly reduces the number of reactions in the network.With the proposed cracking reaction scheme coupled with special pseudo-components,a predictive one-dimensional steady state model for fluid catalytic cracking risers is formulated in the sense that for a given riser and given catalyst,the model parameters are independent of stock oils,product schemes and other operational conditions.The great correlating and predicting capability of the resulted model is tested with production data in different scenarios of four commercial risers.展开更多
A 3-D computationalframework was suggested to model stable growth of a macroscopic crack under model I condition. The Gurson-Tverpaaof dilatant plasticity model for voided materials describes the damage process. Fixed...A 3-D computationalframework was suggested to model stable growth of a macroscopic crack under model I condition. The Gurson-Tverpaaof dilatant plasticity model for voided materials describes the damage process. Fixed-sized, computational cell elements (containing voids) defined over a thin layer at the cmck plane simulate the ductile crack extension. Outside of this layer, the material remains undamaged by the void growth. The micro-mechanics parumeters controlling cmck growth are the thickness Of computational cell layen D, and the initial void porosity, fo. These parameters are calculated through analyses of ductile tearing to match R-curve obtained from testing of deep notch bend specimens for welded joints. The R-curve for the double edge notched tension specimens is eNctively predicted using these pammeters.The predicted R-curve gives a good agreement with the expemment results.展开更多
文摘Based on the Hamiltonian governing equations of plane elasticity for sectorial domain, the variable separation and eigenfunction expansion techniques were employed to develop a novel analytical finite element for the fictitious crack model in fracture mechanics of concrete. The new analytical element can be implemented into FEM program systems to solve fictitious crack propagation problems for concrete cracked plates with arbitrary shapes and loads. Numerical results indicate that the method is more efficient and accurate than ordinary finite element method.
基金The work was supported by the National Natural Science Foundation of China(Nos.11872155 and 11362002)the Guangxi Natural Science Foundation(No.2016GXNSFAA380261)the innovation project of Guangxi Graduate Education(YCSW2019045).
文摘An extended dielectric crack model is proposed to capture the effects of the physical properties of crack interior on crack-tip thermoelectroelastic fields.The typical crack-face boundary conditions can be retrieved by considering the limiting cases of electrical permeability and thermal conductivity inside a crack.Making use of the Fourier transform technique,the problem of a thermopiezoelectric strip weakened by a Griffith crack is investigated and transformed to solve the system of the second kind Fredholm integral equations with Cauchy kernel.The Lobatto-Chebyshev collocation method is used to form a nonlinear system of algebraic equations,which is solved by elaborating on an algorithm.The crack-tip thermoelectroelastic fields are determined by using the approximate solutions.Numerical simulations are carried out to show the variations of the fracture parameters of concern under applied thermoelectromechanical loads,the physical properties of the dielectric medium inside the crack and the geometry of the cracked thermopiezoelectric strip.Some comparisons with the experimental results are reported to reveal the effectiveness of the extended dielectric crack model.
文摘An elastic analysis of an internal central crack with bridging fibers parallel to the free surface in an infinite orthotropic anisotropic elastic plane was performed. A dynamic model of bridging fiber pull-out of composite materials was presented. Resultingly the fiber failure is governed by maximum tensile stress, the fiber breaks and hence the crack extension should occur in self-similar fashion. By the methods of complex functions, the problem studied can be transformed into the dynamic model to the Reimann-Hilbert mixed boundary value problem, and a straightforward and easy analytical solution is presented. Analytical study on the crack propagation subjected to a ladder load and an instantaneous pulse loading is obtained respectively for orthotropic anisotropic body. By utilizing the solution, the concrete solutions of this model are attained by ways of superposition.
基金supported by the National Natural Science Foundation of China(Grant No.52278333)the China Scholarship Council(CSC)and the Science and Technology Department of Liaoning Province(Grant No.2024JH2/102500069).
文摘Peridynamics(PD)is an effective method for simulating the spontaneous initiation and propagation of tensile cracks in materials.However,it faces great challenges in simulating compression-shear cracking of geomaterials due to the lack of efficient contact-friction models.This paper introduces an original contact-friction model that leverages twin mesh and potential function principles within PD to model rock cracking under tensile and compressive stresses.The contact detection algorithm,based on space segmentation axis-aligned bounding box(AABB)tree data structure,is used to address the significant challenge of highly efficient contact detection in compression and shear problems.In this method,the twin mesh and potential function are utilized to quantify contact detection and contact degree,as well as friction behavior.This is in contrast to the distance and circular contact area model,which lacks physical significance in the classical PD method.As demonstrated by the tests on specimens containing cracks,the proposed model can capture 8 types of secondary fractures,reduce the contact detection error by about 29%e56%,and increase the contact retrieval efficiency by over 1600 times compared to the classic PD models.This significantly enhances the capability of PD to simulate the initiation,expansion,and coalescence of intricate compression-shear cracks.
