The breakage mechanism of the polycrystalline diamond compact(PDC) cutters was analyzed by the energy theory of bending waves. The cutting tests of granite block were conducted on a multifunctional testing device by u...The breakage mechanism of the polycrystalline diamond compact(PDC) cutters was analyzed by the energy theory of bending waves. The cutting tests of granite block were conducted on a multifunctional testing device by using the cutter at three kinds of negative fore angles of 30°, 45° and 60°. The results show that, when the edge of the PDC layer is broken, the layer of tungsten cobalt is broken a little under the angle of 30°, while the layer of tungsten cobalt is broken continuously under the angle of 60°, their maximum depths are about 2 and 7 mm respectively in the two cases. The eccentric distance mainly depends on the negative fore angle of the cutter. When the cutter thrusts into the rock under an attack angle of 60°, the energy of bending waves reaches the maximum since the eccentric distance is the maximum. So the damage of cutter is the most serious. This test result is consistent with the conclusion of theoretical analysis well. The eccentric distance from the axial line of cutter to the point of action between the rock and cutter has great effect on the breakage of the cutter. Thus during the process of cutting, the eccentric distance should be reduced to improve the service life of PDC cutters.展开更多
A new method of system failure analysis was proposed. First, considering the relationships between the failure subsystems,the decision making trial and evaluation laboratory(DEMATEL) method was used to calculate the d...A new method of system failure analysis was proposed. First, considering the relationships between the failure subsystems,the decision making trial and evaluation laboratory(DEMATEL) method was used to calculate the degree of correlation between the failure subsystems, analyze the combined effect of related failures, and obtain the degree of correlation by using the directed graph and matrix operations. Then, the interpretative structural modeling(ISM) method was combined to intuitively show the logical relationship of many failure subsystems and their influences on each other by using multilevel hierarchical structure model and obtaining the critical subsystems. Finally, failure mode effects and criticality analysis(FMECA) was used to perform a qualitative hazard analysis of critical subsystems, determine the critical failure mode, and clarify the direction of reliability improvement.Through an example, the result demonstrates that the proposed method can be efficiently applied to system failure analysis problems.展开更多
Failure mode and effect analysis(FMEA)is a preven-tative risk evaluation method used to evaluate and eliminate fail-ure modes within a system.However,the traditional FMEA method exhibits many deficiencies that pose ch...Failure mode and effect analysis(FMEA)is a preven-tative risk evaluation method used to evaluate and eliminate fail-ure modes within a system.However,the traditional FMEA method exhibits many deficiencies that pose challenges in prac-tical applications.To improve the conventional FMEA,many modified FMEA models have been suggested.However,the majority of them inadequately address consensus issues and focus on achieving a complete ranking of failure modes.In this research,we propose a new FMEA approach that integrates a two-stage consensus reaching model and a density peak clus-tering algorithm for the assessment and clustering of failure modes.Firstly,we employ the interval 2-tuple linguistic vari-ables(I2TLVs)to express the uncertain risk evaluations provided by FMEA experts.Then,a two-stage consensus reaching model is adopted to enable FMEA experts to reach a consensus.Next,failure modes are categorized into several risk clusters using a density peak clustering algorithm.Finally,the proposed FMEA is illustrated by a case study of load-bearing guidance devices of subway systems.The results show that the proposed FMEA model can more easily to describe the uncertain risk information of failure modes by using the I2TLVs;the introduction of an endogenous feedback mechanism and an exogenous feedback mechanism can accelerate the process of consensus reaching;and the density peak clustering of failure modes successfully improves the practical applicability of FMEA.展开更多
In this study,the dynamic stress concentration factors(DSCF)around a straight-wall arch tunnel(SWAT)were solved analytically utilizing the complex variable function methods and Duhamel’s integral.The effects of wavel...In this study,the dynamic stress concentration factors(DSCF)around a straight-wall arch tunnel(SWAT)were solved analytically utilizing the complex variable function methods and Duhamel’s integral.The effects of wavelength,incident angle,and blasting rising time on the DSCF distribution were analyzed.Theoretical results pointed out dynamic disturbances resulting in compressive stress concentration in the vertical direction and tensile stress in the incident direction.As the wavelength and rising time increased,there was a tendency for the amplitude of stress concentration to initially rise and then converge.Moreover,a series of 3D FEM models were established to evaluate the effect of different initial stress states on the dynamic failure of the tunnel surrounding rock.The results indicated that the failure of the surrounding rock was significantly influenced by the direction of the static maximum principal stress and the direction of the dynamic disturbance.Under the coupling of static and blasting loading,damage around the tunnel was more prone to occur in the dynamic and static stress concentration coincidence zone.Finally,the damage modes of rock tunnel under static stress and blasting disturbance from different directions were summarized and a proposed support system was presented.The results reveal the mechanisms of deep-buried rock tunnel destruction and dynamically triggered rockburst.展开更多
