Laser spot weld bonding of mild steel

Laser spot weld bonding (LSWB) is a new joining process, which combines laser spot welding with a layer of structural adhesive in a single joint. The purpose of this paper is to introduce a new LSWB process with a special pulsed laser. With this method, the impact of adhesive gas on molten pool is weakened, and the gas can exhaust from the gap of the metal sheets. The carbon decomposed from the adhesive diffuses into the molten pool and changes the microstructure of the weld joint. The joint is mainly composed of martensite and bainite, and twinned martensite is found in the interface between the adhesive layer and metal sheet. In tensile shear test, LSWB specimens give the highest energy absorption compared with laser spot welded samples and adhesive bonded samples.     

Spot Welding–Adhesive Joints: Modelling and Testing

Modelling and testing of hybrid joints obtained by combination of two simple techniques, i.e., by application of spot welding and adhesive, is reported. The joints were subjected to uniaxial tension. The experiments were performed for: 1) a pure joining of the parts by spot welding and 2) spot welding–adhesive joining of the structural elements. A new experimental method was elaborated with application of two digital image correlation (DIC) systems. The method allowed for online monitoring of the deformation process of the joined elements with complex shapes. Modelling of the hybrid joints response to mechanical loading was performed by ABAQUS code. Damage process in the adhesive layer was taken into account. The obtained results lead to the conclusion that the strengthening of joints by the application of adhesive significantly improves static strength and energy absorption. The visible degradation process of the adhesive layer which started prior to the maximum value of force carrying the hybrid joint was obtained.     

A Prediction Method of the Behavior of Adhesively Bonded Structures under Cyclic Shear Loading Based on a Characterization of the Viscous Aspects of the Adhesive in an Assembly

The capabilities of structural bonding are more and more used. Estimating the abilities of an adhesive to endure repetitive loadings and to keep stable its mechanical properties along service life is an essential point to analyze in order to conduct fatigue assessments. The aim of this study is to develop a predictive tool for describing the fatigue behavior of an adhesive in an assembly under cyclic loadings. The approach developed analyzes the influence of viscosity on the mechanical behavior of an adhesive in an assembly based on monotonic and creep test results. Thanks to the evaluation of viscous phenomena, it is possible to predict the cyclic response of the adhesive. The experimental approach uses a unique bonded joint designed to limit the stress concentrations and with a maximum stress state in the center of the adhesive. In this paper, following the strategy developed under monotonic loading, experimental results under cyclic loading are presented for different types of loading using several load ratios and amplitudes. These results underline that the evolution of viscous deformations depends on the loading type. Under shear loading and for a ductile structural adhesive, the experimental results are well described using a viscoelastic–viscoplastic constitutive model with nonlinear viscous parameters. This model makes it possible to analyze the influence of different parameters on the mechanical response of bonded joints under cyclic shear loadings.     

Experimental Analysis of Static and Fatigue Strength Properties in Press-Fitted and Adhesively Bonded Steel–Aluminium Components

Press-fitted and adhesively bonded joints (Hybrid Joints) are increasingly used as an alternative way to traditional structural joining techniques. The main achievable benefits can be summarized in the possibility of maximizing the load transfer (torque or axial) and reducing both the weight and the stress field of the components, by taking advantage of the adhesive strength. Hybrid joints studies can be found in literature mainly on steel–steel components (Steel Hybrid Joints). The aim of this paper is to provide some relevant information on the static and fatigue strength properties in the case of steel–aluminium components (Mixed Hybrid Joints), from the experimental tests performed on a high strength, single-component adhesive which cures anaerobically. The use of the adhesive increases the press-fitted joint performances, with respect to its release force: the adhesive static shear strength is about 9 MPa, whereas the adhesive endurance limit is about 6 MPa, in presence of a stress ratio R = 0.1.     

Effect of bonding defects on shear strength in tension of lap joints having brittle adhesives

In this paper we examine how the joint strength of lap joints containing a brittle adhesive may be affected by partial removal of adhesive from the bonded area. It is found that the shear strength in tension of a lap joint specimen is governed essentially by the leading edges of the joint and not by the bonded area.     

