Dynamic Resistance and Energy Absorption of Sandwich Beam via a Micro-Topology Optimization

The current research of sandwich structures under dynamic loading mainly focus on the response characteristic of structure.The micro-topology of core layers would sufficiently influence the property of sandwich structure.However,the micro deformation and topology mechanism of structural deformation and energy absorption are unclear.In this paper,based on the bi-directional evolutionary structural optimization method and periodic base cell(PBC)technology,a topology optimization frame work is proposed to optimize the core layer of sandwich beams.The objective of the present optimization problem is to maximize shear stiffness of PBC with a volume constraint.The effects of the volume fraction,filter radius,and initial PBC aspect ratio on the micro-topology of the core were discussed.The dynamic response process,core compression,and energy absorption capacity of the sandwich beams under blast impact loading were analyzed by the finite element method.The results demonstrated that the overpressure action stage was coupled with the core compression stage.Under the same loading and mass per unit area,the sandwich beam with a 20%volume fraction core layer had the best blast resistance.The filter radius has a slight effect on the shear stiffness and blast resistances of the sandwich beams.But increasing the filter radius could slightly improve the bending stiffness.Upon changing the initial PBC aspect ratio,there are three ways for PBC evolution:The first is to change the angle between the adjacent bars,the second is to further form holes in the bars,and the third is to combine the first two ways.However,not all three ways can improve the energy absorption capacity of the structure.Changing the aspect ratio of the PBC arbitrarily may lead to worse results.More studies are necessary for further detailed optimization.This research proposes a new topology sandwich beam structure by micro-topology optimization,which has sufficient shear stiffness.The micro mechanism of structural energy absorption is clarified,it is significant for structural energy absorption design.

Microscopic study on the key process and influence of efficient synthesis of natural gas hydrate by in situ Raman analysis of water microstructure in different systems with temperature drop

Gas hydrate technology has considerable potential in many fields.However,due to the lack of understanding of the micro mechanism of hydrate formation,it has not been commercially applied so far.Gas hydrate formation is essentially a gas-liquid-solid phase transition of water and gas molecules at a certain temperature and pressure.The key to the hydrate formation is the transformation of water molecule from disordered arrangement to ordered arrangement.In this process,weakly hydrogen bonded water will be correspondingly converted to strongly hydrogen bonded water.Through in situ Raman analysis and experiments,the position change of the corresponding peaks of the strongly hydrogen bonded water and the weakly hydrogen bonded water was compared in this work,and the key microscopic process and influence of gas hydrate formation in different systems were comprehensively studied and summarized.It is found that,with the decrease of temperature,the OAH of the weakly hydrogen bonded water remains unchanged when the temperature drops to a certain value,which is the key to the transformation of water into cage hydrate rather than ice.The conversion from the weakly hydrogen bonded water to the strongly hydrogen bonded water is closely related to the gas-liquid interface force,the hydrophilicity/hydrophobicity of the promoter,the ionization degree of liquid,and the electrostatic field of the system.Among the four most common promoters,tetrahydrofuran(THF)has the highest efficiency in promoting methane(CH4)hydrate formation.Therefore,this study provides a scientific direction and basis for the development of high efficient hydrate formation promoters,which can effectively weaken the hydrogen bond of weakly hydrogen bonded water and promote the conversion of weakly hydrogen bonded water to strongly hydrogen bonded water.

NEW ROD-SHAPED ULTRASONIC MICROMOTOR AND ITS DRIVING PRINCIPLE

A new rod-shaped traveling wave ultrasonic micromotor is developed. In the micromotor, five pieces of piezoelectric ceramics clamped by two metal cylinders are used as its stator. The driving principle of the rodshaped ultrasonic motor is simulated. The stator structure and the position to lay these piezoelectric ceramics are calculated to improve the electro mechanical conversion efficiency. A flexible rotor is designed to reduce the radial slip between the stator and the rotor, and to improve the motor efficiency. The prototype motor and its micror driver are tested. The motor is 9 mm in out-diameter, 15 mm in length and 3.2 g in weight. When the motor operates with the first bending frequency （72 kHz） of the stator, its maximal rotational speed and the torque reach 520 r/rain and 4.5 mN · m. Results show that the motor has good stability. The speed fluctuation is controlled within 3% by the frequency automatic tracking technique.

