小截面方管结构CFRP复合材料的超声检测方法

新型飞行器已采用小截面碳纤维增强树脂基(Carbon Fiber Reinforce Polymer, CFRP)复合材料方管结构。针对该类复合材料方管的材料组成和结构特点,分析和对比了常用的超声穿透法、超声反射法和整体超声穿透法对复合材料方管内部质量检测的适用性,提出了超声对面内壁反射法。采用超声对面内壁反射法对试块中的人工缺陷和实际产品进行检测。结果表明,采用该检测方法能够全部检出试样中的10 mm×10 mm的人工分层缺陷,且可有效地检测实际产品的分层和孔洞缺陷。     

Ultrasonic six-axis deformation sensing

In this paper, we describe a newly developed deformation sensing scheme in a soft medium, which is based on precise encoding and decoding of deformation components into ultrasound wavefronts. It can detect three translational components and three rotational components of displacement around a transmitter position nearly simultaneously. We assume a cell structure that consists of a 2×2 ultrasonic transmitter matrix and a 2×2 ultrasonic receiver matrix, which are placed face to face at a distance of a few tens of wavelengths. All of the transmitter elements are driven sinusoidally and simultaneously, but they are switched into the same, reversed, or quadrature phases to generate a particular shape of wavefront on the receiver matrix. The receiver elements are connected in such a way to obtain amplitude and spatial gradients of the wavefront at a center of the receiver matrix. First, we describe the transduction theory for the six dimensions and show the orthogonality, locality, and simultaneity of this sensing scheme. Then, we describe the fabrication and experimental evaluation of the cell. We also describe a prototype tactile sensor in which a single cell is embedded in a flexible hemispherical fingertip-like body     

负泊松比点阵结构填充薄壁管轴向压缩行为及吸能特性

薄壁填充结构具有轻量化、高比吸能的优点,被广泛应用于航空航天、汽车、轨道交通等工程领域。负泊松比结构在受到冲击时力学性能会逐渐增强,因此本文基于双箭头型负泊松比点阵提出一种新型薄壁填充管吸能结构,通过准静态压缩实验和有限元数值模拟方法研究了新型填充管在压缩载荷作用下的变形失效模式与力学响应。建立了平均碰撞力的理论预测模型,并通过有限元分析验证了模型可靠性,在此基础上研究了负泊松比点阵结构的细观设计参数对填充管抗压缩性能的影响规律。结果表明,填充管在压缩载荷作用下的失效模式为局部屈曲失效,相比于单一薄壁管与点阵结构,填充管具有更好的抗压缩性能;通过参数分析明确了通过增加胞元杆件壁厚和下支撑杆夹角,能显著提高填充管抗压缩性能,这将为后续负泊松比点阵填充结构的抗冲击优化设计提供重要参考。     

An aging model for surface acoustic wave devices

The authors present a study of the phase-aging kinetics of a 591.2 MHz quartz-crystal surface acoustic wave (SAW) filter intended for application in an undersea telecommunication system. At aging temperatures from 50 to 140 degrees C, a previously established SAW-device aging model describes the time dependence of the phase aging. The results of an investigation of the temperature dependence of the coefficients in this aging model allows the authors to extend the model, capturing both the time and the temperature dependence of the degradation. They then identify and assess the sources of variation, or error, affecting the data and model, estimate the distributions of the errors, and incorporate these error distributions in the extended aging model. This leads to a composite aging model that describes the time and temperature dependence of the complete phase-aging distribution. The authors use this composite model to predict end-of-life phase-aging distributions, demonstrating that the devices exhibit the high level of stability required by the application.     

应用于热声机械的声波平面传递装置

应用于热声机械的声波平面传递装置,由柔性部分和刚性片部分组成.通过引入柔性结构,将传递声波所必需的弹性部分和惯性部分分开,实现刚性片的平面运动,从而达到声波的平面传递.依据弹性部分的不同形式,声波平面传递装置有3种形式:弹性膜型、折环型和弹性环型.将这种装置应用于热声机械中,可以大大改善热声系统中声波传递的性能,拓展热...     

Three-dimensional finite-elements modeling and simulation of rotary-draw bending process for thin-walled rectangular tube

According to the characteristics of the rotary-draw bending process of a thin-walled rectangular tube, a three-dimensional finite-elements model of this process is built under the ABAQUS/explicit environment based on the solution of several key techniques, such as contact boundary condition treating, material properties definition, meshing technology, etc. The actions of pressure die, wiper die, clamp die and mandrel are considered in the modeling process. Then the reliability of the model is validated by comparison with experiments in the literature. Furthermore, numerical simulation and analysis of the thin-walled rectangular tube bending process of 3A21 aluminum alloy have been carried out by using the model. The distribution laws of tangential stress in the process have been analyzed. The results show that the maximum tangential stress increases sharply in the initial stage and then keeps nearly constant with the progress of the bending process. The circumferential compressive stress zone is basically unchanged when the bending process becomes stable.     

