线膨胀系数对拉伸剪切性能的影响

为获得高强稳定的粘接,绝不可忽视被粘材料和胶黏剂的线膨胀系数对粘接件力学性能的影响。西北工业大学理学院高分子研究所对此进行了专门实验研究,采用改性环氧胶黏剂粘接不同的材料,并对粘接件进行拉伸剪切强度测定和温度影响试验,试验条件为120℃／8h＋180℃／2d,得出了很有价值的结论：（1）被粘材料线膨胀系数不同,使胶层在热冷（热处理和冷却）变化过程中受内应力作用而破坏,同时热空气进入胶层而使胶层氧化变色,致使胶黏剂界面结合强度和胶黏剂本身强度降低,结果拉伸剪切强度下降。例如,     

硅溶胶改性紫外光固化环氧丙烯酸酯胶黏剂的研究

以正硅酸乙酯（TEOS）为无机前驱体,γ-甲基丙烯酰氧丙基三甲氧基硅烷（KH-570）为偶联剂,HCl为催化剂,采用溶胶-凝胶（Sol-Gel）法制得了硅溶胶,并以此硅溶胶对自制的紫外光固化环氧丙烯酸酯（EA）胶黏剂进行改性。通过傅立叶红外光谱（FT-IR）表征了EA的结构,通过热分析以及力学性能测试表征了此复合胶黏剂的热性能以及力学性能。结果表明：硅溶胶的加入显著地提高了环氧丙烯酸酯胶黏剂的耐高低温性能以及热稳定性,当硅溶胶的固体质量为体系总质量的40%时,复合胶黏剂在-196℃、室温、100℃的拉伸剪切强度分别提高了600%、320%、400%;热分解温度提高了50℃。     

长适用期丙烯酸酯结构胶黏剂的研究

室温固化丙烯酸酯胶黏剂由于适用期短,操作时间不够的问题限制了其在粘接较大面积材料中的应用。制备了一种适用期为40min的丙烯酸酯结构胶黏剂,并对其进行了含磷丙烯酸酯对适用期影响的研究,探讨了长适用期丙烯酸酯结构胶黏剂的耐温性能、耐热老化、耐水老化性能,采用热重分析对胶黏剂进行了分析。结果表明:含磷丙烯酸酯含量为3%时,胶黏剂适用期可达40min;制备的丙烯酸酯胶黏剂耐温性能较好,80℃和100℃剪切强度分别为11.75MPa、6.49MPa;丙烯酸酯胶黏剂经100℃老化8000h后,80℃和100℃剪切强度上升分别为14.04MPa、8.54MPa,室温和60℃剪切强度下降分别为14.76MPa、14.21MPa;在耐水老化8000h后,60℃和80℃剪切强度变化很小分别为17.62MPa、11.52MPa。     

环氧-酮酐耐高温胶黏剂的制备与研究

制备了环氧树脂-二苯酮四羧酸二酐(BTDA)耐高温胶黏剂。通过BTDA/E51的比例与胶黏剂剪切强度关系,证明BTDA/E51在60%~80%之间,胶黏剂在常温和高温(230℃)下力学性能优异。研究了不同固化机制下胶黏剂力学性能。测定了胶黏剂在各温度下的剪切强度,表明室温到230℃之间,力学性能稳定。通过TGA分析以及热老化评价,表明胶黏剂的耐热性能优异。通过与市售ECCOBAND-104强度比较,表明该环氧-酮酐胶黏剂耐热稳定性更高。     

改性丙烯酸酯结构胶黏剂的研制

研制了一种对粘接表面处理要求不严格的丙烯酸酯结构胶黏剂.胶黏剂体系中加入粘接促进剂含磷丙烯酸酯,使铝合金表面在除油的情况下,丁腈橡胶含量在16%时,剥离强度可达到4.5N/mm,剪切强度达到28.3MPa.胶黏剂在耐水1000h后,20℃剪切强度为27.6MPa,100℃剪切强度为11.9MPa.胶黏剂在100℃老化5...     

硅烷偶联剂及其水解物对环氧树脂拉伸剪切强度的影响

以双酚A和环氧氯丙烷为原料,通过缩聚反应制得环氧树脂;将硅烷偶联剂γ-甲基丙烯酰氧基丙基三甲氧基硅烷(KH-570)在酸催化下水解,得到水解物。探讨了KH-570及其水解物用量对环氧树脂胶黏剂拉伸剪切强度的影响。结果表明,不加KH-570及其水解物时,环氧树脂胶黏剂的拉伸剪切强度最大为2.47 MPa;只加KH-570水解物时,环氧树脂胶黏剂的拉伸剪切强度最大为3.28 MPa;只加入KH-570时,环氧树脂胶黏剂的拉伸剪切强度最大为5.23 MPa。在KH-570水解物与环氧树脂的质量比相同条件下,随着KH-570用量的增大,环氧树脂胶黏剂的剪切强度先增后减,在KH-570的用量为环氧树脂质量的15%时达到最大;相同KH-570用量下,随着KH-570水解物用量的增大,环氧树脂胶黏剂的剪切强度先增后减,在KH-570水解物和环氧树脂的质量比为5∶5时达到最大。当KH-570的用量为环氧树脂质量的15%、KH-570水解物与环氧树脂的质量比为5∶5时,环氧树脂胶黏剂的拉伸剪切强度达到9.36 MPa。     