Load transfer in adhesive double-sided patch joints

In this work, the application of adhesively bonded joints to connect two structural elements with a double-sided patch is studied. On the basis of the shear lag model, a simple closed-form solution was obtained. The analytical solutions can be used to predict the shear stress in the adhesive and the load transfer between the structural elements and the external patches. The load and shear stress distributions in the adhesively bonded region are presented. For verification of the analytical model, finite element analyses were employed to calculate the load transfer and shear stress for the double-sided patch joint under static tensile loadings. Good agreement was found between the theoretical predictions and numerical results. To obtain a better understanding of the joints, the effects of adhesive thickness, adhesive shear modulus and patch Young's modulus on the load transfer and shear stress distributions were investigated. The results show that the maximum shear stress occurs at the edge of the adhesive. The maximum value of the shear stress increases as the adhesive shear modulus and patch Young's modulus increase and as the adhesive thickness decreases. A more gradual load transfer can be achieved by increasing the adhesive thickness and decreasing the adhesive shear modulus. The simple analytical solution presented in this paper has the advantages of avoiding the numerical difficulties and giving explicit relationship between the stress state and joint parameters. Moreover, from the designer's point of view a closed-form and easy-to-use solution is preferred.     

Analysis and design of adhesively bonded joints for fatigue and fracture loading: a fracture-mechanics approach

An experimental–computational fracture-mechanics approach for the analysis and design of structural adhesive joints under static loading is demonstrated by predicting the ultimate fracture load of cracked lap shear and single lap shear aluminum and steel joints bonded using a highly toughened epoxy adhesive. The predictions are then compared with measured values. The effects of spew fillet, adhesive thickness, and surface roughness on the quasi-static strength of the joints are also discussed. This fracture-mechanics approach is extended to characterize the fatigue threshold and crack growth behavior of a toughened epoxy adhesive system for design purposes. The effects of the mode ratio of loading, adhesive thickness, substrate modulus, spew fillet, and surface roughness on the fatigue threshold and crack growth rates are considered. A finite element model is developed to both explain the experimental results and to predict how a change in an adhesive system affects the fatigue performance of the bonded joint.     

Strength of Adhesively-Bonded Butt Joints of Tubes Subjected to Combined High-Rate Loads

The dynamic strength of adhesively-bonded joints was investigated experimentally. The strength of the bonded joints under combined high rate loading was measured using the clamped Hopkinson bar method. Tubular butt joints bonded by epoxy resin were used for the experiment. Combined stress waves of tension and torsion were applied to the specimens. The strength of the adhesively-bonded joint was determined by measuring the stress waves propagated in the load output tube of the specimen. It was found that the dynamic strength of the adhesive joints was greater than the static strength under tensile and shear load.     

Increasing single-lap joint strength by adherend curvature-induced residual stresses

Single-lap joint (SLJ) geometry is the most widely used type of adhesive joint geometry. In this joint, peel stresses occur at the overlap ends due to load eccentricity and the presence of shear-free adhesive termination surfaces. These peel stresses, along with the transverse tensile stresses which occur along the overlap longitudinal axes, and adhesive shear stresses, ultimately cause joint failure. Obviously, reductions in these stresses should result in higher joint strength and increased load capacity. To this end, we exploited elastic spring-back capability of (steel) metal adherends by initially forming curved segments of varying arc lengths and radii at overlap ends. These adherends with curved-end sections were then bonded in single-lap configuration, simply by applying sufficient bonding pressure to elastically flatten the curved segments to result in typically flat overlap sections subsequent to adhesive cure and the removal of bonding pressure. Since the elastic adherend overlap ends tend to revert back to their initial curved form, they exert compressive residual stresses on the adhesive layer in the overlap end regions. We determined that the compressive residual stresses induced in this fashion considerably increased the load capacity of SLJs subjected to tension.     

