开孔聚酰亚胺泡沫粘接性能研究

探讨了BHPI-J-2010胶粘剂的固化度、耐热性、固化工艺、粘接铝的拉剪强度及粘接聚酰亚胺泡沫的可行性;研究了BHPI—J-2010胶粘剂粘接聚酰亚胺泡沫／45号钢的拉伸性能及固化工艺;考查了开孔聚酰亚胺泡沫／45号钢粘接试样高温拉伸和蠕变性能及胶粘剂的使用寿命。结果表明,BHPI—J-2010胶粘剂对开孔聚酰亚胺泡沫具有良好的粘接性能。     

室温固化丙烯酸结构胶的研究

为了满足快速粘接的需要,采用甲基丙烯酸环氧酯和烯类单体制备了一种室温快速固化的结构胶。研究了复合稳定剂对胶体稳定性的影响。测试了粘接时间对粘接强度的影响。结果表明：复合稳定剂用量在0．02％以上时,胶体能稳定贮存一年以上;粘接强度在固化初期明显增长,12h达到最高强度的90％以上;胶体无气味,使用方便,固化速度快,强度增长快,粘接强度高。该结构胶能满足快速粘接、特别适合动荷载情况下快速粘接的使用要求,具有良好的市场前景。     

非异氰酸酯聚氨酯固化剂的制备及性能研究

以间苯二酚二缩水甘油醚为原料,通过CO2插入法合成环碳酸酯化合物（RDGEC）。将其与聚醚胺（D230）聚合,调控比例,制备了系列非异氰酸酯聚氨酯（NIPU）固化剂。详细考察了NIPU与双酚A环氧树脂（E-51）共混体系的固化动力学,对固化试样的粘接性能、热机械性能、热稳定性及断裂面的微观状态进行了研究。研究结果表明：成功制备了RDGEC和系列NIPU固化剂;调控RDGEC与D230反应比例对NIPU的固化反应活性影响较小,但能够有效改变固化体系韧性程度,确定固化工艺为50℃/2 h+100℃/2 h;NIPU与E-51混合固化体系对铝合金具有优异的粘接性能,调控RDGEC与D230比例至1∶1.75时,25℃剪切强度和70℃剪切强度分别为36.98和14.51 MPa,25℃下90°剥离强度达到6.08 kN/m,粘接性能达到最佳;该系列固化试样均表现出优异的热机械性能和热稳定性。     

J-338金属网复合膜的工艺性研究

主要通过剪切强度和90°剥离强度两种测试方法,研究了3种J-338金属网复合膜在不同固化时间、不同固化压力等工艺参数下的粘接强度,据此确定了J-338胶膜的固化工艺参数。J-338胶膜与T300/BA9913预浸料按此固化参数共固化,测试了其在-55℃、23℃和70℃下的粘接强度,并制作了5个工艺典型件。试验结果表明,J-338胶膜与T300/BA9913预浸料固化参数匹配较好,有较好的使用工艺性,对平板类结构有一定变形影响,应用时应避免预浸料表面0°铺层,尽量采用45°方向铺层。     

工艺条件对拉伸试件粘接强度分散性的影响

以铝和丁基橡胶的粘接拉伸试件为研究对象,结合粘接过程被粘面表面处理、涂胶、加压、固化等主要工序,讨论了粘接工艺方式和粘接过程控制对拉伸试件粘接强度分散性的影响。结果表明,在粘接过程中采用适当的表面处理方法、涂胶方式,确定适当的加压压力、涂胶厚度和固化条件,有利于减小粘接件拉伸强度数据的分散性并提高粘接强度。     

仿瓷胶粘剂的研究

本文介绍一种仿瓷环氧胶粘剂,该胶耐酸耐碱,可室温固化,在室温下粘接不锈钢试样,其剪切强度可达30.7MPa;而在130℃时其剪切强度为1.7MPa。可用于修复搪瓷,粘接金属和陶瓷等。     

UV胶粘接ABS固化速率的研究

介绍了紫外光固化速率的基本概念和特点,讨论了光引发剂、预聚物、活性稀释剂及氧阻聚对ABS粘接时固化速率的影响.     

