Micro thermal shear stress sensor based on vacuum anodic bonding and bulk-micromachining

This paper describes a micro thermal shear stress sensor with a cavity underneath, based on vacuum anodic bonding and bulk micromachined technology. A Ti/Pt alloy strip, 2μm×100μm, is deposited on the top of a thin silicon nitride diaphragm and functioned as the thermal sensor element. By using vacuum anodic bonding and bulk-si anisotropic wet etching process instead of the sacrificial-layer technique, a cavity, functioned as the adiabatic vacuum chamber, 200μm×200μm×400μm, is placed between the silicon nitride diaphragm and glass （Corning 7740）. This method totally avoid adhesion problem which is a major issue of the sacrificial-layer technique.

Effect of Dietary Components on the Shear Bond Strength of Orthodontics Brackets after Thermal Aging

Introduction: The stability of orthodontic brackets throughout orthodontic treatment plays a critical role in the treatment’s effectiveness. The present in vitro study was designed to assess the impact of various dietary components on the performance of orthodontic brackets. Methods: Metal orthodontic brackets were bonded to 66 extracted anterior teeth divided into groups based on the solution type: Milk, Gatorade, Cold Coffee, and a control group using water. Each group consisted of 20 teeth except for the control group, which included six teeth. The bracketed teeth were submerged in their respective solutions for 15 minutes three times daily at different intervals to mimic an in vivo environment and were stored in artificial saliva at room temperature (23?C). The specimens underwent artificial aging through 10,000 cycles of thermocycling (representing one clinical year) between 5?C and 55?C. Shade measurements were taken using a VITA Easy Shade device, capturing the classic shade and L*, a*, and b* values. Delta E values were calculated immediately post-bonding and after 7 days, 1 month, 1, and 2 clinical years. The shear bond strength of each bracket was measured using an ultra-tester machine. Results: After two clinical years, significant differences in ΔE color values were observed across all groups, with the most substantial change noted in teeth immersed in cold coffee. Brackets submerged in milk demonstrated lower shear bond strength than other solutions, whereas the control group exhibited the highest shear bond strength (P = 0.01). Conclusion: The study indicates that dietary components significantly influence tooth color stability and the shear bond strength of orthodontic brackets, underscoring the importance of considering these factors in orthodontic treatment planning.

Analysis on Interface Shear Stress of Thermally InsulatedOcean Pipelines Under Installation

It has been proved that the thermally insulated ocean pipeline has advantages over the conventional pipe-in-pipe pipeline. The risk of using the thermally insulated pipeline is that the exterior layers covering the steel pipe may be. pulled off if the shear stress on the interface induced by the pullout fore from the tensioner is greater than the binding fore between two neighboring layers during installation. This paper develops a procedure to calculate the shear stress on the interface. The binding force between two neighboring layers can be determined with full scale model tests. The safety of the thermally insulated pipe under installation can then be checked by comparison of the interface shear stress with the binding force.

Shearing Wind Helicity and Thermal Wind Helicity

Helicity is defined as H ： V ω, where V and ω are the velocity and vorticity vectors, respectively. Many works have pointed out that the larger the helicity is, the longer the life cycle of the weather system is. However, the direct relationship of the helicity to the evolution of the weather system is not quite clear. In this paper, the concept of helicity is generalized as shearing wind helicity （SWH）. Dynamically, it is found that the average SWH is directly related to the increase of the average cyclonic rotation of the weather system. Physically, it is also pointed out that the SWH, as a matter of fact, is the sum of the torsion terms and the divergence term in the vorticity equation. Thermal wind helicity （TWH）, as a derivative of SWH, is also discussed here because it links the temperature field and the vertical wind field. These two quantities may be effective for diagnosing a weather system. This paper applies these two quantities in cylindrical coordinates to study the development of Hurricane Andrew to validate their practical use. Through analyzing the hurricane, it is found that TWH can well describe the characteristics of the hurricane such as the strong convection and release of latent heat. SWH is not only a good quantity for diagnosing the weather system, but also an effective one for diagnosing the development of the hurricane.

