Fatigue strength of vibration‐welded unreinforced nylon butt joints

The fatigue properties of vibration‐welded butt joints in two thermoplastics, nylon 6 and nylon 6,6, are examined in this work. Injection molded plaques were welded under high and low pressure conditions at 212 Hz and at an amplitude of 1.8 mm to a weld penetration of 1.5 mm. Dog‐bone coupons were machined from welded and unwelded plaques and then fatigue cycled in load control at a stress ratio of R = 0.1. The test frequency ranged from 1 to 10 Hz to avoid hysteretic heating. When the temperature rise in the weld region during testing was insignificant, no physical thermal damage was observed. It was found that the nonwelded specimens have longer fatigue lives than the welded ones, while the welded specimens appear to have similar fatigue behavior, except for nylon 6 welded in high pressure, which was slightly inferior. Vibration welding of these materials appears to be viable for structural applications requiring fatigue resistance. POLYM. ENG. SCI. 45:935–944, 2005. © 2005 Society of Plastics Engineers     

The impact strength of butt welded vibration welds related to microstructure and welding history

A study has been made of vibration butt welds between plaques of polypropylene. The quality of the welds, as determined by impact tests, has been examined as a function of the welding variables: pressure and vibration amplitude. In addition, the microstructure of the welds has also been examined, classified, and correlated with the welding variables and weld quality. Penetration as a function of time shows three distinct regimes and It is shown that the impact strength of the welds is independent of time once the third regime is reached. The time required to reach the third regime decreases as pressure or amplitude increases and is more sensitive to amplitude of vibration than to pressure. The highest quality welds were produced at low pressure and low amplitude with corresponding long times to reach regime three and exhibited a unique, readily identifiable microstructure.     

Morphology of PA‐6 vibration welded joints and its effect on weld strength

The microstructure of the heat affected zone (HAZ) in vibration welded joints of polyamide‐6 were studied using polarized light microscopy (PLM), Fourier transform infrared (FTIR) microspectrometry, scanning electron microscopy (SEM), and modulated differential scanning calorimetry (MDSC). PLM images showed the existence of two distinct HAZ layers: an inner layer (HAZ‐I) with small spherulites and an outer deformed layer (HAZ‐II) adjacent to the bulk zone. The thickness of the HAZ‐I and HAZ‐II layers and the size of spherulites in HAZ‐I depended on welding parameters, such as weld pressure and amplitude. The microstructure study of molecular orientation, using birefringence, and crystal phase type, using FTIR, suggests that HAZ‐I originates from a molten polymer film, while HAZ‐II arises in the polymer in the rubbery state. Etched HAZ surfaces also show clear distinction between the two HAZ layers. Therefore, HAZ‐I is renamed as the recrystallized layer and HAZ‐II as the deformed layer. Fracture tests show that the weakest part of the joint occurs in the recrystallized layer region adjacent to the deformed layer. MDSC analysis indicates that the determining factor of the weld strength is the crystallinity of the recrystallized layer, not the thickness of HAZ. POLYM. ENG. SCI., 2008. © 2007 Society of Plastics Engineers     

Fatigue damage evaluation of adhesively bonded butt joints with a rubber-modified epoxy adhesive

A damage evolution of adhesively bonded butt joints with a rubber-modified adhesive has been investigated under cyclic loading. An isotropic continuum damage model coupled with a kinetic law of damage evolution was applied to the butt joint. To solve the kinetic law, analytic and numerical methods were tried: the former solution was derived with some simplifications and the latter one was derived rigorously without simplications. On comparing the analytic solutions with the numerical ones, it was confirmed that differences in the two solutions were small. Furthermore, the estimated S-N curves based on the analytic equation agreed well with experimental data.     

Morphology and strength of polycarbonate to poly(butylene terephthalate) vibration-welded butt joints

Under the right conditions, the strength of vibration-welded butt joints of amorphous polycarbonate (PC) to semicrystalline poly(butylene terephthalate) (PBT) are shown to be as high as the strength of PBT, the weaker of the two materials. Optical, scanning and transmission electron microscopy are used to examine the morphology of the weld zone. Acoustic microscopy is used to visualize poorly bonded regions. The effects of the weld parameters on weld strength and weld morphology are considered in detail.     

The importance of axial misalignment on the long term strength of polyethylene pipe butt fusion joints

The importance of axial misalignment at polyethylene pipe butt fusion joints has been assessed by undertaking elevated temperature lifetime tests. Both medium and high density polyethylene pipes were fusion joined to give aligned and controlled misaligned butt joints. These were tested under either a constant or fluctuating internal pressure loading using conditions that induced failure by slow, stable crck growth. It was observed that the lifetime of a butt joined system depends upon both the internal pressure or pressure range applied and the level of misalignment at the butt fusion joint. Increasing either the internal pressure (range) or the misalignment reduced system performance. These two variables of misalignment and internal pressure (range) may be incorporated into a single parameter, the amplified axial stress (or stress range) at the butt joint. This amplified or butt joint axial stress (or stress range) may be derived by considering the additional bending stresses introduced at the butt joint by virtue of misalignment combined with the axial stress loading.     

