无溶剂型双组分有机硅改性PU胶粘剂的制备与性能研究

以聚醚二元醇(DL-1000)、4,4′-二苯基甲烷二异氰酸酯(MDI)为主要原料合成端-NCO基PU(聚氨酯)预聚体;然后以γ-氨丙基三乙氧基硅烷(KH-550)对其进行嵌段共聚改性,并以3,3′-二氯-4,4′-二氨基二苯基甲烷(MOCA)/蓖麻油作为复合固化剂,制备出无溶剂型双组分有机硅改性PU胶粘剂。研究结果表明:硅烷键已引入PU胶粘剂中;随着KH-550含量的不断增加,胶粘剂的黏度增大、固化时间缩短、室温剪切强度下降且耐热性增强;通过调节不同KH-550含量,可制备出不同性能要求的胶粘剂;该胶粘剂的玻璃化转变温度(-45.9℃)相对较低,说明其耐寒性相对较好。     

Investigating tensile behaviour of toughened epoxy paste adhesives using circumferentially notched cylindrical bulk specimens

Toughened epoxy adhesives are frequently used to bond metals and polymer-matrix composite materials in many structural applications. The mechanical properties of adhesives are often characterised by testing either bulk adhesive specimens or bonded joints (i.e. in-situ form). In this paper, cylindrical bulk specimens with circumferential notches were manufactured and tested to investigate the tensile behaviour of an epoxy paste adhesive toughened with hollow glass microspheres. Bulk specimens were manufactured from the paste adhesive using injection moulding. Tensile tests were conducted for strain-rate and stress triaxiality effects by varying displacement rates and notch radii, respectively. Fracture surfaces were examined using optical and scanning electron microscopy to identify failure mechanisms. The results obtained from the toughened paste adhesive indicate that strain-rate and stress triaxiality influence its tensile fracture behaviour.     

Wedge test of carbon‐nanotube‐reinforced epoxy adhesive joints

Epoxy adhesives reinforced with carbon nanotubes (CNTs) were developed. The distribution of the CNTs in the epoxy matrix was observed with transmission electron microscopy. Joints were formed by unclad 2024‐T3 aluminum adherents bonded with the CNT‐filled epoxy adhesives. The durability of the joints was studied with a wedge test under water at 60°C. The addition of CNTs to the epoxy greatly improved the adhesive joint durability. The initial crack length of the joint with 1 wt % CNTs, which was obtained before the wedge specimen was put into water, was only about 7% of that with neat epoxy. After immersion of the specimens in 60°C water, the joint with neat epoxy failed after 3 h, but all of the joints adhered with different fractions of CNTs were still bound together after the experimental time of 90 h. The significant enhancement by CNTs of the adhesive joint durability was mainly attributed to the high mechanical properties of the CNTs and their ability to resist water. Nevertheless, the experimental results also reveal that the durability of the joints showed an optimum value at approximately 1 wt % CNTs, beyond which a decrease in the property was observed. In addition, the failure mechanism of the joints was also investigated in terms of interfacial failure and cohesive failure. Cohesive dominated failure was found for the joint bonded with 1 wt % CNT‐filled epoxy. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

单组分水性纳米SiO2 /PU粘接剂的制备与性能研究

以甲苯二异氰酸酯(TDI)、聚酯、蓖麻油、纳米SiO2等为主要原料,采用原位聚合复合工艺制备了单组分水性纳米SiO2/聚氨酯粘接剂.讨论了多元醇、纳米材料及其加入方式对所制备产品性能的影响,并通过扫描电镜、DMA动态仪、DSC差热扫描量热仪进行了分析.结果表明,以蓖麻油和聚酯为多元醇组分采用原位聚合复合方法所制备的单组分水性纳米SiO2/聚氨酯粘接剂的粘接强度最好;纳米SiO2的加入,破坏了聚氨酯硬段的结晶,消除了各向异性,同时提高了其模量,降低了内耗因子,但对材料的热分解性能影响不大.     

