旋翼调整片粘接强度分析与影响因素研究

详细分析了旋翼调整片粘接剥离破坏过程和应力分布变化,并研究了粘接宽度和胶层厚度对粘接强度的影响。使用共固化制备相应的粘接试样,通过剥离试验得到接头的破坏模式及载荷-位移曲线。研究结果表明:接头有限元数值分析结果与试验相契合,接头破坏形式为调整片粘接界面的破坏,破坏为从左向右和由边向中逐渐发生失效;粘接强度随胶接宽度的增加而提高,但增长速度逐步变缓,80 mm为较优搭接宽度值;粘接强度受胶层厚度影响较小,增加厚度时粘接强度先缓慢增加后下降。     

衬层预固化程度对衬层/推进剂界面粘接性能的影响

研究了壳体粘接式固体火箭发动机装药中衬层的固化程度对推进剂和衬层间界面粘接性能的影响,采用红外光谱技术对衬层固化过程中微观结构的变化进行了表征,初步探讨了衬层固化程度影响界面粘接强度的机理。结果表明,衬层固化0~8h,-NCO含量迅速下降,衬层与推进剂界面的粘接强度随衬层固化时间的增加而增大;固化8~40h时,衬层中的-NCO含量下降速度减小;衬层与推进剂界面的粘接强度随衬层固化时间的变化不大。     

固体火箭发动机粘接界面变形破坏的细观试验与数值模拟

采用扫描电镜原位拉伸试验观察固体火箭发动机粘接界面试件在拉伸过程的变形和破坏过程,分析了载荷作用下界面失效模式和机理;依据粘接界面细观结构,建立了界面的细观数值模型,考虑了其细观损伤特点,在推进剂内部颗粒与基体之间以及推进剂/衬层之间引入界面元,对界面细观变形和破坏过程进行了数值模拟。结果表明,在外界应变5%时,表现为非均质材料内部应力分布不均,随应变的增加,推进剂内部脱湿形成的微孔洞不断扩展,最终导致界面破坏,界面拉伸失效过程表现为损伤的起裂和扩展,是推进剂内部脱湿和粘接界面脱粘共同作用的结果;界面元能有效地模拟粘接界面的脱粘过程,细观数值计算结果与试验结果吻合,正确反映了粘接界面在拉伸过程中细观损伤萌生与扩展的规律。     

胶粘剂弹性模量对折曲胶接接头应力分布的影响

通过ANSYS有限元软件建立了折曲胶接接头的弹塑性有限元模型,考察了胶粘剂的力学性能参数弹性模量对其应力分布的影响。研究结果表明:四种不同的胶粘剂,其弹性模量越大,胶层中各应力的峰值越大,搭接区被粘物剥离应力峰值逐渐呈现出上升的趋势;当胶粘剂弹性模量为50 MPa时,被粘物的各应力分量存在较大的应力尖角(应力集中现象)。     

应变率对3D打印混凝土抗压性能的影响

为评价应变率对3D打印混凝土动态抗压性能的影响,开展4种应变率下打印混凝土3个正交方向的单轴压缩试验,得到不同加载工况下3D打印混凝土的受压破坏形态和应力-应变曲线,探讨了应变率和不同方向对3D打印混凝土抗压强度、弹性模量、峰值应变及各向异性的影响规律,考虑应变率效应提出3D打印混凝土各个方向动态抗压强度与动态弹性模量的经验计算公式。研究结果表明：3D打印混凝土裂缝萌生于层条间薄弱界面处并沿界面扩展,这些发展于薄弱界面处的裂缝决定了3D打印混凝土的破坏失效;各个方向的动态峰值应力和动态弹性模量均存在一定程度的应变率相关性,Y方向抗压强度率相关性最高;3D打印混凝土的各向异性随着应变率增加而减小,在高应变率下变化幅度很小。     

碳纤维传动轴胶接胶层应力均匀化分析

碳纤维传动轴胶接联接在传递载荷时,会出现端部胶层应力大、中间应力小的现象,这种现象会使胶接接头的胶层首先从端部破坏,影响联接性能。从应变角度阐述胶接胶层应力曲线规律,说明了影响胶层应力分布的因素有胶层内、外周向变形量和胶层厚度,提出几种胶接胶层应力均匀化方法,并用有限元分析方法进行了验证。结果表明:(1)增加胶层厚度可以使胶层应力均匀化,但均匀化程度不明显,且在工程中会增加胶层缺陷;(2)采用变胶层厚度的鼓形结构胶接能够使胶层应力均匀化明显,最后指出影响鼓形胶接胶层应力均匀化的因素有变厚度胶层长度L、胶层的最大厚度H。     