共固化成型无人机用复合材料/蜂窝夹层结构面板的性能

针对无人机结构工程设计和工艺方案需要,通过试验比较几种预浸料在共固化成型工艺状态下制备的蜂窝夹层结构面板与在相同固化工艺条件下制备的层压板的力学性能,得出可直接采用共固化工艺制造无人机飞机机体结构的结论.性能结果显示,由所选择的适用于共固化工艺的预浸料所制备的面板与层压板试样的力学性能基本是相当的,但面板的层间剪切强度却明显比层压板的低.     

新型可见光固化口腔正畸粘合剂研制

介绍了一种新型可见光固化正畸粘合剂的组成、性能及正畸粘接的工艺。此粘合剂由一种单组分液体底胶和单组分糊剂组成。与化学固化粘合剂相比,其操作使用方便,固化时间短。这种新型粘合剂的粘接强度完全满足了正畸粘合剂的要求。     

异氰酸酯底胶对压敏胶粘接性能的影响

了异氰酸酯底胶对于提高压敏胶粘接性能的影响，分别以单面和双面压敏胶带与钢、铝、铜、玻璃试片粘接，制备了剥离试样和拉剪试样，并分别测试了性能。结果发现，对于两种试样，异氰酸酯 胶均可大幅提高其粘接强度，适当延长涂底胶后的晾置时间，以及贴合后的放置时间有利于粘接性能的提高。     

Vaporized solvent bonding of polymethyl methacrylate

This investigation highlights rationale of vaporized solvent bonding for fabrication of transparent polymers such as polymethyl methacrylate (PMMA) in terms of optical transparency and bond strength. Vaporized solvent bonding is employed to fabricate the polymer, and its bonding characteristics with appropriate solvents are analyzed. It is observed that chloroform exhibits superior bonding characteristics in comparison with other solvents such as acetone, ethanol, and dichloromethane. In order to see the effect of prior surface modification carried out by ultraviolet (UV) irradiation and low-pressure plasma, surface energy of the polymer was estimated. It is observed that due to surface modification of PMMA by UV irradiation and low-pressure plasma, surface energy of the polymer increases considerably. However, due to exposure under UV irradiation and low-pressure plasma, molecular weight of PMMA decreases and atomic force microscopy (AFM) studies reveal that the topography of PMMA changes significantly resulting in deterioration of vaporized solvent bonding strength. Therefore, in the case of vaporized solvent bonding, increase in surface energy of the polymer is not a primary factor rather retention of molecular weight is more necessary.     

Estimation of Weibull parameters for the flexural strength of PMMA‐based bone cements

The wide scatter of data observed in the strength of bone cements based on poly(methyl methacrylate) (PMMA) can be described properly by the two‐parameter Weibull function. However, the statistical character of the distribution leads to an uncertainty in the parameters evaluated from a limited number of experiments. This study is concerned with the analysis of the methods of estimation as well as sample size on the estimates of the Weibull parameters. The maximum likelihood method, moments method, and linear regression method were studied. Monte Carlo simulations were carried out in order to assess the influence of the number of specimens tested on the Weibull parameters calculated by the different methods. The number of specimens tested displayed a large influence upon the calculated Weibull modulus. By applying weighing factors to the linear regression method, the standard deviation of Weibull parameters decreased significantly. As a compromise between minimizing both the dispersion of the evaluation method and the experimental effort, the use is suggested of the linear regression method with a minimum number of 20 specimens in a nonweighted analysis and 10 in a weighted analysis.     

Effect of Argon Plasma Pretreatment on Tensile Bond Strength of a Silicone Soft Liner to Denture Base Polymers

This study evaluated the effect of argon plasma treatment on tensile bonding of heat-cured and auto-polymerized acrylic resins prior to the processing of a silicone soft liner. Both types of polymethylmethacrylate (PMMA) resins were treated with argon plasma for 1 min or 10 min (n = 5). A control group, including untreated resin specimens, was also formed. After processing of the soft liner, the specimens were deflasked and stored dry for 24 h, and they were then subjected to tensile bond strength testing. In order to see the plasma effect on the resin surface chemistry, representative specimens were analysed by XPS. Highest tensile bond strengths were observed in the 1-min exposure group for each resin, and 10-min exposure yielded the lowest bond strength likely due to the damaging effect of the plasma treatment. XPS analysis showed that the O/C ratios increased greatly in treated samples and that the binding energy values were not significantly changed.     