Comparison of fracture behavior between acrylic and epoxy adhesives

An experimental study was conducted on the strength of adhesively bonded steel joints, prepared epoxy and acrylic adhesives. At first, to obtain strength characteristics of these adhesives under uniform stress distributions in the adhesive layer, tensile tests for butt, scarf and torsional test for butt joints with thin-wall tube were conducted. Based on the above strength data, the fracture envelope in the normal stress-shear stress plane for the acrylic adhesive was compared with that for the epoxy adhesive. Furthermore, for the epoxy and acrylic adhesives, the effect of stress triaxiality parameter on the failure stress was also investigated. From those comparison, it was found that the effect of stress tri-axiality in the adhesive layer on the joint strength with the epoxy adhesive differed from that with the acrylic adhesive. Fracture toughness tests were then conducted under mode l loading using double cantilever beam (DCB) specimens with the epoxy and acrylic adhesives. The results of the fracture toughness tests revealed continuous crack propagation for the acrylic adhesive, whereas stick-slip type propagation for the epoxy one. Finally, lap shear tests were conducted using lap joints bonded by the epoxy and acrylic adhesives with several lap lengths. The results of the lap shear tests indicated that the shear strength with the epoxy adhesive rapidly decreases with increasing lap length, whereas the shear strength with the acrylic adhesive decreases gently with increasing the lap length.     

Bonding adhesive joints with radio-frequency dielectric heating

The feasibility of using radio-frequency (RF) dielectric heating to cure thermoset adhesives has been evaluated. Thermoset and thermoplastic polymer panels have been bonded to steel using conventional one-and two-part epoxy and two-part urethane adhesives. Process cycle times for adhesive cure using RF heating were about 20 to 60 seconds, compared with about 20 to 30 minutes for the same materials using conventional oven-cure methods. Thermoset substrates bonded included glass fibre-reinforced composite panels based on sheet moulding compound (SMC) and resin transfer moulding styrene-vinylester (RTM). Thermoplastics such as polycarbonate, polyarylate, Noryl, ABS and polymethylmethacrylate were also successfully bonded. RF bonding experiments were performed by preparing and testing lap-shear joints as well as by joining a large test structure with a 25 mm x 1.25 m bondline. Bonding of painted steel to SMC composite, SMC to SMC and steel to RTM composite were also accomplished using the RF dielectric heating process.     

Effect of silicon carbide nanoparticles on the adhesion strength of steel–epoxy composite joints bonded with acrylic adhesives

This paper reports a study on the effect of silicon carbide nanoparticles on the adhesion strength of steel–glass/epoxy composite joints bonded with two-part structural acrylic adhesives. The introduction of nanosilicon carbide in the two-part acrylic adhesive led to a remarkable enhancement in the shear and tensile strength of the composite joints. The shear and tensile strengths of the adhesive joints increased with adding the filler content up to 1.5?wt%, after which decreased with adding more filler content. Also, addition of nanoparticles caused a reduction in the peel strength of the joints. DSC analysis revealed that Tg values of the adhesives rose with increase in the nanofiller content. The equilibrium water contact angle was decreased for adhesives containing nanoparticles. SEM micrographs revealed that addition of nanoparticles altered the fracture morphology from smooth to rough fracture surfaces.     

Tensile strength of two-part epoxy paste adhesives: Influence of mixing technique and micro-void formation

Two-part epoxy paste adhesives are frequently used to bond metals and composite materials in many structural applications. After mixing two reactive parts (by weight or volume ratio), adhesive paste is applied to the substrate surfaces and cured at elevated temperatures. Air-entrapment during mixing and/or application process often produces micro-voids in the adhesive bondlines and influences the strength of the bonded joints. In this work, void formation was investigated using two adhesive mixing techniques: (a) dual-cartridge and static-mixer with a dispenser and (b) hand-mix. Flat adhesive sheets were cured by mixing a two-part epoxy adhesive, and bulk specimens with notches were cut using CNC-machining. Using X-ray microtomography scans, the micro-voids were detected and material porosity was evaluated. Furthermore, tensile tests were performed on the specimens and two-dimensional digital image correlation (2D DIC) was employed to analyse the surface strain concentrations near the notches. The fracture surfaces were examined using optical and scanning electron microscopy. The results indicated that mixing technique influences the formation of micro-voids and thus the tensile strength of two-part epoxy paste adhesives.     