Investigating the influence of radiation on glass fibre composites is essential for their use in space and aerospace environment.Gaining insight into the damage mechanisms caused by gamma irradiation,can improve the s...Investigating the influence of radiation on glass fibre composites is essential for their use in space and aerospace environment.Gaining insight into the damage mechanisms caused by gamma irradiation,can improve the safety and resilience of structures.This paper is aimed at investigating the failure mode and damage of gamma-irradiated repurposed pultruded glass fibre-reinforced polyester subjected to lowvelocity impact using three types of non-destructive techniques.Three sets of differently layered configurations(CRC,WCRW,W2CR2C)consisting of chopped(c),roving(r),and weaved(w)fibre-reinforced polyester are applied in this study.Drop hammer test is applied to evaluate the low-impact resistance properties of Gamma-irradiated composite at 100 kGy,500 kGy,and 1000 kGy.Preliminary flexural and hardness tests are conducted to further assess the behaviour of irradiated polymer composites.Further,the damage modes associated with the low-impact test are characterised using infrared thermography,flat panel digital radiography,and microscope observation.The results show that the composites irradiated with various doses display good impact resistance at 20 J,presenting minor damages in the form of dents on the surface.The irradiated CRC and WCRW display best impact resistance at 500 kGy,while W2CR2C at 1000 kGy.This shows that the layering sequence of reinforcement fibre can influence the impact resistance of irradiated composites.Apart from that,the application of non-destructive techniques show different damage mechanisms in the form resin cracks,yarn splitting/fracture,and matrix splitting when the composites are exposed at high and low irradiation doses.These findings offer valuable data for the defence industry,particularly in the areas of repair,maintenance,and the development of new materials.展开更多
With the development of large-scale complicated modern power systems, the requirement for the associated protection scheme tends to be more stringent and its combination more complex. However, it is very difficult to ...With the development of large-scale complicated modern power systems, the requirement for the associated protection scheme tends to be more stringent and its combination more complex. However, it is very difficult to figure out the factors of failure of such systems. This paper proposes a Petri net model of a transmission line protection relaying system, including three types of relays as well as an automatic reclosing device, and shows how to diagnose serial failure of the system by analyzing invariant sets of the model. Furthermore, it gives four basic types of failure sequences and its execution is much more intuitive and effective than the traditional method.展开更多
The analytical solutions for predicting the exact shape of collapse mechanisms in shallow tunnels with arbitrary excavation profiles were obtained by virtue of the upper bound theorem of limit analysis and variation p...The analytical solutions for predicting the exact shape of collapse mechanisms in shallow tunnels with arbitrary excavation profiles were obtained by virtue of the upper bound theorem of limit analysis and variation principle according to Hoek-Brown failure criterion. The seepage force was included in the upper bound limit analysis, and it was computed from the gradient of excess pore pressure distribution. The seepage was regarded as a work rate of external force. The numerical results of roof collapse in square and circular tunnels with different rock parameters were derived and discussed, which proves to be valid in comparison with the previous work. The influences of different parameters on the shape of collapsing blocks were also discussed.展开更多
In order to study the dynamic and electrical coupling response characteristics of Metal Oxide Semiconductor Controlled Thyristor(MCT)high-voltage switch under the synergic action of mechanical load and high voltage,th...In order to study the dynamic and electrical coupling response characteristics of Metal Oxide Semiconductor Controlled Thyristor(MCT)high-voltage switch under the synergic action of mechanical load and high voltage,the separated Hopkinson pressure bar(SHPB)test system was used to simulate different impact load environments,and combined with the multi-layer high-voltage ceramic capacitor charging and discharging system,the instantaneous electrical signals of MCT high-voltage switch were collected.Combined with numerical simulation and theoretical analysis,the failure mode and stress wave propagation characteristics of MCT high voltage switch