Friction spot welding of PMMA with PMMA/silica and PMMA/silica-g-PMMA nanocomposites functionalized via ATRP

In the present study, the feasibility of Friction Spot Welding (FSpW) of a commercial-grade poly(methyl methacrylate) (PMMA) (PMMA GS) and PMMA 6N/functionalized silica (SiO₂) nanocomposites was investigated. The silica nanoparticles were functionalized via atom transfer radical polymerization (ATRP) with PMMA chains to achieve a uniform dispersion in the polymer matrix. The successful functionalization of silica nanoparticles with PMMA chains via ATRP was evaluated by ATR-FT-IR and TGA measurements. Rheological investigations of the silica nanocomposites showed a plateau of the storage modulus G′ at low frequencies (0.01–0.03 rad/s) as a result of elastic particle–particle interactions. Overlap friction spot welds consisting of PMMA GS and a 2 wt% SiO₂-g-PMMA nanocomposite were successfully prepared and compared to spot joints of PMMA GS welded with PMMA 6N and PMMA 6N/silica nanocomposite with 2 wt% unfunctionalized silica nanoparticles. Raman mappings of selected areas of cross-sectional plastographic specimens revealed an increased mixing behavior between the two polymer plates in the case of PMMA GS/2 wt% SiO₂-g-PMMA joints. Although the joints welded with PMMA 6N/silica nanocomposites showed a reduction of 22% in lap shear strength and 21% displacement at peak load compared with the neat PMMA spot welds, they can compete with other state-of-the-art PMMA welding techniques such as thermal bonding and ultrasonic welding, which indicates the potential of friction spot welding as an alternative fabrication technology for joining future nanocomposite engineering parts.     

Strength Analysis of Yttria-Stabilized Tetragonal Zirconia Polycrystals

Tensile strength of Y₂O₃-stabilized ZrO₂ polycrystals (Y-TZP) was measured by a newly developed tensile testing method with a rectangular bar. The tensile strength of Y-TZP was lower than that of the three-point bend strength, and the shape of the tensile strength distribution was quite different from that of the three-point bend strength distribution. It was difficult to predict the distribution curve of the tensile strength using the data of the three-point bend strength by one-modal Weibull distribution. The distribution of the tensile strength was analyzed by two- or three-model Weibull distribution coupled with an analysis of fracture origins. The distribution curve of the three-point bend strength which was estimated by multimodal Weibull distribution agreed favorably with that of the measured three-point bend strength values. A two-modal Weibull distribution function was formulated approximately from the distributions of the tensile and three-point bend strengths, and the estimated two-modal Weibull distribution function for the four-point bend strength agreed well with the measured four-point bend strength.     

Accurate determination of fiber strength distributions

Tensile strengths of small‐diameter ceramic fibers are commonly obtained from measured fracture loads on individual fibers and the average cross‐sectional area of the entire fiber population. The goal of the present article is to provide a critical assessment of the consequences of using the average fiber area in the inferred strength distribution. The issues are addressed through established theorems in convolution and uncertainty propagation as well as Monte Carlo simulations. Systematic errors introduced by using the average area are well‐represented by simple analytical formulae. The formulae are couched in terms of the coefficient of variation in fiber area and the dispersion in fiber strengths, characterized by the Weibull modulus. In turn, the formulae are used to determine the true values of Weibull modulus and reference strength from their nominal values. Random uncertainties associated with a finite number of tests decay slowly with number, in accordance with an inverse root scaling. When systematic errors are conflated with random uncertainties, accurate determination of the true Weibull modulus becomes increasingly challenging, even for seemingly large numbers of strength measurements. The results are used to assess the fidelity of previously‐reported experimental results based on nominal strength data.     