Adhesive strength of steel–epoxy composite joints bonded with structural acrylic adhesives filled with silica nanoparticles

This paper reports a study on the effect of silica nanoparticles on the adhesion strength of steel–glass/epoxy composite joints bonded with two-part structural acrylic adhesives. The introduction of nano-silica in the two-part acrylic adhesive led to a remarkable enhancement in the shear and tensile strength of the composite joints. The shear and tensile strengths of the adhesive joints increased with addition of the filler content up to 1.5 wt%, after which decreased with addition of more filler content. Also, addition of nanoparticles caused a reduction in the peel strength of the joints. Differential scanning calorimeter analysis revealed that T_g values of the adhesives rose with increasing the nanofiller content. The equilibrium water contact angle was decreased for adhesives containing nanoparticles. Scanning electron microscope micrographs revealed that addition of nanoparticles altered the fracture morphology from smooth to rough fracture surfaces.     

Experimental Analysis of the Bondline Stress Concentrations to Characterize the Influence of Adhesive Ductility on the Composite Single Lap Joint Strength

Adhesively bonded composite single lap joints were experimentally investigated to analyze the bondline stress concentrations and characterize the influence of adhesive ductility on the joint strength. Two epoxy paste adhesives—one with high tensile strength and low ductility, and the other with relatively low tensile strength and high ductility—were used to manufacture composite single lap joints. Quasi-static tensile tests were conducted on the single lap joints to failure at room temperature. High magnification two-dimensional digital image correlation was used to analyze strain distributions near the adhesive fillet regions. The failure mechanisms were examined using scanning electron microscopy to understand the effect of adhesive ductility on the joint strength. For a given surface treatment and laminate type, the results show that adhesive ductility significantly increases the joint strength by positively influencing stress distribution and failure mechanism near the overlap edges. Moreover, it is shown that high magnification two-dimensional digital image correlation can successfully be used to study the damage initiation phase in composite bonded joints.     

Effect of material on the mechanical behaviour of adhesive joints for the automotive industry

One parameter that influences adhesively bonded joints performance is the adherend material and its effect should be taken into consideration in the design of adhesive joints. In this work, the effect of material on the mechanical behaviour of adhesive joints was investigated experimentally and numerically by single lap joints (SLJs) with different adherend materials (high strength steel, low strength steel and composite). The adhesives selected were two new modern tough structural adhesives used in the automotive industry. It was found that, for relatively short overlaps in SLJs bonded with structural modern tough adhesives, failure is dominated by adhesive global yielding and the influence of material on joint strength is not significant. For larger overlaps, the failure is not anymore due to global yielding and the effect of material becomes more important. Moreover, it was possible to evaluate which adhesive is more suited for each material.     

Parametric study of adhesive joints with composites

Adhesively-bonded joints are increasingly used in aeronautical industry. Adhesive joints permit to join complex shapes and reduce the weight of structures. The need to reduce the weight of airplanes is also increasing the use of composites. Composites are very anisotropic: in the fibre directions, unidirectional composites can be very strong and stiff, whereas the transverse and shear properties are much lower. Bonded joints experience peel loading, so the composite may fail in transverse tension before the adhesive fails. That is why it is important to study these joints and try to find reliable ways to predict the strength of joints with composite adherends. The main goal of this study was to understand the failure in adhesive joints with composites, bonded with adhesives with different characteristics, and find reliable ways to predict them. Experimental tests were carried with single lap joints with composite adherends and different adhesives, brittle and ductile, with several overlap lengths. A Cohesive Zone Model (CZM) was taken into consideration to predict the results observed during the experimental tests. The experimental results were also compared with simple analytical models and the suitability of each model was evaluated for each bonded system.     

水性环氧树脂包覆有机蒙脱土制备木材胶粘剂

摘要：水性环氧树脂通常含有水溶性分子或分子链，导致在高温和潮湿条件下作为木材胶粘剂时耐水性及力学性能较差。采用有机改性的纳米蒙脱土改性水性环氧树脂增强水性环氧树脂胶粘剂的耐水性及力学性能。并通过乳液包覆蒙脱土的方法与直接共混的方法对比，研究了不同添加量有机蒙脱土（0%，3%，6%，9%）对胶粘剂性能的影响。胶粘剂的耐水性及力学性能通过测量胶粘剂在干燥及潮湿条件下的剪切强度来表示。通过TGA、SEM、TEM、DSC研究了复合胶粘剂的热稳定性和结构。结果表明，在水性环氧树脂中添加有机改性的纳米蒙脱土，可以有效地提高胶粘剂的粘结强度，此外，采用乳液包有机覆蒙脱土的方法比直接共混的方法制备得到胶粘剂，有机蒙脱土在胶粘剂中分布更均匀，具有更优异的力学性能，说明有机蒙脱土在复合材料中的分散质量是影响复合胶粘剂性能的主要原因。     