were determined.The mechanical and electrical coupling response characteristics and failure mechanism of MCT high voltage switch under dynamic load were revealed from macroscopic and microscopic levels.The results show that the damage modes of MCT high-voltage switches can be divided into non-functional damage,recoverable functional damage,non-recoverable damage and structural damage.Due to the gap between the metal gate and the oxide layer,the insulating oxide layer was charged.After placing for a period of time,the elastic deformation of the metal gate partially recovered and the accumulated charge disappeared,which induced the recoverable functional damage failure of the device.In addition,obvious cracks appeared on both sides of the monocrystalline silicon inside the MCT high-voltage switch,leading to unrecoverable damage of the device.展开更多
Photoconductive semiconductor switch(PCSS)can be applied in pulsed high power systems and microwave techniques.However,reducing the damage and increasing the lifetime of silicon carbide(SiC)PCSS are still faced severe...Photoconductive semiconductor switch(PCSS)can be applied in pulsed high power systems and microwave techniques.However,reducing the damage and increasing the lifetime of silicon carbide(SiC)PCSS are still faced severe challenges.In this study,PCSSs with various structures were prepared on 4-inch diameter,500μm thick high-purity semi-insulating 4H-SiC substrates and their on-state resistance and damage mechanisms were investigated.It was found that the PCSS of an Au/TiW/Ni electrode system annealed at 950℃had a minimum on-state resistance of 6.0Ωat 1 kV bias voltage with a 532 nm and 170 mJ pulsed laser by backside illumination single trigger.The backside illumination single trigger could reduce on-state resistance and alleviate the damage of PCSS compared to the frontside trigger when the diameter of the laser spot was larger than the channel length of PCSS.For the 200 s trigger test by a 10 Hz laser,the black branch-like ablation on Au/TiW/Ni PCSS was mainly caused by thermal stress owing to hot carriers.Replacing metal Ni with boron gallium co-doped zinc oxide(BGZO)thin films annealed at 400℃,black branch-like ablation was alleviated while concentric arc damage was obvious at the anode.The major causes of concentric arc are both pulsed laser diffraction and thermal effect.展开更多
The influences of soil dilatancy angle on three-dimensional （3D） seismic stability of locally-loaded slopes in nonassociated flow rule materials were investigated using a new rotational collapse mechanism and quasi-...The influences of soil dilatancy angle on three-dimensional （3D） seismic stability of locally-loaded slopes in nonassociated flow rule materials were investigated using a new rotational collapse mechanism and quasi-static coefficient concept. Extended Bishop method and Boussinesq theorem were employed to establish the stress distribution along the rupture surfaces that are required to obtain the rate of internal energy dissipation for the nonassociated flow rule materials in rotational collapse mechanisms. Good agreement was observed by comparing the current results with those obtained using the translational or rotational mechanisms and numerical finite difference method. The results indicate that the seismic stability of slopes reduces by decreasing the dilatancy angle for nonassociated flow rule materials. The amount of the mentioned decrease is more significant in the case of mild slopes in frictional soils. A nearly infinite slope under local loading, whether its critical failure surface is 2D or 3D, not only depends on the magnitude of the external load, but also depends on the dilataney angle of soil and the coefficient of seismic load.展开更多
Environmental stress screening (ESS) is a technological process to reduce the costly early field failure of electronic components. This paper builds an optimization model for ESS of electronic components to obtain the...Environmental stress screening (ESS) is a technological process to reduce the costly early field failure of electronic components. This paper builds an optimization model for ESS of electronic components to obtain the optimal ESS duration. The failure phenomena of ESS are modeled by mixed distribution, and optimal ESS duration is defined by maximizing life-cycle cost savings under the condition of meeting reliability requirement.展开更多
The static test of 13 square hollow section(SHS) X-joints with different β and different types of plate reinforcement under in-plane moment in brace was carried out. Experimental test schemes, failure modes of specim...The static test of 13 square hollow section(SHS) X-joints with different β and different types of plate reinforcement under in-plane moment in brace was carried out. Experimental test schemes, failure modes of specimens, moment-vertical displacement curves, moment-deformation of the chord, and strain strength distribution curves were presented. The effect of β and plate reinforcement types on in-plane flexural property of SHS X-joints was studied. Results show that punching shear of chord face disappears, brace material fracture appears and concave and convex deformation of chord decrease when either collar plates or doubler plates were welded on chord face. Moment-vertical displacement curves of all specimens have obvious elastic, elastic-plastic and plastic stages. As β increases, the in-plane flexural ultimate capacity and initial stiffness of joints of the same plate reinforcement type increase, but ductility of joints decreases. With the same β, the in-plane flexural initial stiffness and ultimate capacity of doubler plate reinforced joints, collar plate reinforced joints, and unreinforced joints decrease progressively. Thickness of reinforcement plate has no obvious effect on in-plane flexural initial stiffness and ultimate capacity of joints. As thickness of reinforcement plate increases, the ductility of reinforced X-joints decreases. The concave and convex deformation of every specimen has good symmetry;as β increases, the yield and ultimate deformation of chord decrease.展开更多