A two-dimensional stress analysis and strength evaluation of band adhesive butt joints subjected to tensile loads

The stresses in band adhesive butt joints, in which two adherends are bonded partially at the interfaces, are analyzed, using a two-dimensional theory of elasticity, in order to demonstrate the usefulness of the joints. In the analysis, similar adherends and adhesive bonds, which are bonded at two or three regions, are, respectively, replaced by finite strips. In the numerical calculations, the effects of the ratio of Young's moduli for adherends to that for adhesives, the adhesive thickness, the bonding area and position, and the load distribution are shown on the stress distributions at interfaces. It is seen that band adhesive joints are useful when the bonding area and positions are changed with external load distributions. Photoelastic experiments and the measurement of the adherend strains were carried out. The analytical results are in a fairly good agreement with the experimental results. In addition, a method for estimating the joint strength is proposed by using the interface stress distribution obtained by the analysis. Experiments concerning joint strength were performed and fairly good agreement is found between the estimated values and the experimental results.     

Improved weld strength of vibration welded polyoxymethylene/multiwalled carbon nanotubes hybrid nanocomposites

In this study, carbon nanotubes reinforced polyoxymethylene with different filler loadings was joined by using linear vibration welding technique. The tensile properties of vibration welded polyoxymethylene nanocomposites with different carbon nanotube contents were studied as functions of filler loading and weld pressure. The results showed that the addition of carbon nanotubes into polyoxymethylene slightly improved the matrix tensile strength and pronounced decreased the ductility of pure polyoxymethylene. Interestingly, the weld strength of the nanocomposites was also higher than the polymer matrix strength even at high weld pressure of 2 MPa. Possible reasons for this high weld strength are discussed based on the morphological investigations. POLYM. ENG. SCI., 56:636–642, 2016. © 2016 Society of Plastics Engineers     

Stress analysis and strength estimation of butt adhesive joints of dissimilar hollow cylinders under impact tensile loadings

The stress variations in butt adhesive joints of dissimilar hollow cylinders subjected to impact tensile loadings are analyzed in elastic and elasto-plastic deformation ranges using a finite element method (FEM). The FEM code name employed is DYNA3D. The effects of Young's modulus ratio between dissimilar adherends and the adhesive thickness on the stress variations at the interfaces are examined. In addition, the process of rupture at the interfaces of the joint is simulated. The stress distributions in the joints under static loadings are also analyzed by FEM. The characteristics of the stress variations in the joints under impact loadings are compared with those in the joints under static loadings. Also, the joint strengths under impact loadings are estimated by elasto-plastic FEM. It is found that the maximum value of the maximum principal stress σ ₁ occurs at the outside edge of the lower interface. It is also found that the maximum principal stress σ ₁ at the lower interface decreases as the adhesive thickness increases. The characteristics of the joints under impact loadings are found to be opposite to those under static loadings. Furthermore, differences in the characteristics of the stress variations are shown between the dissimilar joints and the similar joints. In addition, the experiments were carried out to measure the strain response and strains in the butt adhesive joints under both impact and static loadings using strain gauges. Furthermore, joint strengths under both impact and static loadings were measured. Fairly good agreements are observed between the numerical and the measured results.     

Experimental investigations and probabilistic strength prediction of linear welded double lap joints composed of timber

Wood-to-wood bonds obtained by means of friction welding are a relatively new type of connections holding high potential to compete with existing structural adhesives, since a load bearing bond is formed almost instantaneously. This paper addresses the question to which extent welding of wood can be considered for structural joining of load bearing timber elements. For this purpose, experimental investigations in form of tensile-shear tests on welded double-lap joints were carried-out, in which a set of parameters, including overlap length and layer thickness, has been varied. In addition to the experimental analysis, the stress–strain state inside of the connection was determined numerically, taking into account the mechanical complexity of the involved components. It could be concluded that (1) failure of the bond is triggered by a combination of shear and tensile stresses acting in the interface, but also that (2) joint strength is not linearly correlated to stress magnitudes. The mechanical behaviour of the welded interface was characterised by a series of off-axis tests, including its statistical components. The results from this characterisation and the numerical modelling were combined in the framework of a strength prediction routine. Finally, experimental and numerical results are compared, allowing for a validation of the suggested approach.     

Determination of the impact tensile strength of structural adhesive butt joints with a modified split Hopkinson pressure bar

The impact tensile strength of structural adhesive butt joints was determined with a modified split Hopkinson pressure bar using hat-shaped specimens. A typical two-part structural epoxy adhesive (Scotch weld^® DP-460) and two different adherend materials (Al alloy 7075-T6 and commercially pure titanium) were used in the adhesion tests. The impact tensile strength of adhesive butt joints with similar adherends was evaluated from the peak value of the applied tensile stress history. The corresponding static tensile strengths were measured on an Instron testing machine using joint specimens of the same geometry as those used in the impact tests. An axisymmetric finite element analysis was performed to investigate the static elastic stress distributions in the adhesive layer of the joint specimens. The effects of loading rate, adherend material and adhesive thickness on the joint tensile strength were examined. The joint tensile strength was clearly observed to increase with the loading rate up to an order of 10⁶ MPa/s, and decrease gradually with the adhesive thickness up to nearly 180 μm, depending on the adherend materials used. The loading rate dependence of the tensile strength was herein discussed in terms of the dominant failure modes in the joint specimens after static and impact testing.     