Analysis of Fracture Probabilities in Nonuniformly Stressed Brittle Materials

The results of theoretical studies on the effect of nonuniform stress fields encountered in prismatic beams under bending on the fracture of brittle materials are described. Derivations were carried out to determine the risk of rupture of bending specimens subjected to a symmetrical four-point load of arbitrary spacing, the symmetric three-point loading and pure bending forming limiting cases of this more general loading. The analysis was based on materials obeying the Weibull distribution function with assumptions for either volumetric or surface flaw dispersion conditions. The predicted strengths of bending and tensile specimens are compared. An analytical method for the determination of the three Weibull parameters from a pure bending test is proposed. This method, based on the best fit of a theoretical curve to the experimental data, was applied successfully to experimental results on Columbia Resin, a brittle amorphous polymer.     

Fatigue performance of DIARC® plasma coated bonded metal specimens

The fatigue performance of DIARC^® vacuum plasma surface treatment for titanium, stainless-steel and aluminium structural bonding was tested with double lap shear test specimens. In the metal surface treatment, a nanoscale DIARC Bindo coating is deposited on the substrates in a vacuum chamber. The DIARC-treated surface is ready for bonding and does not require any additional treatments, chemicals or primers containing hazardous CrVI chromium. Finite element method was used in analysing the test specimens. The tests were performed at room temperature dry and at room temperature after hot and wet exposure. The specimens were cycled with constant amplitude loading until failure or until 10 million cycles. The fatigue performance of the DIARC coating was found acceptable. There were no interfacial failures between the DIARC coating and metal or between the DIARC coating and adhesive. The residual strengths of all specimens after 10 million cycles were comparable to the static strength.     

Effect of talc/MMA in situ polymerization on mechanical properties of PVC‐matrix composites

In this study, polymethyl methacrylate (PMMA)‐coated talc was produced by the in situ polymerization of methyl methacrylate on the talc surface. The polymerization reaction was performed by both batch and semicontinuous emulsion processes. The polymerization kinetics, particle size and distribution, grafting efficiency, and coated‐talc morphology were systematically investigated. It was found that the talc particles have no effect on the polymerization of PMMA. The PMMA produced was found to cover the talc surface well. However, only a small amount can be grafted onto the talc. The size distribution of talc particles treated by semicontinuous emulsion polymerization is more uniform than by batch polymerization. The treated talc was subsequently used as filler in a poly(vinyl chloride) (PVC) matrix, and mechanical properties of the PMMA‐coated‐talc/PVC composites were studied. Morphological structure of PVC‐matrix composites revealed that the PMMA coating on talc improved the dispersion of talc in the PVC matrix and enhanced the interfacial adhesion between the talc and PVC. The mechanical properties of the composites, especially the impact strength, were found to be improved. There appears to be a critical covering thickness of PMMA on the talc surface for optimum toughening. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 2105–2112, 2001     

Mechanical property and gas filtration behavior of porous reaction bonded Si3N4 with monodispersed PMMA as pore former

Porous Si₃N₄ ceramics were prepared by gel casting combined with a reaction bonding route using monodispersed PMMA as the pore former, and Isobam was used as a gel agent. With the PMMA addition varying from 0 to 20 wt.%, the bending strength was degraded from 94.0 to 39.1 MPa owing to the increased porosity and decreased bulk density. The β-Si₃N₄ prismatic grains and round pores introduced by the monodispersed PMMA micro balls would endow the samples with high strength, and the permeability of the resulting samples was increased obviously with the increase of PMMA addition. Flue gas filtration test exhibited that the filtration efficiency of the porous ceramics filter was not degraded with introducing of the PMMA pore former, even though the permeability was increased obviously. The block type of the sample with 20-wt.% PMMA additions during filtration was cake filtration, which indicates that the sample has the characteristic of being reusable after back-blowing in flue gas filtration applications. Porous Si₃N₄ with high strength and permeability fabricated via the reaction bonding route exhibits great potential for low-cost high-performance ceramics filters.