In this paper, the exact Bayesian limits, taking conjugate and noninformative prior distribution, and the exact fiducial limits for the mean of the lognormal distribution are presented. They can be found iteratively b...In this paper, the exact Bayesian limits, taking conjugate and noninformative prior distribution, and the exact fiducial limits for the mean of the lognormal distribution are presented. They can be found iteratively by one-dimension integral on a finite interval. The new algorithm is very convenient and with high accuracy. It can meet the practical engineering need excellently. However, the primitive algorithm is rather cumbersome. By the way, the very close approximate limits with a simple algorithm are derived. They can be applied immediately to engineering. Otherwise, they can also be used as a search interval to find the root of equation for the exact limits.展开更多
In order to testify and examine the ability and correctness of an expert system for diagnosing the faults in the electrical power system of a certain kind of satellite, the authors have developed a simulated testbed a...In order to testify and examine the ability and correctness of an expert system for diagnosing the faults in the electrical power system of a certain kind of satellite, the authors have developed a simulated testbed according to the operational principle of the electrical power system. This paper takes the solar battery array as an instance to introduce the designing principle of its hardware circuits, and presents the methods to design the interface and the software program of the single-chip microprocessor system. The software scheme of the upper computer is introduced at the end of this paper. It has been proved that this simulated system could effectively achieve the complete functions coupled with the simple design by using of various mature techniques in the fields of electronic circuits, single-chip microprocessor and numerical emulation.展开更多
Dongjiahe Coal Mine belongs to the Carboniferous Permian coal field which has a high degree of karst and fissure development.This paper takes the working face of Dongjiahe Coal Mine as an example;through the microseis...Dongjiahe Coal Mine belongs to the Carboniferous Permian coal field which has a high degree of karst and fissure development.This paper takes the working face of Dongjiahe Coal Mine as an example;through the microseismic(MS)monitoring system arranged on the working face,the moment tensor theory was used to invert the focal mechanism solution of the anomalous area of the floor MS event;combining the numerical simulation and field data,the underlying floor faults were identified by the stress inversion method.The results show that:1)Moment tensors were decomposed into three components and the main type of rupture in this area is mixed failure according to the relative criterion;2)The hidden fault belongs to the reversed fault,its dip angle is approximately 70°,and the rupture length is 21 m determined by the inversion method of the initial dynamic polarity and stress in the focal mechanism;3)The failure process of the fault is divided into three stages by numerical simulation method combined with the temporal and spatial distribution of MS events.The results can provide a reference for early warning and evaluation of similar coal mine water inrush risks.展开更多
基金Project(06JJ20094) supported by the Natural Science Foundation of Hunan Province, China
文摘The breakage mechanism of the polycrystalline diamond compact(PDC) cutters was analyzed by the energy theory of bending waves. The cutting tests of granite block were conducted on a multifunctional testing device by using the cutter at three kinds of negative fore angles of 30°, 45° and 60°. The results show that, when the edge of the PDC layer is broken, the layer of tungsten cobalt is broken a little under the angle of 30°, while the layer of tungsten cobalt is broken continuously under the angle of 60°, their maximum depths are about 2 and 7 mm respectively in the two cases. The eccentric distance mainly depends on the negative fore angle of the cutter. When the cutter thrusts into the rock under an attack angle of 60°, the energy of bending waves reaches the maximum since the eccentric distance is the maximum. So the damage of cutter is the most serious. This test result is consistent with the conclusion of theoretical analysis well. The eccentric distance from the axial line of cutter to the point of action between the rock and cutter has great effect on the breakage of the cutter. Thus during the process of cutting, the eccentric distance should be reduced to improve the service life of PDC cutters.
