Continuous carbon fiber reinforced silicon carbide(C/SiC)composites are often subjected to low-velocity impacts when utilized as structural materials for thermal protection.However,research on in-plane impact damage a...Continuous carbon fiber reinforced silicon carbide(C/SiC)composites are often subjected to low-velocity impacts when utilized as structural materials for thermal protection.However,research on in-plane impact damage and multiple impact damage of C/SiC composites is limited.To investigate the in-plane impact damage behavior of C/SiC composites,a drop-weight impact test method was developed for strip samples,and these results were subsequently compared with those of C/SiC composite plates.Results show that the in-plane impact behavior of C/SiC strip samples is similar to that of C/SiC composite plates.Variation of the impact load with displacement is characterized by three stages:a nearly linear stage,a severe load drop stage,and a rebound stage where displacement occurs after the impact energy exceeds its peak value.Impact damage behavior under single and multiple impacts on 2D plain and 3D needled C/SiC composites was investigated at different impact energies and durations.Crack propagation in C/SiC composites was studied by computerized tomography(CT)technique.In the 2D plain C/SiC composite,load propagation between layers is hindered during impact,leading to delamination and 90°fiber brittle fracture.The crack length perpendicular to the impact direction increases with impact energy increases,resulting in more serious 0°fiber fracture and a larger area of fiber loss.In the 3D needled C/SiC composite,load propagates between the layers during impact through the connection of needled fibers.The fibers continue to provide substantial structural support,with notable instances of fiber pull-off and debonding.Consequently,the impact resistance is superior to that of 2D plain C/SiC composite.When the 3D needled C/SiC composite undergoes two successive impacts of 1.5 J,the energy absorption efficiency of the second impact is significantly lower,accompanied by a smaller impact displacement.Moreover,the total energy absorption efficiency of these two impacts of 1.5 J is lower than that of a single 3.0 J impact.展开更多
With the continuous evolution of electronic technology,field-programmable gate array(FPGA)has demonstrated significant advantages in the realm of signal acquisition and processing,and signal acquisition plays a pivota...With the continuous evolution of electronic technology,field-programmable gate array(FPGA)has demonstrated significant advantages in the realm of signal acquisition and processing,and signal acquisition plays a pivotal role in the practical applications of laser gyros.By analysis of the output signals from a laser gyro and an accelerometer,this paper presents a circuit design for signal acquisition of the laser gyro based on domestic devices.The design incorporates a finite impulse response(FIR)filter to process the gyro signal and employs a small-volume,impact-resistant quartz flexible accelerometer for signal aquisition.Simulation results demonstrate that the errors in X,Y,and Z axes fall within acceptable ranges while meeting filtering requirements.The use of FPGA for signal acquisition and preprocessing enhances configuration flexibility,which provides an idea and method for optimizing performance and processing signals in laser gyro applications.展开更多
Coal waste(CW)could be used for soil stabilization due to the pozzolanic elements it contains.There hasn’t been much investigation into how different fibers affect the mechanical qualities of stabilized sand,although...Coal waste(CW)could be used for soil stabilization due to the pozzolanic elements it contains.There hasn’t been much investigation into how different fibers affect the mechanical qualities of stabilized sand,although adding fibers of any kind to soils may improve the soil because of fiber characteristics like rigidity.For this reason,several tests were carried out on sand that contained 6%cement(by dry weight of used sand),5 wt%CW,0 wt%,0.25 wt%,and 0.50 wt%fiber,as well as the unconfined compressive strength(UCS)test,indirect tensile strength(ITS)test,unconsolidated undrained(UU)triaxial test,scanning electron microscope(SEM)test and ultrasonic pulse velocity(UPV)test.The results showed that in comparison to other fiber reinforced mix designs,the specimen reinforced with 0.5%fibers and the mix design of 0.25 wt%glass and 0.25 wt%polypropylene(PP)fibers exhibited the maximum strength.Examining the impact of fiber type found that glass fibers influence PP strength more favorably than other fiber types.The use of PP fibers is an excellent solution for the problem of large strains in design processes,while adding glass fibers is considered a suitable treatment for issues related to small strains.展开更多
Carbon fiber-reinforced polymer(CFRP)is widely used in aerospace applications.This kind of material may face the threat of high-velocity impact in the process of dedicated service,and the relevant research mainly cons...Carbon fiber-reinforced polymer(CFRP)is widely used in aerospace applications.This kind of material may face the threat of high-velocity impact in the process of dedicated service,and the relevant research mainly considers the impact resistance of the material,and lacks the high-velocity impact damage monitoring research of CFRP.To solve this problem,a real high-velocity impact damage experiment and structural health monitoring(SHM)method of CFRP plate based on piezoelectric guided wave is proposed.The results show that CFRP has obvious perforation damage and fiber breakage when high-velocity impact occurs.It is also proved that guided wave SHM technology can be effectively used in the monitoring of such damage,and the damage can be reflected by quantifying the signal changes and damage index(DI).It provides a reference for further research on guided wave structure monitoring of high/hyper-velocity impact damage of CFRP.展开更多
