Experimental Studies of the Strength of an Adhesive Joint in a State of Combined Stress

The adhesive strength of a butt-type specimen of two cylinders is experimentally studied. Combined stresses are applied on the adhesive layer by subjecting the specimen to combined axial load, torsion and internal pressure. The effects of the surface roughness, the thickness of adhesive layers and the combined stresses on the adhesive strength are examined for the specimens of various metals bonded with epoxy resin. The adhesive failure locus under the combined stress state are represented by a polynominal equation of stress tensors.     

Stress Distribution and Strength of T-type Adhesive Joint with Reinforcement for Bending Moment

The stress distribution in the adhesive layer of T-type adhesive-bonded butt joint between rigid adherends has been measured experimentally, and the equation relating the maximum stress in the adhesive layer to the bending moment applied to the joint and to the joint dimensions was derived. The equation is used to calculate the adhesive strength of a T-type joint from the measured breaking load. These strengths show reasonable agreement with experimental values.

The distribution in the adhesive layer of a T-type adhesive joint with the reinforcement having the section of a right-angled isosceles triangle has been measured experimentally. The strength efficiency of the reinforcement η and the strengthening magnification of the reinforcement μ are discussed geometrically comparing with the equation. The values of η and μ measured by the experiments showed good agreement with the values obtained geometrically.     

The Strength of Adhesive Joints

The main rules pertaining to the strength of adhesive joints are: (1) This strength is a mechanical (or rheological) property. The local stress which causes the extension of a pre-existing crack can be determined only if the stress pattern in the whole adhint is known and the intensification of stress at flaws is taken into account. (2) The rupture occurs in a material, not between two materials. Consequently, the molecular forces across the adhesive-adherend interface are irrelevant, and the “adhesion tension” does not determine the adhint strength.     

弹性建筑涂料拉伸强度测量结果的不确定度评定

为了评定弹性建筑涂料拉伸强度测定结果的分散性,根据JJF1059-1999《测量不确定度评定与表示》的评定原则和检测工作经验,通过对检测过程的分析,提出了测量弹性建筑涂料拉伸强度时影响测量结果的不确定度的主要因素有:样品不均匀性引起的不确定度;试验设备引起的不确定度;检测人员重复测量引起的不确定度。     

OPP膜用聚氨酯复合粘合剂的研究

采用丙酮法制备水性聚氨酯树脂,再复配聚醋酸乙烯酯乳液和松香乳液,提高了水性聚氨酯树脂粘合剂与0PP膜的粘合性。研究了粘合剂组成、烘干时间对0PP膜粘合性的影响,最后进行了优化正交实验。优化结果表明,当聚氨酯与聚醋酸乙烯酯乳液、松香乳液的配比（质量比）为11：9：3,干燥温度60℃,干燥时间为60s时,聚氨酯复合胶粘剂的力学性能较好,其抗拉强度为12．1N·mm^-2以。     

氯丁接枝胶粘剂粘合剥离力的影响因素

介绍了对氯丁橡胶（CR）和甲基丙烯酸甲酯（MMA）接技胶粘剂的粘合剥离力有影响的几个因素。     

Effect of Surface Roughness on the Adhesive Strength of the Heat-Resistant Adhesive RTV88

Heat-resistant adhesive RTV88 is a hyper-elastic material and so far there have been little research on using RTV88 in adhesive joints. In this study, the effect of surface roughness on the adhesive strength of RTV88 was examined. Aluminum adherends were first sandblasted in order to generate rough surfaces, and then tensile–shear tests on Al/RTV88 single lap joints were performed. The shear strength was shown to be influenced by surface roughness. Peel failure was dominant when the surface roughness was at a low level. However, cohesive failure was the major type of failure when the surface roughness was at a high level. Effective area, peel failure area, and cohesive failure area were introduced to explain the effects of surface roughness on the adhesive strength. An empirical relation for the failure force was proposed, based on these parameters. Tensile tests of the RTV88 bonding was performed in order to obtain the necessary data. Finally, the empirical relation for the failure force was verified by tensile–shear test results.     

