Prognostics and health management （PHM） significantly improves system availability and reliability, and reduces the cost of system operations. Design for testability （DFT） developed concurrently with system design...Prognostics and health management （PHM） significantly improves system availability and reliability, and reduces the cost of system operations. Design for testability （DFT） developed concurrently with system design is an important way to improve PHM capability. Testability modeling and analysis are the foundation of DFT. This paper proposes a novel approach of testability modeling and analysis based on failure evolution mechanisms. At the component level, the fault progression-related information of each unit under test （UUT） in a system is obtained by means of failure modes, evolution mechanisms, effects and criticality analysis （FMEMECA）, and then the failure-symptom dependency can be generated. At the system level, the dynamic attributes of UUTs are assigned by using the bond graph methodology, and then the symptom-test dependency can be obtained by means of the functional flow method. Based on the failure-symptom and symptom-test dependencies, testability analysis for PHM systems can be realized. A shunt motor is used to verify the application of the approach proposed in this paper. Experimental results show that this approach is able to be applied to testability modeling and analysis for PHM systems very well, and the analysis results can provide a guide for engineers to design for testability in order to improve PHM performance.展开更多
The test selection and optimization （TSO） can improve the abilities of fault diagnosis, prognosis and health-state evalua- tion for prognostics and health management （PHM） systems. Traditionally, TSO mainly focuse...The test selection and optimization （TSO） can improve the abilities of fault diagnosis, prognosis and health-state evalua- tion for prognostics and health management （PHM） systems. Traditionally, TSO mainly focuses on fault detection and isolation, but they cannot provide an effective guide for the design for testability （DFT） to improve the PHM performance level. To solve the problem, a model of TSO for PHM systems is proposed. Firstly, through integrating the characteristics of fault severity and propa- gation time, and analyzing the test timing and sensitivity, a testability model based on failure evolution mechanism model （FEMM） for PHM systems is built up. This model describes the fault evolution- test dependency using the fault-symptom parameter matrix and symptom parameter-test matrix. Secondly, a novel method of in- herent testability analysis for PHM systems is developed based on the above information. Having completed the analysis, a TSO model, whose objective is to maximize fault trackability and mini- mize the test cost, is proposed through inherent testability analysis results, and an adaptive simulated annealing genetic algorithm （ASAGA） is introduced to solve the TSO problem. Finally, a case of a centrifugal pump system is used to verify the feasibility and effectiveness of the proposed models and methods. The results show that the proposed technology is important for PHM systems to select and optimize the test set in order to improve their performance level.展开更多
The study of clastic rock failure evolution under true triaxial stress is an important research topic;however,it is rarely studied systematically due to the limitation of monitoring technology.In this study,true triax...The study of clastic rock failure evolution under true triaxial stress is an important research topic;however,it is rarely studied systematically due to the limitation of monitoring technology.In this study,true triaxial compression tests were conducted on clastic rock specimens to investigate the effect of cementation and intermediate principal stress(s2)on the failure mechanism.The complete stressestrain curves were obtained,while the acoustic emission(AE)was monitored to indirectly evaluate the evo-lution of tensile and shear cracks,and crack evolution under true triaxial compression was imaged in real time by a high-speed camera.The results showed that the deformation and failure characteristics of clastic rock were closely related to the cementation type and intermediate principal stress.On the basis of the distribution characteristics of the ratio of rise time to amplitude(RA)and the average frequency(AF)of AE signals,tensile cracks of the contact cementation specimen propagated preferentially.Meanwhile,the enhancement of specimen cementation promoted the evolution of shear cracks,and the increase inσ_(2)promoted the evolution of tensile cracks.Moreover,the mesoscale cracking mechanism of clastic rock caused by cementation andσ_(2)under true triaxial compression was analyzed.The failure patterns of clastic rock under true triaxial compression were divided into three modes:structure-induced,structure-stress-induced and stress-induced failures.This study confirms the feasibility of high-speed camera technology in true triaxial testing,and has important implications for elucidating the disaster mechanism of deep tunnels in weak rocks.展开更多
