The mechanical properties of secondary cells are crucial to the safety and reliability of battery packs,which can fail due to extrusion and vibration in a vehicle crash.To analyze the structural response of the second...The mechanical properties of secondary cells are crucial to the safety and reliability of battery packs,which can fail due to extrusion and vibration in a vehicle crash.To analyze the structural response of the secondary cell and its other dynamic behaviors,the experiment and some numerical simulations were carried out based on single reference impact testing.Then,an equivalent constitutive relationship of the secondary cell was proposed to reveal the dynamic properties and used to guide the safety estimation of the battery pack.As the input parameter to the finite element model,the equivalent constitutive relationship,including but not limited to the elastic modulus and stain-stress curve,determines the simulation precision of the battery packs.Compared to the experimental results of the natural frequency of the battery pack,the simulation error is below 2%when the elastic modulus of the secondary cell in the battery pack has been verified.展开更多
To overcome the deficiencies addressed in the conventional PID control and improve the dynamic performance and robustness of the system, a simple design and parameters tuning approach of internal model control-PID （I...To overcome the deficiencies addressed in the conventional PID control and improve the dynamic performance and robustness of the system, a simple design and parameters tuning approach of internal model control-PID （IMC-PID） controller was proposed for the first order plus time-delay （FOPTD） process and the second order plus time-delay （SOPTD） process. By approximating the time-delay term of the process model with the first-order Taylor series, the expressions for IMC-PID controller parameters were derived, and they had only one adjustable parameter 2 which was directly related to the dynamic performance and robustness of the system. Moreover, an analytical approach of selecting 2 was given based on the maximum sensitivity Ms. Then, the robust tuning of the system could be achieved according to the value of Ms. In addition, the proposed method could be extended to the integrator plus time-delay （IPTD） process and the first order delay integrating （FODI） process. Simulation studies were carried out on various processes with time-delay, and the results show that the proposed method could provide a better dynamic performance of both the set-point tracking and disturbance rejection and robustness against parameters perturbation.展开更多
A heavy-haul train-track coupled model is developed. Taking the emergency braking of the 2×104 t combined train as example, the train longitudinal impulse, the coupler dynamic behaviors and wheel-rail interaction...A heavy-haul train-track coupled model is developed. Taking the emergency braking of the 2×104 t combined train as example, the train longitudinal impulse, the coupler dynamic behaviors and wheel-rail interactions of vehicles distributing in the different positions are analyzed. The results indicate that under the coupler compressing forces, the couplers of middle locomotives may tilt to the free swing limits, which induces the unidirectional tilt of their connected wagon couplers. Consequently, the coupler longitudinal forces produce the lateral components, and then affect the wheel-rail dynamic interaction. The performance of the middle locomotive and their neighboring freight wagons deteriorate significantly, becoming the most dangerous parts in the combined train. The wagons disconnecting with the locomotives can basically keep their couplers to stabilize in the centering positions, even though the maximum coupler longitudinal force acts on it. And its corresponding running safety also has little changes.展开更多
To obtain a good drivability and high efficiency of the micro-electric vehicle, a new driving in-wheel motor design was analyzed and optimized. Maxwell software was used to build finite element simulation model of the...To obtain a good drivability and high efficiency of the micro-electric vehicle, a new driving in-wheel motor design was analyzed and optimized. Maxwell software was used to build finite element simulation model of the driving in-wheel motor. The basic features and starting process were analyzed by field-circuit coupled finite element method. The internal complicated magnetic field distribution and dynamic performance simulation were obtained in different positions. No-load and load characteristics of the driving in-wheel motor was simulated, and the power consumption of materials was computed. The conformity of the final simulation results with the experimental data indicates that this method can be used to provide a theoretical basis to make further optimal design of this new driving in-wheel motor and its control system, so as to improve the starting torque and reduce torque ripple of the motor. This method can shorten the development cycle of in-wheel motors and save development costs, which has a wide range of engineering application value.展开更多
