压电薄膜微传感器振动模态的仿真分析

以压电本构方程为基础，建立了压电薄膜微传感器机电耦合的有限元模型，采用有限元分析软件ANSYS7．0对压电薄膜微传感器进行了模态分析，同时分析了压电薄膜微传感器的结构尺寸对振动模态的影响，探讨了影响压电薄膜微传感器工作稳定性和响应速度的关键因素，结果表明为了提高压电薄膜微传感器的工作稳定性和响应速度，应该在符合工艺要求和保证其它特性的前提下，尽量减小微悬臂梁结构长度，增加多晶硅层厚度，限制PZT层厚度，而微悬臂梁宽度的影响较小。     

基于Ansys Workbench的机电产品木质包装箱的结构优化

目的为了节约木材资源,降低包装箱的生产成本,优化某型机电产品木质包装箱的结构尺寸。方法根据产品的外形尺寸、质量分布和运输要求,利用UG软件设计木质包装箱的结构,将其主要承载构件――枕木和纵梁的三维模型导入Ansys Workbench中,然后建立枕木和纵梁的优化模型进行迭代分析求解,获得枕木和纵梁截面尺寸、最大挠度和体积的最优解,再对优化前后的枕木和纵梁结构进行有限元分析比较。结果在满足弯曲强度和刚度的条件下,枕木的最优截面宽度和高度为0.044 m和0.032 m,纵梁的最优截面宽度和高度为0.148m和0.158m;优化后枕木和纵梁的总体积分别降低了41.324%和8.661%,包装箱总质量降低了34.79kg,实现了减少木材用量的优化目标。结论合理增大枕木和纵梁的截面高度可提高其刚度,适当减小枕木和纵梁的截面宽度可显著降低其体积和质量。     

大尺寸立方体开槽超声塑料焊接工具头的优化设计

谐振频率、频率间隔性、振幅均匀度是大尺寸超声塑料焊接工具头设计中的几个主要指标。基于工程实际,以工具头纵向长度、槽宽度及槽长度为设计变量,纵向谐振频率和频率间隔值为状态变量,振幅均匀度为目标函数,利用有限元软件ANSYS的参数化分析技术,对大尺寸立方体超声塑焊开槽工具头进行了优化设计。结果表明,该优化方法能很好地解决大尺寸超声塑焊工具头的设计问题,既提高了设计效率,也降低了设计成本。     

中间主应力对金属悬臂梁承载力的影响

基于双剪统一强度理论使用显式有限差分方法对矩形截面金属悬臂梁承载力的中间主应力影响进行了计算分析。通过分析发现,极限状态下悬臂梁的塑性应变的分布非规则圆扇形,而是接近对称三角形分布。中间主应力对悬臂梁承载能力的影响与梁的厚度有关。平面应力情况的悬臂梁比平面应变的中间主应力影响要低,平面应变情况下中间主应力对金属悬臂梁极限承载力的影响与梁的长度无关,平面应力情况下中间主应力影响随梁长度的增加呈先增大后减小而后趋于恒定的趋势。     

冷弯薄壁型钢受弯构件承载力与延性优化研究

该文旨在通过改变冷弯型钢的截面尺寸来提高其承载力和延性。基于ABAQUS有限元软件建立已有试验模型,计算了不同尺寸下的腹板翼缘加劲截面和腹板加劲的折叠翼缘截面的抗弯承载力及延性,分析了上述2种截面的几何尺寸与抗弯承载力及延性的关系,并采用人工神经网络(ANNs)和遗传算法(GA)对截面尺寸进行优化;采用逼近理想解排序法(TOPSIS)分别确定了2种截面的最佳截面尺寸并提出截面尺寸的优化设计公式。结果表明:对壁厚为1.5 mm的冷弯薄壁型钢构件,在一定范围内增加截面腹板高度可以提高其抗弯承载力,采用较小的平翼缘宽度可以提高其延性,设置加劲肋的措施可以略微增加结构抗弯承载力但显著提高结构延性;在所研究的截面中,腹板加劲的折叠翼缘截面具有更好的力学性能。     