An efficient Galerkin meshfree formulation for three dimensional simulation of large deformation failure evolution in soils is presented. This formulation utilizes the stabilized conforming nodal integration, where fo...An efficient Galerkin meshfree formulation for three dimensional simulation of large deformation failure evolution in soils is presented. This formulation utilizes the stabilized conforming nodal integration, where for the purpose of stability and efficiency a Lagrangian smoothing strain at nodal point is constructed and thereafter the internal energy is evaluated nodally. This formulation ensures the linear exactness, efficiency and spatial stability in a unified manner and it makes the conventional Galerkin meshfree method affordable for three dimensional simulation. The three dimensional implementation of stabilized conforming nodal integration is discussed in details. To model the failure evolution in soil medium a coupled elasto-plastic damage model is used and an objective stress integration algorithm in combination of elasto-damage predictor and plastic corrector method is employed for stress update. Two typical numerical examples are shown to demonstrate the effectiveness of the present method for modeling large deformation soil failure.展开更多
The permeability evolution of rock during the progressive failure process is described. In combination with the strength degradation index, the degradation formulas of s and a, which are dependent on the plastic confi...The permeability evolution of rock during the progressive failure process is described. In combination with the strength degradation index, the degradation formulas of s and a, which are dependent on the plastic confining strain component, the material constants of Hock-Brown failure criterion are presented, and a modified elemental scale elastic-brittle-plastic constitutive model of rock is established. The rela- tionship between volumetric strain and permeability through tri-axial compression is investigated. Based on the above, a permeability evolution model is established. The model incorporates confining pressure- dependent degradation of strength, dilatancy and corresponding permeability evolution. The model is implemented in FLAC by the FISH function method. The permeability evolution behavior of rock is inves-tigated during the progressive failure process in a numerical case. The results show that the model is cap- able of reproducing, and allowing visualization of a range of hydro-mechanical responses of rock. The effects of confining pressure on degradation of strength, dilatancy and permeability evolution are also reflected.展开更多
The mechanical responses and ultimate failure patterns of rocks are associated with the failure mechanism evolution.In this study,smoothed particle hydrodynamics(SPH)method with the mixed-mode failure model is propose...The mechanical responses and ultimate failure patterns of rocks are associated with the failure mechanism evolution.In this study,smoothed particle hydrodynamics(SPH)method with the mixed-mode failure model is proposed to probe into failure mechanism evolutions for disc specimens upon loading.The tensile damage model and the Drucker-Prager model are used to calculate the tensile failure and shear failure of the material,respectively.It is concluded that for flaw-unfilled disc specimens,the crack coalescence mechanism in the rock bridge area is affected by the flaw inclination angle and the material property.Considering disc specimens with filled flaws,the incremental rate of tensile damage grows more rapidly when the disc and filling material have a closer ratio of tensile strength to cohesion,which makes the entire specimen response greater brittleness.Furthermore,with the increasing non-uniformity of filling distribution,the incremental rate of tensile-activated damage decreases and the disc specimen performs more ductile.Besides,the influence of the fillings is greater when the flaw inclination angle is approaching 45°.It is proved that the proposed SPH method can be used to simulate the failure mechanism evolution of rocks,which lays a foundation for the study of more complex rock failure.展开更多
To study the mechanical and damage evolution properties of sandstone under triaxial compression, we analyzed the stress strain curve characteristics, deformation and strength properties, and failure process and charac...To study the mechanical and damage evolution properties of sandstone under triaxial compression, we analyzed the stress strain curve characteristics, deformation and strength properties, and failure process and characteristics of sandstone samples under different stress states. The experimental results reveal that peak strength, residual strength, elasticity modulus and deformation modulus increase linearly with confining pressure, and failure models transform from fragile failure under low confining pressure to ductility failure under high confining pressure. Macroscopic failure forms of samples under uniaxial compression were split failure parallel to the axis of samples, while macroscopic failure forms under uniaxial compression were shear failure, the shear failure angle of which decreased linearly with confin- ing pressure. There were significant volume dilatation properties in the loading process of sandstone under different confining pressures, and we analyzed the damage evolution properties of samples based on acoustic emission damage and volumetric dilatation damage, and established damage constitutive model, realizing the real-time Quantitative evaluation of samnles damage state in loading process.展开更多