The effect of Li(2.0 wt%)addition on mechanical properties and ageing precipitation behavior of Al-3.0 Mg 0.5 Si was investigated by tensile test,dynamic elasticity modulus test,scanning electron microscopy(SEM),trans...The effect of Li(2.0 wt%)addition on mechanical properties and ageing precipitation behavior of Al-3.0 Mg 0.5 Si was investigated by tensile test,dynamic elasticity modulus test,scanning electron microscopy(SEM),transmission electron microscopy(TEM)and high-resolution transmission electron microscopy(HRTEM)images.The results show that the tensile strength of the Li-containing alloy can be significantly improved;however,the ductility is sharply decreased and the fracture mechanism changes from ductile fracture to intergranular fracture.The elasticity modulus of the Li-containing alloy increases by 11.6%compared with the base alloy.The microstructure observation shows that the Li addition can absolutely change the precipitation behavior of the base alloy,andδ′-Al_(3)Li phase becomes the main precipitates.Besides,β′′-Mg_(2)Si andδ′-Al_(3)Li dual phases precipitation can be visibly observed at 170℃ ageing for 100 h,although the quantity ofδ′-Al_(3)Li phase is more thanβ′′-Mg_(2)Si phase.The width of the precipitate-free zone(PFZ)of the Li-containing alloy is much wider at the over-ageing state than the base alloy,which has a negative impact on the ductile and results in the decrease of elongation.展开更多
The effects of adding alloy element zinc on the static and dynamic mechanical properties of copper-zinc alloy were investigated. Tensile and low cycle fatigue behaviors of the C11000 copper and H63 copper-zinc alloy w...The effects of adding alloy element zinc on the static and dynamic mechanical properties of copper-zinc alloy were investigated. Tensile and low cycle fatigue behaviors of the C11000 copper and H63 copper-zinc alloy were obtained by using a miniature tester that combined the functions of in situ tensile and fatigue testing. A piezoelectric actuator was adopted as the actuator for the fatigue testing, and the feasibility of the fatigue actuator was verified by the transient harmonic response analysis based on static tensile preload and dynamic sinusoidal load. The experimental results show that the yield strength and tensile strength of the C11000 copper are improved after adding 37%(mass fraction) zinc, and H63 copper-zinc alloy presents more obvious cyclic hardening behavior and more consumed irreversible plastic work during each stress cycle compared with C11000 copper for the same strain controlled cycling. Additionally, based on the Manson-Coffin theory, the strain-life equations of the two materials were also obtained. C11000 copper and H63 copper-zinc alloy show transition life of 16832 and 1788 cycles, respectively.展开更多
Based on theory of variable-mass system thermodynamics, the dynamic mathematic models of each component of the horizontal steam-launch system were established, and by the numerical simulation of the system launching p...Based on theory of variable-mass system thermodynamics, the dynamic mathematic models of each component of the horizontal steam-launch system were established, and by the numerical simulation of the system launching process, the thermodynamics and kinetics characteristics of the system with three valves of different flow characteristics were got. The simulation results show that the values of the peak-to-average ratios of dimensionless acceleration with the equal percentage valve, the linear valve and the quick opening valve are 1.355, 1.614 and 1.722, respectively, and the final values of the dimensionless velocities are 0.843, 0.957 and 1.0, respectively. In conclusion, the value of the dimensionless velocity with the equal percentage valve doesn't reach the set value of 0.90 when the dimensionless displacement is 0.82, while the system with the linear valve can meet the launching requirement, as well as the fluctuation range of dimensionless acceleration is less than that of the quick opening valve. Therefore, the system with the linear valve has the best performance among the three kinds of valves.展开更多
The effect of T6I6 treatment on the dynamic mechanical and microstructure behaviour of Al-Si-Mg-Cu cast alloy was investigated using split Hopkinson pressure bar(SHPB), transmission electron microscopy(TEM), and highr...The effect of T6I6 treatment on the dynamic mechanical and microstructure behaviour of Al-Si-Mg-Cu cast alloy was investigated using split Hopkinson pressure bar(SHPB), transmission electron microscopy(TEM), and highresolution transmission electron microscopy(HRTEM). Besides, the impact resistances of T6I6 and T6 motor shells of new energy vehicles made of Al-Si-Mg-Cu cast alloy were compared using a trolley crash test. The results indicated that the main strengthening-phases of the T6 peak-aged and T6I6 peak-aged alloy were GP zone and β″ precipitates. T6I6treatment can increase the density and size of β″ precipitates in peak-aged alloy and enhance both its tensile strength(σb)and elongation(δ). The dynamic toughness values of T6I6 samples are 50.34 MJ/m^(3) at 2000 s^(-1) and 177.34 MJ/m^(3) at 5000 s^(-1) which are 20% and 12% higher than those of T6 samples, respectively. Compared with a T6 shell, the overall deformation of T6I6 shell is more uniform during the crash test. At an impact momentum of 3.5×10;kg·m/s, the T6I6shell breaks down at 0.38 s which is 0.10 s later than the T6 shell.展开更多