冷弯薄壁方钢管梁柱加腋节点抗震性能研究

摘要：汶川地震后冷弯薄壁方钢管在灾区重建过程中得到了大量使用,但其梁柱节点的连接方式和力学性能等尚需进一步研究。为此,文中基于结构实际受力情况设计了一种三维双节点试验模型,对不同轴压比下冷弯薄壁方钢管梁柱加腋节点和普通节点的8个试件进行了足尺试验,通过对比分析研究了低周往复荷载作用下加腋节点的破坏模式、滞回曲线及评价节点抗震性能的主要参数（承载力、延性、刚度退化和能量耗散系数等）。同时,利用ANSYS对各节点进行了有限元数值计算,并与试验结果进行了对比分析进一步对加腋节点进行了研究。结果表明：试验与有限元数值计算结果吻合良好,验证了理论分析的正确性;加劲腋板提高了节点的初始刚度和承载力,钢管梁的弹塑性性能得到了充分发挥,不同轴压比下均出现了塑性铰,导致加腋节点各试件的最终破坏均是由钢管梁塑性变形过大出现局部屈曲引起;加劲腋板提高了节点的延性系数及往复变形次数,延长了变形时间,增大了节点的粘滞阻尼和耗能性性能,改善了节点的抗震性能;随轴压比增加,加腋节点塑性变形减小,脆性破坏特征增加,各耗能系数均相应降低。     

Crushing analysis and multi-objective optimization design for bionic thin-walled structure

Thin-walled structure has gained increasing attention and been widely used in the field of mechanical engineering due to their extraordinary energy absorption capacity and light weight. In this paper, we introduced a new energy absorbed structure named as bionic thin-walled structure (BTS) based on the structural characteristics of horsetails. In this study, six kinds of BTSs with different cross-sectional configurations under lateral loading conditions were investigated using nonlinear finite element method through LS-DYNA. According to the numerical results, it can be found that the cell number, inner wall diameter and wall thickness of the BTS had significant effect on the crashworthiness of the structure. In order to obtain the optimal design among the six kinds of BTSs, the six BTSs were optimized using a metamodel-based multi-objective optimization method which was developed by employing polynomial regression (PR) metamodel and multi-objective particle swarm optimization (MOPSO) algorithm. In the optimization process, we aimed to achieve maximum value of specific energy absorption (SEA) and minimum value of maximum impact force (MIF). Meanwhile, we also optimized the traditional thin-walled structures, i.e., the circular and square tubes. Based on the comparison of the Pareto fronts obtained by the multi-objective optimizations, we found that the crashworthiness of the BTSs was better than that of the circular and square tubes and the best BTS among the six kinds of BTSs was different when the limit of MIF was different. And, the optimal designs of the BTSs were found to have excellent energy absorption capacity under lateral impact and could be used in the future vehicle body.     

Simulation of surface acoustic wave devices

The Mason crossed-field circuit model is generalized to simulate apodized interdigital transducers without channel division. The apodized transducer model is based on the transmission line model, and the artificial transformer with different voltage and current coupling ratios is used to independently obtain the transfer function and radiation admittance. In addition, a heuristic expression for transformer current ratios is used to approximate the radiation admittance of apodized transducers. Through comparing with the multichannel model, this unichannel model is illustrated to successfully describe the frequency response of apodized interdigital transducers.     

Josephson effect devices and low-frequency field sensing

Three major areas of application of the Josephson effect are recognized; absolute standards, millimetre and sub-millimetre wave sensing, and dc and low-frequency current, voltage, and magnetic field sensing. In the latter area, single junction rf-biased low-inductance loop devices in a number of different forms (junction types and loop geometries) have been developed with sensitivities of the order of 10⁻¹⁵ T (10⁻¹¹ G) or 10⁻¹⁹ V. These sensors are being used in applications as diverse as magnetocardiography and absolute noise thermometry in the millikelvin range. As amplifiers, they are characterized by demonstrated equivalent noise temperatures of less than a few millikelvin, and probably a few microkelvin (theoretical). Highly reliable thin-film loop devices in a number of different forms have been developed in several laboratories, but the more easily-made point-contact devices are probably the most widely used. Many of the characteristics of the devices can be easily interpreted with the aid of a pendulum analogue.     

