Fusion simulation of electrofusion polyethylene joints for gas distribution

Fusion simulation is one of the key techniques used in designing and producing electrofusion joints for gas distribution and in evaluating fusion joint integrity. This paper describes the results of numerical simulation of the thermal fusion process, using the finite element method. A nonlinear heat transfer computer program was used to obtain the temperature profile of an electrofusion joint at fusion. It was found that the temperature experimentally measured at the fusion interface by insertion of a thermocouple agreed with the temperature computed by fusion simulation. In addition, as both the temperature at the fusion interface and the resin temperature close to the wire corresponding to the mechanical strength of the fusion part were measured, it was confirmed that the proper heating conditions for each joint could be determined based on the results of the fusion simulation.     

Design and performance evaluation of vacuum cleaners using cyclone technology

A cyclone technology for a vacuum cleaner—axial inlet flow cyclone and the tangential inlet flow cyclone — to collect dusts efficiently and reduce pressure drop has been studied experimentally. The optimal design factors such as dust collection efficiency, pressure drop, and cut-size being the particle size corresponding to the fractional collection efficiency of 50% were investigated. The particle cut-size decreases with reduced inlet area, body diameter, and vortex finder diameter of the cyclone. The tangential inlet twin-flow cyclone has good performance taking into account the low pressure drop of 350 mmAq and the cut-size of 1.5 μm in mass median diameter at the flow rate of 1 m³/min. A vacuum cleaner using tangential inlet twin-flow cyclone shows the potential to be an effective method for collecting dusts generated in the household.     

A non-isothermal healing model for strength and toughness of fusion bonded joints of amorphous thermoplastics

A study to investigate the influence of processing on the fusion bonding of graphite (AS4) poly(etheretherketone) (PEEK) thermoplastic composites (BASF commingled PEEK/graphite NCS woven fabric) using a polyetherimide (PEI) film at the interface is presented. Fundamental to all fusion bonding processes is the intermolecular diffusion between surfaces in intimate contact. A model based on the healing theory of amorphous polymers has been proposed to predict strength and toughness as a function of non-isothermal process history. This model considers two different microscopic failure mechanisms of a healed interface. For the first time, using non-isothermal data and proper data reduction procedures, it is possible to differentiate between these two mechanisms, which are otherwise indistinguishable from isothermal data. Temperature dependent reptation times representative of the kinetics of chain diffusion in the polymer have been evaluated for both mechanisms over a large range of process temperatures using fracture tests conducted on lap shear specimens manufactured using a hot press. Three alternate and independent techniques to estimate the reptation time in PEI indicate that the model based on the average interpenetration distance is most representative of the physical system. Lap shear strength predictions based on this formulation have been generated for various non-isothermal conditions measured in the hot press and are within 20% of the experimental data. The model was used to show that in isothermal processes, maximum strength and toughness can be achieved in less than 1 s for temperatures exceeding 290°C. Application of the model to a highly non-isothermal technique such as resistance welding using amorphous film technology is also presented. Model predictions show that asymptotic strength may be achieved in relatively short process times with appropriate welding conditions.     

Stress analysis and strength evaluation of bonded shrink fitted joints subjected to torsional loads

This paper deals with the stress analysis and strength evaluation of bonded shrink fitted joints subjected to torsion. The stress distributions in the adhesive layer of bonded shrink fitted joints are analyzed by the axisymmetric theory of elasticity when an external torsion is applied to the upper end of the shaft. The effects of the outer diameter and the stiffness of rings on the interface stress distributions are clarified by numerical calculations. Using the interface stress distributions, the joint strength is predicted. In addition, the joint strength was measured experimentally. It is seen that rupture of the adhesive layer is initiated from the upper edge of the interface when torsion is applied to the upper end of the shaft. The numerical results are in fairly good agreement with the experimental results. It was found that the joint strength of bonded shrink fitted joints is greater than that of shrink fitted joints.     

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.     

Microstructure and mechanical strength of Ti3AlC2 joints bonded using oxides as interlayer

Ti₃AlC₂ ceramics were successfully joined with TiO₂ and Nb₂O₅ respectively as interlayers via solid-state diffusion bonding at 1300 °C. The joints bonded with TiO₂ and Nb₂O₅ exhibit distinct microstructures. Two continuous thin Al₂O₃ oxidation layers with a thickness around 1 μm were formed in the joints bonded with TiO₂. Between the oxidation layers there exists a dense oxycarbide (TiC_1-xO_x) layer. For the joint bonded with Nb₂O₅, a dense bonding layer with Nb₂AlC and Nb₄AlC₃ grains surrounded by thin Al₂O₃ oxidation layers at the grain boundaries were obtained. The shear strength of the final joints shows clear dependences on both the thickness and microstructure of the joints. Smaller joint thickness and the microstructure with complex phases favour for higher shear strength. Those result implies that bonding with oxides is a practical and efficient method for joining Ti₃AlC₂.     

