On the Structure and Strength of Solvent-Welded Joints: The Intrinsic Joint Strength and the Effect of Dissolved Polymer in the Solvent Cement

It is proposed that the intrinsic strength of a solvent-welded joint can be represented by the magnitude of its critical principal strain. A large critical principal strain implied a high intrinsic weld strength. With poly(vinylchloride) adherends, solvent welds formed using pure tetrahydrofuran (THF) and cyclohexanone bonding solvents had high intrinsic joint strengths while solvent welds from pure methyl ethyl ketone (MEK) bonding solvent had lower intrinsic joint strength. In the THF bonding system, the introduction of dissolved polymer in the bonding agent led to significant decreases in the strength of the solvent-welded joint. Additions of up to 2% by weight of dissolved polymer in the MEK bonding agent increased the strength of the solvent weld. However, further increases in the dissolved polymer content in MEK bonding agent also led to decreases in strength.     

Influence of the Bonding Solvent on the Structure and Strength of Solvent Welded Joints

The influence of the bonding solvent on the strength of solvent welded joints has been studied. Strong solvent welds are produced with solvents having the greatest ability to dissolve the polymer and not with solvents which could diffuse most rapidly into the adherend. The formation of a gel layer of highly mobile chains (on the application of a good solvent to the mating surfaces) promotes extensive and intimate bonding across the original interface so that no plane of weakness is obtained. Such welds exhibit high strength since they do not have any preferred plane of failure and extensive deformation of the weld accompanies crack initiation and propagation. When a poorer bonding solvent is used, solvent welds with lower strengths are obtained since soft and weak interfacial layers form at the original interfaces of the weld.     

The Differential Displacements and the Failure in Solvent-Welded Lap Joints

A recent analytical model for adhesive joints proposed by Yue and Cherry for analysing and predicting the strength of solvent-welded lap joints is examined. The experimental verification of an important assumed basis of the applicability of this model to solvent-welded joints is considered. The differential strain in the composite adhesive layer of the solvent-welded joint was shown to be approximately equal to the differential strain in its final adhesive layer. The differential strain and hence the stress concentration was largest near the edge of the overlap. Fractography suggested that failure of the joint initiated at the edge of the overlap.     

The Differential Displacements and the Failure in Solvent-Welded Lap Joints

A recent analytical model for adhesive joints proposed by Yue and Cherry for analysing and predicting the strength of solvent-welded lap joints is examined. The experimental verification of an important assumed basis of the applicability of this model to solvent-welded joints is considered. The differential strain in the composite adhesive layer of the solvent-welded joint was shown to be approximately equal to the differential strain in its final adhesive layer. The differential strain and hence the stress concentration was largest near the edge of the overlap. Fractography suggested that failure of the joint initiated at the edge of the overlap.     

Strength and Microstructure of Solvent Welded Joints of Polycarbonate

The relationship of joint strength of solvent welded joints of polycarbonate to their microstructure is investigated. We used three solvents - butanone, acetone, and cyclohexanone - to test the effect of solubility parameters, and a mixture of cyclohexanone with ethanol to test the effect of a cosolvent; the effect of variation of welding temperature-on both the joint strength and the microstructure is also investigated. Three fracture modes in shear, tensile and tear tests are analyzed. Polycarbonate treated with butanone has maximum joint strength. Cyclohexanone at 78 vol% in ethanol produces the maximum joint strength of polycarbonate. The joint strength of polycarbonate joints welded with cyclohexanone increases with the temperature at which the weld is made. Comparing microstructure with joint strength, tongues, equiaxed dimples and elongated dimples are responsible for the maximum shear, tensile and tear strength, respectively.     

Temperature dependence of polymer interaction: Relevance to adhesion

Acid-base interaction parameters, obtained from inverse gas chromatographic data, have been studied as function of temperature for a series of homopolymers. Acid-base functionality varies inversely with temperature, permitting the identification of a critical temperature where acid-base interaction abates, leaving dispersion forces to act at the surface. Polymer assemblies, prepared at temperatures encompassing the critical values, display a discontinuity in lap-shear bond strength. In inherently incompatible pairs, the abatement of unfavorable acid-base forces enhanced bond strength. An adverse effect was noted in assemblies containing polymers with favorable acid-base interaction. Bond strengths of assemblies joined above critical temperatures display a time-dependent reversion to equilibrium values when exposed to lower temperatures.     