基金Project(51275205)supported by the National Natural Science Foundation of China
文摘A new method of system failure analysis was proposed. First, considering the relationships between the failure subsystems,the decision making trial and evaluation laboratory(DEMATEL) method was used to calculate the degree of correlation between the failure subsystems, analyze the combined effect of related failures, and obtain the degree of correlation by using the directed graph and matrix operations. Then, the interpretative structural modeling(ISM) method was combined to intuitively show the logical relationship of many failure subsystems and their influences on each other by using multilevel hierarchical structure model and obtaining the critical subsystems. Finally, failure mode effects and criticality analysis(FMECA) was used to perform a qualitative hazard analysis of critical subsystems, determine the critical failure mode, and clarify the direction of reliability improvement.Through an example, the result demonstrates that the proposed method can be efficiently applied to system failure analysis problems.
基金supported by the Fundamental Research Funds for the Central Universities(22120240094)Humanities and Social Science Fund of Ministry of Education China(22YJA630082).
文摘Failure mode and effect analysis(FMEA)is a preven-tative risk evaluation method used to evaluate and eliminate fail-ure modes within a system.However,the traditional FMEA method exhibits many deficiencies that pose challenges in prac-tical applications.To improve the conventional FMEA,many modified FMEA models have been suggested.However,the majority of them inadequately address consensus issues and focus on achieving a complete ranking of failure modes.In this research,we propose a new FMEA approach that integrates a two-stage consensus reaching model and a density peak clus-tering algorithm for the assessment and clustering of failure modes.Firstly,we employ the interval 2-tuple linguistic vari-ables(I2TLVs)to express the uncertain risk evaluations provided by FMEA experts.Then,a two-stage consensus reaching model is adopted to enable FMEA experts to reach a consensus.Next,failure modes are categorized into several risk clusters using a density peak clustering algorithm.Finally,the proposed FMEA is illustrated by a case study of load-bearing guidance devices of subway systems.The results show that the proposed FMEA model can more easily to describe the uncertain risk information of failure modes by using the I2TLVs;the introduction of an endogenous feedback mechanism and an exogenous feedback mechanism can accelerate the process of consensus reaching;and the density peak clustering of failure modes successfully improves the practical applicability of FMEA.
基金Project(12072376)supported by the National Natural Science Foundation of ChinaPoject(10533220215858)supported by the Fundamental Research Funds for the Central Universities,China。
文摘In this study,the dynamic stress concentration factors(DSCF)around a straight-wall arch tunnel(SWAT)were solved analytically utilizing the complex variable function methods and Duhamel’s integral.The effects of wavelength,incident angle,and blasting rising time on the DSCF distribution were analyzed.Theoretical results pointed out dynamic disturbances resulting in compressive stress concentration in the vertical direction and tensile stress in the incident direction.As the wavelength and rising time increased,there was a tendency for the amplitude of stress concentration to initially rise and then converge.Moreover,a series of 3D FEM models were established to evaluate the effect of different initial stress states on the dynamic failure of the tunnel surrounding rock.The results indicated that the failure of the surrounding rock was significantly influenced by the direction of the static maximum principal stress and the direction of the dynamic disturbance.Under the coupling of static and blasting loading,damage around the tunnel was more prone to occur in the dynamic and static stress concentration coincidence zone.Finally,the damage modes of rock tunnel under static stress and blasting disturbance from different directions were summarized and a proposed support system was presented.The results reveal the mechanisms of deep-buried rock tunnel destruction and dynamically triggered rockburst.