This study reports the investigation of the thermomechanical behavior of aluminum alloys(AI-1060,A1-6061,and A1-7075)under the combined action of tensile loading and laser irradiations.The continuous wave ytterbium fi...This study reports the investigation of the thermomechanical behavior of aluminum alloys(AI-1060,A1-6061,and A1-7075)under the combined action of tensile loading and laser irradiations.The continuous wave ytterbium fiber laser(wavelength 1080 nm)was employed as the irradiation source,while tensile loading was provided by the tensile testing machine.The effects of various pre-loading and laser power densities on the failure time,temperature distribution,and the deformation behavior of aluminum alloys are analyzed.The experimental results represent the significant reduction in failure time for higher laser power densities and for high preloading values,which implies that preloading may contribute a significant role in the failure of the material at elevated temperature.Fracture on a microscopic scale was predominantly ductile comprising micro-void nucleation,growth,and coalescence.The AI-1060 specimens behaved plastically to some extent,while A1-6061 and A1-7075 specimens experienced catastrophic failure.The reason and characterization of ma-terial failure by tensile and laser loading are explored in detail.A comparative behavior of under-tested materials is also investigated.This work suggests that studies considering only combined loading are not enough to fully understand the mechanical behavior of under-tested materials.For complete characterization,one should consider the effect of heating as well as loading rate and the corresponding involved processes with the help of thermomechanical coupling and the thermal elastic-plastic theory.展开更多
The behavior of nonlinear vibration for symmetric angle-ply laminated plates including the material viscoelasticity and damage evolution is investigated. By employing the von Karman＇s nonlinear theory, strain energy ...The behavior of nonlinear vibration for symmetric angle-ply laminated plates including the material viscoelasticity and damage evolution is investigated. By employing the von Karman＇s nonlinear theory, strain energy equivalence principle and Boltzmann superposition principle, a set of governing equations of nonlinear integro-differential type are derived. By applying the finite difference method, Newmark method and iterative procedure, the governing equations are solved. The effects of loading amplitudes, exciting frequencies and different ply orientations on the critical time to failure initiation and nonlinear vibration amplitudes of the structures are discussed. Numerical results are presented for the different parameters and compared with the available data.展开更多
基金the National Natural Science Foundation of China(No.51175502)
文摘Prognostics and health management （PHM） significantly improves system availability and reliability, and reduces the cost of system operations. Design for testability （DFT） developed concurrently with system design is an important way to improve PHM capability. Testability modeling and analysis are the foundation of DFT. This paper proposes a novel approach of testability modeling and analysis based on failure evolution mechanisms. At the component level, the fault progression-related information of each unit under test （UUT） in a system is obtained by means of failure modes, evolution mechanisms, effects and criticality analysis （FMEMECA）, and then the failure-symptom dependency can be generated. At the system level, the dynamic attributes of UUTs are assigned by using the bond graph methodology, and then the symptom-test dependency can be obtained by means of the functional flow method. Based on the failure-symptom and symptom-test dependencies, testability analysis for PHM systems can be realized. A shunt motor is used to verify the application of the approach proposed in this paper. Experimental results show that this approach is able to be applied to testability modeling and analysis for PHM systems very well, and the analysis results can provide a guide for engineers to design for testability in order to improve PHM performance.
基金supported by the National Natural Science Foundation of China(51175502)
文摘The test selection and optimization （TSO） can improve the abilities of fault diagnosis, prognosis and health-state evalua- tion for prognostics and health management （PHM） systems. Traditionally, TSO mainly focuses on fault detection and isolation, but they cannot provide an effective guide for the design for testability （DFT） to improve the PHM performance level. To solve the problem, a model of TSO for PHM systems is proposed. Firstly, through integrating the characteristics of fault severity and propa- gation time, and analyzing the test timing and sensitivity, a testability model based on failure evolution mechanism model （FEMM） for PHM systems is built up. This model describes the fault evolution- test dependency using the fault-symptom parameter matrix and symptom parameter-test matrix. Secondly, a novel method of in- herent testability analysis for PHM systems is developed based on the above information. Having completed the analysis, a TSO model, whose objective is to maximize fault trackability and mini- mize the test cost, is proposed through inherent testability analysis results, and an adaptive simulated annealing genetic algorithm （ASAGA） is introduced to solve the TSO problem. Finally, a case of a centrifugal pump system is used to verify the feasibility and effectiveness of the proposed models and methods. The results show that the proposed technology is important for PHM systems to select and optimize the test set in order to improve their performance level.