胶鞋胶面附着力强度的研究

胶面鞋附着力的波动,会直接影响到其内部质量,物理性能是否达到国际标准。而这一标准直接体现在胶面鞋与鞋里布之间的粘着力。通过改变配方及加工工艺,使胶面鞋附着力达到国际标准。     

Wetting Kinetics and the Strength of Adhesive Joints

The work of adhesion, depending solely on the contact angle and surface tension, is unreliable as a guide to the strength of a joint. The kinetics of joint formation, exemplified by the rate of wetting, is also important and can be measured by rate of change of contact angle, a process for which an empirical equation has previously been suggested. A proposed mechanism introduces a viscosity term into the differential form of this equation.

A series of metal lacquers was prepared from epoxy, U/F and M/F resins in various ratios and also epoxy/P/F and epoxy/acrylic mixtures. Stainless steel substrates, coated with these lacquers were then cemented together using polyethylene as an adhesive. It is shown that joint strength correlates better with a high wetting constant (γ/ηL) than with a low contact angle except where this is very low.     

Wetting Kinetics and the Strength of Adhesive Joints

The work of adhesion, depending solely on the contact angle and surface tension, is unreliable as a guide to the strength of a joint. The kinetics of joint formation, exemplified by the rate of wetting, is also important and can be measured by rate of change of contact angle, a process for which an empirical equation has previously been suggested. A proposed mechanism introduces a viscosity term into the differential form of this equation.

A series of metal lacquers was prepared from epoxy, U/F and M/F resins in various ratios and also epoxy/P/F and epoxy/acrylic mixtures. Stainless steel substrates, coated with these lacquers were then cemented together using polyethylene as an adhesive. It is shown that joint strength correlates better with a high wetting constant (γ/ηL) than with a low contact angle except where this is very low.     

Mixed-Mode Strength of Thin Adhesive Films: Experimental Characterization Through a Tubular Specimen with Reduced Edge Effect

The present work deals with the characterization of adhesives in thin film under uniform and multi-axial loading conditions. The tests are carried out with a tubular butt bonded specimen, previously developed by the authors, which ensures both shear and normal uniform stress fields inside the adhesive layer. Stress analysis is performed analytically and shows that, in addition to the axial stress, both radial and circumferential stress components are present in the adhesive layer due to Poisson's effect. This leads to a high level of stress triaxiality especially when only axial loading is considered. The experimental tests performed on eight different loading modes show that the adhesive behaves better under shear stress rather than under normal tensile stress, and its strength increases under compressive mixed mode loading. Among literature criteria for equivalent stress, the Stassi D'Alia criterion provides a clear equivalent failure stress value for the adhesive here examined, regardless of the stress triaxiality.     

Strength of Adhesive Joints Immersed in Different Solutions

Polymethyl methacrylate/epoxy/polymethyl methacrylate (PMMA/epoxy/PMMA) and aluminium/ epoxy/aluminium joints were immersed in different reagents including saline water, distilled water, sodium hydroxide solution, and sulphur dioxide solution. The joints were immersed in the reagents with and without a constant tensile load. The joints were also tested in air. Four loading periods were selected. At the end of each loading period, the joints were loaded in a tensile testing machine until failure. The results of the tests showed that the tensile strength of the aluminium joints was reduced, while that of polymethyl methacrylate was increased after immersion. The same results were obtained regardless of whether the submerged joint was loaded or not. Moreover, corrosion was found on the aluminium joints immersed in the sodium chloride solution and sulphur dioxide solution.     

The Interaction Parameter and the Strength of Adhesive Joints

A “blister test” technique has been used to determine the fracture surface energy of a range of adhesive joints formed using a polyurethane adhesive and a range of solid substrates. For each adhesive pair examined the work of adhesion was calculated from the contact angles formed by liquids for which the polar and dispersion force components of the surface tension are known. For each adhesive pair, the solubility parameter of adhesive and substrate were determined by swelling measurements in a range of liquids. Although cohesive failure of the joints was observed for some of the pairs for which the solubility parameters were matched, this was not true for all such pairs and an explanation of this behaviour has been sought in a new calculation of the volume interaction component of the molecular interaction parameters.     