In order to evaluate the seismic stability of reinforced soil walls against bearing capacity failure,the seismic safety factor of reinforced soil walls was determined by using pseudo-dynamic method,and calculated by c...In order to evaluate the seismic stability of reinforced soil walls against bearing capacity failure,the seismic safety factor of reinforced soil walls was determined by using pseudo-dynamic method,and calculated by considering different parameters,such as horizontal and vertical seismic acceleration coefficients,ratio of reinforcement length to wall height,back fill friction angle,foundation soil friction angle,soil reinforcement interface friction angle and surcharge.The parametric study shows that the seismic safety factor increases by 24-fold when the foundation soil friction angle varies from 25°to 45°,and increases by 2-fold when the soil reinforcement interface friction angle varies from 0 to 30°.That is to say,the bigger values the foundation soil and/or soil reinforcement interface friction angles have,the safer the reinforced soil walls become in the seismic design.The results were also compared with those obtained from pseudo-static method.It is found that there is a higher value of the safety factor by the present work.展开更多
In the industrial production, the dynamic cooling pre-aging treatment was employed to replace the isothermal pre-aging during the continuous heat treatment production of Al-Mg-Si alloy automotive sheets. The effects o...In the industrial production, the dynamic cooling pre-aging treatment was employed to replace the isothermal pre-aging during the continuous heat treatment production of Al-Mg-Si alloy automotive sheets. The effects of dynamic cooling pre-aging treatment on mechanical properties and paint-bake hardening behavior of an Al-Mg-Si alloy sheet are proposed in this study. The scanning electron microscopy, transmission electron microscopy, tensile test, Vickers hardness test, and differential scanning calorimetry were conducted for the purpose. It was found that the dynamic cooling pre-aging treatment at low temperature region led to the decreasing of cluster II, resulting in the deterioration of the ability of the paint-bake hardening. With the increase of the cooling pre-aging temperature, the increasing of cluster II effectively improved the stability against natural aging and the paint-bake hardening ability. The optimized dynamic cooling pre-aging temperature was ~150 ℃. In this condition, the hardness increase of the alloy sheet with pre-aging treatment is low during storage at room temperature. The high yield strength increment is obtained after paint-bake hardening.展开更多
In order to investigate the mechanical properties and stress-strain curves of concrete at different ages under impact load,the impact compression tests of concrete at age of 1, 3, 7, 14 and 28 d were conducted with a ...In order to investigate the mechanical properties and stress-strain curves of concrete at different ages under impact load,the impact compression tests of concrete at age of 1, 3, 7, 14 and 28 d were conducted with a large diameter split Hopkinson pressure bar, respectively. Based on statistical damage theory and Weibull distribution, combining the analysis of the change laws of stressstrain curves and viscosity coefficient of concrete with age, a damage constitutive model that can reflect the variation in dynamic mechanical properties with age was proposed. The stress-strain curves calculated from the proposed model are in good agreement with those from experimental data directly.展开更多
To explore the influence of double liquid quenching on the cutting performance of the 7A09 aluminum alloy,quasi-static compression and dynamic impact tests were carried out on the 7A09 aluminum alloy after double liqu...To explore the influence of double liquid quenching on the cutting performance of the 7A09 aluminum alloy,quasi-static compression and dynamic impact tests were carried out on the 7A09 aluminum alloy after double liquid quenching using an MTS810.23 universal testing machine and split-Hopkinson pressure bar(SHPB).The experimental data were fitted to obtain the Johnson–Cook constitutive model parameters of the alloy.Simulations of the machining process were carried out using the Deform-3D finite element software.The results showed that the rheological stress increased with the increase in strain rate and the decrease in temperature.The increase in the cutting speed and feed caused the cutting temperature to rise sharply,whereas the influence of the cutting amount on the cutting temperature was weak.Because of the presence of chip nodules,there was extremum in the cutting force vs cutting speed curves.The increase in the feed and cutting depth increased the cutting area Ac,so the cutting force also increased.The simulation results were verified by experiments.The simulation predictions were in good agreement with the test values,and the cutting force and temperature variations with the cutting parameters were the same.Thus,the correctness of the 7A09 aluminum alloy finite element model was verified.展开更多