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.     

金属工件的表面处理及胶接工艺对胶接剪切强度的影响

采用环氧树脂-DDS固化体系作为胶接剂,探讨了各种金属表面处理方法、胶接时对胶接面施加的压力、胶层厚度等因素对胶接剪切强度的影响.结果表明,对不锈钢工件采用盐酸氧化法及草酸-硫酸氧化法进行表面处理,得到的胶接剪切强度最好;对铝合金工件采用硅酸磷酸钠法进行表面处理,得到的胶接剪切强度最高.胶接时对胶接面施加0.1～0.4Mpa的压力、胶层厚度在0.10～0.23 mm范围内时胶接效果最好.由于处理液对金属表面产生适度的化学腐蚀,改变了金属表面的物理化学性质,表现出更好的可浸润性和更强的表面吸附力,可以有效地提高胶接剪切强度.     

Outline of an Algorithm for Computation of the Strength of Polymer Adhesive Joints

An algorithm based on hierarchical polymer structure is proposed for calculation of the adhesive joint strength. This hierarchy enables one to describe the behavior of polymer adhesive joints taking into account specific characteristics of all the levels by combining together physico-chemical concepts of the formation of adhesive systems and their fracture mechanics.

In order to prove the validity of the described approach electroless copper plated ABS-copolymers were studied experimentally.

The developed approach makes it possible to take into consideration the effect of the parameters characterizing the formation of an adhesive joint on its strength properties.     

不同金属表面处理对高分子材料与金属连接强度影响

分别利用喷砂、氢氧化钠阳极氧化和激光毛化3种方法对钛合金板进行了表面处理,通过提高其表面粗糙度,来达到提高相应金属–高分子连接件连接强度的目的。其中激光毛化处理能有效提高相应连接件的拉伸性能,而氢氧化钠阳极氧化处理可以有效提高连接件的剥离强度。综合这两种处理方法所制备的金属–高分子连接件的连接强度得到明显提高,拉伸强度为322 MPa,断裂伸长率为5.1%,剥离强度为4.70 N/cm。     

The Effect of Temperature on the Strength of Adhesively-Bonded Composite-Aluminium Joints

Different materials have different coefficients of thermal expansion, which is a measure of the change in length for a given change in temperature. When different materials are combined structurally, as in a bonded joint, a temperature change leads to stresses being set up. These stresses are present even in an unloaded joint which has been cured at say 150°C and cooled to room temperature. Further stresses result from operations at even lower temperatures.

In addition to temperature-induced stresses, account also has to be taken of changes in adhesive properties. Low temperatures cause the adhesive to become more brittle (reduced strain to failure), while high temperatures cause the adhesive to become more ductile, but make it less strong and more liable to creep.

Theoretical predictions are made of the strength of a series of aluminium/CFRP joints using three different adhesives at 20°C and 55°C. Various failure criteria are used to show good correlation with experimental results.     

The Effect of Temperature on the Strength of Adhesively-Bonded Composite-Aluminium Joints

Different materials have different coefficients of thermal expansion, which is a measure of the change in length for a given change in temperature. When different materials are combined structurally, as in a bonded joint, a temperature change leads to stresses being set up. These stresses are present even in an unloaded joint which has been cured at say 150°C and cooled to room temperature. Further stresses result from operations at even lower temperatures.

In addition to temperature-induced stresses, account also has to be taken of changes in adhesive properties. Low temperatures cause the adhesive to become more brittle (reduced strain to failure), while high temperatures cause the adhesive to become more ductile, but make it less strong and more liable to creep.

Theoretical predictions are made of the strength of a series of aluminium/CFRP joints using three different adhesives at 20°C and 55°C. Various failure criteria are used to show good correlation with experimental results.     