Thermal Fluctuations Limit the Adhesive Strength of Compliant Solids

For compliant solids, the stress required to separate an interface (its adhesive strength) appears to be much lower than that calculated by computing intersurface interactions. We explore the hypothesis that the adhesive strength is limited in value by thermal fluctuations. In a simple model of an interface, molecules bridging the two surfaces are represented by linear entropic springs. Asymptotic and numerical analyses are carried out to evaluate the adhesive strength and effective work of adhesion. For stiff materials, adhesive strength is found to be equal to the intrinsic strength—the maximum value of intersurface stress computed ignoring fluctuations. For compliant materials, adhesive strength is significantly reduced and is on the order of the elastic modulus. The effective work of adhesion agrees with the intrinsic work of adhesion for stiff materials and can decay slowly with increasing compliance.     

Long Term Strength of Structural Adhesive Joints

The long term static strength of adhesive joints is analyzed in terms of a modified Prot method and sustained load tests. Data from the failure times under different loading rates are used to predict the static stress that an adhesive joint will withstand for an infinite time, i.e., the endurance limit. Despite theoretical shortcomings, the method is found to give reasonable estimates of the endurance limit as determined by standard sustained load tests. The ratio of the short term lap shear strength to the endurance limit is found to be independent of adhesive modulus, temperature, and sample geometry. For engineering calculations on lap shear structural adhesive joints under a static load (at 23°C, 50% R.H.), the endurance limit may be assumed to be equal to 0.25 of the short term strength.     

Thermal Fluctuations Limit the Adhesive Strength of Compliant Solids

For compliant solids, the stress required to separate an interface (its adhesive strength) appears to be much lower than that calculated by computing intersurface interactions. We explore the hypothesis that the adhesive strength is limited in value by thermal fluctuations. In a simple model of an interface, molecules bridging the two surfaces are represented by linear entropic springs. Asymptotic and numerical analyses are carried out to evaluate the adhesive strength and effective work of adhesion. For stiff materials, adhesive strength is found to be equal to the intrinsic strength—the maximum value of intersurface stress computed ignoring fluctuations. For compliant materials, adhesive strength is significantly reduced and is on the order of the elastic modulus. The effective work of adhesion agrees with the intrinsic work of adhesion for stiff materials and can decay slowly with increasing compliance.     

Long Term Strength of Structural Adhesive Joints

The long term static strength of adhesive joints is analyzed in terms of a modified Prot method and sustained load tests. Data from the failure times under different loading rates are used to predict the static stress that an adhesive joint will withstand for an infinite time, i.e., the endurance limit. Despite theoretical shortcomings, the method is found to give reasonable estimates of the endurance limit as determined by standard sustained load tests. The ratio of the short term lap shear strength to the endurance limit is found to be independent of adhesive modulus, temperature, and sample geometry. For engineering calculations on lap shear structural adhesive joints under a static load (at 23°C, 50% R.H.), the endurance limit may be assumed to be equal to 0.25 of the short term strength.     

Comparison of Strength of Triaxial Porcelains Containing Alumina and Silica

The types of fractures in a whiteware body containing quartz vary as a function of quartz grain size. The transition from one type of fracture to another is illustrated by strength, thermal expansion, and water absorption, as well as microstructural observations. The thermal expansion behavior of compositions containing alumina does not vary as a function of grain size, thus showing the absence of fracture in white-ware bodies containing alumina.     

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.     

PC与PP透明复合膜胶粘剂的研究

通过对ＰＣ与ＰＰ透明胶粘剂配方与工艺的研究,了胶粘剂涂布量、固化温度和时间、增粘剂的种类和用量对复合膜的剥离强度的影响。