钛合金‑芳纶纤维复合材料单搭接胶接接头渐进破坏分析

采用芳纶纤维复合材料与钛合金制备单搭接胶接连接实验件。利用万能实验机、DIC、应变采集系统等手段,对胶接接头的极限载荷、应变场、应变分布和破坏模式进行表征,分析了拉伸载荷下胶接接头的应变分布规律和复合材料层合板刚度折减规律,探究了异质材料单搭接胶接接头的破坏过程。结果表明,胶接接头破坏模式为搭接接头两端胶层界面破坏,中间部位复合材料层间破坏。接头破坏过程为渐进破坏,受载时复合材料端头产生较大的剪切应变,裂纹在此处萌生,并不断向钛合金端头扩展,扩展部位复合材料层合板刚度不断折减,直到搭接面积过小胶层突然发生界面破坏。     

A simple approach for characterizing the performance of metallic tubular adhesively-bonded joints under torsion loading

Adhesive bonding of joints is one of the most commonly and widely used joining methods in piping systems. This work is concerned with the investigation of the influence of the non-linear behavior of the adhesive used in such bonded joints on their performance. The parametric analysis module of ABAQUS was used to model the joint. The model facilitated the analysis of different geometric, loading and material characteristics of the system, in particular the adhesive nonlinearity, which is of prime interest in this work. By using the Ramberg–Osgood plasticity model, the failure threshold of the adhesive for various joint lengths (hereafter referred to overlap length) was characterized. The plasticity model used in this study was fine-tuned using only a limited number of known parameters, through comparison with the results of the finite element (FE) simulation. The results obtained from the FE analysis were verified by experimental results. The FE strategy is demonstrated to be an effective means for predicting the capacity of such joints, where conducting a pure shear test is either impossible or difficult to accomplish. Contrary to the findings based on the elastic finite element analysis, the plasticity analysis revealed that the overlap length affects the ultimate strength of the joint.     

Strength of cylindrical butt joints bonded with epoxy adhesives under combined static or high-rate loading

The influence of loading rates and the combined stress states of tension and shearing on the strength, strain, and absorbed energy of an adhesively bonded joint was experimentally investigated. Cylindrical butt joint specimens were prepared and strength tests were performed on the specimens with a servo-controlled hydraulic testing machine that combined tension and torsion loading. Two types of epoxy adhesives, ductile and brittle, were applied to the specimens. The tests were performed under a quasi-static condition of 6.67×10⁻² MPa/s and a high-rate loading condition of 1.00×10³ MPa/s. The results of the combined loading tests showed that the states of the fractured surfaces were not affected by the loading rates. As for the ratio of tensile and shear loading, adhesive failure tended to partially occur when the ratio of shear loading was very high. The strength points for the specimens bonded with each adhesive were distributed in a stress plane of tension and shearing and could be fitted with a curve that was described by an equation with exponential parameters that were not influenced by the strain rate; however, other parameters that described the intercepts were influenced. The failure strains and absorbed energies for the brittle adhesive were slightly dependent on the strain rate, but this dependency was unclear for the ductile adhesive.     

The influence of temperature and cyclic loading on adhesion in polycarbonate-polyurethane-glass adhesive joint

The paper deals with the influence of temperature and cyclic loading on adhesion and transparency of the adhesive joint consisting of soda-lime-silica glass and polycarbonate (PC) bonded with polyurethane (PU) adhesive film. The tested joint represents critical part of transparent armored glass used in vehicles. Dynamic tension creep tests were performed at temperatures to which armored glass is commonly exposed (25, 50, 60, 70, and 80?°C). Sawtooth loading mode was performed to 650?N and the sine loading in the force range 0–1550?N. The aim of the paper was to discover conditions causing delamination of the adhesive joint and glass milky appearance during the use. Delamination of soda-lime-silica glass/PU adhesive interface occurred at 25?°C after load to 1550?N without the change of transparency. Both dynamic and static tension creep tests performed to 400?N led to plastic deformation of PU adhesive at and above 70?°C, in preference at both ends and circumference edges of adhesive joint, and thus, to loss of transparency, but extent of deformation differed. Milky maps observed after sawtooth load to 650?N at 80?°C reflected delaminated areas of highly deformed PU adhesive. Temperature of 70?°C was found out to be the critical parameter being in synergy effect with different thermal expansion of PC and PU adhesive.     