An Application of the Modified Shear Lag Model to Study the Influence of Thermal Residual Stresses on the Stiffness and Yield Strength of Short Fiber Reinforced Metal Matrix Composites

The modified shear lag model proposed recently was applied to calculate thermal residual stresses and subsequent stress distributions under tensile and compressive loadings. The expressions for the elastic moduli and the yield strengths under tensile and compressive loadings were derived which take account of thermal residual stresses. The asymmetries in the elastic modulus and the yield strength were interpreted using the derived expressions and the obtained results of the stress calculations. The model predictions have exhibited good agreements with the experimental results and also with the other theoretical predictions

KRMN-TYPE EQUATIONS FOR A HIGHER-ORDER SHEARDEFORMATION PLATE THEORY AND ITS USE IN THE THERMAL POSTBUCKLING ANALYSIS

arman-type nonlinear large deflection equations are derived occnrding to theReddy's higher-order shear deformation plate theory and used in the thermal postbuckling analysis The effects of initial geometric imperfections of the plate areincluded in the present study which also includes th thermal effects.Simply supported,symmetric cross-ply laminated plates subjected to uniform or nomuniform parabolictemperature distribution are considered. The analysis uses a mixed GalerkinGolerkinperlurbation technique to determine thermal buckling louds and postbucklingequilibrium paths.The effects played by transverse shear deformation plate aspeclraio, total number of plies thermal load ratio and initial geometric imperfections arealso studied.

TC11钛合金动态热塑互动行为研究

利用分离式霍普金森压杆对TC11钛合金平板帽形试样进行动态加载,基于高频红外点阵测温技术捕捉了剪切区温升随加载时间变化的历程,结合热传导理论分析和动态剪切数值模拟,分析了动态剪切过程中剪切区温升随时间和空间的分布规律。研究结果表明,在动态剪切加载下,TC11钛合金表现出脆性的变形行为,剪切区最高温升为430℃,且在实验所覆盖的加载速率范围内,加载速率对动态剪切温升影响不明显;显著的温升主要集中在剪切区中心附近100μm量级区域内,温升区具有高度局部化的特征,且剪切区维持较高温度所持续的时间在10μs量级。理论研究和数值模拟发现,动态加载下剪切区内最高温度可达751℃,剪切区温度时空分布规律与实验结果保持一致。实验和数值模拟结果均显示,剪切区最高温升发生在材料断裂时刻,表明剪切区显著温升应来源于剪切变形造成的应变高度集中发展。

高温预处理对杨木正交胶合木剪力墙抗侧力性能的影响

[目的]研究往复荷载作用时国产速生杨木正交胶合木(CLT)剪力墙的抗侧力性能,阐明木材高温预处理和加速老化对剪力墙抗侧力性能的影响,为高温改性技术和国产速生木材在建筑结构中的高效利用提供参考。[方法]以木结构建筑常用的进口欧洲云杉规格材为对照,以相同强度等级的国产速生杨木为研究对象,选用180℃为预处理温度对杨木进行高温改性,制备5面全尺寸正交胶合木剪力墙,开展往复荷载作用时加速老化前后正交胶合木剪力墙的抗侧力性能试验。[结果]与相同层板强度等级的欧洲云杉正交胶合木剪力墙相比,往复荷载作用时未处理杨木正交胶合木剪力墙的极限承载力、弹性抗侧刚度、耗能能力分别降低5.8%、12.9%、8.0%;木材经高温预处理、墙体经加速老化或二者联合处理后,杨木正交胶合木剪力墙的抗侧力性能指标不同程度降低;与未处理杨木正交胶合木墙体相比,加速老化处理后,墙体的极限承载力、弹性抗侧刚度、耗能能力分别降低9.4%、9.7%、11.2%;木材经高温预处理后,经加速老化,墙体的极限承载力、弹性抗侧刚度、耗能能力变化较小,分别降低2.9%、2.4%、5.0%。[结论]往复荷载作用时,国产速生杨木正交胶合木剪力墙的抗侧力性能略低于相同层板强度等级的欧洲云杉正交胶合木剪力墙,水平力作用时二者具有相似破坏模式,均为抗拔连接件节点处钉子被剪断;木材经高温预处理、墙体经加速老化或二者联合处理后,杨木正交胶合木剪力墙的破坏模式均为底部墙角抗拔连接件处木材被拉断或劈裂破坏;木材高温预处理能够有效降低加速老化对剪力墙抗侧力性能的影响,具有相对较好的抗老化能力;建立正交胶合木剪力墙极限承载力计算模型,理论值与试验值误差小于10%。