基金funded by Universiti Tenaga Nasional(UNITEN),Malaysia for supporting this research under the Dato'Low Tuck Kwong International Grant,project code 20238002DLTKsupport for this work from the Ministry of Higher EducationMalaysia through the Higher Institution Center of Excellence(HICoE 2023-JPT(BPKI)1000/016/018/34(5))program+2 种基金supported by Tenaga Nasional Berhad(TNB)and UNITEN through the BOLD Refresh Postdoctoral Fellowships under Grant J510050002-IC-6 BOLDREFRESH2023-Centre of ExcellencePrince Sultan University for their supportIndustrial Technology Division,Malaysian Nuclear Agency for their support in this research work.
文摘Investigating the influence of radiation on glass fibre composites is essential for their use in space and aerospace environment.Gaining insight into the damage mechanisms caused by gamma irradiation,can improve the safety and resilience of structures.This paper is aimed at investigating the failure mode and damage of gamma-irradiated repurposed pultruded glass fibre-reinforced polyester subjected to lowvelocity impact using three types of non-destructive techniques.Three sets of differently layered configurations(CRC,WCRW,W2CR2C)consisting of chopped(c),roving(r),and weaved(w)fibre-reinforced polyester are applied in this study.Drop hammer test is applied to evaluate the low-impact resistance properties of Gamma-irradiated composite at 100 kGy,500 kGy,and 1000 kGy.Preliminary flexural and hardness tests are conducted to further assess the behaviour of irradiated polymer composites.Further,the damage modes associated with the low-impact test are characterised using infrared thermography,flat panel digital radiography,and microscope observation.The results show that the composites irradiated with various doses display good impact resistance at 20 J,presenting minor damages in the form of dents on the surface.The irradiated CRC and WCRW display best impact resistance at 500 kGy,while W2CR2C at 1000 kGy.This shows that the layering sequence of reinforcement fibre can influence the impact resistance of irradiated composites.Apart from that,the application of non-destructive techniques show different damage mechanisms in the form resin cracks,yarn splitting/fracture,and matrix splitting when the composites are exposed at high and low irradiation doses.These findings offer valuable data for the defence industry,particularly in the areas of repair,maintenance,and the development of new materials.
文摘With the development of large-scale complicated modern power systems, the requirement for the associated protection scheme tends to be more stringent and its combination more complex. However, it is very difficult to figure out the factors of failure of such systems. This paper proposes a Petri net model of a transmission line protection relaying system, including three types of relays as well as an automatic reclosing device, and shows how to diagnose serial failure of the system by analyzing invariant sets of the model. Furthermore, it gives four basic types of failure sequences and its execution is much more intuitive and effective than the traditional method.
基金Project(2013CB036004)supported by the National Basic Research Program of ChinaProjects(51178468,51378510)supported by National Natural Science Foundation of China
文摘The analytical solutions for predicting the exact shape of collapse mechanisms in shallow tunnels with arbitrary excavation profiles were obtained by virtue of the upper bound theorem of limit analysis and variation principle according to Hoek-Brown failure criterion. The seepage force was included in the upper bound limit analysis, and it was computed from the gradient of excess pore pressure distribution. The seepage was regarded as a work rate of external force. The numerical results of roof collapse in square and circular tunnels with different rock parameters were derived and discussed, which proves to be valid in comparison with the previous work. The influences of different parameters on the shape of collapsing blocks were also discussed.