With the growing deployment of smart distribution grid,it has become urgent to investigate the smart distribution grid behavior during transient faults and improve the system stability.The feasibility of segmenting la...With the growing deployment of smart distribution grid,it has become urgent to investigate the smart distribution grid behavior during transient faults and improve the system stability.The feasibility of segmenting large power grids and multiple smart distribution grids interconnections using energy storage technology for improving the system dynamic stability was studied.The segmentation validity of the large power grids and smart distribution grid inverter output interconnections power system using energy storage technology was proved in terms of theoretical analysis.Then,the influences of the energy storage device location and capacity on the proposed method were discussed in detail.The conclusion is obtained that the ESD optimal locations are allocated at the tie line terminal buses in the interconnected grid,respectively.The effectiveness of the proposed method was verified by simulations in an actual power system.展开更多
Cam profiles play an important part in the performance of cam mechanisms. Syntheses of cam profile designs and dynamics of cam designs are studied at first. Then, a cam profile design optimization model based on the s...Cam profiles play an important part in the performance of cam mechanisms. Syntheses of cam profile designs and dynamics of cam designs are studied at first. Then, a cam profile design optimization model based on the six order classical spline and single DOF(degree of freedom) dynamic model of single-dwell cam mechanisms is developed. And dynamic constraints such as jumps and vibrations of followers are considered. This optimization model, with many advantages such as universalities of applications, conveniences to operations and good performances in improving kinematic and dynamic properties of cam mechanisms, is good except for the discontinuity of jerks at the end knots of cam profiles which will cause vibrations of cam systems. However, the optimization is improved by combining the six order classical spline with general polynomial spline which is the so-called "trade-offs". Finally, improved optimization is proven to have a better performance in designing cam profiles.展开更多
Various control systems for a robotic excavator named LUCIE (Lancaster University Computerized and Intelligent Excavator),were investigated. The excavator is being developed to dig trenches autonomously. One stumbling...Various control systems for a robotic excavator named LUCIE (Lancaster University Computerized and Intelligent Excavator),were investigated. The excavator is being developed to dig trenches autonomously. One stumbling block is the achievement of adequate,accurate,quick and smooth movement under automatic control. Here,both classical and modern approaches are considered,including proportional-integral-derivative (PID) control tuned by conventional Zigler-Nichols rules,linear proportional-integral-plus (PIP) control,and a novel nonlinear PIP controller based on a state-dependent parameter (SDP) model structure,in which the parameters are functionally dependent on other variables in the system. Implementation results for the excavator joint arms control demonstrate that SDP-PIP controller provides the improved performance with fast,smooth and accurate response in comparison with both PID and linearized PIP control.展开更多
The effect of moisture content upon compressive mechanical behavior of concrete under impact loading was studied. The axial rapid compressive loading tests of over 50 specimens with five different saturations were exe...The effect of moisture content upon compressive mechanical behavior of concrete under impact loading was studied. The axial rapid compressive loading tests of over 50 specimens with five different saturations were executed. The technique "split Hopkinson pressure bar"(SHPB) was used. The impact velocity was 10 m/s with corresponding strain rate of 50 s-1. The compressive behavior of materials was measured in terms of stress-strain curves, dynamic compressive strength, dynamic increase factor(DIF) and critical strain at a maximum stress. The data obtained from test indicate that both ascending and descending portions of stress-stain curves are affected by moisture content. However, the effect is noted to be more significant in ascending portion of the stress-strain curves. Dynamic compressive strength is higher at lower moisture content and weaker at higher moisture content.Furthermore, under nearly saturated condition, an increase in compressive strength can be found. The effect of moisture content on the average DIF of concrete is not significant. The critical compressive strain of concrete does not change with moisture content.展开更多
基金supported by the 2019 Postdoctoral Research Project funded by Hefei Municipal Bureau of Human Resources and Social Security and the National key R&D Program of China(2017YFB0102101).