轻钢龙骨复合墙板研究进展

装配式钢结构建筑具有抗震性能好、自重轻、施工速度快等优点,但因与其配套的围护外墙板较少,制约了装配式钢结构的发展。近年来结构轻便、保温性能好、抗震性能优良的轻钢龙骨复合墙板被逐渐应用到装配式钢结构建筑当中。对现有轻钢龙骨复合墙板进行了分类,总结了各类墙板的特点,并介绍了国内外针对墙板的抗弯性能、抗剪性能、抗震性能以及热工性能等方面的研究现状。在此基础上,分析了轻钢龙骨复合墙板存在的问题,提出了一种热工与防火性能好、自重轻、连接安全可靠、管线易于分离且可工业化生产的新型轻钢龙骨复合墙板。

含硼三烯丙基化合物改性环氧树脂的研究

采用含硼三胺(TAB)和香草醛衍生的烯类化合物(AM)为原料,通过希夫碱合成反应设计制备了一种含硼三烯丙基化合物(TABM),通过改变TABM的添加量得到一系列改性树脂(E-51+TABM)。对固化后树脂的结构、热稳定性、热机械性能、拉伸剪切性能、阻燃性能以及微观断裂形貌进行了表征。研究结果表明:(1)红外光谱和核磁氢谱的测试结果均表明,成功地制备了目标产物TABM。(2)热稳定性和热机械性能研究表明,随着TABM用量的增加,固化后环氧树脂的储能模量和残碳率也随之增大,但其玻璃化转变温度和交联密度降低。这表明TABM的添加可以降低材料的刚性,提升环氧树脂的韧性。(3)添加TABM后,环氧树脂在室温和100℃条件下的拉伸剪切强度均得到提升,当添加10份TABM时,拉伸剪切强度在25℃的条件下提升了25.5%,在100℃的条件下提升了37.5%。(4)随着树脂中TABM含量的增加,固化后树脂的极限氧指数(LOI)值也随之提升,直到添加量达到20份时达到最大值,说明TABM的添加,使得固化后树脂的阻燃性得到了有效改善。(5)微观断裂形貌分析表明,共混树脂(E-51+TABM)的断裂韧性得到了提高。

2D-C/SiC复合材料的面内剪切本构模型

为了表征2D-C/SiC复合材料的面内剪切行为,考虑基体开裂、界面脱粘、纤维桥连弯曲等损伤机制,提出宏细观两尺度下的含损伤体元模型;引入热失配应力的影响,在分别表征卸载弹性应变和残余应变的基础上,建立材料的温度相关面内剪切本构模型。开展室温单调加载和加卸载面内剪切实验,发现残余应变和弹性应变均随剪应力的增大逐渐增大,而卸载模量随剪应力的增大持续减小。将模型用于2D-C/SiC复合材料剪切行为的模拟,结果表明:模型对于弹性应变、残余应变、卸载模量和整体应力-应变曲线的预测值均与实验数据吻合,验证了分析模型的合理性与准确性;在此基础上,给出2D-C/SiC复合材料在不同温度下的面内剪切应力-应变关系曲线,为热结构设计提供参考。

润滑油剪切流动对发电机不稳定振动影响分析

为研究核电站发电机组上发生的不稳定振动现象,建立了考虑润滑油剪切流动热效应的转子动力学分析模型。采用一维能量平衡方程求解润滑油在轴承微小间隙内流动引发的轴颈温差,将温差产生的等效热弯矩作用于转轴上,得到了发电机组转子弯曲变形。采用有限元法建立了弯曲转子在不平衡力激励下的动力学模型。研究结果表明,轴承间隙内润滑油剪切流动会导致轴颈截面出现温差。在核电机组轴承参数合理范围内,温差会达到10℃,其对振动的影响相当于发电机转轴上G2.5级不平衡量的影响。剪切流动产生旋转性不平衡量,导致振动波动。其对振动的影响和润滑油黏度、轴承间隙、偏心率和不平衡力等因素有关。减小润滑油黏度、增大轴承间隙、减小偏心率和不平衡量可以减小不稳定振动。开展了调节润滑油温工程验证试验,试验结果表明提高润滑油温以减小润滑油黏度,有助于减小不稳定振动,计算分析结果与工程实践结果一致。本研究建立的模型能够用于核电站发电机组不稳定振动分析。