基金financial support from the 111 Project(Grant No.B17009)the Liaoning Revitalization Talents Program(Grant No.XLYCYSZX1902).
文摘The study of clastic rock failure evolution under true triaxial stress is an important research topic;however,it is rarely studied systematically due to the limitation of monitoring technology.In this study,true triaxial compression tests were conducted on clastic rock specimens to investigate the effect of cementation and intermediate principal stress(s2)on the failure mechanism.The complete stressestrain curves were obtained,while the acoustic emission(AE)was monitored to indirectly evaluate the evo-lution of tensile and shear cracks,and crack evolution under true triaxial compression was imaged in real time by a high-speed camera.The results showed that the deformation and failure characteristics of clastic rock were closely related to the cementation type and intermediate principal stress.On the basis of the distribution characteristics of the ratio of rise time to amplitude(RA)and the average frequency(AF)of AE signals,tensile cracks of the contact cementation specimen propagated preferentially.Meanwhile,the enhancement of specimen cementation promoted the evolution of shear cracks,and the increase inσ_(2)promoted the evolution of tensile cracks.Moreover,the mesoscale cracking mechanism of clastic rock caused by cementation andσ_(2)under true triaxial compression was analyzed.The failure patterns of clastic rock under true triaxial compression were divided into three modes:structure-induced,structure-stress-induced and stress-induced failures.This study confirms the feasibility of high-speed camera technology in true triaxial testing,and has important implications for elucidating the disaster mechanism of deep tunnels in weak rocks.
基金supported by the National Natural Science Foundation of China (Grant Nos. 10972188, 10602049)the Program for New Century Excellent Talents in University from China Education Ministry (Grant No. NCET-09-0678)the Fundamental Research Funds for the Central Universities of China (Grant No. 2010121073)
文摘An efficient Galerkin meshfree formulation for three dimensional simulation of large deformation failure evolution in soils is presented. This formulation utilizes the stabilized conforming nodal integration, where for the purpose of stability and efficiency a Lagrangian smoothing strain at nodal point is constructed and thereafter the internal energy is evaluated nodally. This formulation ensures the linear exactness, efficiency and spatial stability in a unified manner and it makes the conventional Galerkin meshfree method affordable for three dimensional simulation. The three dimensional implementation of stabilized conforming nodal integration is discussed in details. To model the failure evolution in soil medium a coupled elasto-plastic damage model is used and an objective stress integration algorithm in combination of elasto-damage predictor and plastic corrector method is employed for stress update. Two typical numerical examples are shown to demonstrate the effectiveness of the present method for modeling large deformation soil failure.
基金the National Natural Science Foundation of China (Nos.51274079,51274110 and 51574139)the Natural Science Foundation of Hebei Province (No.E2013208148)
文摘The permeability evolution of rock during the progressive failure process is described. In combination with the strength degradation index, the degradation formulas of s and a, which are dependent on the plastic confining strain component, the material constants of Hock-Brown failure criterion are presented, and a modified elemental scale elastic-brittle-plastic constitutive model of rock is established. The rela- tionship between volumetric strain and permeability through tri-axial compression is investigated. Based on the above, a permeability evolution model is established. The model incorporates confining pressure- dependent degradation of strength, dilatancy and corresponding permeability evolution. The model is implemented in FLAC by the FISH function method. The permeability evolution behavior of rock is inves-tigated during the progressive failure process in a numerical case. The results show that the model is cap- able of reproducing, and allowing visualization of a range of hydro-mechanical responses of rock. The effects of confining pressure on degradation of strength, dilatancy and permeability evolution are also reflected.