Understanding the equation of state of cold dense matter,i.e.,those inside neutron stars,is a key problem in the multi-messenger astronomical era.In order to facilitate the scientific discussions between different com...Understanding the equation of state of cold dense matter,i.e.,those inside neutron stars,is a key problem in the multi-messenger astronomical era.In order to facilitate the scientific discussions between different commu-nities in the relevant fields,particularly between nuclear physicists and astrophysicists,we have organized the Dialo-gue at the Dream Field(DDF2024).The participants explored topics of various fields such as pulsar astrophysics,transient phenomena,hadronic and nuclear matter,supra-nuclear matter with quark degree of freedom,numerical relativity.This involved discussions on the mechanisms,model constructions,observational impacts,and introduc-tions of new facilities.In-depth exchanges were carried out through invited talks and free discussions,as well as a visit to view the FAST telescope.展开更多
In order to improve the charging efficiency of lead acid battery, shorten the charging time and avoid the battery polarization, a new charging method was put forward. Based on the analyzed results of charging charact...In order to improve the charging efficiency of lead acid battery, shorten the charging time and avoid the battery polarization, a new charging method was put forward. Based on the analyzed results of charging characteristic of lead acid battery, a pulse quick charger is designed to adjust the charging current pulse’s amplitude and pulse width automatically stage by stage according to the measured battery voltage and feedback current. Compared with other kinds of quick chargers, it has such characteristics as shorter charging time, higher charging efficiency and lower temperature increasing during the charging process. As a result, the battery polarization is reduced efficiently.展开更多
The grain refinement of superalloy IN718 under the action of low voltage pulsed magnetic field was investigated. The experimental results show that fine equiaxed grains are acquired under the action of low voltage pul...The grain refinement of superalloy IN718 under the action of low voltage pulsed magnetic field was investigated. The experimental results show that fine equiaxed grains are acquired under the action of low voltage pulsed magnetic field. The refinement effect of the pulsed magnetic field is affected by the melt cooling rate and superheating. The decrease of cooling rate and superheating enhance the refinement effect of the low voltage pulsed magnetic field. The magnetic force and the melt flow during solidification are modeled and simulated to reveal the grain refinement mechanism. It is considered that the melt convection caused by the pulsed magnetic field, as well as cooling rate and superheating contributes to the refinement of solidified grains.展开更多
基金Aeronautical Science Foundation of China(2021Z057053001)。
文摘Continuous carbon fiber reinforced silicon carbide(C/SiC)composites are often subjected to low-velocity impacts when utilized as structural materials for thermal protection.However,research on in-plane impact damage and multiple impact damage of C/SiC composites is limited.To investigate the in-plane impact damage behavior of C/SiC composites,a drop-weight impact test method was developed for strip samples,and these results were subsequently compared with those of C/SiC composite plates.Results show that the in-plane impact behavior of C/SiC strip samples is similar to that of C/SiC composite plates.Variation of the impact load with displacement is characterized by three stages:a nearly linear stage,a severe load drop stage,and a rebound stage where displacement occurs after the impact energy exceeds its peak value.Impact damage behavior under single and multiple impacts on 2D plain and 3D needled C/SiC composites was investigated at different impact energies and durations.Crack propagation in C/SiC composites was studied by computerized tomography(CT)technique.In the 2D plain C/SiC composite,load propagation between layers is hindered during impact,leading to delamination and 90°fiber brittle fracture.The crack length perpendicular to the impact direction increases with impact energy increases,resulting in more serious 0°fiber fracture and a larger area of fiber loss.In the 3D needled C/SiC composite,load propagates between the layers during impact through the connection of needled fibers.The fibers continue to provide substantial structural support,with notable instances of fiber pull-off and debonding.Consequently,the impact resistance is superior to that of 2D plain C/SiC composite.When the 3D needled C/SiC composite undergoes two successive impacts of 1.5 J,the energy absorption efficiency of the second impact is significantly lower,accompanied by a smaller impact displacement.Moreover,the total energy absorption efficiency of these two impacts of 1.5 J is lower than that of a single 3.0 J impact.