A Two-dimensional Stress Analysis and Strength of Single-lap Adhesive Joints of Dissimilar Adherends Subjected to External Bending Moments

The stress distributions of single-lap adhesive joints of dissimilar adherends subjected to external bending moments are analyzed as a three-body contact problem by using a two-dimensional theory of elasticity (plane strain). In the analysis, dissimilar adherends and an adhesive are replaced by finite strips. In the numerical calculations, the effects of the ratio of Young's moduli of adherends, the adherend thickness ratio and the adherend length ratio between dissimilar adherends on the stress distributions at the interfaces are examined. The results show that the stress singularity occurs at the ends of the interfaces, and its intensity is greater at the interface of the adherend with smaller Young's modulus. It is also noted that the singular stress is greater at the interface of the thinner adherend. It is found that the effect of the adherend length ratio on the stress singularity at the interfaces is very small. Joint strength is predicted by using the interface stress and it was measured by experiments. From the analysis and the experiments, it is found that the joint strength increases as Young's modulus of adherends and the adherend thickness increase while the effect of the adherend lengths on the joint strength is small. For verification of the analysis, a finite element analysis (FEA) is carried out. A fairly good agreement of the interface stress distribution is seen between the analytical and the FEA results.     

不同纤维对水泥浆体强度和孔结构的影响

研究了废纸纤维、UFS00纤维素纤维和聚丙烯纤维对水泥浆体抗折强度和抗压强度的影响.通过氮吸附法对水泥浆体的孔结构进行了测试,分析了三种纤维掺入后对水泥浆体孔结构的改变.试验结果表明:密封养护条件下,三种纤维对水泥浆体强度和孔结构的影响是不同的,废纸纤维对水泥浆体强度和优化孔结构方面的影响略次于UF500纤维素纤维,但优于聚丙烯纤维,从成本方面考虑,用废纸纤维代替UF500纤维素纤维是值得尝试的.     

Theoretical and Experimental Analysis of the Scarf Joint Bonded Structure: Influence of the Adhesive Thickness on the Micro-mechanical Behavior

In this work, we have studied the influence of the adhesive thickness on the micro-mechanical behavior of a scarf joint bonded structure loaded in uniaxial tension. Adherends are made of mild steel containing 0.18% Carbon (French Standard XC18), the adhesive is a two-component epoxy resin with a 5800 MPa elastic modulus. The experimental method is based on strain gauge measurements and acoustic emission. It makes it possible to determine the following zones:

—the areas of the joint where the start of microcracks occurs (threshold Fd);

—the areas where crack propagation occurs (threshold Fg) up to the failure (threshold Fr). The experimental results confirm the good correlation between the different thresholds. They also show that there is an optimal adhesive thickness close to 0.1 mm, which confers to the scarf joint the greatest resistance to microcrack initiation and crack extension. We have compared our experimental measurements with the main theories in this domain to determine their limits and their fields of application, particularly in the angular singularities regions near the ends of the lap.     

Theoretical and Experimental Analysis of the Scarf Joint Bonded Structure: Influence of the Adhesive Thickness on the Micro-mechanical Behavior

In this work, we have studied the influence of the adhesive thickness on the micro-mechanical behavior of a scarf joint bonded structure loaded in uniaxial tension. Adherends are made of mild steel containing 0.18% Carbon (French Standard XC18), the adhesive is a two-component epoxy resin with a 5800 MPa elastic modulus. The experimental method is based on strain gauge measurements and acoustic emission. It makes it possible to determine the following zones:

—the areas of the joint where the start of microcracks occurs (threshold Fd);

—the areas where crack propagation occurs (threshold Fg) up to the failure (threshold Fr). The experimental results confirm the good correlation between the different thresholds. They also show that there is an optimal adhesive thickness close to 0.1 mm, which confers to the scarf joint the greatest resistance to microcrack initiation and crack extension. We have compared our experimental measurements with the main theories in this domain to determine their limits and their fields of application, particularly in the angular singularities regions near the ends of the lap.     

The Effect of Ageing and Environment on the Static and Fatigue Strength of Adhesive Joints

This paper describes the results of a durability programme designed to test the effects of ageing and environment on the performance of adhesive joints. Specimens were kept under a variety of loading and environmental conditions and the paper reports results of static and fatigue tests after 8-9 years storage. Some adhesive joints showed excellent durability performance, while others were adversely affected by the environment, particularly high humidity and natural exposure. It was found that the effect of ageing on static and fatigue performance is not necessarily the same.     