电子胶粘剂界面弱化的机理探讨及影响因素分析

对粘接理论和界面处的微观作用力进行了讨论,并对影响电子胶粘剂界面粘接强度的关键因素进行了探讨。本文研究认为,吸附理论、互锁理论和扩散理论描述的微观作用力对电子胶粘剂的粘接具有重要贡献,而静电理论和吸盘理论描述的微观作用力可以忽略不计;界面化学组成、润湿程度、界面污染、界面形貌、温度和中间相厚度会显著影响界面粘接力。最后从上述关键因素出发,结合相关工程经验,对电子胶粘剂的界面弱化机理进行了梳理。     

复合材料粘接修理结构中胶层的应力分布

利用有限元方法,研究了复合材料粘接修理结构中胶层的弹性模量对其应力分布的影响。分析了胶层出现屈服和未屈服两种情况下,胶层的第1主应力,剥离应力和xy面剪切应力的分布随胶层弹性模量的变化情况。胶层的第1主应力随弹性模量的增大而增大,未屈服时,应力分布梯度也逐渐增大,大部分载荷集中到胶层的端部和破孔边缘。但是,出现屈服时,应力分布梯度则逐渐下降,大部分胶层承担相应的载荷。最大剥离应力出现在胶层的端部,并随胶层弹性模量的增大而增大。胶层两个粘接面的xy面剪切应力分布并不一样,但都随着胶层弹性模量的增大而增大。     

补片尺寸对胶层应力分布的影响

粘接修理结构中,胶层起着传递载荷的作用。其应力状态对于粘接修理结构有着重要的影响。为此,本文用有限元法分析了复合材料粘接修理结构中胶层应力分布随补片尺寸的变化。研究表明,增加补片长度和厚度可以提供补片分担载荷的作用,但是,对胶层的性能要求提高。胶层中大部分区域的应力较低,大部分载荷靠较小面积的胶层传递。修理试样的破坏形式的变化反映了胶层应力分布的变化。     

建筑用碳纤维增强复合板/钢的界面粘接性能研究

采用两种不同胶粘剂(T_c和T₁)对建筑用碳纤维增强复合板(CFRP)/钢进行粘接处理,考察了胶粘剂厚度和种类对碳纤维增强复合板/钢的界面粘接性能的影响,并对其破坏模式进行了分析。研究结果表明:随着胶粘剂厚度增加,T_c胶粘剂试件界面承载力平均值呈现逐渐增加趋势,界面破坏模式从CFRP板层间剪切破坏过渡为胶粘剂耦合层间剪切破坏,并逐渐演变成CFRP板断裂耦合层间剪切破坏模式;T₁胶粘剂试件的界面承载力随着胶粘剂厚度的增加而逐渐减小,界面破坏模式均为CFRP板层间剪切破坏模式。     

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。     

Experimental Investigation of the Interphase in an Epoxy-Aluminum System

The interphase in an epoxy-aluminum system has been revealed and characterized using scanning electron microscopy, ion etching, energy-dispersive x-ray analysis, and nano-indentation. The interphase was of irregular thickness, nominally between 2 and 6 μ, and corresponds to a region of greater resistance to ion etching and a marked absence of the silica particles used in the epoxy adhesive. Nano-indentation tests, traversing various sections of the interphase from the aluminum to the bulk resin, showed that the interphase region had, on average, an effective elastic modulus (E/(1-v²)) that was 13% greater than that of the bulk resin, far from the aluminum. The interphase was also approximately 4% harder than the bulk adhesive.     

Mechanical properties of soft liner–poly(methyl methacrylate)‐based denture material

In this study, the mechanical properties of two different permanent soft lining materials and their bonding to poly(methyl methacrylate) (PMMA) were compared. Both of the soft liners were heat‐cured commercial materials. The polymerization was carried out by conventional methods suggested by manufacturer, and the curing was done at the temperature of boiling water for 5, 15, 25, and 35 min. The sample groups were tested in the computer‐aided tensile‐testing machine at a rate of 2 mm/min. The slow rate helps the collection of more and more reliable data. At this time, the stress–strain curves were used to calculate ultimate tensile strength, elastic modulus, resilience, and toughness. The measurements were carried for PMMA, Molloplast B, Flexor, and a combination of PMMA/soft liner. After introducing the soft lining material on PMMA of the same thickness, the new material structure was more elastic than the original PMMA. Flexor showed adhesive failure at studied curing periods, but Molloplast B gave larger tear strength values and cohesive rather than adhesive failure at the 25‐min and 35‐min curing times. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 467–474, 2002     

Nanoscale characterization of interphase properties in maleated polypropylene‐treated natural fiber‐reinforced polymer composites