3-D FEM stress analysis and strength evaluation of single-lap adhesive joints subjected to impact tensile loads

The stress wave propagations and interface stress distributions in the single-lap adhesive joint under impact tensile loads are analyzed using the three-dimensional finite element method (3D-FEM) taking into account the strain rate sensitive of the adhesive using Cowper–Symonds constitutive model. It is found that the rupture of the joint initiates near the middle area of the edges of the interfaces along the width direction. In addition, the effects of Young's modulus of the adherend, the overlap length and the thickness of the adhesive layer, and the initial impact velocity of the impacted mass on the stress wave propagations and the interface stress distributions are examined. The characteristics are compared with those of the joint under static loads, which show the different properties. Furthermore, experiments are also carried out for measuring the strain responses and the joint strength. A fairly good agreement is observed between the numerical and the measured results. The strength of the single-lap adhesive joint, which is described using impact energy, is obtained between 5.439 and 5.620 J for the present joint.     

A three-dimensional finite-element stress analysis and strength evaluation of stepped-lap adhesive joints subjected to static tensile loadings

Stress distributions in stepped-lap adhesive joints subjected to static tensile loadings are analyzed using three-dimensional finite-element calculations. For establishing an optimum design method of the joints, the effects of the adhesive Young's modulus, adhesive thickness and number of steps on the interface stress distributions are examined. The results show that the maximum value of the maximum principal stress σ₁ occurs at the edge of the adhesive interfaces. The maximum value of the stress σ₁ decreases as the adhesive Young's modulus and number of steps increase and as the adhesive thickness decreases under static loadings. A method for estimating the joint strength under static loadings is proposed using interface stress distributions. For verification of the finite-element method calculations, experiments were carried out to measure the strains and the joint strengths under static loadings. Fairly good agreements were found between the numerical and the experimental results.     

Stress analysis and strength evaluation of single-lap band adhesive joints of dissimilar adherends subjected to external bending moments

Single-lap band adhesive joints of dissimilar adherends subjected to external bending moments are analyzed as a four-body contact problem using a two-dimensional theory of elasticity (plane strain state). In the analysis, the upper and lower adherends and the adhesive which are bonded in two regions are replaced by finite strips. In the numerical calculations, the effects of the ratio of Young's moduli of the adherends, the ratio of the adherend thicknesses, and the ratio of the band length to the half lap length on the stress distributions at the interfaces are examined. A method for estimating the joint strength is proposed using the interface stress and strain obtained by the analysis. An elasto-plastic finite element analysis (EP-FEA) was conducted for predicting the joint strength more exactly. Experiments to measure strains and the joint strength were also carried out. The results show that the strength of a single-lap band adhesive joint is almost the same as that of a single-lap adhesive joint in which the two adherends are completely bonded at the interfaces. Thus, the single-lap band adhesive joints are useful in the design of single-lap joints.     

Predicting the strength of adhesively bonded joints of variable thickness using a cohesive element approach

One major characteristic of bonded structures is the highly localised nature of deformation near sharp corners, ply-terminations, and ends of joints where load transfer occurs. This paper presents an investigation of the use of a cohesive zone model in predicting the strong effects of stress concentration due to varying adherend thickness on the pull-off strength measured by the Pneumatic Adhesion Tensile Testing Instrument. A comparison is made with the point-strain-at-a-distance criterion, where the plastic deformation of the adhesive is analysed using a modified Drücker–Prager/cap plasticity material model. The fracture properties of the cohesive zone model were determined using double-cantilever and end-notch flexural specimens, and the cohesive strengths were measured using tensile and lap shear tests. Comparisons with experimental results reveal that the cohesive zone model with perfectly plastic (or non-strain-softening) cohesive law provides accurate predictions of joint strengths.     