文摘With the continuous evolution of electronic technology,field-programmable gate array(FPGA)has demonstrated significant advantages in the realm of signal acquisition and processing,and signal acquisition plays a pivotal role in the practical applications of laser gyros.By analysis of the output signals from a laser gyro and an accelerometer,this paper presents a circuit design for signal acquisition of the laser gyro based on domestic devices.The design incorporates a finite impulse response(FIR)filter to process the gyro signal and employs a small-volume,impact-resistant quartz flexible accelerometer for signal aquisition.Simulation results demonstrate that the errors in X,Y,and Z axes fall within acceptable ranges while meeting filtering requirements.The use of FPGA for signal acquisition and preprocessing enhances configuration flexibility,which provides an idea and method for optimizing performance and processing signals in laser gyro applications.
文摘Coal waste(CW)could be used for soil stabilization due to the pozzolanic elements it contains.There hasn’t been much investigation into how different fibers affect the mechanical qualities of stabilized sand,although adding fibers of any kind to soils may improve the soil because of fiber characteristics like rigidity.For this reason,several tests were carried out on sand that contained 6%cement(by dry weight of used sand),5 wt%CW,0 wt%,0.25 wt%,and 0.50 wt%fiber,as well as the unconfined compressive strength(UCS)test,indirect tensile strength(ITS)test,unconsolidated undrained(UU)triaxial test,scanning electron microscope(SEM)test and ultrasonic pulse velocity(UPV)test.The results showed that in comparison to other fiber reinforced mix designs,the specimen reinforced with 0.5%fibers and the mix design of 0.25 wt%glass and 0.25 wt%polypropylene(PP)fibers exhibited the maximum strength.Examining the impact of fiber type found that glass fibers influence PP strength more favorably than other fiber types.The use of PP fibers is an excellent solution for the problem of large strains in design processes,while adding glass fibers is considered a suitable treatment for issues related to small strains.
基金supported by the National Natural Science Foundation of China(Nos.51921003,52275153)the Fundamental Research Funds for the Central Universities(No.NI2023001)+2 种基金the Research Fund of State Key Laboratory of Mechanics and Control for Aero-space Structures(No.MCAS-I-0423G01)the Fund of Pro-spective Layout of Scientific Research for Nanjing University of Aeronautics and Astronauticsthe Priority Academic Program Development of Jiangsu Higher Education Institu-tions of China.
文摘Carbon fiber-reinforced polymer(CFRP)is widely used in aerospace applications.This kind of material may face the threat of high-velocity impact in the process of dedicated service,and the relevant research mainly considers the impact resistance of the material,and lacks the high-velocity impact damage monitoring research of CFRP.To solve this problem,a real high-velocity impact damage experiment and structural health monitoring(SHM)method of CFRP plate based on piezoelectric guided wave is proposed.The results show that CFRP has obvious perforation damage and fiber breakage when high-velocity impact occurs.It is also proved that guided wave SHM technology can be effectively used in the monitoring of such damage,and the damage can be reflected by quantifying the signal changes and damage index(DI).It provides a reference for further research on guided wave structure monitoring of high/hyper-velocity impact damage of CFRP.
文摘Understanding the equation of state of cold dense matter,i.e.,those inside neutron stars,is a key problem in the multi-messenger astronomical era.In order to facilitate the scientific discussions between different commu-nities in the relevant fields,particularly between nuclear physicists and astrophysicists,we have organized the Dialo-gue at the Dream Field(DDF2024).The participants explored topics of various fields such as pulsar astrophysics,transient phenomena,hadronic and nuclear matter,supra-nuclear matter with quark degree of freedom,numerical relativity.This involved discussions on the mechanisms,model constructions,observational impacts,and introduc-tions of new facilities.In-depth exchanges were carried out through invited talks and free discussions,as well as a visit to view the FAST telescope.
文摘In order to improve the charging efficiency of lead acid battery, shorten the charging time and avoid the battery polarization, a new charging method was put forward. Based on the analyzed results of charging characteristic of lead acid battery, a pulse quick charger is designed to adjust the charging current pulse’s amplitude and pulse width automatically stage by stage according to the measured battery voltage and feedback current. Compared with other kinds of quick chargers, it has such characteristics as shorter charging time, higher charging efficiency and lower temperature increasing during the charging process. As a result, the battery polarization is reduced efficiently.
基金Project(2010CB631205)supported by the National Basic Research Program of ChinaProject(51034012)supported by the National Natural Science Foundation of China
文摘The grain refinement of superalloy IN718 under the action of low voltage pulsed magnetic field was investigated. The experimental results show that fine equiaxed grains are acquired under the action of low voltage pulsed magnetic field. The refinement effect of the pulsed magnetic field is affected by the melt cooling rate and superheating. The decrease of cooling rate and superheating enhance the refinement effect of the low voltage pulsed magnetic field. The magnetic force and the melt flow during solidification are modeled and simulated to reveal the grain refinement mechanism. It is considered that the melt convection caused by the pulsed magnetic field, as well as cooling rate and superheating contributes to the refinement of solidified grains.