纳米银浆低温烧结工艺及可靠性分析

对纳米银浆烧结前后的微观组织形貌进行分析,研究了不同烧结温度、烧结时间和升温速率对纳米银浆烧结样件剪切强度的影响,并对比分析了Au80Sn20和纳米银浆两种不同连接材料对GaN芯片散热性能的影响。结果表明:GaN芯片通过纳米银浆烧结到管壳后,银层与金层之间存在一个明显的互扩散层,实现了芯片和壳体之间优异互连。在烧结温度200℃、时间90 min、升温速率5℃/min的烧结条件下,样件剪切强度可达47.2 MPa。纳米银浆与Au80Sn20装配的芯片温度分布基本一致,但纳米银浆散热性能优于Au80Sn20。在经历温度冲击、扫频振动、温度循环及射频老炼试验后,纳米银浆烧结的芯片热阻波动不明显,剪切力性能略微提升。

高功率半导体用纳米银焊膏的研究现状

第3代半导体作为核心部件,使得更紧凑、高频率、高功率的电子器件在射频和微波电子、能源转换与储存、雷达和通信等领域展现出广泛的应用潜力。然而,高性能电子器件对其封装材料的导电性、导热性以及连接处的机械性能提出了更为严格的要求。纳米银焊膏因其卓越的低温烧结性能和在高温环境下的出色表现引起了广泛关注。然而,国内银粉和银焊膏产品的质量相对较低,且研发过程缺乏理论指导,必须依赖进口材料。基于高功率半导体用纳米银焊膏,综述了通过液相化学还原法合成纳米银粉的研究进展,以及纳米银焊膏的烧结机理、影响其性能的因素和控制方法,有望为国内纳米银焊膏的研发和生产提供有益的指导和支持。

直线往复密封性能影响因素分析

以手动泵密封结构为研究对象,旨在获得直线往复运动过程中的密封性能。基于ANSYS Workbench仿真平台,以接触压力和剪应力为密封失效判定依据,研究预密封过程中剪应力分布规律,分析工作过程中压缩率、流体压力、配合间隙、摩擦系数、材料硬度对密封性能影响,讨论磨损和热变形对失效形式的激励作用。结果表明:预密封过程中,密封圈在高压缩率时从内部出现断裂失效的概率较大;工作状态下,密封圈接触压力呈非对称分布,在高流体压力、大配合间隙、高摩擦系数及低材料硬度时导致间隙挤出,密封圈从挤出部分表面断裂失效;磨损增大泄漏失效风险,热变形增大剪切失效风险,高温增大油膜泄漏量。

Research on Measurement of Bed Shear Stress Under Wave-Current Interaction

The movement of sediment in estuary and on coast is directly restricted by the bed shear stress. Therefore, the research on the basic problem of sediment movement by the bed shear stress is an important way to research the theory of sediment movement. However, there is not a measuring and computing method to measure the bed shear stress under a complicated dynamic effect like wave and current. This paper describes the measurement and test research on the bed shear stress in a long launder of direct current by the new instrument named thermal shearometer based on micro-nanotechnology. As shown by the research results, the thermal shearometer has a high response frequency and strong stability. The measured results can reflect the basic change of the bed shear stress under wave and wave-current effect, and confirm that the method of measuring bed shear stress under wave-current effect with thermal shearometer is feasible. Meanwhile, a preliminary method to compute the shear stress compounded by wave-current is put forward according to the tested and measured results, and then a reference for further study on the basic theory of sediment movement under a complicated dynamic effect is provided.