Ultrasonic wave propagation in temperature gradients

Ultrasonic methods are being developed for sensing and control of high temperature material processes such as welding and solidification. One of the problems in these methods is the distortion of the sound field caused by the change in material properties due to temperature gradients. This paper describes a ray-tracing method for calculating the effects of temperature on ultrasonic propagation in such systems. In the ray-tracing method, the material is conceptually divided into a number of plane layers. The refraction at each layer boundary is calculated from Snell's law using the sound speeds determined from the temperatures of the adjacent layers. The time required for an ultrasonic pulse to traverse each layer is also calculated, allowing the determination of the total time along a particular path. The method is applied to calculating the time of arrival of echoes from various interfaces around a molten weld pool.     

锥形多胞薄壁管斜向冲击吸能特性仿真研究

采用有限元仿真,以比能量吸收和冲击峰值力为评价指标,研究了一种轴对称锥形多胞薄壁方管在不同冲击角度下的失效模式和吸能特性,分析了包括长径比、壁厚和锥度在内的结构参数对其斜向冲击吸能特性的影响,并拟合出可用于斜向冲击下比能量吸收和冲击峰值力预测的解析公式。结果表明,锥形多胞薄壁管在斜向冲击下的吸能特性明显优于其他类似薄壁吸能结构;结构参数对其吸能特性影响明显;拟合得到的解析公式为此类结构优化设计提供了参考和依据,并有利于工程实际应用。     

Mid-infrared materials and devices on a Si platform for optical sensing

In this article, we review our recent work on mid-infrared (mid-IR) photonic materials and devices fabricated on silicon for on-chip sensing applications. Pedestal waveguides based on silicon are demonstrated as broadband mid-IR sensors. Our low-loss mid-IR directional couplers demonstrated in SiN_x waveguides are useful in differential sensing applications. Photonic crystal cavities and microdisk resonators based on chalcogenide glasses for high sensitivity are also demonstrated as effective mid-IR sensors. Polymer-based functionalization layers, to enhance the sensitivity and selectivity of our sensor devices, are also presented. We discuss the design of mid-IR chalcogenide waveguides integrated with polycrystalline PbTe detectors on a monolithic silicon platform for optical sensing, wherein the use of a low-index spacer layer enables the evanescent coupling of mid-IR light from the waveguides to the detector. Finally, we show the successful fabrication processing of our first prototype mid-IR waveguide-integrated detectors.     

A strategy for chemical sensing based on frequency tunable acoustic devices

A new acoustic sensor geometry, the magnetic acoustic resonant sensor (MARS), is described. The device comprises a circular 0.5-mm-thick resonant plate fabricated from a wide variety of nonpiezoelectric materials and coated on the underside with a 2.5-microm-thick aluminum film. Harmonic radial shear waves over at least a 2 orders of magnitude frequency range can be induced in the resonant plate by enhanced magnetic direct generation using a noncontacting rf coil and NdFeB magnet. Mass loading with adherent aluminum films produced frequency changes of 106 Hz/nm (40.8 Hz/ng-mm(-2)), while contact with viscous fluids resulted in maximum changes of 15 446 Hz/cP. At an operating frequency of 50 MHz, the device detected viscosity changes as low as 0.0006 cP. The adsorption of proteins such as human IgG and the binding of a complementary antigen, goat anti-human IgG, on the upper nonmetallized surface of the device has been monitored with a detection limit of approximately 75 ng/mL. The binding of substrates and allosteric effectors to glycogen phosphorylase b has provided evidence that the device is very sensitive to viscoelastic changes in adsorbed proteins. The MARS device generates radial shear acoustic waves over a broad bandwidth that are unaffected by the conductivity of the solution. These results suggest that simple metal, glass, crystalline, or polycrystalline plates can be used as a new type of tunable acoustic immunosensor.     

一种薄壁吸能结构的设计优化

研究了一种薄壁结构在耐撞指标下的轴向冲击吸能特性。采用非线性有限元软件ABAQUS对结构的冲击过程进行仿真,并结合径向基函数法(RBF),根据耐撞性指标优化了这种吸能结构的截面,得到了较为理想的结构形式。数值结果表明采用该方法可以精确地确定优化参数,使结构比吸能(Es)得到明显提高。     

螺旋行波管衰减器炭涂层的特性表征

分别采用热解沉积、胶体石墨涂刷和电弧放电法在行波管(TWT)刚玉支撑杆上涂覆了吸波炭涂层,以改善TWT稳定性.通过一种带孔窄频-高波-道管的实验装置,应用无向量网络解析器实施反射和透射波测量,测得6.0GHz频段涂层杆的衰减程度.并利用一种软件高频结构模拟器(HFSS)进行了模拟.结果表明:胶体石墨涂层显示出最大的损失或吸光率.是适宜的衰减器涂料.HFSS模拟的结果与实验结果吻合.