纤维层厚和叉指电极间距对MFC电输出性能的影响

采用层叠-切割法制备了不同纤维层厚度的高固含量MFC压电纤维复合材料.通过改变其叉指电极间距,探讨MFC结构对其电输出性能的影响.结果表明,纤维层厚度适当增加,叉指电极间距适当减小均能提高MFC俘能器的输出电压,改变纤维层厚度还可以调节MFC的谐振频率.当纤维层厚度为0.3 mm、叉指电极间距为0.5 mm时,MFC悬臂梁俘能器在负载为1000 kΩ时的输出功率为4.8μW,功率密度为18 mW/m2,且具有良好的输出稳定性.     

ECC修复既有RC梁界面粘结与受弯性能试验研究

基于ECC修复既有混凝土梁的弯曲试验,主要分析了界面粗糙度、ECC层厚度与既有混凝土梁损伤参数对修复梁界面粘结和受弯性能的影响.研究结果表明:界面粗糙度和既有混凝土梁损伤参数对界面粘结性能的影响较为显著,而ECC厚度的影响则不太明显.与RC梁相比,修复梁的裂缝形态有明显改善,截面刚度得到提高,各特征荷载值均有不同水平的增长,由于ECC层的承拉与阻裂作用,修复梁开裂荷载的提高幅度最大,且适当增大界面粗糙度、ECC层厚度及减小损伤参数的修复梁,其受弯性能改善的就越明显.     

基于材料与结构的介电弹性体驱动性能优化研究进展

针对介电弹性体驱动性能的优化问题，详细综述了降低弹性模量和介电损耗以及提高介电常数及电击穿场强的原理和方法，并列举讨论了最新研究成果和进展；介绍了基于叠层技术的超薄多层介电弹性体、复合纤维增强的各向异性介电弹性体、柔性电极图案化和空间布局等改进工艺及结构设计；综述并总结了各项技术的最新研究进展和代表性成果，展望了介电弹性体驱动性能的优化发展趋势。     

BFRP侧向约束对GFRP带肋筋与混凝土粘结性能的影响

为考察BFRP侧向约束对GFRP带肋筋与混凝土粘结性能的影响,对36个GFRP筋混凝土拉拔试件进行试验研究,主要试验参数为BFRP侧向约束层数(0层、1层、2层和3层)和混凝土相对保护层厚度c/d(1.6、2.2和3.0)。试验结果表明:BFRP侧向约束使拉拔试件的破坏模式由混凝土劈裂破坏转为GFRP带肋筋的拔出破坏;试件的粘结强度和达到粘结强度所对应的滑移量、侧向约束应力会随BFRP侧向约束层数的增加而增大;相同BFRP侧向约束层数下,相对粘结强度随着c/d的增大而增大,但达到粘结强度所对应的侧向约束应力却随c/d的增大呈指数减小;相对粘结强度增加量随着达到粘结强度时侧向约束应力的增加呈对数增加。     

NdFeB磁粉表面电沉积包覆纳米金属层研究

在NdFeB磁粉表面包覆金属层是改变其性质的有效手段,但目前常用的化学沉积法、电化学沉积法与化学气相沉积法等都无法实现磁粉表面完整、牢固的包覆.探索新的NdFeB磁粉表面金属完整包覆技术具有重要的理论意义及应用价值.根据NdFeB片状磁粉在磁场下的磁化特征,设计了磁力搅拌流化床电解槽,利用电沉积实现磁粉表面的纳米金属层包覆.测量了磁粉包覆前后的磁性能和电极电位,测定了包覆不同厚度Cu对磁粉制成粘结磁体抗压强度的影响.结果表明,利用磁力搅拌流化床电沉积法可以实现NdFeB磁粉的完全包覆,包覆层厚度可以控制在纳米尺度.磁粉包覆后的磁性能和电极电位发生了明显改变,包覆铜样品的粘结磁体抗压强度明显提高.     