基金Youth Talent Project of Basic Scientific Research Project of Liaoning Province Education Department(Grant No.LJKZ0270)Youth Project of Basic Scientific Research Project of Liaoning Province Education Department(Grant No.LJKQZ2021055).
文摘In order to study the dynamic and electrical coupling response characteristics of Metal Oxide Semiconductor Controlled Thyristor(MCT)high-voltage switch under the synergic action of mechanical load and high voltage,the separated Hopkinson pressure bar(SHPB)test system was used to simulate different impact load environments,and combined with the multi-layer high-voltage ceramic capacitor charging and discharging system,the instantaneous electrical signals of MCT high-voltage switch were collected.Combined with numerical simulation and theoretical analysis,the failure mode and stress wave propagation characteristics of MCT high voltage switch were determined.The mechanical and electrical coupling response characteristics and failure mechanism of MCT high voltage switch under dynamic load were revealed from macroscopic and microscopic levels.The results show that the damage modes of MCT high-voltage switches can be divided into non-functional damage,recoverable functional damage,non-recoverable damage and structural damage.Due to the gap between the metal gate and the oxide layer,the insulating oxide layer was charged.After placing for a period of time,the elastic deformation of the metal gate partially recovered and the accumulated charge disappeared,which induced the recoverable functional damage failure of the device.In addition,obvious cracks appeared on both sides of the monocrystalline silicon inside the MCT high-voltage switch,leading to unrecoverable damage of the device.
基金National Key R&D Program of China(2021YFA0716304)Shanghai Science and Technology Programs(22511100300,23DZ2201500)。
文摘Photoconductive semiconductor switch(PCSS)can be applied in pulsed high power systems and microwave techniques.However,reducing the damage and increasing the lifetime of silicon carbide(SiC)PCSS are still faced severe challenges.In this study,PCSSs with various structures were prepared on 4-inch diameter,500μm thick high-purity semi-insulating 4H-SiC substrates and their on-state resistance and damage mechanisms were investigated.It was found that the PCSS of an Au/TiW/Ni electrode system annealed at 950℃had a minimum on-state resistance of 6.0Ωat 1 kV bias voltage with a 532 nm and 170 mJ pulsed laser by backside illumination single trigger.The backside illumination single trigger could reduce on-state resistance and alleviate the damage of PCSS compared to the frontside trigger when the diameter of the laser spot was larger than the channel length of PCSS.For the 200 s trigger test by a 10 Hz laser,the black branch-like ablation on Au/TiW/Ni PCSS was mainly caused by thermal stress owing to hot carriers.Replacing metal Ni with boron gallium co-doped zinc oxide(BGZO)thin films annealed at 400℃,black branch-like ablation was alleviated while concentric arc damage was obvious at the anode.The major causes of concentric arc are both pulsed laser diffraction and thermal effect.
文摘The influences of soil dilatancy angle on three-dimensional （3D） seismic stability of locally-loaded slopes in nonassociated flow rule materials were investigated using a new rotational collapse mechanism and quasi-static coefficient concept. Extended Bishop method and Boussinesq theorem were employed to establish the stress distribution along the rupture surfaces that are required to obtain the rate of internal energy dissipation for the nonassociated flow rule materials in rotational collapse mechanisms. Good agreement was observed by comparing the current results with those obtained using the translational or rotational mechanisms and numerical finite difference method. The results indicate that the seismic stability of slopes reduces by decreasing the dilatancy angle for nonassociated flow rule materials. The amount of the mentioned decrease is more significant in the case of mild slopes in frictional soils. A nearly infinite slope under local loading, whether its critical failure surface is 2D or 3D, not only depends on the magnitude of the external load, but also depends on the dilataney angle of soil and the coefficient of seismic load.
文摘Environmental stress screening (ESS) is a technological process to reduce the costly early field failure of electronic components. This paper builds an optimization model for ESS of electronic components to obtain the optimal ESS duration. The failure phenomena of ESS are modeled by mixed distribution, and optimal ESS duration is defined by maximizing life-cycle cost savings under the condition of meeting reliability requirement.