新型含羟基的聚氨酯丙烯酸酯/环氧丙烯酸酯胶黏剂的研制

以异佛尔酮二异氰酸酯(IPDI)、聚丙二醇(PPG)、4,5-环氧环己烷-1,2-二甲酸二缩水甘油酯(TDE-85)、丙烯酸(AA)及缩水甘油为原料合成了新型含羟基的聚氨酯丙烯酸酯(PUA)预聚物和TDE-85环氧丙烯酸酯(EA)预聚物,探讨了温度对反应的影响。通过傅立叶红外光谱(FT-IR)分析证实了PUA和EA的结构。用扫描电镜(SEM)、力学性能测试对该两种基体树脂的相容性、以此复合树脂配置成胶黏剂的拉伸剪切强度进行了研究。结果表明:在PUA/EA体系中,当二者的比例为50/50时,综合性能最好,25℃时拉伸剪切强度为13.4MPa,-196℃时为12.9MPa。     

蓖麻油基多元醇改性聚氨酯胶黏剂的研究

以绿色可再生的蓖麻油(CO)和甘油为原料进行酯交换,然后将其产物(P-CO)与六氢苯酐(HHPA)进行酯化反应制备了蓖麻油基多元醇(P-HHPA-CO),将P-HHPA-CO和甘油代替传统的石油类多元醇,与异氟尔酮二异氰酸酯(IPDI)在无催化剂条件下合成了环保型脂肪族聚氨酯胶黏剂,并对不同NCO/OH摩尔比制备的聚氨酯胶黏剂涂膜进行了热重分析、差示扫描量热分析、拉伸力学性能测试、剥离及剪切强度测试。结果表明,制得的P-HHPACO羟值为219mg KOH/g;当摩尔比为1.3时,聚氨酯胶黏剂涂膜的T剥离强度达到399.2N/m;摩尔比为1.5时,剪切强度达到7.1N/mm²。     

胶层厚度对环氧胶粘剂使用环境下力学性能影响的试验研究

为了研究不同厚度胶粘剂在其使用环境条件下对力学性能的影响,从两种金属结构环氧胶粘剂中各挑选了两种厚度的胶粘剂,并在不同的使用环境下研究不同胶层厚度对剪切强度、剥离强度、平面拉伸强度和蠕变的影响。研究结果表明:在高低温环境、湿热环境、JP-4燃油浸泡处理的试样件剪切强度、平面拉伸强度性能以及蠕变试验中,0.3 mm的胶层厚度比0.6 mm胶层厚度对胶粘剂的力学性能影响大;在盐雾环境、阻燃液压油浸泡处理的试样件剪切强度以及蜂窝剥离强度试验中,胶层厚度对胶粘剂力学性能的影响不明显;在3型试验液浸泡处理的试样件剪切强度以及滚筒剥离强度试验中,0.6 mm的胶层厚度比0.3 mm胶层厚度对胶粘剂的力学性能影响大。     

一种非流淌型高强度丙烯酸酯胶黏剂的研制

介绍了一种室温固化非流淌型高强度丙烯酸酯胶黏剂的研制。分别通过填料增稠、弹性体增稠和超细尼龙粉增稠三种工艺制得非流淌型丙烯酸酯胶黏剂;对三种胶黏剂外观和力学性能进行对比,发现超细尼龙粉增稠工艺制成的丙烯酸酯胶黏剂在两方面均优于另外两种工艺制备的胶黏剂。使用该工艺制成了非流淌型高强度丙烯酸酯胶黏剂,对其力学性能进行测试,发现该胶黏剂可室温固化,对金属铝、钛合金、钢材等材料均有很好的粘接效果,可适用于一些特殊部位的粘接。     

复合材料/金属胶接结构研究进展及发展趋势

胶接连接应用日渐广泛,特别是在汽车和航空航天等结构领域。首先分析了复合材料/金属胶接连接方式的特点,重点介绍了接头中的次弯曲效应、异质材料间刚度与热膨胀系数的不匹配特性以及载荷传递特性。然后总结了提高胶接接头强度的研究进展,主要包括增大胶接长度和宽度、选择胶黏剂、表面处理、增加胶瘤和被粘合物形状的设计等方面。最后对胶接接头的发展趋势进行了展望。     