钽镁酸钡缓冲层对锆钛酸铅铁电薄膜性能的影响

采用溶胶–凝胶工艺在Pt/Ti/Si O2/Si基片上,通过引入钽镁酸钡[Ba(Mg1/3Ta2/3)O3,BMT]缓冲层,制备了锆钛酸铅[Pb(Zr0.52Ti0.48)O3,PZT]铁电薄膜。研究了BMT缓冲层对PZT铁电薄膜结晶和性能的影响。结果表明:引入BMT缓冲层利于PZT薄膜的生长;PZT薄膜具有钙钛矿结构,且没有裂纹、结晶良好、致密性好;缓冲层的厚度对PZT铁电薄膜的微观结构和铁电性能有重要影响。随BMT缓冲层厚度增加,PZT晶粒增大,介电损耗tanδ逐渐减少,介电常数εr和剩余极化强度Pr先增大后减少,矫顽场Ec先减少后增大。当BMT缓冲层厚约为10 nm时,PZT薄膜具有最优的铁电性能:εr=1 850,Pr=20.2μC/cm2,Ec=43.9 k V/mm。这与BMT与PZT具有相似的晶格常数、较小的晶格失配度和相近的禁带宽度有关。     

胶粘剂在地下管廊施工中纤维锚杆的应用研究

为了提高地下管廊施工中纤维锚杆的稳定性和安全性,研究了胶粘剂种类和厚度对碳纤维复合锚杆剪切性能的影响,通过基于界面断裂能计算方法得到了界面极限承载力并与实测值进行了对比。结果表明,在相同粘结层厚度时,采用Tc的胶粘剂试件的界面极限承载力都高于T1胶粘剂试件;随着粘结层厚度增加,Tc为胶粘剂时试件的极限承载力平均值逐渐增大,而T1为胶粘剂时试件的极限承载力平均值逐渐减小。最优碳纤维锚杆粘结层厚度都为1mm。粘结层厚度对试件的刚度影响较小,弹性模量更大的胶粘剂可以为粘结试件提供更大的剪切刚度,而弹性模量较小试件的协调变形能力更强。碳纤维复合锚杆的极限承载力测试结果与基于界面断裂能的预测结果较好吻合。研究结果可为碳纤维复合锚杆的极限承载力预测提供参考。     

压电纤维复合材料极化响应电极结构优化

采用有限元软件COMSOL Mutilphysics模拟仿真,从极化电场加载的角度分析了电极结构对压电纤维复合材料(MFC)中压电纤维极化电场分布的影响,发现电极间距增大和宽度减小,有利于增大纤维中均匀活性区域,提高有效电场的加载,从而获得高压电性,同时电极间距的调控效果更为明显。实验制备MFC并进行了铁电响应和压电性能表征,结果表明:适当增大叉指电极间距和减小叉指电极宽度,能有效提高MFC的极化响应程度进而改善了其压电性能,实验结果与模拟仿真一致。     

影响背板层间剥离强度的几大因素分析

介绍了太阳能电池背板的结构和保证背板层间剥离强度的重要性.从胶粘剂的粘结固化机理、主固比、涂胶量、基材、车间复合工艺、后期熟化温度及时间等方面阐述了影响背板层间剥离强度的因素,其中主固比增大,初粘力提高,但耐湿热性下降;主固比减小,初粘力下降,但耐湿热性提高;胶层的厚度与层间剥离强度有密切关系,一般在保证不缺胶粘剂的情况下,层间剥离强度随胶层厚度的减少而增大,胶层过厚或太薄,胶层内形成气泡或缺陷的几率就会增大.最后提出了复合型背板层间剥离强度目前存在的问题及改进思路.     

基于十字交叉法的陶瓷胶粘剂剪切蠕变性能研究

本研究设计了“十字交叉法”陶瓷胶粘剂剪切蠕变试验装置,选取刚性环氧树脂及柔性硅酮结构胶进行剪切蠕变试验,研究了环境温度、剪切应力、粘结面积等因素对胶粘剂剪切蠕变的影响,通过模型拟合对胶粘剂的剪切蠕变行为进行了分析和预测,探究了两种胶粘剂的蠕变破坏模式。结果表明:采用十字交叉法能够准确便捷地测试陶瓷胶粘剂的蠕变性能。增大胶粘层柔性、提高环境温度、增大剪切应力都会加速蠕变的发展,但粘结面积对蠕变速率无明显影响。刚性环氧树脂胶粘剂试样的蠕变失效形式为粘结层内聚破坏及界面脱粘,符合时间硬化模型;柔性硅酮结构胶试样失效形式为粘结层内聚破坏,符合Burgers模型。     

Effects of Bonding Layer Characteristics on Strain Transmission and Bond Fatigue Performance