MICRO MECHANICAL ANALYSIS OF 3-D WOVEN COMPOSITES

A micro mechanical model is carried out to predict micro stresses and macro elastic properties of 3-D woven composites. A unit cell is composed of two phases. One is fiber yarn and the other is resin or fiber yarn in transverse. The additional shearing introduced by bending of fiber yarn is considered. The method to determine the microstructure is also discussed. This model is applied to the analysis of a 3-D woven graphite/epoxy composite. Micro stresses of the cell are studied, and then macro modulus is obtained by employing the average method. The predictions agree well with experimental results.

Micro Mechanical Model of 3D Woven Composites

A combined beam model representing the periodicity of the microstructure and micro deformation of 3D woven composites is developed for predicting mechanical properties. The model considers the effects of off axial tension/compression and bending/shearing couplings as well as the mutual reactions of fiber yarns. The method determining microstructure by using woven parameters is described for a typical 3D woven composite material. An analytical cell, constructed by a minimum periodic section of yarn and interlayer matrix, is adopted. Micro stresses in the cell under in-plane tensile loading are obtained by using the proposed beam model and macro modulus is then obtained by the averaging method. Material tests and a 2D micro FEM analysis are made to evaluate this model. Analyses reveal that micro stress caused by tensile/bending coupling effect is not negligible in the stress analysis.

STRENGTH ANALYSIS OF CLAMPING IN MICRO/NANO SCALE EXPERIMENTS

Two kinds of clamping in micro/nano scale experiments are investigated in this paper, one based on electron-beam-induced deposition, and the other on the van der Waals interaction. The clamping strength and mechanism are analyzed both theoretically and experimentally. The influence of relative humidity on the micro/nano clamping and the method of electrostatic clamping are discussed. The clamping strength and performance of different clamping methods are compared considering the size and material of the clamped objects, and the application environments.

Effect of Stirring Velocity in Micro Fused-Casting for Metal on Microstructure and Mechanical Properties of A356 Aluminum Alloy Slurry

A novel micro fused-casting for metal（MFCM） process for producing A356 aluminum alloy slurry was proposed. MFCM means that the refined metal slurry is pressed out from the outlet of bottom of crucible to the horizontal movable plate. With the aid of 3D manufacturing software, the melt is solidified and formed layer by layer. The stirring could keep the ingredients and the heat diffusion of metal slurry uniform in the crucible due to the shear force breaking down the dendrite arms. The solidus and liquidus temperatures of A356 alloy were 559.2 and 626.3 ℃, respectively, which were measured by differential scanning calorimetry（DSC）. Effect of different stirring velocities of MFCM on the microstructure and mechanical properties of A356 slurry was investigated with the pouring temperature controlled at 620 ℃. The microstructure and mechanical performance were the best when the stirring velocity was 1 200 r/min in MFCM. The microstructures of the A356 aluminum alloy slurry were mainly composed of fine spherical or rose grains. The average roundness and average grain size reached 2.2 and 41 μm and the tensile strength of A356 alloy slurry reached 207.8 MPa, while the average vickers hardness was 81.1 HV.

Preparation and Electrochemical Characteristics of Three-dimensional Manganese Oxide Micro-supercapacitor Electrode

In order to increase the electrode surface area and enhance the charge storage capacity, we study the micro electro mechanical system technology to fabricate three-dimensional high aspect ratio micro-electrode structure based on glass. The anodic constant potential method is employed to deposit manganese oxide as electroactive substances on the micro-electrode surface. Cyclic voltammetry and constant current charge-discharge method are both used to prepare electrode electrochemical performance testing, with a two-dimensional electrode without structure for comparison. Experimental results show that three-dimensional elec- trode structure can effectively enhance the charge storage capacity. At 1.0 mA/cm2 charge- discharge density, the three-dimensional electrode shows a capacitance of 17.88 mF/cm2, seven times higher than the two-dimensional electrode.