Diagnosis criterion for damage monitoring of adhesive joints by a piezoelectric method

Adhesive joints have been widely used for fastening thin adherends because they can distribute the load over a larger area than mechanical joints, require no holes, add very little weight to the structure and have superior fatigue resistance. Since the reliability of an adhesive joint is dependent on many parameters, such as the shape of joint, type of applied load and environment, an accurate prediction of the fatigue life of adhesive joints is seldom possible, which necessitates an in situ damage monitoring of the joints during their operation. Recently, a piezoelectric method using the piezoelectric characteristics of epoxy adhesives has been successfully developed for adhesive joints because it can continuously monitor the damage of adhesively bonded structures without producing any defects induced by inserting a sensor. Therefore, in this study, the damage of adhesive joints was monitored by the piezoelectric method during torsional fatigue tests in order to develop the diagnosis criterion for damage monitoring of adhesive joints by the piezoelectric method. The diagnosis criterion was developed by analyzing damage monitoring signals under various test conditions and adopting normalized parameters.     

Research on the static strength performance of adhesive single lap joints subjected to extreme temperature environment for automotive industry

Adhesive bonding technique is widely studied and adopted in automotive industry in recent years, which leads to satisfactory joint mechanical properties and lightweight effects. In this study, the static mechanical performance of adhesively bonded joints after different temperature exposures was investigated through joint quasi-static shear-strength test. A response surface method using MATLAB programming was utilised to analyse the influences of exposure temperature and adhesive mechanical attributes on joint static strength. Visual inspection and scanning electron microscopy were later performed on the fracture surfaces to explain the failure mechanisms. Test results showed that long-term temperature exposure caused degradation in joint strength and failure displacement. It was found through response surface curve that comparing to higher temperature exposure, lower temperature causes greater and faster environmental degradation. Different types of fracture surfaces in the overlap zone were also detected through comparing adhesive joints under different environmental treatments.     

Preparation of a new polymer-modified adhesive mortar using fine iron tailings as aggregate

In this paper, a new polymer-modified adhesive mortar is prepared using the fine iron tailings, eco-cement, redispersible latex powder, additives, and water. In our study, the fine iron tailings are used to replace the natural river sand as the mortar aggregate and the optimal process conditions are determined by the orthogonal experiment. The obtained results are shown as follows: The ratios of cement–sand and polymer–cement are 1:2.5 and 4%, respectively, with the aggregate modulus 0.81 and water reducing agent 0.5% (cement-based). The properties of the polymer-modified adhesive mortar obtained under the optimal process conditions conform to JC/T 547-2005 (China Professional Standard: Ceramic Tile Adhesive). Moreover, the microstructure of the polymer-modified adhesive mortar is studied and discussed. The results show that the network formed by the intertwined polymer film can prevent the merger of micro-cracks and improve the adhesive mortars’ overall cohesion. Therefore, adding polymer to the adhesive mortar can improve its failure stress and enhance its bonding strength.     

Polymeric reaction of polymer-monomer system irradiated by low energy electron beam. III. Adhesive property of pressure sensitive adhesive

Application of low-energy electron beam to nonsolvent-type pressure-sensitive adhesive is investigated. Adhesive properties such as peel strength, dead load strength, and ball tack were closely related to the reaction behavior (gel fraction and graft efficiency) of the acrylate polymer-monomer system. The reaction behavior is eluciadated by combining the measurements of gel fraction, infrared spectrum of gel, and molecular weight distribution detected by gel permeation chromatogrophy. It was found that the adhesive property of electro beamcured adhesives depends on the molecular weight of added polymer, monomer concentration, and irradiation dose. Graft polymerization and moderate crosslinking by electron beam irradiation especially contribute to superior high adhesive properties.     

An experimental method dedicated to the dynamic characterization of structural adhesives under drop weight conditions

Adhesive bonding is a commonly used method in multi-materials assemblies dedicated to the transport fields. In order to ensure structures integrity and users safety, the knowledge of the mechanical behaviour of structural adhesives used in these assemblies under impact conditions appears to be an essential prerequisite. To date, numerous tests combining usual specimens geometry e.g. single lap joint, butt joint, etc. and high velocity testing rigs exist and are used. Among these, most allow comparative studies and a few provide a partial identification of the material properties of the investigated adhesive.In this study, an experimental method dedicated to the dynamic characterization of structural adhesives under drop weight condition is proposed. On the basis of existing works, a modified Arcan specimen and a dynamic tensile testing mean were developed and are presented. The Arcan geometry allows to test the adhesive under various loading directions and so to obtain its mechanical response envelope. Design strategies are also implemented in order to obtain time stable and quasi-homogeneous stress distributions in the adhesive during the tests.At last, the dynamic characterization of a Dow^® Betamate^TM 1496 V adhesive is proposed. Results are repeatable and show a strain rate dependent behaviour validating the appropriateness of the experimental approach.     