Abstract

Fiber Bragg Grating (FBG) sensor arrays can be used to monitor the mechanical behavior of large composite structures. However, brittle FBG sensors, especially multiplexed FBG sensors can be easily damaged when they are installed in flexible structures. As a protection for brittle FBG sensors, epoxy packaged FBG sensors have been suggested. Packaged FBG sensors are usually installed using epoxy adhesives onto the composite specimen since they have high mechanical, heat-resistance and insulation properties. However, the adhesive could decrease strain transmission from the bonding layer and suffer from aging problem. In this paper, strain transmission and bond fatigue performance of the bonding layer depending on the elastic modulus of adhesive, elastic modulus of packaging material and bonding layer thickness are discussed. Static tests were performed to evaluate the effects of bonding layer thickness and elastic modulus ratio of adhesive to the packaging material on strain transmission. Fatigue tests were performed to evaluate the bond fatigue performance depending on the elastic modulus of the adhesive and bonding layer thickness. It was observed that thin bonding layer with high elastic modulus gave high strain transmission, however, it suffered from debonding problem. The elastic modulus ratio and the bonding layer thickness resulting in high strain transmission while maintaining a long bond fatigue life were found in this study.     

固体火箭发动机粘接界面力学性能的有限元计算及参数分析

基于界面粘接模型假设,采用界面共节点有限元分析方法,计算了粘接系统的应力与应变分布,探讨了各层材料性能参数和结构参数对粘接系统力学性能的影响。结果表明,随着衬层弹性模量增加,应力集中程度严重;绝热层的弹性模量对粘接系统的力学性能影响很小,衬层厚度对应力、应变的分布基本没影响;中间相模量和厚度是影响界面粘接质量的主要因素。高的中间相弹性模量和厚度会使应力集中程度增强,使粘接破坏更趋于内聚破坏而不是界面破坏。合理的中间相参数可改善粘接系统的粘接质量。     

Adhesive Failure of Model Acrylic Pressure Sensitive Adhesives

An axisymmetric adhesion apparatus was used to characterize the adhesive and viscoelastic properties of acrylic block copolymer layers that behave as model pressure sensitive adhesives. The mechanisms of deformation were summarized and related to the structure and linear viscoelastic response of each model adhesive. In cases where the area between the adhesive layer and adhering surface remained circular and shrunk uniformly during detachment, the adhesive failure criterion can be quantified and compared to predictions from linear elastic fracture mechanics. The nature of adhesive failure can not be reconciled with these traditional, low-strain approaches, but is consistent with models of large strain elasticity, provided that the finite thickness of the adhesive layer is taken into account. A dimensionless ratio involving the adhesive strength, elastic modulus and adhesive layer thickness can be used to define the regime in which the adhesive failure criterion can be quantified with linear elastic fracture mechanics.     

Adhesive Failure of Model Acrylic Pressure Sensitive Adhesives

An axisymmetric adhesion apparatus was used to characterize the adhesive and viscoelastic properties of acrylic block copolymer layers that behave as model pressure sensitive adhesives. The mechanisms of deformation were summarized and related to the structure and linear viscoelastic response of each model adhesive. In cases where the area between the adhesive layer and adhering surface remained circular and shrunk uniformly during detachment, the adhesive failure criterion can be quantified and compared to predictions from linear elastic fracture mechanics. The nature of adhesive failure can not be reconciled with these traditional, low-strain approaches, but is consistent with models of large strain elasticity, provided that the finite thickness of the adhesive layer is taken into account. A dimensionless ratio involving the adhesive strength, elastic modulus and adhesive layer thickness can be used to define the regime in which the adhesive failure criterion can be quantified with linear elastic fracture mechanics.     

胶粘剂特性和厚度对劈裂载荷作用下胶接接头应力分布的影响

运用三维弹塑性有限元法对劈裂栽荷作用下的胶接接头(即劈裂接头)承载后的应力分布特征进行了分析，重点研究了胶粘剂层厚度对劈裂接头应力分布的影响。结果表明，胶粘剂的性能对应力分布有较大影响，提高胶粘剂强度和减小胶层厚度，均导致胶层应力集中加剧，各向正应力峰值呈上升趋势，各向剪切应力则正好相反；并且劈裂接头中应力分布以三向主应力为主，剪切应力的存在亦不可忽略。故在不引起过大应力集中和较大胶层缺陷条件下采用高强度的胶粘荆和较厚胶层对提高劈裂接头强度有利，实验结果与有限元分析相吻合。     

