In this study, three rapid repair techniques are proposed to retrofit circular bridge piers that are severely damaged by the flexural failure mode in major earthquakes. The quasi-static tests on three 1：2.5 scaled ci...In this study, three rapid repair techniques are proposed to retrofit circular bridge piers that are severely damaged by the flexural failure mode in major earthquakes. The quasi-static tests on three 1：2.5 scaled circular pier specimens are conducted to evaluate the efficiency of the proposed repair techniques. For the purpose of rapid repair, the repair procedure for all the specimens is conducted within four days, and the behavior of the repaired specimens is evaluated and compared with the original ones. A finite element model is developed to predict the cyclic behavior of the repaired specimens and the numerical results are compared with the test data. It is found that all the repaired specimens exhibit similar or larger lateral strength and deformation capacity than the original ones. The initial lateral stiffness of all the repaired specimens is lower than that of the original ones, while they show a higher lateral stiffness at the later stage of the test. No noticeable difference is observed for the energy dissipation capacity between the original and repaired pier specimens. It is suggested that the repair technique using the early-strength concrete jacket confined by carbon fiber reinforced polymer （CFRP） sheets can be an optimal method for the rapid repair of severely earthquake-damaged circular bridge piers with flexural failure mode.展开更多
With the aid of the micro-mechanical model of knitted fabric proposed in Part 1 we analyze the buckling of a knitted fabric sheet when it is subjected to a tension along the wale direction. The large deformation of th...With the aid of the micro-mechanical model of knitted fabric proposed in Part 1 we analyze the buckling of a knitted fabric sheet when it is subjected to a tension along the wale direction. The large deformation of the fabric sheet in the critical configuration is considered and, to avoid possible deviation due to the approximation of the theory of thin plate, the three-dimensional theory of instability is used. The fabric sheet is considered as a three-dimensional body and all boundary conditions are satisfied. It is shown that the buckling of the fabric sheet is possible, two buckling modes and the corresponding buckling conditions are obtained, but only the flexural mode is physically possible as observed in experiments.展开更多
Unusual quadratic dispersion of flexural vibrational mode and red-shift of Raman shift of in-plane mode with increas- ing layer-number are quite common and interesting in low-dimensional materials, but their physical ...Unusual quadratic dispersion of flexural vibrational mode and red-shift of Raman shift of in-plane mode with increas- ing layer-number are quite common and interesting in low-dimensional materials, but their physical origins still remain open questions. Combining ab initio density functional theory calculations with the empirical force-constant model, we study the lattice dynamics of two typical two-dimensional （2D） systems, few-layer h-BN and indium iodide （InI）. We found that the unusual quadratic dispersion of flexural mode frequency on wave vector may be comprehended based on the com- petition between atomic interactions of different neighbors. Long-range interaction plays an essential role in determining the dynamic stability of the 2D systems. The frequency red-shift of in-plane Raman-active mode from monolayer to bulk arises mainly from the reduced long-range interaction due to the increasing screening effect.展开更多
Existing rotary ultrasonic motors operating in extreme environments cannot meet the requirements of good environmental adaptability and compact structure at same time,and existing ultrasonic motors with Langevin trans...Existing rotary ultrasonic motors operating in extreme environments cannot meet the requirements of good environmental adaptability and compact structure at same time,and existing ultrasonic motors with Langevin transducers show better environmental adaptability,but size of these motors are usually big due to the radial arrangement of the Langevin transducers.A novel dual driving face rotary ultrasonic motor is proposed,and its working principle is experimentally verified.The working principle of the novel ultrasonic motor is firstly proposed.The 5th in-plane flexural vibration travelling wave,excited by the Langevin transducers around the stator ring,is used to drive the rotors.Then the finite element method is used in the determination of dimensions of the prototype motor,and the confirmation of its working principle.After that,a laser Doppler vibrometer system is used for measuring the resonance frequency and vibration amplitude of the stator.At last,output characteristics of the prototype motor are measured,environmental adaptability is tested and performance for driving a metal ball is also investigated.At room temperature and 200 V(zero to peak) driving voltage,the motor’s no-load speed is 80 r/min,the stalling torque is 0.35 N·m and the maximum output power is 0.85 W.The response time of this motor is 0.96 ms at the room temperature,and it decreases or increases little in cold environment.A metal ball driven by the motor can rotate at 210 r/min with the driving voltage 300 V(zero to peak).Results indicate that the prototype motor has a large output torque and good environmental adaptability.A rotary ultrasonic motor owning compact structure and good environmental adaptability is proposed,and lays the foundations of ultrasonic motors’ applications in extreme environments.展开更多