The determination of dynamic strength of single lap joints using the split Hopkinson pressure bar

The current investigation focuses on the determination of the strength of adhesive-bonded single lap joints under impact with the use of a split Hopkinson pressure bar (Kolsky bar). For this, experiments were conducted at different loading rates, for identical metallic adherends bonded by a two-part epoxy adhesive. Four different types of specimens were adopted, all with a given adhesive thickness. The length of overlap and the width of the adherends were varied resulting in four different areas of overlap. It was found that the average strength, as calculated from the readings obtained from a Kolsky bar, increases with decrease of overlap area. An elastodynamic model for the shear strain of the adhesive-bonded single lap joint was developed to investigate this drastic effect of overlap area on the average strength of the joint. The mathematical model was found to be dependent on both the material properties of the adherend and adhesive, as well as the structural properties of the joint, viz. the width and the thickness of the adhesive layer. A combined experimental-numerical technique was used to predict the strain distribution over the length of the bond in the adhesive. It was found that the edges of the adhesive were subjected to maximum strain, while a large part of the adhesive was found to exhibit zero shear strain. The effect of the lap length and the width was studied individually. The cumulative effect of averaging the strain over the entire overlap area, was decreased shear strain for an increased overlap area. The Kolsky bar was identified to give conservative values of the shear strength of an adhesive bonded lap joint under high rates of loading.     

Investigation of strength degradation of adhesive-bonded aluminum joints exposed to corrosive environment using electrochemical methods

Interfacial corrosion is responsible for the strength degradation of adhesive-bonded aluminum joints (ABJs) exposed to corrosive environment. In this study, electrochemical noise and electrochemical impedance spectroscopy (EIS) measurements were performed on the aluminum alloy X610-T4PD covered with adhesive (ACA) to understand the interfacial corrosion. And environmental simulation tests (i.e. neutral salt spray (NSS) and hot humidity environment) for ABJ were carried out to investigate the joint strength degradation. Test results indicated that the variations of current and potential in the EN measurement were closely related to the initiation of corrosion in the samples. The Nyquist plots in the EIS measurement for various immersion times showed that the corrosion of ACA accelerated after about 140 h. Furthermore, a linear relationship between the residual strength of ABJ exposed to NSS and the reciprocal of interfacial corrosion resistance (R_t) of ACA was found, which was verified by ABJ exposed to hot humidity environment.     

Microstructure and mechanical strength of transient liquid phase bonded Ti3SiC2 joints using Al interlayer

Based on the structure characteristic of Ti₃SiC₂ and the easy formation of Ti₃Si_1−xAl_xC₂ solid solution, a transient liquid phase (TLP) bonding method was used for bonding layered ternary Ti₃SiC₂ ceramic via Al interlayer. Joining was performed at 1100–1500 °C for 120 min under a 5 MPa load in Ar atmosphere. SEM and XRD analyses revealed that Ti₃Si(Al)C₂ solid solution rather than intermetallic compounds formed at the interface. The mechanism of bonding is attributed to aluminum diffusing into the Ti₃SiC₂. The strength of joints was evaluated by three point bending test. The maximum flexural strength reaches a value of 263 ± 16 MPa, which is about 65% of that of Ti₃SiC₂; for the sample prepared under the joining condition of 1500 °C for 120 min under 5 MPa. This flexural strength of the joint is sustained up to 1000 °C.     

粘接设计中设计基准强度和实际容许强度的计算方法

1前言粘接技术因其独特的性能而广泛应用于各工业领域。但是,它不像焊接、螺栓连接等成熟技术那样有据可循,其接头设计必须经大量试验验证,受施工时间和客观条件限制这是很难做到的。日本的学者原贺康介多年来对此问题进行了大量研究。他认为可靠性高的粘接接头必须满足以下2点:接头破坏时其内聚破坏需占40%以上;初始粘接强度的变化系数必须小于     

Fatigue strength of vibration welded thermoplastic butt joints

Fatigue data are presented for the strengths of 120-Hz vibration-welded butt joints of four resins: the three amorphous polymers polycarbonate (PC), polyetherimide (PEI), and modified polyphenylene oxide; and the semicrystalline polymer poly(butylene terephthalate). Data are also presented for the fatigue strength of 250-Hz vibration welds of the high-temperature polymer PEI. For all the welds, fatigue strength was evaluated through 10-Hz, tension-tension, load-controlled tests at an R value (ratio of minimum stress) of 0.1. Surprisingly, for all the stress levels studied, none of the PC test specimens failed at the welds, indicating that the fatigue strength of PC welds equals that of the base resin. This is not true of the other three resins, except at relatively low stress levels. For each of the four resins, macrographs are used to highlight the differences between the failure surfaces of monolithic specimens and specimens that failed at the welds.     