文摘The mechanical properties of secondary cells are crucial to the safety and reliability of battery packs,which can fail due to extrusion and vibration in a vehicle crash.To analyze the structural response of the secondary cell and its other dynamic behaviors,the experiment and some numerical simulations were carried out based on single reference impact testing.Then,an equivalent constitutive relationship of the secondary cell was proposed to reveal the dynamic properties and used to guide the safety estimation of the battery pack.As the input parameter to the finite element model,the equivalent constitutive relationship,including but not limited to the elastic modulus and stain-stress curve,determines the simulation precision of the battery packs.Compared to the experimental results of the natural frequency of the battery pack,the simulation error is below 2%when the elastic modulus of the secondary cell in the battery pack has been verified.
基金Project(2007011049) supported by the Natural Science Foundation of Shanxi Province,China
文摘To overcome the deficiencies addressed in the conventional PID control and improve the dynamic performance and robustness of the system, a simple design and parameters tuning approach of internal model control-PID （IMC-PID） controller was proposed for the first order plus time-delay （FOPTD） process and the second order plus time-delay （SOPTD） process. By approximating the time-delay term of the process model with the first-order Taylor series, the expressions for IMC-PID controller parameters were derived, and they had only one adjustable parameter 2 which was directly related to the dynamic performance and robustness of the system. Moreover, an analytical approach of selecting 2 was given based on the maximum sensitivity Ms. Then, the robust tuning of the system could be achieved according to the value of Ms. In addition, the proposed method could be extended to the integrator plus time-delay （IPTD） process and the first order delay integrating （FODI） process. Simulation studies were carried out on various processes with time-delay, and the results show that the proposed method could provide a better dynamic performance of both the set-point tracking and disturbance rejection and robustness against parameters perturbation.
基金Projects(51605315,51478399)supported by the National Natural Science Foundation of ChinaProject(2013BAG20B00)supported by the National Key Technology R&D Program of ChinaProject(TPL1707)supported by the Open Project Program of the State Key Laboratory of Traction Power,China
文摘A heavy-haul train-track coupled model is developed. Taking the emergency braking of the 2×104 t combined train as example, the train longitudinal impulse, the coupler dynamic behaviors and wheel-rail interactions of vehicles distributing in the different positions are analyzed. The results indicate that under the coupler compressing forces, the couplers of middle locomotives may tilt to the free swing limits, which induces the unidirectional tilt of their connected wagon couplers. Consequently, the coupler longitudinal forces produce the lateral components, and then affect the wheel-rail dynamic interaction. The performance of the middle locomotive and their neighboring freight wagons deteriorate significantly, becoming the most dangerous parts in the combined train. The wagons disconnecting with the locomotives can basically keep their couplers to stabilize in the centering positions, even though the maximum coupler longitudinal force acts on it. And its corresponding running safety also has little changes.
基金Project(CSTC2009AC6051) supported by Ministry of Major Science & Technology of Chongqing, ChinaProject(CDJXS12110010) supported by the Fundamental Research Funds for the Central Universities, China
文摘To obtain a good drivability and high efficiency of the micro-electric vehicle, a new driving in-wheel motor design was analyzed and optimized. Maxwell software was used to build finite element simulation model of the driving in-wheel motor. The basic features and starting process were analyzed by field-circuit coupled finite element method. The internal complicated magnetic field distribution and dynamic performance simulation were obtained in different positions. No-load and load characteristics of the driving in-wheel motor was simulated, and the power consumption of materials was computed. The conformity of the final simulation results with the experimental data indicates that this method can be used to provide a theoretical basis to make further optimal design of this new driving in-wheel motor and its control system, so as to improve the starting torque and reduce torque ripple of the motor. This method can shorten the development cycle of in-wheel motors and save development costs, which has a wide range of engineering application value.