Contact resonance force microscopy has been used to evaluate the effect of maleated polypropylene (MAPP) concentration on interphase thickness as well as the spatial distribution of mechanical properties within the interphase of cellulose fiber‐reinforced polypropylene composites. The average interphase thickness values ranged from 25 nm to 104 nm for different concentrations of MAPP. The interphase region showed a gradient in the elastic modulus, with a gradual decrease in modulus from fiber to matrix. The interphase region in the specimen containing 0% MAPP showed a narrow interphase with steep gradient in modulus from fiber to matrix, whereas the use of MAPP significantly increased the interphase thickness which resulted in a more gradual change in modulus from fiber to matrix. POLYM. ENG. SCI., 2013. © Society of Plastics Engineers     

Effects of short fiber tip geometry and inhomogeneous interphase on the stress distribution of rubber matrix sealing composites

The normal and interfacial shear stress distributions with flat fiber tip of short‐fiber‐reinforced rubber matrix sealing composites (SFRC) compared with the shear lag model were investigated by using the finite element method (FEM). The results indicate that stress values do not agree with those calculated by the shear lag model. The effect of different geometrical shapes of fiber tip on the stress distributions of SFRC was also investigated. The geometrical shapes of fiber tip under present investigation are flat, semi‐elliptical, hemispherical, and circular cone, respectively. The results show that the hemispherical fiber tip transfers the load with less stress concentration and is contributed to controlling the interface debonding failure more effectively than other shapes of fiber tip. Further study on the effect of the inhomogeneous interphase properties on the normal and interfacial shear stresses of hemispherical fiber tip was also conducted. The results indicate that the normal stress increases with the increase of the interphase thickness and interfacial shear stress remains unchanged, and the normal stress values of SFRC with interphase are higher than those without interphase. The interphase elastic modulus has no influence on the stress distributions along the direction to the fiber axis. The stress distributions along the radial direction in the interphase end are largely dependent on the interphase elastic modulus, and the interfacial shear stress is larger than the normal stress, which reveals that a significant part of the external load is transferred from the fiber to the matrix through shear stresses within the interphase. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41638.     

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.     

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.     

Multiscale modeling of interface debonding effect on mechanical properties of nanocomposites

Mechanical behavior of SiO₂ nanoparticle‐epoxy matrix composites was investigated via finite element analysis with an emphasis on the nanofiller‐interphase debonding effect using a three‐dimensional nanoscale representative volume element (RVE). The new model, in which a cohesive zone material (CZM) layer is considered as an inclusion‐interphase bonding, can be applied to polymer nanocomposites reinforced by inclusions of different forms, including spherical, cylindrical, and platelet shapes. Upon validation by experimental data, the model was used to study the effects of interphase properties, nanoparticle size, and inclusion volume fraction on the mechanical properties of nanocomposites. According to the results, taking into account the inclusion‐interphase debonding provides more precise results compared with perfect bonding, especially in nanocomposites with nanoparticles of smaller size. Moreover, the outcomes disclosed that the amount of changes in the elastic modulus by particle size variation is higher when the relative thickness (the interphase thickness to the particle diameter ratio) increases. For relative thicknesses lower than a critical value, the particle size and the interphase properties have negligible effect on the elastic modulus of the nanocomposite, and the elastic modulus of nanocomposite mostly depends on nanofiller content. POLYM. COMPOS., 38:789–796, 2017. © 2015 Society of Plastics Engineers     

Experimental and Numerical Study of Adhesively Bonded CFRP Scarf-Lap Joints Subjected to Tensile Loads

The tensile performance of adhesively bonded CFRP scarf-lap joints was investigated experimentally and numerically. In this study, scarf angle and adherend thickness were chosen as design parameters. The lap shear strength is not directly proportional to scarf angle and adherend thickness for the brittle adhesive studied in the paper. The major failure mode includes cohesive shear failure and adherend delamination failure. The results present a stepped failure morphology along the bondline in the adhesive layer. A finite element model based on cohesive zone model was established to further investigate the stress distribution of scarf-lap joints with different lap parameters. The numerical results were compared with the experiment results, showing a good agreement, thus verifying the validity of the established numerical model.     

粘结层对压电纤维复合材料机电响应行为的影响

本文从功能材料力-电耦合的角度分析了粘结层参数对压电纤维复合材料(macro fiber composites, MFC)机电响应行为的影响。通过有限元模拟计算发现,减少粘结层厚度及增大其介电常数有利于缓解MFC介电失配现象,提高有效电场加载,从而获得高压电性。试验制备了MFC并进行了驱动及传感性能表征,试验结果与模拟仿真一致。减少粘结层厚度和弹性模量,及增大其介电常数,能有效增大MFC尖端位移和输出电压,提高驱动和传感性能。该研究对驱动和传感用MFC的设计提供了指导。