Elastoplastic finite element stress analysis and strength evaluation of adhesive lap joints of hollow shafts subjected to tensile loads

The stress distributions in adhesive lap joints of dissimilar hollow shafts subjected to tensile loads have been analyzed by the elastoplastic finite element method, taking the nonlinear behaviors of the adhesive and the hollow shafts into consideration. A prediction method for the joint strength has been proposed based on the Mises equivalent stress distribution in the adhesive and the frictional resistance between the adhesive and the shaft after rupture of the adhesive. In the experiments, three different kinds of adhesive lap joints were made, i.e. the inner and outer hollow shafts were aluminum alloy/aluminum alloy, steel/steel, and steel/aluminum alloy combinations, and the tensile strength of each joint was measured. From the numerical calculations, in the case of the two hollow shafts made of the same material, the tensile strength increases with an increase of Young's modulus of the shaft and in the case of the two hollow shafts made of different materials, the tensile strength increases when the inner hollow shaft of larger Young's modulus is bonded to the outer one of smaller Young's modulus. Also, the effects of the overlap length and the inner diameter of the inner shaft on the tensile strength of the joint are discussed. By comparing the predicted values of the tensile strength with the experimental results, it was shown that the proposed prediction method could estimate the tensile strength of the adhesive lap joints of hollow shafts within an error of about 15%.     

An evaluation of strength wearout models for the lifetime prediction of adhesive joints subjected to variable amplitude fatigue

Almost all structural applications of adhesive joints will experience cyclic loading and in most cases this is irregular in nature, a form of loading commonly known as variable amplitude fatigue (VAF). This paper is concerned with the VAF of adhesively bonded joints and has two main parts. In the first part, results from the experimental testing of adhesively bonded single lap joints subjected to constant and variable amplitude fatigue are presented. It is seen that strength wearout of bonded joints under fatigue is non-linear and that the addition of a small number of overloads to a fatigue spectrum can greatly reduce the fatigue life. The second part of the paper looks at methods of predicting VAF. It was found that methods of predicting VAF in bonded joints based on linear damage accumulation, such as the Palmgren–Miner rule, are not appropriate and tend to over-predict fatigue life. Improved predictions of fatigue life can be made by the application of non-linear strength wearout methods with cycle mix parameters to account for load interaction effects.     

Bonding performance after aging of fusion bonded hybrid joints

The investigations of this article are showing the bonding performance after aging of hybrid fusion bonds in combination with a laser pre-treatment. The investigated materials are a galvanized steel (HX340 LAD Z100MB) and two glass fiber reinforced Polyamide 6 materials. In order to achieve a structural strength of the fusion bond a laser pre-treatment is used. The investigation is focusing on the changes from the laser pre-treatment to the galvanized surface by analyzing the steel surface with a scanning electron microscope, energy disperse X-ray spectroscopy, micro sections and surface roughness measurements. The composition of the applied thermoplastic materials is not in the focus of the article which is why different manufacturers for the fiber reinforced thermoplastic material have been chosen. The aging of the samples is done by a climate change (PV1200) and a salt spray (PV1210) test in order to evaluate different aging mechanisms. Furthermore the investigation is providing a crucial finding by showing the impact of a batch change on the achievable lap-shear strength by comparing two batches from the same manufacturer. The results of the laser surface pre-treatment show that the zinc coating of the steel adherend is reduced significantly and does not provide a closed coating. The climate change test after 100 cycles showed no decrease of lap-shear strength compared to the reference when the highest investigated pre-treatment intensity is applied to the surface. The salt spray test showed a corrosion of the pre-treated area for laser pre-treatment settings which generate a low amount of oxygen on the surface. The pre-treatment settings generating a more oxidized surface (medium and high intensity) showed only a minor influence on the achievable lap-shear strength after 90 cycles.     

Innovative approach to testing the quality of fusion joints

Abstract

The exterior beads formed during a butt fusion process were used for non-destructive testing of the quality of butt-fused HDPE pipe joints. This innovative concept was tested using a dimensionless quality parameter that is based on tensile energy to break (TEB) values obtained from tensile testing of both the bead and joint specimens. The results show an r² of 0·87 for a linear regression between these two sets of specimens, which supports the hypothesis that the external bead squeezed out of a butt-fused joint can be used to test the quality of the joint itself. Statistical analysis was carried out to determine the effects of other tested parameters. Furthermore, four distinct failure modes have been identified and a quality test protocol using the quality parameter is proposed.