复合材料框架胶接接头超声检测研究

针对碳纤维复合材料框架胶接接头的胶接质量问题,提出了使用0.5～10 MHz的宽带窄脉冲探头单侧进行脉冲回波法快速检测。采取试验与理论相结合的方法,采集11种常用接头结构超声波,对其传播特性和检测信号特性进行分析。研究结果表明:试验提出的方法实现了对复合材料框架胶接接头的胶接质量检测,对实际工程检测具有较强的指导意义。     

风电叶片前缘胶接结构的超声检测技术研究

风电叶片前缘为胶接结构,胶接质量的优劣直接影响到叶片的使用寿命。应用超声脉冲回波法对风电叶片前缘胶接结构进行检测,并通过CIVA仿真分析了探头频率对胶接结构超声检测结果的影响。试验采用设计的超声波双晶探头对风电叶片前缘试块进行了检测。分析结果表明,超声波双晶探头能够接收到明显的胶接区域缺陷回波,可以方便地实现风电叶片前缘胶接结构的检测。     

傅里叶变换在玻璃钢复合材料胶接质量检测中的应用

通过对钢/玻璃钢的胶接质量的超声信号进行傅里叶变换并分析,发现超声波在钢里面产生了共振。因胶接良好时玻璃钢对超声信号的衰减使得其共振幅值要明显小于脱粘超声信号,再通过对比不同特征下的超声C扫描图像,发现只有在基频幅值下的超声C扫检测效果和常规超声C扫检测效果一致。因此可以通过超声幅-频曲线来评价钢/玻璃钢的胶接界面是否存在脱粘。     

复合材料叶片包边粘接超声检测方法

新型航空发动机风扇叶片采用了纤维增强树脂基复合材料叶片前缘与薄金属包边粘接的结构。针对叶片包边的材料组成和结构特点,分析了常用的超声穿透法和超声反射法对叶片包边粘接质量检测的适用性,提出了超声C扫穿透法和高分辨超声A扫对面反射法结合的检测方法。结果表明,采用提出的检测方法能够全部检出试样中5 mm×5 mm的Ⅰ界面和Ⅱ界面人工脱粘缺陷,且可有效地检测实际产品中的包边脱粘缺陷。     

复材/复材二次胶接胶接质量及强度影响因素研究

通过不同尺寸的高温结构胶-双马基碳纤维层压板的二次胶接试验,对二次胶接过程中影响胶接内部质量和胶接强度的因素进行了分析。结果表明,在胶接反应过程中,复材板与复材板之间的实际配合间隙大于复材板制造的叠合公差,准确测量配合间隙及适当进行胶膜补充是提高胶接质量的重要保障,通过模拟胶接过程来测量配合间隙可行。对大尺寸胶接界面,通过提高胶膜的流动性能够提高胶接质量,但却降低了胶接强度。胶接强度随胶膜厚度增加而增加,但达到极值后随胶层厚度的增加而减小。     

配合间隙对蜂窝夹层结构板芯胶接质量的影响与研究

设计制作了一系列带有不同配合间隙的蜂窝夹芯结构试验件,并对试验件的内部性能和机械性能进行了测试,分析了配合间隙对蜂窝夹层结构胶接性能的影响。研究发现当蜂窝芯与面板的配合间隙大于胶膜的厚度时就会发生板芯脱粘;当使用发泡胶对配合间隙部位进行局部补偿时,可以获得合格的板芯胶接质量,且不降低结构的机械性能;对配合间隙使用胶膜校验检测时,低真空度有利于校验结果的可靠性,从而确保板芯的胶接质量;且蜂窝芯型面加工成阶梯状相比斜平面更有利于板芯胶接的质量。     