基金Project(2016YFB0300802)supported by the National Key Research and Development Program of China。
文摘The effect of Li(2.0 wt%)addition on mechanical properties and ageing precipitation behavior of Al-3.0 Mg 0.5 Si was investigated by tensile test,dynamic elasticity modulus test,scanning electron microscopy(SEM),transmission electron microscopy(TEM)and high-resolution transmission electron microscopy(HRTEM)images.The results show that the tensile strength of the Li-containing alloy can be significantly improved;however,the ductility is sharply decreased and the fracture mechanism changes from ductile fracture to intergranular fracture.The elasticity modulus of the Li-containing alloy increases by 11.6%compared with the base alloy.The microstructure observation shows that the Li addition can absolutely change the precipitation behavior of the base alloy,andδ′-Al_(3)Li phase becomes the main precipitates.Besides,β′′-Mg_(2)Si andδ′-Al_(3)Li dual phases precipitation can be visibly observed at 170℃ ageing for 100 h,although the quantity ofδ′-Al_(3)Li phase is more thanβ′′-Mg_(2)Si phase.The width of the precipitate-free zone(PFZ)of the Li-containing alloy is much wider at the over-ageing state than the base alloy,which has a negative impact on the ductile and results in the decrease of elongation.
基金Projects(51275198,51422503)supported by the National Natural Science Foundation of ChinaProject(2012YQ030075)supported by Special Funds for Development of National Major Scientific Instruments and Equipments,China+1 种基金Project(NECT-12-0238)supported by Program for New Century Excellent Talents in University,ChinaProject(20150520108JH)supported by Young Scientist Fund of Jilin Province of China
文摘The effects of adding alloy element zinc on the static and dynamic mechanical properties of copper-zinc alloy were investigated. Tensile and low cycle fatigue behaviors of the C11000 copper and H63 copper-zinc alloy were obtained by using a miniature tester that combined the functions of in situ tensile and fatigue testing. A piezoelectric actuator was adopted as the actuator for the fatigue testing, and the feasibility of the fatigue actuator was verified by the transient harmonic response analysis based on static tensile preload and dynamic sinusoidal load. The experimental results show that the yield strength and tensile strength of the C11000 copper are improved after adding 37%(mass fraction) zinc, and H63 copper-zinc alloy presents more obvious cyclic hardening behavior and more consumed irreversible plastic work during each stress cycle compared with C11000 copper for the same strain controlled cycling. Additionally, based on the Manson-Coffin theory, the strain-life equations of the two materials were also obtained. C11000 copper and H63 copper-zinc alloy show transition life of 16832 and 1788 cycles, respectively.
基金Project(20080431380)supported by the National Postdoctoral Science Foundation,China
文摘Based on theory of variable-mass system thermodynamics, the dynamic mathematic models of each component of the horizontal steam-launch system were established, and by the numerical simulation of the system launching process, the thermodynamics and kinetics characteristics of the system with three valves of different flow characteristics were got. The simulation results show that the values of the peak-to-average ratios of dimensionless acceleration with the equal percentage valve, the linear valve and the quick opening valve are 1.355, 1.614 and 1.722, respectively, and the final values of the dimensionless velocities are 0.843, 0.957 and 1.0, respectively. In conclusion, the value of the dimensionless velocity with the equal percentage valve doesn't reach the set value of 0.90 when the dimensionless displacement is 0.82, while the system with the linear valve can meet the launching requirement, as well as the fluctuation range of dimensionless acceleration is less than that of the quick opening valve. Therefore, the system with the linear valve has the best performance among the three kinds of valves.