Application of Micro Electro Mechanical System(MEMS)Technology in Photoacoustic Imaging

Photoacoustic imaging(PAI)is a new biomedical imaging technology that provides a mixed contrast mechanism and excellent spatial resolution in biological tissues.It is a non-invasive technology that can provide in vivo anatomical and functional information.This technology has great application potential in microscopic imaging and endoscope system.In recent years,the devel-opment of micro electro mechanical system(MEMS)technology has promoted the improvement and miniaturization of the photoacoustic imaging system,as well as its preclinical and clinical appli-cations.This paper introduces the research progress of MEMS technology in photoacoustic micro-scope systems and the miniaturization of photoacoustic endoscope ultrasonic transducers,and points out the shortcomings of existing technology and the direction of future development.

INTERFACE DAMAGE ANALYSIS OF FIBER REINFORCED COMPOSITES WITH DUCTILE MATRIX

A cohesive zone model is employed to simulate the fiber/matrix interface damage of composites with ductile matrix. The study is carried out to investigate the dependence of the interface damage and the composite tensile strength on the micro parameters of the composite. These parameters contain fiber packing pattern, fiber volume fraction, and the modulus ratio of the fiber to the matrix. The investigation reveals that though the high fiber vo lume fraction, the high fiber′s modulus and the square fiber packing can supply strong reinforcement to the composite, the interface damage is susceptible in these cases. The tensile strength of the composite is dominated by the interface strength when the interface debonding occurs.

运用研磨和化学机械抛光技术制备高品质的石英薄膜

石英薄膜的质量是决定各种石英基底的微纳器件品质高低的关键所在。阐述如何运用研磨和化学机械抛光CMP(Chemical&Mechanical Polishing)技术获得高品质石英薄膜的方法。由于石英属于高硬度材料,选用金刚石研磨液和球墨铸铁研磨盘对石英衬底进行研磨,以获得较高的研磨速率和较好的研磨后的表面粗糙度。在石英CMP中,采用特殊的"两步抛"工艺,对衬底进行抛光。第一步粗抛抛光液采用金刚石颗粒直径为0.3μm的研磨液与SiO2颗粒直径为50 nm的抛光液相混合,第二步精抛只采用SiO2的抛光液。实验结果表明,采用上述技术,可以获得高品质的石英薄膜,厚度为(25.1±3.2)μm,表面粗糙度约为0.89 nm(RMS)。

Robust fault detection filter and its application in MEMS-based INS/GPS

Since any disturbance and fault may lead to significant performance degradation in practical dynamical systems,it is essential for a system to be robust to disturbances but sensitive to faults.For this purpose,this paper proposes a robust fault-detection filter for linear discrete time-varying systems.The algorithm uses H∞ estimator to minimize the worst possible amplification from disturbances to estimate errors,and H_ index to maximize the minimum effect of faults on the residual output of the filter.This approach is applied to the MEMS-based INS/GPS.And simulation results show that the new algorithm can reduce the effect of unknown disturbances and has a high sensitivity to faults.

Negative Corona Discharge Ion Source Under Ambient Conditions with Mini Line-cylinder Electrodes

A novel ambient negative corona discharge ion source with mini line-cylinder electrodes is designed. The diameters of inner and outer electrode are 0.16 and 4 mm respectively. With a special assembly method, a perfect coaxiality of the two electrodes is obtained. An injection system utilizing a temperature control technique, achieves a constant and stable concentration of the sample, which is critical to the experiment. The formulas of the corona onset voltage of line-cylinder electrodes are also introduced. The experiment results show that negative substances such as formic acid and acetic acid can be ionized under ambient conditions. When combined with micro electrical mechanical system fabricationprocess, the volume of the ion source can be reduced dramatically, but there is an undesirable surface discharge. To solve the surface discharge problem, an improved structure was designed and tested. The simplicity of the interface of the ion source makes it suitable for mass spectrometer, micro mass spectrometer, ion mobility spectrometer, and high-field asymmetric waveform ion mobility spectrometer applications.