复合材料泡沫夹层结构的缺陷评定方法研究

本文以厚壁碳纤维复合材料为面板,硬质聚氨酯泡沫为芯材制造复合材料泡沫夹层结构,模拟实际生产过程中容易出现的面板与芯材之间界面的脱粘和界面胶层过厚的现象,采用人工制造试块的方法,研究了超声波探伤对夹层复合材料缺陷的评定方法,解决了实际检测过程中的疑问,为夹层复合材料结构产品的质量检验提供依据。得出了粘接良好区胶层过厚不会被判定为脱粘的结论。     

VARI成型泡沫夹层复合材料界面质量控制方法研究

采用本体树脂涂覆、胶膜和辅助织物粘贴在泡沫加工表面的方法分别改善胶接界面,解决了真空树脂浸渗工艺(VARI)制备的非屈曲碳纤维织物(NCF)/聚甲基丙烯胺(PMI)泡沫夹芯复合材料中泡沫与蒙皮的脱粘问题。结果表明,在相同VARI工艺参数条件下,采用890树脂涂覆的方法可以达到大约80%区域面积的良好粘接界面,对应的抗平拉强度提高了30%;同时胶膜和辅助织物粘贴方法则可达到接近100%改善胶接界面质量的效果,其对应的抗平拉强度则分别提高了76%和56%。     

碳纤维复合材料蜂窝夹层结构的无损检测方法研究

本文介绍了碳纤维复合材料蜂窝夹层结构常见的内部缺陷,这些缺陷的存在将直接影响蜂窝结构的机械性能和工作性能,必须对其进行无损检测。利用超声脉冲反射法对其内部缺陷进行检测作了详细介绍,分别对复合材料蒙皮可能出现的分层、疏松和高空隙率缺陷及蒙皮与蜂窝夹芯之间界面的脱粘缺陷进行检测,对出现的波形进行分析,并判断波形产生的原因,认为超声脉冲反射法对碳纤维复合材料蜂窝夹层结构内部缺陷检测是一种行之有效的方法。     

网络化智能液位仪设计

介绍具有两个超声波换能器为检测探头的网络化智能液位仪的实现,具有温度补偿和自诊断功能.仪表以Microchip公司的PIC18F258单片机为核心,驱动超声波探头发出脉冲信号,回波信号被超声探头接收,转换成脉冲电压,利用单片机内嵌的捕捉功能测出时间,从而测得距离;通过两个探头获得数据的比较,实现系统的自诊断和校正功能;用软件保证传感器在网络上通信时有最大传输速率.仪表已经进入实用化阶段,核心部分已申报发明专利(200610097403.8)和实用新型专利(200620124925.8).     

FRP筋加固砌体结构界面粘结性能的研究现状

表面嵌入式(NSM)加固法为纤维增强塑料筋(FRP筋)加固砌体结构常用的方法,FRP筋脱粘破坏为其首要的破坏形态,研究FRP筋与砌体间的粘结性能和脱粘机理成了这项加固技术的关键。综述了国内外学者关于拉拔试验、界面剪切试验、弯曲试验以及数值模拟的研究进展,对NSM-FRP筋加固砌体结构的界面粘结性能进行了研究。研究发现加固砌体结构的变形能力、能量耗散能力和延性得到了显著增加,增加FRP筋的埋设深度可以有效提高脱粘荷载。最后使用收集到的试验数据对各种粘结性能相关公式进行了校核,对今后拟开展的研究提出了建议。     

Direct Observations of Debonding of Reinforcing Grains in Silicon Nitride Ceramics Sintered with Yttria Plus Alumina Additives

As in fiber-reinforced composites, debonding, which allows the elongated reinforcing grains to at least partially separate from the rest of the matrix, is a critical part of the toughening mechanism in self-reinforced silicon nitrides. In situ high-resolution electron microscopy observations reveal that the debonding path can occur at the interface between the grains and continuous nanometer-thick intergranular film (IGF) or within the IGF depending on the film's composition, which varies with the yttria to alumina ratio in the fixed total amount of sintering additives. Theoretical calculations reveal that the bonding across the interface can be weakened by decreasing the Al and O content ( z ) of the epitaxial Si_{6– Z} Al _Z O _Z N_{8– Z} layer on the grains, which is consistent with the observations of interfacial debonding. However, evidence also indicates that weakening of the amorphous network of the IGF occurs with increase in yttrium levels that can be responsible for the observed mixture of debonding by crack propagation along the interface and within the IGF when the sintering additive contains the highest yttria:alumina ratio.     