Effect of MWCNT filled epoxy adhesives on the quality of adhesively bonded joints

Most adhesively bonded joints exhibit adhesive or cohesive failure, i.e. failure at the adhesive/adherend interface or within the adhesive, respectively. The main objective of this study is to investigate the effect of surface modification of the metal substrate accompanied by modification of the adhesive properties on the strength and failure mechanism of bonded joints. A 5061 aluminium alloy has been used as the metal substrate onto which two types of surface treatments were applied; chemical surface modification and gritblasting. A standard epoxy resin was used as the adhesive medium, in which multi-wall carbon nanotubes (MWCNTs) were dispersed, with a range of weight fraction content (from 0.03% to 0.5%). The resin was fully characterised by mechanical testing in order to determine the optimum weight fraction to enhance its properties. Aluminium to aluminium and glass fibre reinforced polymer (GFRP) composite to aluminium single lap joints bonded with either pure epoxy resin or MWCNT reinforced epoxy resin were subsequently manufactured and tested. The tests show a moderate increase of the joint strength when MWCNTs are added into the adhesive with the failure mechanism changing from cohesive to adhesive. In addition, the comparison between different surface preparation methods shows that gritblasting results in considerably improved adhesive strength over chemical treatment.     

Steel-Epoxy Composite Joints Bonded with Nano-TiO2 Reinforced Structural Acrylic Adhesive

This article reports a study on the effect of TiO₂ nanoparticles on the adhesion strength of steel–glass/epoxy composite joints bonded with two-part structural acrylic adhesives. The introduction of nano-TiO₂ in the two-part acrylic adhesive led to a remarkable enhancement in the shear and tensile strength of the composite joints. The shear and tensile strengths of the adhesive joints increased with adding the filler content up to 3 wt.%, after which it decreased with adding more filler content. Also, addition of nanoparticles caused a reduction in the peel strength of the joints. Differential scanning calorimeter analysis revealed that glass transition temperature (T_g) values of the adhesives rose with increasing the nano-filler content. The equilibrium water contact angle decreased for adhesives containing nanoparticles. Scanning electron microscope micrographs revealed that addition of nanoparticles altered the fracture morphology from smooth to rough fracture surfaces.     

Static failure analysis of adhesive single lap joints

In this paper it is proposed a phenomenological framework to perform the failure analysis of a family of adhesive single lap joints. The theory is conceived for adhesives with quasi-brittle behaviour and highly resistant adherends. The main goal is to predict the rupture force using model equations that combine enough mathematical simplicity to allow their usage in engineering problems with the capability of describing a complex nonlinear mechanical behaviour. The material constants that appear in the model equations are identified for an adhesive/adherend system consisting of ASTM A36 steel plates bonded with an epoxy/ceramic composite. Results from experimental tensile testing of joints with different bonded areas were compared with model prediction showing a good correlation.     

Non-destructive characterization of bondlines in composite adhesive joints

Aerospace structures use polymeric composite materials extensively. These composite materials are normally bonded together by adhesives to form structural parts. The existence of any kind of defects or discontinuities in the bonds is completely undesirable for such applications. Ultrasonic imaging (UI) is a widely used technique for non-destructive evaluation (NDE) and can be adopted to evaluate the integrity of such adhesively-bonded joints. However, characterization of adhesive bonds in composite materials using UI has deficiencies due to problems such as high acoustic attenuation and high signal-to-noise ratio. These problems can be attributed to the inhomogeneity in composite structures. The present study addresses the problems of detection of disbonds and porosity in adhesively bonded carbon fiber reinforced composite panels. Five sets of adhesively-joined carbon/epoxy composites with different adherend surface preparations were fabricated and subjected to UI. The panels contained known defects in the bondline of the samples. UI results are interpreted to identify various existing defects such as voids, cracks and disbonds in the joints. Attenuation coefficient values for all types of composites are utilized to ascertain the validity of the image analysis.     