大截面碳纤维导线卡线器夹嘴优化设计

卡线器夹嘴长度决定着平行移动式导线卡线器的整体尺寸和质量,也决定着被夹持导线是否会发生损伤。针对夹嘴长度多以导线直径乘放大倍率、试验验证的方法确定,缺乏一定理论支撑,通过对1 660 mm²大截面碳纤维导线的结构特点进行分析,并利用试验得出碳纤维导线芯棒径向耐压强度判据。参考1 250 mm²导线应力仿真结果得出型线铝股塑性范围判据,取夹嘴长度为350,325,275 mm,对1 660 mm²大截面碳纤维导线进行仿真研究,并根据仿真结果优化设计了适用于JLZ2X1/F2A-1660/95-492型1 660 mm²大截面碳纤维导线卡线器。优化后的导线卡线器的夹嘴长度减小了21.9%,质量减小了25.0%。研究结果可为卡线器的设计和优化提供参考依据。     

不同截面形状悬臂梁双晶压电振子发电能力建模与实验研究

为了研究截面形状对悬臂梁双晶压电振子发电能力的影响,本文根据压电方程和热平衡原理分别建立了截面形状为矩形、梯形和三角形悬臂梁双晶压电振子压电发电的数学模型,对截面形状对压电梁发电能力的影响进行了数值模拟与有限元仿真分析,并进行了实验验证。研究结果表明,在相同压电材料体积下,三角形压电振子最大输出功率为4.5mW,约为矩形压电振子的3.3倍,三角形压电振子相比于矩形和梯形压电振子具有更大的发电能力,可有效提高有限体积下压电振子的输出特性。     

粉末衍射中背比的发散狭缝宽度和长度效应

Bragg-Brentano几何粉末衍射中峰位、峰形和峰强的准确测量决定着粉末X射线衍射图谱的质量,同时也是正确表征材料晶体结构的前提和关键。光路中发散狭缝的尺寸会直接影响衍射峰的强度,并且不合理的发散狭缝设置会显著影响小尺寸试样的衍射峰形状。研究了发散狭缝宽度效应和长度效应对小尺寸试样衍射图谱峰背比的影响。结果表明:发散狭缝的宽度和长度限制了照射在试样上的光斑长度和宽度,光斑的宽度和长度如果大于试样的,会引起背底在低角度和高角度的显著升高,即随着发散狭缝宽度和长度的增大,衍射图谱中低角度和高角度的峰背比也会显著降低。因此,对于小尺寸试样,考虑到光斑的水平发散和垂直发散,狭缝宽度和长度的设置以小于试样的实际尺寸为宜。     

用户型缆桥交换机中塑料卡扣的仿真分析与结构优化

本文对用户型缆桥交换机的卡扣尺寸优化进行了仿真模拟研究。通过ANSYS Workbench建立计算模型,采用正交试验法,主要分析了卡钩厚度、卡钩长度、卡钩宽度、导入角、拆卸角、顶部厚度和配合深度共7个关键尺寸对2种评价指标的影响规律和主次关系。结果表明,卡钩长度、配合深度、导入角和拆卸角对装入力和拆卸力的影响较显著,其优化尺寸分别为7mm、25°、55°和0.8mm。基于对应力分布和受力分析的比较,和原卡扣相比,优化后卡扣的装入力和拆卸力更符合设计要求。     

三维自由弯曲技术及变形区长度优化数值模拟研究

目的 开展自由弯曲变形区长度优化研究,获得外径为15 mm、壁厚为2 mm的6061-T6铝合金管材的最优A值。方法 从三维自由弯曲成形技术的基本原理及控制程序入手,基于有限元分析方法,利用ABAQUS仿真软件对管材三维自由弯曲成形过程进行数值模拟,研究成形过程中管材弯曲变形区的受力过程变化,分析变形区长度(A)对弯曲成形结果的影响规律。基于最优的变形区长度,对制冷系统管路中的6061-T6铝合金复杂空间弯曲构件进行仿真模拟及实际成形试验。结果 试验成形构件尺寸与模拟成形构件尺寸相近且均接近设计尺寸,试验成形构件最大壁厚减薄率不超过9%,最大截面畸变率不超过5%,具有较好的成形质量。结论 目标构件的有限元模拟及成形试验验证了变形区长度优化结果的准确性。     