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supported by Project SinoProbe-07 of Chinathe National Natural Science Foundation of China (Grant No. D0408/4097409)+1 种基金the Knowledge Innovation Program of the Chinese Academy of Sciences (Grant No. KJCX2-YW-N42)the Key Important Project of the National Natural Science Foundation of China (Grant No. 10734070)
文摘The study has analyzed the relationship between the water-drainage sluice process of reservoir, stress triggers and shadows of earthquake and porosity variability of fault slip zone. First, the pore pressure, pressure gradient, viscous stress and Reynolds stress to reservoir-earthquake fault slip problem are analyzed, and these are un-negligible factors of the extended coulomb failure stress under ultra-high temperature and pressure condition. Second, the porosity tensor and permeability tensor are studied, the relationship between Zipingpu reservoir and Longmenshan slip has been analyzed, and the extended viscous stress and Reynolds stress as function of time and infiltration process are obtained. Last, some primary conclusions about the flow-solid coupled facture mechanism to the Zipingpu reservoir and Longmenshan slip problem are presented, which can help understand the flow-solid coupled facture mechanism of reservoir-coseismic fault slip problem.
基金Project supported by the National Natural Science Foundation of China (Nos.50375130and50323003), the Special Foundation of National Excellent Ph.D.Thesis (No.200234) and thePlanned Itemforthe Outstanding Young Teachers ofMinistry ofEducationofChina (No.2101)
文摘Experimental study is performed on the probabilistic models for the long fatigue crack growth rates (da/dN) of LZ50 axle steel. An equation for crack growth rate was derived to consider the trend of stress intensity factor range going down to the threshold and the average stress effect. The probabilistic models were presented on the equation. They consist of the probabilistic da/dN-ΔK relations, the confidence-based da/dN-ΔK relations, and the probabilistic- and confidence-based da/dN-ΔK relations. Efforts were made respectively to characterize the effects of probabilistic assessments due to the scattering regularity of test data, the number of sampling, and both of them. These relations can provide wide selections for practice. Analysis on the test data of LZ50 steel indicates that the present models are available and feasible.
基金Project(51622404)supported by Outstanding Youth Science Foundation of the National Natural Science Foundation of ChinaProjects(51374215,11572343,51904092)supported by the National Natural Science Foundation of China+2 种基金Project(2016YFC0801404)supported by the State Key Research Development Program of ChinaProject(KCF201803)supported by Henan Key Laboratory for Green and Efficient Mining&Comprehensive Utilization of Mineral Resources,Henan Polytechnic University,ChinaProject supported by Beijing Excellent Young Scientists,China
文摘The understanding of crack propagation characteristics and law of rocks during the loading process is of great significance for the exploitation and support of rock engineering.In this study,the crack propagation behavior of rocks in triaxial compression tests was investigated in detail.The main conclusions were as follows:1)According to the evolution characteristics of crack axial strain,the differential stress?strain curve of rocks under triaxial compressive condition can be divided into three phases which are linear elastic phase,crack propagation phase,post peak phase,respectively;2)The proposed models are applied to comparison with the test data of rocks under triaxial compressive condition and different temperatures.The theoretical data calculated by the models are in good agreement with the laboratory data,indicating that the proposed model can be applied to describing the crack propagation behavior and the nonlinear properties of rocks under triaxial compressive condition;3)The inelastic compliance and crack initiation strain in the proposed model have a decrease trend with the increase of confining pressure and temperature.Peak crack axial strain increases nonlinearly with the inelastic compliance and the increase rate increases gradually.Crack initiation strain has a linear relation with peak crack axial strain.