Impact of multiwall carbon nanotubes on the fatigue strength of adhesive joints

This paper presents the results of research undertaken to determine the possibility of improving the fatigue properties of peel-loaded adhesive joints by dispersing multiwall carbon nanotubes (MWCNTs) into epoxy-based adhesives. The fatigue strength tests were carried out on an electromagnetic inductor with the resonance frequency of the adhesively bonded joint specimen. The tests were conducted for three types of epoxy adhesives whose properties were modified through the introduction of multiwalled carbon nanotubes, into their structure. Carbon nanotubes were synthesized by means of the Chemical Vapour Deposition (CVD) method with Fe-Co catalysts. A quantity of 1 wt.% of the dried material was dispersed into the epoxy adhesives. The results of the fatigue strength tests revealed a significant improvement of the fatigue lifetime of adhesive joints due to MWCNT introduction as filler for epoxy adhesives. In the case of the Epidian 57/PAC adhesive composition, a more than twofold increase in the fatigue lifetime was obtained (an increase of 106.8%). For the Bison Epoxy adhesive composition, the fatigue lifetime increased by 69.3%. The fatigue strength for the best result increased by about 13%.     

Failure and stress analysis of internal pressurized composite pipes joined with sleeves

Failure and stress analyses were carried out for composite pipes adhesively joined with sleeves subjected to internal pressure. In the study, the composite pipes and sleeves were E glass fiber/epoxy with different fiber orientation angles. Circular pieces cut from four layered composite pipes with different orientation angle were used as sleeves. Composite pipes with different orientation angle were bonded using DP410 and DP490 type adhesives. The codes of a numerical model were generated via ANSYS software package for the numerical analyses, and the numerical results were verified using experimental results. The problems were analyzed by using a calculation method based on finite elements method (FEM). The finite element analyses (FEA) were carried out to predict the failure internal pressure. Radial, tangential, axial and shear stress values were obtained via numerical analyses for composite pipes and adhesive layers in the thickness direction. In addition, Von–Mises stress distributions that develop on the adhesive were obtained as well. The effects of orientation angle, sleeve length and adhesive type on strength of composite pipe and bonded zone were examined. The results showed that the adhesive type has higher effect on the strength of bonded composite pipes when compared with orientation angle and sleeve length. In addition, increase in sleeve length increased the failure internal pressure.     

Failure behavior of adhesively bonded joints with a rubber modified epoxy adhesive under tensile-shear combined cyclic loading

Rubber-modified epoxy adhesives are used widely as structural adhesive owing to their properties of high fracture toughness. In many cases, these adhesively bonded joints are exposed to cyclic loading. Generally, the rubber modification decreases the static and fatigue strength of bulk adhesive without flaw. Hence, it is necessary to investigate the effect of rubber-modification on the fatigue strength of adhesively bonded joints, where industrial adhesively bonded joints usually have combined stress condition of normal and shear stresses in the adhesive layer. Therefore, it is necessary to investigate the effect of rubber-modification on the fatigue strength under combined cyclic stress conditions. Adhesively bonded butt and scarf joints provide considerably uniform normal and shear stresses in the adhesive layer except in the vicinity of the free end, where normal to shear stress ratio of these joints can cover the stress combination ratio in the adhesive layers of most adhesively bonded joints in industrial applications.

In this study, to investigate the effect of rubber modification on fatigue strength with various combined stress conditions in the adhesive layers, fatigue tests were conducted for adhesively bonded butt and scarf joints bonded with rubber modified and unmodified epoxy adhesives, wherein damage evolution in the adhesive layer was evaluated by monitoring strain the adhesive layer and the stress triaxiality parameter was used for evaluating combined stress conditions in the adhesive layer. The main experimental results are as follows: S–N characteristics of these joints showed that the maximum principal stress at the endurance limit indicated nearly constant values independent of combined stress conditions, furthermore the maximum principal stress at the endurance limit for the unmodified adhesive were nearly equal to that for the rubber modified adhesive. From the damage evolution behavior, it was observed that the initiation of the damage evolution shifted to early stage of the fatigue life with decreasing stress triaxiality in the adhesive layer, and the rubber modification accelerated the damage evolution under low stress triaxiality conditions in the adhesive layer.