Thickness dependence of Gc for shear lip propagation from a single crack propagation specimen: aluminium 6061-T6 alloy,cold-rolled copper and BPA polycarbonate

Values ofG _c for ductile crack propagation in a series of double cantilever beam specimens, each with a single side groove of constant depth, increase linearly with net section thickness. If a single side groove with linearly varying depth is cut in a double cantilever beam specimen, the tapered net section thickness results in a plastic zone, the crosssection area of which increases linearly with crack length. The attendantG _c increases in proportion to the plastic zone size in such a specimen. A single properly designed tapered section specimen appears to be capable of providing estimates of (a) the dependence of shear lipG _c on shear lip width, (b) the natural shear lip width and shape, and (c) the shear lip plastic strain. G _c and plastic zone data from specimens of both kinds are reported for aluminium 6061-T6 alloy, cold-rolled copper and BPA polycarbonate. Results of uniaxial tensile tests and of centre-notch tensile tests are also reported for comparison purposes.G _cs, plastic zone sizes and plastic zone strains vary from material to material and appear to reflect in part the drawing and necking characteristics seen in uniaxial tensile tests.     

Modeling Piezoresistive Microcantilever Sensor Response to Surface Stress for Biochemical Sensors

This paper considers mechanical stress and strain in a piezoresistive cantilever sensor under surface stress loading, which is the loading condition that occurs in biochemical sensing applications. Finite element simulations examine the piezoresistor sensitivity due to changes in cantilever length, width, and thickness, and piezoresistor size, location, and depth. A few unexpected results are found. Unlike cantilevers designed for atomic force microscopy, cantilevers for biochemical sensing should be short and wide. While shallow piezoresistors offer good sensitivity, the piezoresistor may extend far into the thickness of the cantilever and still be quite effective. The paper concludes with comments on design guidelines for piezoresistive cantilever sensors.     

Nanocantilever signal transduction by electron transfer

Microfabricated cantilever beams promise to bring about a revolution in the field of chemical, physical, and biological sensor development. The resonance frequency of a microfabricated cantilever shifts sensitively because of mass loading from molecular adsorption. The minimum detectable adsorbed mass on a cantilever sensor can be increased by orders of magnitude by changing the dimensions of the device; smaller and thicker cantilevers offer higher resonance frequency and therefore better mass detection sensitivity. Here we describe micromachined silicon cantilevers that are 0.5 to 4 microns in length, fabricated with the use of a focused ion beam (FIB). In addition, we demonstrate a technique for detection of the cantilever resonance frequency that is based on electron transfer.     

三维编织复合材料中纤维束横截面形状的研究

采用计算机图象分析技术,重点对三维编织复合材料微观结构中纤维束的横截面形状进行了全面的研究。结果表明:在复合材料的内部、边部和角部,纤维束的横截面形状是不同的。并初步探讨了纤维束横截面面积的变化与花节长度的关系。      

Hole effects on lateral buckling of laminated cantilever beams

In this study, the effects of hole diameter and hole location on the lateral buckling behaviour of woven fabric laminated composite cantilever beams have been investigated. In the experimental studies, two different groups of samples were used; samples with a single circular hole and samples with no hole. The critical buckling load for each sample was then determined experimentally. For the numerical analyses, ANSYS 10.0 finite element program was utilized. It has been noted that there is a good agreement between experimental results and those of finite element analyses. On the basis of this harmony, the numerical analyses of some models having different dimensions and fiber orientations have been done by changing length and width of the beam, diameter and location of the hole. It has been concluded that the effects of the hole diameter and hole location on the lateral buckling behaviours is very important, especially for the short beams.     