Two-Dimensional thermal analysis of resistance welded thermoplastic composites

A transient two-dimensional thermal model for resistance welding of thermoplastic composites is presented. A parametric study is conducted that yields insight into the welding process enabling some critical process and material parameters to be identified. Time to melt is predicted by the model and is successfully compared to experimental observations. Local heating and meltthrough can also be explained by the transient thermal model in agreement with experimental observations. Mode I fracture toughness of unidirectional graphite reinforced poly(etheretherketone) resistance welded double cantilever beam specimens are conducted under various process conditions. Experimental results indicate that under optimum process conditions, the interlaminar fracture toughness of the bulk compression-molded thermoplastic composite material can be achieved using resistance heating as a joining technique.     

Strength of glass-filled modified polyphenylene oxide vibration-welded butt joints

The strengths of glass-filled modified polyphenylene oxide (GF-MPPO) welds relative to the strengths of GF-MPPO are shown to depend on specimen thickness. (Modified polyphenylene oxide is a blend of poly (2,6-dimethyl-1,4-phenylene ether) and high-impact polystyrene.) Relative strengths on the order of 70 and 87 percent can be achieved in 6.1 and 3.18-mm-thick specimens, respectively. Welds of GF-MPPO to modified polyphenylene oxide (MPPO) can easily attain the strength of MPPO, the weaker of the two materials. In contrast to MPPO, in which weld strength decreases with increased weld pressure, the strengths of GF-MPPO to GF-MPPO welds and GF-MPPO to MPPO welds, are not affected by weld pressure.     

FEM stress analysis and strength of adhesive butt joints of similar hollow cylinders under static and impact tensile loadings

The stress wave propagations in butt adhesive joints of similar hollow cylinders subjected to static and impact tensile loadings are analyzed in elastic and elasto-plastic deformation ranges using the finite-element method (FEM). The impact loading is applied to the joint by dropping a weight. The upper end of the upper adherend is fixed and the lower adherend of which the lower end is connected to a guide bar is subjected to the impact loading. The FEM code employed is DYNA3D. The effects of the adhesive thickness and Young's modulus of the adhesive on the stress wave propagation at the interfaces are examined. In addition, the characteristics of the joints subjected to impact loadings are compared with those of the joints under static loadings and the joint strengths are estimated by using the interface stress distributions. It is found that the maximum value of the maximum principal stress, σ₁ occurs at the outside edge of the interface of the lower adherend to which the impact loading is applied. The maximum value of the maximum principal stress, σ₁ increases as Young's modulus of the adhesive increases when the joints are subjected to impact loadings. It is found that the characteristics of the joints subjected to impact loadings are opposite to those subjected to static loadings. In addition, experiments were carried out to measure the strain response of the butt adhesive joints subjected to impact and static tensile loadings using strain gauges and the joint strengths were also measured. Fairy good agreements are observed between the numerical and the measured results.     

Quality analysis of hybrid adhesive-spot welded joints

In the paper, practical aspects of hybrid adhesive-welded joints are described. For the joints made of low-alloy car-body sheet steel HS340LA 1.2 mm thick at selected variable process parameters, a wide range of destructive and non-destructive tests was carried-out. The joints were made using three constructional adhesives, one of those dedicated for hybrid joints. For this adhesive, the most favourable hardening conditions were established. Quality analysis of hybrid joints was based on ultrasonic testing with use of an RSWA (Resistance Spot Weld Analyser) device, metallographic examinations, basic mechanical testing and tests at complex stress state, visual testing with a high-speed camera. Results were compared with adhesive bonding and spot welding. The whole research is summarized with conclusions drawn on the grounds of experimental and analytical results.     

压力管道金属材料焊接接头的流动加速腐蚀性能

通过温度、压力、流速可控的流动加速腐蚀实验机,模拟某冷凝水管线工况,对20钢分别与20钢、Q345R钢和304不锈钢焊接接头的流动加速腐蚀性能进行研究。通过扫描电镜(SEM)和能谱仪(EDS)对腐蚀产物进行表征。结果表明:腐蚀速率从大到小依次为20钢-20钢、20钢-Q345R钢、20钢-304不锈钢;相对于20钢母材,3种焊接接头的腐蚀电流均变小,腐蚀电位均向正方向偏移,构成电偶腐蚀时加速了母材的腐蚀速度。在介质流动的状态下,20钢-20钢焊接接头腐蚀产物膜为柱状,20钢-Q345R钢焊接接头腐蚀产物膜为分层片状结构,20钢-304不锈钢焊接接头腐蚀产物为网状结构,其覆盖率从大到小依次为20钢-Q345R,20钢-304不锈钢,20钢-20钢。     

Ceramic material used in forming welded joints

Translated from Steklo i Keramika, No. 10, pp. 19–20, October, 1989.