基金supported by Science Challenge Project of China (No. TZ2018007)National Natural Science Foundation of China (Nos. 11872088 and51975546)。
文摘This paper investigates the influence of crack orientation on damage quantification using Lamb wave in plate structures. Finite element simulation is performed to acquire Lamb wave signal responses for different configurations of crack orientations and crack lengths. Two Lamb wave features, namely the normalized amplitude and the phase change, are used as damage sensitive features to develop a crack size quantification model. A hypothesis based on the geometrical influence on signal features is proposed, and the crack size quantification model incorporating the orientation angle is established using the hypothesis. An index of Probability of Reliable Quantification(PRQ) is proposed to evaluate the performance of the model. The index can be used to determine the sizing risk in terms of probabilities. A realistic aluminum plate is used to obtain the experimental data using piezoelectric(PZT) wafer-type sensors around a center through crack. The experimental data are used to validate the overall method. Results indicate that the proposed model can yield reliable results for size quantification of inclined cracks.
基金Supported by the National Natural Science Foundation of China(U1462206)
文摘A coupled system simulating both firebox and reactor is established to study the naphtha pyrolysis in an industrial tubular furnace.The firebox model is based on zone method including combustion,radiation,and convection to simulate heat transfer in the furnace.A two-dimensional recirculation model is proposed to estimate the flow field in furnace.The reactor model integrates the feedstock reconstruction model,an auto-generator of detail kinetic schemes,and the reactor simulation model to simulate the reaction process in the tubular coil.The coupled simulation result is compared with industrial process and shows agreement within short computation time.
文摘Jujube fruit cracking has become a major concern in jujube production. It can affect fruit quality and yield and crop productivity, resulting in significant economic loss. Recent advances in jujube fruit cracking research provide opportunities to improve our understanding of the impacts of environmental factors and plant physiological metabolism on jujube fruit cracking. In this article, we have developed a novel systemic modeling software for jujube fruit cracking. The potential function and value of this modeling software are presented. Current issues and future research directions in the modeling of jujube fruit cracking system are also discussed. To our knowledge, this is the first functional and/or integrated modeling software developed for the management of jujube fruit cracking.
基金financial support from the China Scholarship Councilthe Long Term Structural Methusalem Funding by the Flemish Government
文摘Single-event microkinetic(SEMK) model of the catalytic cracking of methylcyclohexane admixed with 1-octene over REUSY zeolites at 693 K—753 K in the absence of coke formation is enhanced. To keep consistency with the wellknown carbenium ion chemistry, hydride transfer forming and consuming allylic carbenium ions in the aromatization of cycloparaffins are further investigated and differentiated. The reversibility of endocyclic β-scission and cyclization reactions is refined by accounting explicitly for the reacting olefins and resulting cycloparaffins in the corresponding thermodynamics. 24 activation energies for the reactions involved in the cracking of cycloparaffins are obtained by the regression of 15 sets of experimental data upon taking the resulting 37 main cracking products, i. e., responses into account. The enhanced SEMK model can adequately describe the catalytic behavior of 37 main products with conversion and temperature.
基金supported by the China Postdoctoral Science Foundation(No.2021M693706).
文摘Here,the stress corrosion crack growth behaviour of a high-strength low-alloy steel under anodic poten-tial was investigated in artificial seawater.As applied potential shifts positively,the crack growth rate first increases and then decreases.The crack growth behaviour is controlled by the mechano-electrochemical effect at the crack tip.Even under anodic potential,hydrogen embrittlement(HE)occurs at the crack tip,and HE is the main factor of crack growth.A model of mechano-electrochemical effect at the crack tip is developed to study the phenomenon.It was found that applied potentials change the crack growth behaviour via involvement in HE and anodic dissolution at the crack tip.The critical value of applied potential affecting crack growth is the crack tip potential of-0.0591 pH.
基金partially supported by the National Natural Science Foundation of China(61273188,61473312)Taishan Scholar Construction Engineering Special Funding of Shandong
文摘This paper proposes a case study in the control of a heavy oil pyrolysis/cracking furnace with a newly extended U-model based pole placement controller(U-PPC). The major work of the paper includes: 1) establishing a control oriented nonlinear dynamic model with Naphtha cracking and thermal dynamics; 2) analysing a U-model(i.e., control oriented prototype) representation of various popular process model sets; 3)designing the new U-PPC to enhance the control performance in pole placement and stabilisation; 4) taking computational bench tests to demonstrate the control system design and performance with a user-friendly step by step procedure.