氯丁橡胶与金属热硫化型胶膜的研究

采用机械共混法和胶料成膜技术制备出一种酚醛树脂(PF)-橡胶型膜状胶粘剂(胶膜)。结果表明:当n(37%甲醛)∶n(苯酚)∶n(氢氧化钠)=1.8∶1∶0.1、反应温度为70℃和反应时间为2.5 h时,合成的甲阶PF具有较高的羟甲基含量(28.3%),满足PF-橡胶型胶膜的制备要求;当m(氯丁橡胶)∶m(氯化天然橡胶)∶m(PF)∶m(炭黑)=100∶(5～10)∶(70～80)∶40、m(PF)∶m(硼酚醛树脂)=4∶1时,胶膜的剪切强度超过5.0 MPa、180°剥离强度超过4.0 kN/m且胶接件的破坏形式多为橡胶内聚破坏;该胶膜具有较好的热稳定性(热失重温度为300℃左右),满足氯化橡胶生胶片与金属之间的热硫化胶接要求;该胶膜与适宜底胶配合而成的双涂型胶接体系,可实现氯化橡胶生胶片与树脂基复合材料之间的热硫化胶接。     

On the shock-based determination of the adhesive strength at a substrate-coating interface

Evaluating the bonding strength at the interface between two layers is an issue of considerable practical interest for a wide variety of engineering applications involving coatings, such as thermal protective ceramics coated on engine blades. Spallation under laser driven shock loading is one of the experimental means to test interface debonding. However, numerical simulations are usually needed to infer a quantitative value of the bonding strength from such tests, where the coating free surface velocity is usually the only measurable variable. In this paper, the analysis of the propagation and interactions of compression and release waves leading to spall fracture in a shock-loaded material is detailed, then it is extended to a substrate-coating system. Different cases are considered, depending on the acoustic impedances of the substrate and coating materials and on the duration of the loading pressure pulse with respect to the wave transit time through the coating thickness. In each case, the interfacial strength can be analytically estimated from the velocity variations without resorting to numerical models.     

复合材料孔隙含量超声检测系统的设计研究

本文结合碳纤维复合材料内部孔隙含量的超声检测理论模型,阐述了计算机控制超声检测系统数据采集和数据处理的原理和实施方法.重点对数字超声卡的操作、时域波形信号的处理、复合材料孔隙率的C扫描成像显示以及直方图分析等关键问题进行分析研究,开发相应的软件应用模块,构建合适的自动化超声检测系统,以满足实际工程中超声检测的要求.     

Low energy impact on the interface of bamboo-steel composites

The bamboo-steel composite structure is a newly developed structure, combining Phyllostachys Pubescens (also called Moso bamboo) plywood and cold-formed thin-walled steel with structural adhesive. The aim of this study is to investigate the debonding propagation mechanism in detail at the bamboo-steel adhesive bonding interface (bamboo-steel interface) under low-energy impact using a progressive failure model. A three-dimensional cohesive zone model with reloading traction-separation law was adapted to simulate and characterize the progressive adhesive debonding at the bamboo-steel interface. Results show that the model can predict the failure behavior of the bamboo-steel interface under low-energy impact. The stress distribution and debonding propagation of the bamboo-steel interface were analyzed. The results reveal that the debonding is mostly due to the shear stress and the tensile peeling stress at the impact loading stage and the unloading stage, respectively. Furthermore, analyses of the impact failure show that the shear stress at the impact loading stage is generated by the tangential sliding between the steel sheet and bamboo plywood due to different flexural stiffness, while the tensile peeling stress at the unloading stage is due to the normal separation owing to different rebounding of the two different materials.     