Simulation of adhesive joints using the superimposed finite element method and a cohesive zone model

Adhesive joints have been widely used in various fields because they are lighter than mechanical joints and show a more uniform stress distribution if compared with traditional joining techniques. Also they are appropriate to be used with composite materials. Therefore, several studies were performed for the simulation of the bonded joints mechanical behavior. In general for adhesive joints, there is a scale difference between the adhesive and the substrate in geometry. Thus, mesh generation for an analysis is difficult and a manual mesh technique is needed. This task is not efficient and sometimes some errors can be introduced. Also, element quality gets worse.In this paper, the superimposed finite element method is introduced to overcome this problem. The superimposed finite element method is one of the local mesh refinement methods. In this method, a fine mesh is generated by overlaying the patch of the local mesh on the existing mesh called the global mesh. Thus, re-meshing is not required.Elements in the substrate are generated. Then, the local refinement using the superimposed finite element method is performed near the interface between the substrate and the adhesive layer considering the shape of the element, the element size of the adhesive layer and the quality of the generated elements. After performing the local refinement, cohesive elements are generated automatically using the interface nodes. Consequently, a manual meshing process is not required and a fine mesh is generated in the adhesive layer without the need for any re-meshing process. Thus, the total mesh generation time is reduced and the element quality is improved. The proposed method is applied to several examples.     

Evaluation of natural rubber latex-based PSAs containing aliphatic hydrocarbon tackifier dispersions with different softening points—Adhesive properties at different conditions

Natural rubber latex-based water–borne pressure sensitive adhesives (PSAs) have been formulated with three aliphatic hydrocarbon water-based dispersions (varying softening points) at two different resin addition levels (25% and 50%). Time–temperature superposition analysis using WLF approximations for adhesive peel has revealed that the adhesives formulated with 50% resin addition level show good adhesive behavior. It has also been determined from time–temperature superposition analysis that peel force increases systematically with softening point and peel rate. Correlation of viscoelastic behavior with adhesive properties suggests that at least 50% resin addition level is needed to bring the natural rubber-based formulations into PSA criteria as defined by Dahlquist and others. Adhesive property evaluations performed on a high surface energy substrate (stainless steel) and low surface energy substrate (LDPE) suggested that optimum tack, peel and shear properties at room temperature were obtained for a formulation containing a higher softening point dispersion (95 °C) at 50% resin addition level. Adhesive peel and tack tend to follow softening point trends as well. A 25% tackifier dispersion addition level did not provide any significant adhesion. Humid aging (50 °C and 100% relative humidity) evaluations of the water–borne adhesives seem to correlate well with the room temperature adhesive property observations.     

ADHESION ENHANCEMENT THROUGH CONTROL OF ACID-BASE INTERACTIONS

Adhesive bond strengths have been determined for lap-shear joints of PS/LLDPE and PS/CPE, a chlorinated version of polyethylene. Joints were formed at temperatures in the range of 180–280°C. In PS/LLDPE, bond strength at lower joining temperatures is compromised by the inability of LLDPE to act as electron acceptor to the donor properties of PS. However, at T?≥?260°C, PS becomes a fluid capable of interacting through dispersion forces only, leading to enhanced diffusion across the PS/LLDPE interface and much stronger adhesive bonds. An acid–base pairing is in effect in joints of PS/CPE, resulting in strong joints made at T?≤?240°C. The probable loss of acid-base interaction between the polymers at higher T, coupled with a failure of diffusion across the interface, leads to a lowering of the joint bond strength. Control over interfacial interactions is demonstrated to be a vital factor in the development of adhesive bonds.     

Review on adhesive joints and their application in hybrid composite structures

Composites have been used extensively in various engineering applications including automotive, aerospace, and building industries. Hybrid composites made from two or more different reinforcements show enhanced mechanical properties required for advanced engineering applications. Several issues in composites were resolved during the last few years through the development of new materials, new methods and models for hybrid joints. Many components in automobile are joined together either by permanent or temporary fastener such as rivets, welding joint and adhesively bonded joints. Increasing use of bonded structures is envisaged for reducing fastener count and riveted joints and there by drastically reducing assembly cost. Adhesive bonding has been applied successfully in many technologies. In this paper, scientific work on adhesively bonded composites and hybrid composites are reviewed and discussed. Several parameters such as surface treatment, joint configuration, material properties, geometric parameters, failure modes, etc. that affect the performance of adhesive bonded joints are discussed. Environmental factors like pre-bond moisture and temperature, method of adhesive application are also cited in detail. A specific case of adhesive joints in hybrid bonded-bolted joints is elaborated. As new applications are expanding in the field of composites joining and adhesive joints, it is imperative to use information on multiple adhesives and their behaviour in different environmental conditions to develop improved adhesive joint structure in mechanical applications.