基金partially funded by the National Natural Science Foundation of China (No.51805262)
文摘This paper proposes a model-based prognostics method that couples the Extended Kalman Filter(EKF) and a new developed linearization method. The proposed prognostics method is developed in the context of fatigue crack propagation in fuselage panels where the model parameters are unknown and the crack propagation is affected by different types of uncertainties. The coupled method is composed of two steps. The first step employs EKF to estimate the unknown model parameters and the current damage state. In the second step, the proposed efficient linearization method is applied to compute analytically the statistical distribution of the damage evolution path in some future time. A numerical case study is implemented to evaluate the performance of the proposed method. The results show that the coupled EKF-linearization method provides satisfactory results: the EKF algorithm well identifies the model parameters, and the linearization method gives comparable prediction results to Monte Carlo(MC) method while leading to very significant computational cost saving. The proposed prognostics method for fatigue crack growth can be used for developing predictive maintenance strategy for an aircraft fleet, in which case, the computational cost saving is significantly meaningful.
文摘The propagation for the model I crack in aluminum single crystal has been directly studied by in-situ TEM observation.The equation of energy barrier of the dislocation building-up and emission at the model I crack tip has been established by means of Peierls-Nabarro dislocation model and starting from angle of energy.By means of calculation,the critical value of spontaneous emission of the dislocations from tip of the model I crack was obtained.
文摘The internal cracks in continuously cast slabs are attributed to the excessive tensile strain occurring at the solidifying frontduring the continuous casting process. Based on the understanding, a model for diagnosing the formation of the internal cracks was established, in which the strains at the solidifying front caused by' bulging, straightening or unbending, and roll misalignment were calculated and compared with a critical strain value to estimate whether the internal cracks form. Moreover, the established model was appliedto a real slab caster to reveal the distribution of the strains in casting direction and its effect on the internal cracks. It was proved that themodel was reliable and useful for optimizing the operation of continuous casting.
文摘The purpose of this study was to develop an analytical model to predict the time required for cracking of concrete due to corrosion of the iron reinforcement. The concrete and cement specimens used for this study were batched with cover material ranging from 0.75 to 1.3 in (1.91 to 3.30 cm). The extent of cover material was not formulated into the model under the assumption that crack initiation would tend to produce visible cracking within a relatively short time period. The model was derived using both Hooke’s Law and the volume expansion induced by the corrosion oxides. Correlation achieved with specimen cracking data from the literature was relatively good with a 95% level of confidence. This model presents a key benefit to facility and infrastructure managers by enabling them to plan the time when corrosion mitigating actions are required. It also provides a significant convenience as the condition of the concrete structure or its environment changes over time. The only parameter that needs to be updated over time is the corrosion rate measurement. This single parameter captures the most influential impact that stems from several other parameters which tend to be required in models that are more mechanistically definitive.
基金Supported by the National Natural Science Foundation of China(21676012)the Fundamental Research Funds for the Central Universities(Project YS1404)the National High Technology Research and Development Program of China(2007AA04Z191)
文摘A new generic reaction in the form of PC_i→PC_m+[i,m]→PC_m+λi,m coke+surplusage has been proposed for describing the catalytic cracking behavior of petroleum narrow cuts or pseudo-components(PCs),where the rate constant formula is derived from the transition state theory and the coking amount is correlated to the properties of the intermediate substance [i,m].In composing the cracking reaction network for feedstock and product oils,only the product PC m of the proposed generic reaction is used,which together with a criterion for excluding exothermic reactions,distinctly reduces the number of reactions in the network.With the proposed cracking reaction scheme coupled with special pseudo-components,a predictive one-dimensional steady state model for fluid catalytic cracking risers is formulated in the sense that for a given riser and given catalyst,the model parameters are independent of stock oils,product schemes and other operational conditions.The great correlating and predicting capability of the resulted model is tested with production data in different scenarios of four commercial risers.
文摘A 3-D computationalframework was suggested to model stable growth of a macroscopic crack under model I condition. The Gurson-Tverpaaof dilatant plasticity model for voided materials describes the damage process. Fixed-sized, computational cell elements (containing voids) defined over a thin layer at the cmck plane simulate the ductile crack extension. Outside of this layer, the material remains undamaged by the void growth. The micro-mechanics parumeters controlling cmck growth are the thickness Of computational cell layen D, and the initial void porosity, fo. These parameters are calculated through analyses of ductile tearing to match R-curve obtained from testing of deep notch bend specimens for welded joints. The R-curve for the double edge notched tension specimens is eNctively predicted using these pammeters.The predicted R-curve gives a good agreement with the expemment results.