可聚合琥珀酸双酯磺酸钠乳化合成聚丙烯酸酯纳米乳液

采用半连续种子乳液聚合工艺,在可聚合乳化剂十六烷基烯丙基琥珀酸双酯磺酸钠(Ⅰ)和辛基酚聚氧乙烯醚烯丙基琥珀酸双酯磺酸钠(Ⅱ)存在下,合成了聚丙烯酸酯纳米乳液,探讨了可聚合乳化剂种类及用量、聚合温度、引发剂用量、聚合时间对丙烯酸酯乳液聚合及性能的影响,通过FTIR、TEM和DSC对聚合产物进行了表征分析。结果表明,可聚合乳化剂参与了与丙烯酸酯的共聚反应,所得聚合物乳胶膜的玻璃化温度为23.5℃;与传统乳化剂十二烷基硫酸钠(SDS)相比,可聚合乳化剂可提高乳胶膜的耐水性;当m(Ⅰ)∶m(Ⅱ)=1∶2,乳化剂质量分数2%,聚合温度85℃,引发剂质量分数0.5%,聚合时间2 h时,所得乳液的固体分质量分数为32.70%,平均粒径72.3 nm,分布指数0.143,吸水率4.57%。     

Direct Observation of Cavitation and Fibrillation in a Probe Tack Experiment on Model Acrylic Pressure-Sensitive-Adhesives

The adhesion mechanisms of two acrylic Pressure-Sensitive-Adhesives on a stainless steel probe are investigated with a custom-designed probe tack apparatus. Our setup allows the simultaneous acquisition of a nominal stress and strain curve, and the observation of the adhesive film from underneath the transparent substrate. The temperature was varied in the range -20°C to 50°C and the debonding rate in the range 1–10000 μm/s. For all conditions we observed, upon debonding, the formation of cavities at or near the interface between the probe and the film. These cavities initially grew predominantly in the plane of the film but, at higher values of nominal strain, the walls between the cavities were stretched in the direction normal to the plane of the ifim to become a fibrillar structure. The transition from a cavitated structure to a fibrillar one was only found within a time-temperature window of rheological properties of the adhesive, while the adhesion energy was found to be mainly related to the elongational properties of the adhesive. The maximum tensile stress observed in the probe tack experiment was directly related to the appearance of the cavities and showed a good correlation with the shear modulus of the adhesive, while the adhesion energy was found to be mainly related to the elongational properties of the adhesive. The presence of 2% acrylic acid as a comonomer had a negligible effect on the maximum stress but a very important one on the formation of a fibrillar structure and on the locus of failure.     

Direct Observation of Cavitation and Fibrillation in a Probe Tack Experiment on Model Acrylic Pressure-Sensitive-Adhesives

The adhesion mechanisms of two acrylic Pressure-Sensitive-Adhesives on a stainless steel probe are investigated with a custom-designed probe tack apparatus. Our setup allows the simultaneous acquisition of a nominal stress and strain curve, and the observation of the adhesive film from underneath the transparent substrate. The temperature was varied in the range -20°C to 50°C and the debonding rate in the range 1-10000 μm/s. For all conditions we observed, upon debonding, the formation of cavities at or near the interface between the probe and the film. These cavities initially grew predominantly in the plane of the film but, at higher values of nominal strain, the walls between the cavities were stretched in the direction normal to the plane of the ifim to become a fibrillar structure. The transition from a cavitated structure to a fibrillar one was only found within a time-temperature window of rheological properties of the adhesive, while the adhesion energy was found to be mainly related to the elongational properties of the adhesive. The maximum tensile stress observed in the probe tack experiment was directly related to the appearance of the cavities and showed a good correlation with the shear modulus of the adhesive, while the adhesion energy was found to be mainly related to the elongational properties of the adhesive. The presence of 2% acrylic acid as a comonomer had a negligible effect on the maximum stress but a very important one on the formation of a fibrillar structure and on the locus of failure.