基于MEMS加速度计的强振动记录黑匣子的设计

设计基于MEMS加速度传感器的一种强震记录黑匣子,采用SOC系列C8051F005型单片机对MEMS加速度传感器的输出信号进行A/D转换,记录该设备安装点位所经受的强振加速度值,并通过LCD16032显示一分钟内的振动加速度峰值。该系统具有体积小、安装与操作方便、免维护等特性。

Noise estimation and filtering method of MEMS gyroscope based on EMMAP

Aiming at the problems of low measurement accuracy,uncertainty and nonlinearity of random noise of the micro electro mechanical system(MEMS)gyroscope,a gyroscope noise estimation and filtering method is proposed,which combines expectation maximum(EM)with maximum a posterior(MAP)to form an adpative unscented Kalman filter(UKF),called EMMAP-UKF.According to the MAP estimation principle,a suboptimal unbiased MAP noise statistical estimation model is constructed.Then,EM algorithm is introduced to transform the noise estimation problem into the mathematical expectation maximization problem,which can dynamically adjust the variance of the observed noise.Finally,the estimation and filtering of gyroscope random drift error can be realized.The performance of the gyro noise filtering method is evaluated by Allan variance,and the effectiveness of the method is verified by hardware-in-the-loop simulation.

Modeling and Simulation of MOEMS Gyroscope Based on TE-TM Mode Converter

A novel structure design of micro optic electro mechanical system（MOEMS）gyroscope is presented in this paper.The structure combining surface acoustic wave（SAW）sensor,optical waveguide diffractive component,electro-optical modulator etc.is integrated on a LiNbO3 substrate as the gyroscope for sensing rotating angular velocity,and an optical readout device is added on the traditional SAW typed TE-TM mode converter as the detecting device.The principles of the MOEMS are discussed in the paper,and simulation result shows that there would be apparent advantages of higher precision and stronger anti-vibration capacity.

Energy barrier for configurational transformation of graphene nanoribbon on nanotube

A graphene nanoribbon （GNR） has two basic configurations when winding on the outer surface of a carbon nanotube （CNT）： helix and scroll. Here the transformation between the two configurations is studied utilizing molecular dynamics simulations. The energy barrier during the transformation as well as its relationship with the interfacial energy and the radius of CNT are investigated. Our work offers further insights into the formation of desirable helix/scroll of GNR winding on nanotubes or nanowires, and thus can enable novel design of potential graphene-based electronics.

Real-Time, Automatic and Wireless Bridge Monitoring System Based on MEMS Technology

Currently, the monitoring of bridges in China heavily relies on manual operation, which has several major problems. It generally takes a very long time to complete an inspection process on bridges. The manual data is sometimes unreliable or even wrong in the case of careless operation. The inspection activity itself is dangerous for inspectors, e.g., bridges are located in the sea or river. Some semi-automatic monitoring methods are recently employed, but they are either very expensive or do not work properly. Therefore, the traditional bridge monitoring process becomes an increasing challenge for bridge operators. In this paper, a real-time and automatic bridge monitoring system is presented to meet the bridge monitoring needs, and MEMS （Micro Electro Mechanical Systems） are the key building block in this system. By using the MEMS-based sensors, it is much more efficient and accurate in monitoring bridges with the measurement of inclination, acceleration, displacement, moisture, temperature, stress and other data.

Integration of Strain Sensors on Additively Manufactured Implantable Devices

The development of personalized healthcare is rapidly growing thanks to the support of low-power electronics,advanced fabrication processes and secured data transmission protocols.Long-acting drug delivery systems able to sustain the release of therapeutics in a controllable manner can provide several advantages in the treatment of chronic diseases.Various systems under development control drug release from an implantable reservoir via concentration driven diffusion through nanofluidic membranes.Given the high drug concentration in the reservoir,an inward osmotic fluid transport occurs across the membrane,which counters the outward diffusion of drugs.The resulting osmotic pressure buildup may be sufficient to cause the failure of implants with associated risks to patients.Confidently assessing the osmotic pressure buildup requires testing in vivo.Here,using metal and polymer AM(additive manufacturing)processes,we designed and developed implantable drug reservoirs with embedded strain sensors to directly measure the osmotic pressure in drug delivery implants in vitro and in vivo.

From MEMS to NEMS： Smart Chips with Senses and Muscles

The last half-century was transformed by the electronic revolution that essentially reproduced the human brain and its computing capacity on a chip. But over time, scientists have realized that something was missing to give life, so to speak, to the small chip with a brain： One needed to awaken its senses and develop its muscles! This challenge was solved through MEMS （micro electro mechanical systems）. Indeed, MEMS today are equipped with the sense of sight, smell, hearing, taste and touch through microsensors. They are also capable of physical exertion through small muscles called microactuators. These new capabilities open wide fields of imagination and important specific applications.