基金Projects(51278209 and 51478047) supported by the National Natural Science Foundation of ChinaProject(ZQN-PY110) supported by Promotion Program for Young and Middle-aged Teacher in Science and Technology Research of Huaqiao University,China+1 种基金Project(2014FJ-NCET-ZR03) supported by Program for New Century Excellent Talents in Fujian Province University,ChinaProject(JA13005) supported by Incubation Programme for Excellent Young Science and Technology Talents in Fujian Province Universities,China
文摘The static test of 13 square hollow section(SHS) X-joints with different β and different types of plate reinforcement under in-plane moment in brace was carried out. Experimental test schemes, failure modes of specimens, moment-vertical displacement curves, moment-deformation of the chord, and strain strength distribution curves were presented. The effect of β and plate reinforcement types on in-plane flexural property of SHS X-joints was studied. Results show that punching shear of chord face disappears, brace material fracture appears and concave and convex deformation of chord decrease when either collar plates or doubler plates were welded on chord face. Moment-vertical displacement curves of all specimens have obvious elastic, elastic-plastic and plastic stages. As β increases, the in-plane flexural ultimate capacity and initial stiffness of joints of the same plate reinforcement type increase, but ductility of joints decreases. With the same β, the in-plane flexural initial stiffness and ultimate capacity of doubler plate reinforced joints, collar plate reinforced joints, and unreinforced joints decrease progressively. Thickness of reinforcement plate has no obvious effect on in-plane flexural initial stiffness and ultimate capacity of joints. As thickness of reinforcement plate increases, the ductility of reinforced X-joints decreases. The concave and convex deformation of every specimen has good symmetry;as β increases, the yield and ultimate deformation of chord decrease.
文摘In this paper, the exact Bayesian limits, taking conjugate and noninformative prior distribution, and the exact fiducial limits for the mean of the lognormal distribution are presented. They can be found iteratively by one-dimension integral on a finite interval. The new algorithm is very convenient and with high accuracy. It can meet the practical engineering need excellently. However, the primitive algorithm is rather cumbersome. By the way, the very close approximate limits with a simple algorithm are derived. They can be applied immediately to engineering. Otherwise, they can also be used as a search interval to find the root of equation for the exact limits.
文摘In order to testify and examine the ability and correctness of an expert system for diagnosing the faults in the electrical power system of a certain kind of satellite, the authors have developed a simulated testbed according to the operational principle of the electrical power system. This paper takes the solar battery array as an instance to introduce the designing principle of its hardware circuits, and presents the methods to design the interface and the software program of the single-chip microprocessor system. The software scheme of the upper computer is introduced at the end of this paper. It has been proved that this simulated system could effectively achieve the complete functions coupled with the simple design by using of various mature techniques in the fields of electronic circuits, single-chip microprocessor and numerical emulation.
基金Project(2017YFC1503103)supported by the National Key Research and Development Plan of ChinaProjects(51774064,51974055,41941018)supported by the National Natural Science Foundation of China+1 种基金Project(DUT20GJ216)supported by the Fundamental Research Funds for the Central Universities,ChinaProject(51627804)supported by the Special-Funded Program on National Key Scientific Instruments and Equipment Development,China。
文摘Dongjiahe Coal Mine belongs to the Carboniferous Permian coal field which has a high degree of karst and fissure development.This paper takes the working face of Dongjiahe Coal Mine as an example;through the microseismic(MS)monitoring system arranged on the working face,the moment tensor theory was used to invert the focal mechanism solution of the anomalous area of the floor MS event;combining the numerical simulation and field data,the underlying floor faults were identified by the stress inversion method.The results show that:1)Moment tensors were decomposed into three components and the main type of rupture in this area is mixed failure according to the relative criterion;2)The hidden fault belongs to the reversed fault,its dip angle is approximately 70°,and the rupture length is 21 m determined by the inversion method of the initial dynamic polarity and stress in the focal mechanism;3)The failure process of the fault is divided into three stages by numerical simulation method combined with the temporal and spatial distribution of MS events.The results can provide a reference for early warning and evaluation of similar coal mine water inrush risks.