基金Projects(52075166, 51875197) supported by the National Natural Science Foundation of ChinaProjects(2019RS2064,2019GK5043) supported by the Science and Technology Planning Project of Hunan Province,China。
文摘The effect of T6I6 treatment on the dynamic mechanical and microstructure behaviour of Al-Si-Mg-Cu cast alloy was investigated using split Hopkinson pressure bar(SHPB), transmission electron microscopy(TEM), and highresolution transmission electron microscopy(HRTEM). Besides, the impact resistances of T6I6 and T6 motor shells of new energy vehicles made of Al-Si-Mg-Cu cast alloy were compared using a trolley crash test. The results indicated that the main strengthening-phases of the T6 peak-aged and T6I6 peak-aged alloy were GP zone and β″ precipitates. T6I6treatment can increase the density and size of β″ precipitates in peak-aged alloy and enhance both its tensile strength(σb)and elongation(δ). The dynamic toughness values of T6I6 samples are 50.34 MJ/m^(3) at 2000 s^(-1) and 177.34 MJ/m^(3) at 5000 s^(-1) which are 20% and 12% higher than those of T6 samples, respectively. Compared with a T6 shell, the overall deformation of T6I6 shell is more uniform during the crash test. At an impact momentum of 3.5×10;kg·m/s, the T6I6shell breaks down at 0.38 s which is 0.10 s later than the T6 shell.
文摘In order to evaluate the seismic stability of reinforced soil walls against bearing capacity failure,the seismic safety factor of reinforced soil walls was determined by using pseudo-dynamic method,and calculated by considering different parameters,such as horizontal and vertical seismic acceleration coefficients,ratio of reinforcement length to wall height,back fill friction angle,foundation soil friction angle,soil reinforcement interface friction angle and surcharge.The parametric study shows that the seismic safety factor increases by 24-fold when the foundation soil friction angle varies from 25°to 45°,and increases by 2-fold when the soil reinforcement interface friction angle varies from 0 to 30°.That is to say,the bigger values the foundation soil and/or soil reinforcement interface friction angles have,the safer the reinforced soil walls become in the seismic design.The results were also compared with those obtained from pseudo-static method.It is found that there is a higher value of the safety factor by the present work.
基金Project(2020YFF0218200) supported by the National Key R&D Program of China。
文摘In the industrial production, the dynamic cooling pre-aging treatment was employed to replace the isothermal pre-aging during the continuous heat treatment production of Al-Mg-Si alloy automotive sheets. The effects of dynamic cooling pre-aging treatment on mechanical properties and paint-bake hardening behavior of an Al-Mg-Si alloy sheet are proposed in this study. The scanning electron microscopy, transmission electron microscopy, tensile test, Vickers hardness test, and differential scanning calorimetry were conducted for the purpose. It was found that the dynamic cooling pre-aging treatment at low temperature region led to the decreasing of cluster II, resulting in the deterioration of the ability of the paint-bake hardening. With the increase of the cooling pre-aging temperature, the increasing of cluster II effectively improved the stability against natural aging and the paint-bake hardening ability. The optimized dynamic cooling pre-aging temperature was ~150 ℃. In this condition, the hardness increase of the alloy sheet with pre-aging treatment is low during storage at room temperature. The high yield strength increment is obtained after paint-bake hardening.
基金Project(2010CB732004)supported by National Basic Research Program of ChinaProject(50934006)supported by the National Natural Science Foundation of China
文摘In order to investigate the mechanical properties and stress-strain curves of concrete at different ages under impact load,the impact compression tests of concrete at age of 1, 3, 7, 14 and 28 d were conducted with a large diameter split Hopkinson pressure bar, respectively. Based on statistical damage theory and Weibull distribution, combining the analysis of the change laws of stressstrain curves and viscosity coefficient of concrete with age, a damage constitutive model that can reflect the variation in dynamic mechanical properties with age was proposed. The stress-strain curves calculated from the proposed model are in good agreement with those from experimental data directly.
基金Projects(51575289,51705270)supported by the National Natural Science Foundation of ChinaProject(2019GHY112068)supported by the Key Research and Development of Shandong,China
文摘To explore the influence of double liquid quenching on the cutting performance of the 7A09 aluminum alloy,quasi-static compression and dynamic impact tests were carried out on the 7A09 aluminum alloy after double liquid quenching using an MTS810.23 universal testing machine and split-Hopkinson pressure bar(SHPB).The experimental data were fitted to obtain the Johnson–Cook constitutive model parameters of the alloy.Simulations of the machining process were carried out using the Deform-3D finite element software.The results showed that the rheological stress increased with the increase in strain rate and the decrease in temperature.The increase in the cutting speed and feed caused the cutting temperature to rise sharply,whereas the influence of the cutting amount on the cutting temperature was weak.Because of the presence of chip nodules,there was extremum in the cutting force vs cutting speed curves.The increase in the feed and cutting depth increased the cutting area Ac,so the cutting force also increased.The simulation results were verified by experiments.The simulation predictions were in good agreement with the test values,and the cutting force and temperature variations with the cutting parameters were the same.Thus,the correctness of the 7A09 aluminum alloy finite element model was verified.