Acoustic frequency combs(AFCs)contain equidistant coherent signals with unconventional possibilities on metrology.Previously,implementation of AFCs on mechanical microresonators with large air damping loss is difficul...Acoustic frequency combs(AFCs)contain equidistant coherent signals with unconventional possibilities on metrology.Previously,implementation of AFCs on mechanical microresonators with large air damping loss is difficult,which restricted their atmospheric applications.In this work,we explore the potentials of a composite diamond/silicon microcantilever for parametric generation of AFCs in ambient air.We discover that the diamond layer provides a viable route to reduce the linewidth of the primary flexural mode,yielding a 7.1-times increase of the quality factor.We develop a parametric driving scheme that enables generation of AFCs through injection locking and sequential nonlinear dynamic transitions involving subharmonic synchronization(Arnold tongue),and chaotic dynamics.Ultimately,we realize AFCs with a frequency range extending 800 kHz in the air.This work advances the understanding of AFCs and provides a viable route towards their applications in ambient air for high precision metrology.展开更多
The use of bulk piezoelectric transducer arrays in medical imaging is a well-established technology that operates based on thickness mode piezoelectric vibration.Meanwhile,advancements in fabrication techniques have l...The use of bulk piezoelectric transducer arrays in medical imaging is a well-established technology that operates based on thickness mode piezoelectric vibration.Meanwhile,advancements in fabrication techniques have led to the emergence of micromachined alternatives,namely,piezoelectric micromachined ultrasound transducer(PMUT)and capacitive micromachined ultrasound transducer(CMUT).These devices operate in flexural mode using piezoelectric thin films and electrostatic forces,respectively.In addition,the development of flexible ultrasound transducers based on these principles has opened up new possibilities for biomedical applications,including biomedical imaging,sensing,and stimulation.This review provides a detailed discussion of the need for flexible micromachined ultrasound transducers(MUTs)and potential applications,their specifications,materials,fabrication,and electronics integration.Specifically,the review covers fabrication approaches and compares the performance specifications of flexible PMUTs and CMUTs,including resonance frequency,sensitivity,flexibility,and other relevant factors.Finally,the review concludes with an outlook on the challenges and opportunities associated with the realization of efficient MUTs with high performance and flexibility.展开更多
基金National Natural Science Foundation of China under Grant No.51678150Science for Earthquake Resilience under Grant No.XH17064Australian Research Council Discovery Early Career Researcher Award(DECRA)
文摘In this study, three rapid repair techniques are proposed to retrofit circular bridge piers that are severely damaged by the flexural failure mode in major earthquakes. The quasi-static tests on three 1：2.5 scaled circular pier specimens are conducted to evaluate the efficiency of the proposed repair techniques. For the purpose of rapid repair, the repair procedure for all the specimens is conducted within four days, and the behavior of the repaired specimens is evaluated and compared with the original ones. A finite element model is developed to predict the cyclic behavior of the repaired specimens and the numerical results are compared with the test data. It is found that all the repaired specimens exhibit similar or larger lateral strength and deformation capacity than the original ones. The initial lateral stiffness of all the repaired specimens is lower than that of the original ones, while they show a higher lateral stiffness at the later stage of the test. No noticeable difference is observed for the energy dissipation capacity between the original and repaired pier specimens. It is suggested that the repair technique using the early-strength concrete jacket confined by carbon fiber reinforced polymer （CFRP） sheets can be an optimal method for the rapid repair of severely earthquake-damaged circular bridge piers with flexural failure mode.
基金The project supported by the National Natural Science Foundation of China(10272079)
文摘With the aid of the micro-mechanical model of knitted fabric proposed in Part 1 we analyze the buckling of a knitted fabric sheet when it is subjected to a tension along the wale direction. The large deformation of the fabric sheet in the critical configuration is considered and, to avoid possible deviation due to the approximation of the theory of thin plate, the three-dimensional theory of instability is used. The fabric sheet is considered as a three-dimensional body and all boundary conditions are satisfied. It is shown that the buckling of the fabric sheet is possible, two buckling modes and the corresponding buckling conditions are obtained, but only the flexural mode is physically possible as observed in experiments.
基金Project supported by the Major Program of Aerospace Advanced Manufacturing Technology Research Foundation from NSFC and CASC,China(Grant No.U1537204)the National Key Research and Development Program of China(Grant No.2017YFA0206301)the National Natural Science Foundation of China(Grant No.51702146)
文摘Unusual quadratic dispersion of flexural vibrational mode and red-shift of Raman shift of in-plane mode with increas- ing layer-number are quite common and interesting in low-dimensional materials, but their physical origins still remain open questions. Combining ab initio density functional theory calculations with the empirical force-constant model, we study the lattice dynamics of two typical two-dimensional （2D） systems, few-layer h-BN and indium iodide （InI）. We found that the unusual quadratic dispersion of flexural mode frequency on wave vector may be comprehended based on the com- petition between atomic interactions of different neighbors. Long-range interaction plays an essential role in determining the dynamic stability of the 2D systems. The frequency red-shift of in-plane Raman-active mode from monolayer to bulk arises mainly from the reduced long-range interaction due to the increasing screening effect.