基金This work is supported in part by the National Natural Science Foundation of China(No.51779084)。
文摘The mechanical responses and ultimate failure patterns of rocks are associated with the failure mechanism evolution.In this study,smoothed particle hydrodynamics(SPH)method with the mixed-mode failure model is proposed to probe into failure mechanism evolutions for disc specimens upon loading.The tensile damage model and the Drucker-Prager model are used to calculate the tensile failure and shear failure of the material,respectively.It is concluded that for flaw-unfilled disc specimens,the crack coalescence mechanism in the rock bridge area is affected by the flaw inclination angle and the material property.Considering disc specimens with filled flaws,the incremental rate of tensile damage grows more rapidly when the disc and filling material have a closer ratio of tensile strength to cohesion,which makes the entire specimen response greater brittleness.Furthermore,with the increasing non-uniformity of filling distribution,the incremental rate of tensile-activated damage decreases and the disc specimen performs more ductile.Besides,the influence of the fillings is greater when the flaw inclination angle is approaching 45°.It is proved that the proposed SPH method can be used to simulate the failure mechanism evolution of rocks,which lays a foundation for the study of more complex rock failure.
基金the National Natural Science Foundation of China (Nos.51323004 and 51574223)the Postdoctoral Science Foundation of China (No.2015M571842)the Open Research Fund of Research Center of Jiangsu Collaborative Innovation Center for Building Energy Saving and Construction Technology (No.SJXTY1502)
文摘To study the mechanical and damage evolution properties of sandstone under triaxial compression, we analyzed the stress strain curve characteristics, deformation and strength properties, and failure process and characteristics of sandstone samples under different stress states. The experimental results reveal that peak strength, residual strength, elasticity modulus and deformation modulus increase linearly with confining pressure, and failure models transform from fragile failure under low confining pressure to ductility failure under high confining pressure. Macroscopic failure forms of samples under uniaxial compression were split failure parallel to the axis of samples, while macroscopic failure forms under uniaxial compression were shear failure, the shear failure angle of which decreased linearly with confin- ing pressure. There were significant volume dilatation properties in the loading process of sandstone under different confining pressures, and we analyzed the damage evolution properties of samples based on acoustic emission damage and volumetric dilatation damage, and established damage constitutive model, realizing the real-time Quantitative evaluation of samnles damage state in loading process.
基金Project supported by the National Natural Science Foundation of China(Grant No.61605079)the Fundamental Research Funds for the Central Universities,China(Grant No.30916014112-020)
文摘This study reports the investigation of the thermomechanical behavior of aluminum alloys(AI-1060,A1-6061,and A1-7075)under the combined action of tensile loading and laser irradiations.The continuous wave ytterbium fiber laser(wavelength 1080 nm)was employed as the irradiation source,while tensile loading was provided by the tensile testing machine.The effects of various pre-loading and laser power densities on the failure time,temperature distribution,and the deformation behavior of aluminum alloys are analyzed.The experimental results represent the significant reduction in failure time for higher laser power densities and for high preloading values,which implies that preloading may contribute a significant role in the failure of the material at elevated temperature.Fracture on a microscopic scale was predominantly ductile comprising micro-void nucleation,growth,and coalescence.The AI-1060 specimens behaved plastically to some extent,while A1-6061 and A1-7075 specimens experienced catastrophic failure.The reason and characterization of ma-terial failure by tensile and laser loading are explored in detail.A comparative behavior of under-tested materials is also investigated.This work suggests that studies considering only combined loading are not enough to fully understand the mechanical behavior of under-tested materials.For complete characterization,one should consider the effect of heating as well as loading rate and the corresponding involved processes with the help of thermomechanical coupling and the thermal elastic-plastic theory.
基金The project supported by the National Natural Science Foundation of China(10272042)the Special Science Fund of the Doctoral Discipline of the Ministry of Education.China(20020532018)
文摘The behavior of nonlinear vibration for symmetric angle-ply laminated plates including the material viscoelasticity and damage evolution is investigated. By employing the von Karman＇s nonlinear theory, strain energy equivalence principle and Boltzmann superposition principle, a set of governing equations of nonlinear integro-differential type are derived. By applying the finite difference method, Newmark method and iterative procedure, the governing equations are solved. The effects of loading amplitudes, exciting frequencies and different ply orientations on the critical time to failure initiation and nonlinear vibration amplitudes of the structures are discussed. Numerical results are presented for the different parameters and compared with the available data.