磷系阻燃改性聚酯的流变性能

为探究2-羧乙基苯基次磷酸(CEPPA)作为阻燃剂改性合成的阻燃聚酯的可纺性,分别用DSC、TG、毛细管流变仪、旋转流变仪对阻燃改性聚酯进行热稳定性和流变性能测试。结果表明:阻燃聚酯的熔融温度、初始降解温度略微降低,残碳率提高,说明阻燃聚酯的加工温度可降低且成碳效果变好。阻燃聚酯是典型的非牛顿流体,其剪切黏度随着剪切速率的增加而降低,随温度的升高而降低,相比普通聚酯,改性后的阻燃聚酯黏度更低,流动性更好;阻燃改性聚酯的非牛顿指数n均小于1,且随着剪切速率的增加而减小;其黏流活化能随着剪切速率的增加而降低,反映了阻燃聚酯随着剪切速率的增加而对温度的敏感性变小。该研究结果可为阻燃聚酯纤维的制备工艺和参数调整提供参考。

倒装LED微小焊点空洞对其性能的影响

利用SnCu0.7锡膏回流工艺制备倒装LED,针对于焊点微小化引起的焊接缺陷。采用X-ray检测分选出不同空洞率焊点,系统研究了空洞率对于接头键合强度的影响规律及回流焊后接头断口特征,通过有限元仿真;探究空洞率对于芯片散热能力影响特性,同时,本文设计了结温测量实验,验证了仿真结果的准确性。最后通过高温老化实验,深入探究不同空洞率LED样品光通量及光电转换效率变化趋势。结果表明:焊点接头键合强度不完全取决于空洞的数量,空洞的大小及其位置对接头键合强度也会有一定的影响,其次随着空洞率逐渐增大,焊点的断裂模式逐渐由韧性断裂转变为脆韧性混合断裂。随着空洞率增大,LED在正常工作下的芯片结温基本呈线性增长趋势,并且空洞率越大,芯片表现出的散热能力越差,当空洞率约为5%,芯片结温为41.472℃,当空洞率为30%时,芯片结温达到45.969℃。随着空洞率增加,光通量与光电转换效率在高温老化开始阶段呈上升趋势,在500 h后光通量开始逐渐下降,在1500 h节点5%空洞率样品光通量维持率为93.22%比30%空洞率样品的82.37%高10.85%,5%空洞率样品光效为42.5%比30%空洞率样品的30.5%高12%。

湿热环境对T800S/M21碳纤维复合材料基体主导力学性能的影响研究

以T800S/M21碳纤维复合材料为研究对象,在三种吸湿调控与两种试验温度的湿热环境组合下,开展90°拉伸、±45°拉伸以及Ⅰ型与Ⅱ型层间断裂等基体主导力学性能影响试验。研究了湿热环境对基体拉伸及面内剪切模量与强度的影响,获得了湿热环境对层间性能G_(Ⅰc)与G_(Ⅱc)的影响。基于±45°拉伸与裂纹观察试验,获得了剪切刚度退化与厚度面裂纹数量演化规律,并分析了吸湿调控对引起剪切刚度退化的损伤机理影响。结果表明:湿热环境对T800S/M21复合材料基体主导的拉伸与剪切性能产生显著的折减影响,也对层间性能产生退化影响。湿热环境对面内剪切非线性特征产生一定弱化影响,吸湿加速了宏观裂纹产生与剪切刚度退化进程,导致宏观裂纹产生了比微观裂纹更加显著的刚度折减贡献。

环境应力影响下球栅阵列封装焊球仿真分析与力学性能研究

高密度、高性能集成电路主要封装技术采用球栅阵列封装(ball grid array,BGA),其高密度Sn-Pb焊球在极端高、低温及湿热环境的影响下可靠性无法保证。为解决温度变化产生的热膨胀问题,笔者通过有限元仿真计算BGA电路中焊球在高、低温交替循环应力下瞬态黏塑性应变范围,并采用改进的Coffin-Manson经验方程计算器件在温度循环试验下的热疲劳寿命;此外,进一步采用准静态剪切和拉脱试验分析分别经过温度循环及高压蒸煮环境试验后焊球的力学性能,同时采用扫描电子显微镜(scanning electron microscopy,SEM)和能谱分析仪(energy dispersive spectroscopy,EDS)对焊球切面进行分析。研究表明:焊球在温度循环试验下具有较长的疲劳寿命,在不考虑焊球导电与连接性能的前提下,适当环境应力的影响可促使焊球与焊盘界面区域金属间化合物的生成,有效增强了焊球的剪切力学性能。