The Effect of Viscoelasticity of Polymeric Adhesives on Shear Stress Distribution in a Single-Lap Joint

In this paper, the effect of viscoelasticity of adhesives on shear stress distribution in the adhesive layer of a single-lap joint under shear load is studied. The joint comprises two elastic single isotropic adherend layers joined by a viscoelastic adhesive polymer. A three-parameter viscoelastic solid model is used to deduce the governing differential equation in the Laplace domain, which is solved using residue theorem. Results show that for an impulse load of 100 N, the maximum shear stress in the adhesive layer is reduced to 39% of its initial value. Also, the ratio of viscous modulus of the adhesive to its shear modulus has an adverse effect on the peak shear stress. An increase in the thickness of the adhesive layer reduced the induced peak shear stress in the joint. Moreover, the shear strain in the adhesive layer reached its steady value after 1000 seconds.     

Lead magnesium niobate-filled silicone dielectric elastomer with large actuated strain

A silicone dielectric elastomer filled with lead magnesium niobate with a maximum actuated strain of 7.4% at 45 kV/mm was fabricated by optimizing the amount of dielectric filler, amount of plasticizing agent, and crosslink density of the elastomer. The actuated strain of dielectric elastomers (DEs) is determined by both the dielectric constant and the elastic modulus. Although the dielectric constant of the silicone elastomer increased with increasing loading amount of lead magnesium niobate, actuated strain did not increase as expected because the elastic modulus increased at the same time. The elastic modulus of silicone dielectric elastomer was decreased by reducing the crosslink density or adding plasticizing agent, leading to a visible increase in actuated strain. It was also revealed that actuated strain of silicone dielectric elastomer always goes up with increasing ratio of dielectric constant to elastic modulus. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Evaluation of Residual Stress in a Multilayer Ceramic Capacitor and its Effect on Dielectric Behaviors Under Applied dc Bias Field

The residual stress in a multilayer ceramic capacitor (MLCC) has been evaluated by two-dimensional finite element simulation in combination with X-ray diffraction measurement. It is shown that there is a compressive in-plane stress in the active layers of the MLCC, which increases with increases in the number of dielectric layers when both dielectric layer thickness and electrode thickness are kept constant. A good order of magnitude agreement between the residual stresses obtained from two approaches is found. The ɛ– V response of the MLCC with different number of dielectric layers demonstrates that under a given or no applied field, the dielectric permittivity increases with increasing compressive stress. Additionally, under dc bias field, the higher the compressive in-plane stress existing in the MLCC, the more significant the decrease of the dielectric permittivity. These results can be explained through a phenomenological thermodynamic model, including both elastic and electrostatic energy, based on the Ginsburg–Landau–Devonshire theory.     

Structural Analysis of silica aerogels for the interlayer dielectric in semiconductor devices

As semiconductor devices have become miniaturized and highly integrated, interconnection problems such as RC delays, power dissipation, and crosstalk appear. To alleviate these problems, materials with a low dielectric constant should be used for the interlayer dielectric in nanoscale semiconductor devices. Silica aerogel as a porous structure composed of silica and air can be used as the interlayer dielectric material to achieve a very low dielectric constant. However, the problem of its low stiffness needs to be resolved for the endurance required in planarization. The purpose of this study is to discover the geometric effect of the electrical and mechanical properties of silica aerogel. The effects of porosity, the distribution of pores, the number of pores on the dielectric constant, and elastic modulus were analyzed using FEM. The results suggest that the porosity of silica aerogel is the main parameter that determines the dielectric constant and it should be at least 0.76 to have a very low dielectric constant of 1.5. Additionally, while maintaining the porosity of 0.76, the silica aerogel needs to be designed in an ordered open pores structure (OOPS) containing 64 or more pores positioned in a simple cubic lattice point to endure in planarization, which requires an elastic modulus of 8 GPa to prevent delamination.     

MEMS高g加速度传感器封装贴片技术的研究

针对设计的高g加速度传感器,建立封装有限元模型,并利用ANSYS软件仿真分析了贴片热应力及贴片技术对高g加速度传感器性能的影响.分析结果表明,贴片胶的热膨胀系数、弹性模量和厚度是影响热应力的主要因素,同时贴片胶的弹性模量、厚度及贴片胶的量将影响到传感嚣的输出灵敏度.