基金Project(N110404031)supported by the Fundamental Research Funds for the Central Universities,China
文摘With the growing deployment of smart distribution grid,it has become urgent to investigate the smart distribution grid behavior during transient faults and improve the system stability.The feasibility of segmenting large power grids and multiple smart distribution grids interconnections using energy storage technology for improving the system dynamic stability was studied.The segmentation validity of the large power grids and smart distribution grid inverter output interconnections power system using energy storage technology was proved in terms of theoretical analysis.Then,the influences of the energy storage device location and capacity on the proposed method were discussed in detail.The conclusion is obtained that the ESD optimal locations are allocated at the tie line terminal buses in the interconnected grid,respectively.The effectiveness of the proposed method was verified by simulations in an actual power system.
文摘Cam profiles play an important part in the performance of cam mechanisms. Syntheses of cam profile designs and dynamics of cam designs are studied at first. Then, a cam profile design optimization model based on the six order classical spline and single DOF(degree of freedom) dynamic model of single-dwell cam mechanisms is developed. And dynamic constraints such as jumps and vibrations of followers are considered. This optimization model, with many advantages such as universalities of applications, conveniences to operations and good performances in improving kinematic and dynamic properties of cam mechanisms, is good except for the discontinuity of jerks at the end knots of cam profiles which will cause vibrations of cam systems. However, the optimization is improved by combining the six order classical spline with general polynomial spline which is the so-called "trade-offs". Finally, improved optimization is proven to have a better performance in designing cam profiles.
基金Work supported by the Lancaster University,UK and Jiangsu Provincial Laboratory of Advanced Robotics,SooChow University,ChinaProject(BK2009509) supported by the Natural Science Foundation of Jiangsu Province,China+1 种基金Project(K5117827) supported by the Scientific Research Foundation for the Returned Scholars,Ministry of Education of ChinaProject(Q3117918) supported by the Scientific Research Foundation for Young Teachers of Soochow University,China
文摘Various control systems for a robotic excavator named LUCIE (Lancaster University Computerized and Intelligent Excavator),were investigated. The excavator is being developed to dig trenches autonomously. One stumbling block is the achievement of adequate,accurate,quick and smooth movement under automatic control. Here,both classical and modern approaches are considered,including proportional-integral-derivative (PID) control tuned by conventional Zigler-Nichols rules,linear proportional-integral-plus (PIP) control,and a novel nonlinear PIP controller based on a state-dependent parameter (SDP) model structure,in which the parameters are functionally dependent on other variables in the system. Implementation results for the excavator joint arms control demonstrate that SDP-PIP controller provides the improved performance with fast,smooth and accurate response in comparison with both PID and linearized PIP control.
基金Project(50979032)supported by the National Natural Science Foundation of China
文摘The effect of moisture content upon compressive mechanical behavior of concrete under impact loading was studied. The axial rapid compressive loading tests of over 50 specimens with five different saturations were executed. The technique "split Hopkinson pressure bar"(SHPB) was used. The impact velocity was 10 m/s with corresponding strain rate of 50 s-1. The compressive behavior of materials was measured in terms of stress-strain curves, dynamic compressive strength, dynamic increase factor(DIF) and critical strain at a maximum stress. The data obtained from test indicate that both ascending and descending portions of stress-stain curves are affected by moisture content. However, the effect is noted to be more significant in ascending portion of the stress-strain curves. Dynamic compressive strength is higher at lower moisture content and weaker at higher moisture content.Furthermore, under nearly saturated condition, an increase in compressive strength can be found. The effect of moisture content on the average DIF of concrete is not significant. The critical compressive strain of concrete does not change with moisture content.