偏心轴向荷载作用下薄壁箱梁的约束扭转翘曲应力研究

以薄壁箱梁的约束扭转分析理论为基础,将薄壁箱梁所受偏心轴向荷载作为一种外加双力矩荷载考虑,建立偏心轴向荷载作用下薄壁箱梁约束扭转的双力矩这一广义内力的计算公式。为了便于计算翘曲应力,进一步推导了扭转中心位置及主扇性坐标的实用计算公式。通过对一模型箱梁进行计算,并与按通用有限元软件ANSYS壳单元计算结果进行比较,验证了该文方法和所推导公式的正确性。详细分析箱室高宽比以及悬臂板宽度变化对偏心轴向荷载作用下薄壁箱梁约束扭转翘曲应力的影响。研究结果表明:箱室高宽比及悬臂板宽度对悬臂板端部翘曲应力的影响最大,对腹板与上翼缘、下翼缘交接处翘曲应力的影响相对较小;在偏心轴向分布荷载作用下,悬臂箱梁固定端横截面上控制点处的翘曲应力可达到初等梁应力的12%,不容忽视。     

Interlaminar fracture characterization for plain weave fabric composites

For the analysis of laminated composite plates under transverse loading and drilling of composites, all the elastic, strength and fracture properties of the composite plates are essential. Interlaminar critical strain energy release rate properties in mode I, mode II, mixed mode I/II and mode III have been evaluated for two types of plain weave fabric E-glass/epoxy laminates. The double cantilever beam test and the end notch flexure test have been used for mode I and mode II loading. The mixed mode bending test and split cantilever beam test have been used for mixed mode I/II and mode III loading. It is observed that the plain weave fabric composite with lesser strand width has higher interlaminar fracture properties compared to the plain weave fabric composite with more strand width. Further, crack length versus crack growth resistance plots have been presented for mode III loading. In general, it is observed that total fracture resistance is significantly higher than the critical strain energy release rate.     

基于摄动法的多条裂纹欧拉梁特征模态分析

基于摄动理论推导了带多条开口裂纹的欧拉梁的特征模态参数的理论计算公式。采用最直接的方式将梁开口裂纹模拟成梁微段内的横截面折减并用δ函数表达了带开口裂纹的梁沿轴线的截面惯矩和线质量等物理参数。基于此,建立了裂纹梁动力微分方程,并采用一阶摄动理论推导得到了梁的模态频率和振型计算公式。简支梁及悬臂梁算例研究表明,该方法具有很好的精度,与有限元模拟结果及实验结果都能很好地吻合。并采用此方法分析了裂纹深度和位置对带多条开口裂纹梁的特征模态参数的影响。结果表明,裂纹对各阶模态频率虽然影响有限,但其引起的各阶频率变化有着明显的模式,可用于结构损伤定位;裂纹对模态振型影响不明显,但对模态曲率影响比较大,可用于结构损伤位置和程度的诊断。     

基于弹性抗力法的深基坑悬臂支护结构上土压力空间效应分析

深基坑是一个具有长度、宽度、深度的三维空间结构体系。现行设计规范中将其简化为二维平面应变问题进行分析计算,不能反映基坑的空间性状和尺寸效应。基于弹性抗力法引入土压力发挥系数的概念,提出了土压力发挥系数的计算方法。提出基坑悬臂支护结构顶部冠梁的水平位移与简支梁受均布荷载作用下的水平位移具有相似的形式,在此基础上计算深基坑悬臂支护结构上土压力发挥系数、支护结构变形和内力的空间分布规律。工程实例计算表明:考虑土压力空间效应得到的基坑变形与实测结果相符合。     

Effect of initial crack length on the measured bridging law of unidirectional E-glass/epoxy double cantilever beam specimens

In this paper, the effect of initial delamination length is experimentally investigated on obtaining the mode I bridging law of unidirectional E-glass/epoxy double cantilever beam (DCB) specimens manufactured by hand layup method. To this end, an experimental test set-up is established for accurate measurement of crack tip opening displacement (CTOD) using digital image processing method. DCB tests are performed for three different delamination lengths and the corresponding bridging laws are calculated using J-integral approach. Results showed that the maximum bridging stress, the shape of bridging law and energy dissipation in bridging zone are slightly affected by changing initial crack length. In other words, the measured bridging law acts independent of initial delamination length. Therefore, the obtained bridging law can be used with the cohesive elements available in the commercial finite element software to simulate the delamination propagation behavior in unidirectional DCB specimens.