基金supported by National Natural Science Foundation of China(Grant Nos.5120520351275228+7 种基金5107521291123020)Science and Research FoudotionNanjing University of Aeronautics and Astronautics(Grant Nos.56YAH12015NZ2010002S0896-013)Innovation and Entrepreneurship Program of Jiangsuand Priority Academic Program Development of Jiangsu Higher Education Institutions
文摘Existing rotary ultrasonic motors operating in extreme environments cannot meet the requirements of good environmental adaptability and compact structure at same time,and existing ultrasonic motors with Langevin transducers show better environmental adaptability,but size of these motors are usually big due to the radial arrangement of the Langevin transducers.A novel dual driving face rotary ultrasonic motor is proposed,and its working principle is experimentally verified.The working principle of the novel ultrasonic motor is firstly proposed.The 5th in-plane flexural vibration travelling wave,excited by the Langevin transducers around the stator ring,is used to drive the rotors.Then the finite element method is used in the determination of dimensions of the prototype motor,and the confirmation of its working principle.After that,a laser Doppler vibrometer system is used for measuring the resonance frequency and vibration amplitude of the stator.At last,output characteristics of the prototype motor are measured,environmental adaptability is tested and performance for driving a metal ball is also investigated.At room temperature and 200 V(zero to peak) driving voltage,the motor’s no-load speed is 80 r/min,the stalling torque is 0.35 N·m and the maximum output power is 0.85 W.The response time of this motor is 0.96 ms at the room temperature,and it decreases or increases little in cold environment.A metal ball driven by the motor can rotate at 210 r/min with the driving voltage 300 V(zero to peak).Results indicate that the prototype motor has a large output torque and good environmental adaptability.A rotary ultrasonic motor owning compact structure and good environmental adaptability is proposed,and lays the foundations of ultrasonic motors’ applications in extreme environments.
基金the National Science Foundation of China(NSFC)(Grant No.52172296,51472143)the National Key R&D Program of China(NKRD)(2017YFB0405403)the Initiative in Quantum Science of Shandong Provincial Natural Science Foundation(ZR2020LLZ005)for financial support.
文摘Acoustic frequency combs(AFCs)contain equidistant coherent signals with unconventional possibilities on metrology.Previously,implementation of AFCs on mechanical microresonators with large air damping loss is difficult,which restricted their atmospheric applications.In this work,we explore the potentials of a composite diamond/silicon microcantilever for parametric generation of AFCs in ambient air.We discover that the diamond layer provides a viable route to reduce the linewidth of the primary flexural mode,yielding a 7.1-times increase of the quality factor.We develop a parametric driving scheme that enables generation of AFCs through injection locking and sequential nonlinear dynamic transitions involving subharmonic synchronization(Arnold tongue),and chaotic dynamics.Ultimately,we realize AFCs with a frequency range extending 800 kHz in the air.This work advances the understanding of AFCs and provides a viable route towards their applications in ambient air for high precision metrology.
基金supported by EU EIC Transition under grant agreement ID 101057902,as well as KU Leuven Interdisciplinary Networks(ID-N)under grant No.ZKD-6578。
文摘The use of bulk piezoelectric transducer arrays in medical imaging is a well-established technology that operates based on thickness mode piezoelectric vibration.Meanwhile,advancements in fabrication techniques have led to the emergence of micromachined alternatives,namely,piezoelectric micromachined ultrasound transducer(PMUT)and capacitive micromachined ultrasound transducer(CMUT).These devices operate in flexural mode using piezoelectric thin films and electrostatic forces,respectively.In addition,the development of flexible ultrasound transducers based on these principles has opened up new possibilities for biomedical applications,including biomedical imaging,sensing,and stimulation.This review provides a detailed discussion of the need for flexible micromachined ultrasound transducers(MUTs)and potential applications,their specifications,materials,fabrication,and electronics integration.Specifically,the review covers fabrication approaches and compares the performance specifications of flexible PMUTs and CMUTs,including resonance frequency,sensitivity,flexibility,and other relevant factors.Finally,the review concludes with an outlook on the challenges and opportunities associated with the realization of efficient MUTs with high performance and flexibility.