The Effect of Moment and Flexural Rigidity of Adherend on the Strength of Adhesively Bonded Single Lap Joints

In the present study, mechanical properties of different single lap joint configurations derived from adherends with different thicknesses subjected to tensile loading were investigated experimentally and numerically. For this purpose, experimental studies were conducted on two different types of SLJ samples, the first type with identical upper and lower adherend thicknesses and the second with different upper and lower adherend thicknesses. For the first type, five different thickness values were tested. For the second type, the lower adherend thickness was constant while five different upper adherend thickness values were tested. The adhesive was prepared from a two-part paste. After the experimental studies, stress analyses on the SLJs were performed with three-dimensional finite element analysis by considering the geometrical non-linearity and the material non-linearities of the adhesive (DP460) and adherend (AA2024-T3). It was observed that, in single lap joint geometry, variation in the thickness of the adherend and the use of lower and upper adherends with different thickness values changed the stress concentrations at the edges of the overlap regions, affecting the experimental failure load of the joints.     

The Effect of Contamination on Adhesive Strength: Wettability Characterization by the CSC Method

The correlation between the adhesive strength of joints of aluminum alloys and the wettability of their surfaces was studied. Two alloys, Al-1100 and Al-2024, were used, with two commercial epoxy adhesives, FM-73 and FM-300K, and the BR-127 primer. The wettability of the surfaces was modified by applying coatings of silicone oil and stearic acid at various concentrations. Wettability was characterized by the “complete spreading concentration” (CSC) method and by advancing contact angles. The CSC method was proven to be more reliable than contact angle measurements in detecting variations in the surface energy of the aluminum alloys studied. The adhesive strength was measured by the lap shear strength (LSS) and by the T-peel strength. The adhesive strength is only mildly sensitive to the concentration of silicone oil for the two adhesive systems. For FM-300K, the LSS decreases when the concentration of stearic acid in the coating increases. For FM-73, the LSS is only mildly sensitive to the concentration of stearic acid, but the T-peel strength shows appreciable sensitivity. The failure mode becomes more adhesive as the concentration of stearic acid and thereby the CSC increase. It is only mildly dependent on the concentration of silicone oil. The results indicate that silicone oil probably interacts with either the primer or an adhesive component in a way which counteracts the expected decrease in adhesive strength due to the reduction in surface energy and wettability of the adherends. However, the effect of stearic acid on the adhesive strength is associated with decreased wettability. All cases for which a pronounced decrease in the adhesive strength was measured are associated with contact angles larger than 90° and with either high CSC values or nonspreading situations.     

The Effect of Contamination on Adhesive Strength: Wettability Characterization by the CSC Method

The correlation between the adhesive strength of joints of aluminum alloys and the wettability of their surfaces was studied. Two alloys, Al-1100 and Al-2024, were used, with two commercial epoxy adhesives, FM-73 and FM-300K, and the BR-127 primer. The wettability of the surfaces was modified by applying coatings of silicone oil and stearic acid at various concentrations. Wettability was characterized by the “complete spreading concentration” (CSC) method and by advancing contact angles. The CSC method was proven to be more reliable than contact angle measurements in detecting variations in the surface energy of the aluminum alloys studied. The adhesive strength was measured by the lap shear strength (LSS) and by the T-peel strength. The adhesive strength is only mildly sensitive to the concentration of silicone oil for the two adhesive systems. For FM-300K, the LSS decreases when the concentration of stearic acid in the coating increases. For FM-73, the LSS is only mildly sensitive to the concentration of stearic acid, but the T-peel strength shows appreciable sensitivity. The failure mode becomes more adhesive as the concentration of stearic acid and thereby the CSC increase. It is only mildly dependent on the concentration of silicone oil. The results indicate that silicone oil probably interacts with either the primer or an adhesive component in a way which counteracts the expected decrease in adhesive strength due to the reduction in surface energy and wettability of the adherends. However, the effect of stearic acid on the adhesive strength is associated with decreased wettability. All cases for which a pronounced decrease in the adhesive strength was measured are associated with contact angles larger than 90° and with either high CSC values or nonspreading situations.