Numerical design and multi-objective optimisation of novel adhesively bonded joints employing interlocking surface morphology

A novel concept for joining materials is presented which employs adhesive joints with interlocking bond-surface morphology formed on the surfaces of male and female adherends that mechanically interlock in shear when brought together. In the present work, miniature, single-lap joint specimens with a single truncated square pyramid interlocking profile, centred in the bond area, are investigated. The performance of the concept is assessed through finite element analysis (FEA) by incorporating yield criteria representing plasticity in the adherends and a cohesive zone model to represent damage in the adhesive layer. This allows for effective simulation of the joint response until ultimate failure and thus, full assessment of the concept's performance. Various interlocking geometries are explored and refined through an adaptive surrogate modelling design optimisation procedure coupled with FEA. The results indicated that significant improvements in work to failure, of up to 86.5%, can be achieved through the more progressive failure behaviour observed compared to that of a traditional adhesively bonded joint. Improvements in the joint's ultimate failure load can also be achieved with a relatively ductile adhesive system.     

Reliability analysis of bonded joints with variations in adhesive thickness

Bonded joints are used in several industrial applications as a surrogate of more expensive repairs, but their reliability must be ascertained. Failure in a bonded joint mainly occurs in the adhesive due to stress concentrations that directly depend on the adhesive thickness. In practice, it is difficult to ensure a good accuracy of the final adhesive thickness, leading to uncertainty to its spatial variability. This uncertainty greatly influences the strength of the bonded joint. This work deals with one of the main key issues in bonded joints: the influence of the spatial variations in the adhesive thickness on the reliability of the joint and an excessive shear stress level caused by the adhesive thickness variations may lead to failure. This paper provides reliability analysis by considering the adhesive thickness as a stochastic field. The experimental thickness field is obtained so as to identify the stochastic parameters. These parameters are then introduced in a structural reliability model to evaluate the failure probability. Results show the influence of adhesive thickness uncertainty on bonded joint failure.     

Glass/epoxy composites and aluminium alloy joint using Kevlar® intermediate layer and nanoclay-reinforced epoxy adhesive

Adhesive lap joint between glass fibre/epoxy composites and aluminium alloy (2014 T4) was prepared by an in situ moulding process using a matched die mould. The surface of aluminium alloy was treated with chromic acid before adhesive bonding. Lap shear strength and fatigue life were evaluated in tensile mode and tension–compression mode (at 40% of lap shear load of adhesive joint), respectively. Knurling on the surface of aluminium alloy improved the lap shear strength of the adhesive joint but did not influence the fatigue life of the same. Lap shear strength and fatigue life of adhesive joint made with neat epoxy adhesive and reinforcement of an intermediate layer of Kevlar^® between glass/epoxy composite and aluminium alloy were observed to be 0.44?kg/mm² and 3.6?×?10⁵ cycles, respectively. In another case, lap shear strength and fatigue life of similar type of adhesive joint made from nanoclay (Cloisite 30B)-reinforced epoxy adhesive and without reinforcement of an intermediate layer of Kevlar^® were observed to be 0.38?kg/mm² and 2.3?×?10⁵ cycles, respectively. Whereas, lap shear strength and fatigue life of adhesive joint made from nanoclay-reinforced epoxy adhesive along with the reinforcement of an intermediate layer of Kevlar^® were 0.48?kg/mm² and 3.9?×?10⁵ cycles, respectively. Therefore, adhesive joint made from nanoclay-reinforced epoxy adhesive along with the reinforcement of an intermediate layer of Kevlar^® was the best.     

Stress Analysis of Generally Asymmetric Single Lap Adhesively Bonded Joints

An analysis is presented that predicts shear and peel stresses in an adhesively bonded single lap joint having general asymmetric configuration. The single lap joint is under tension loading together with moments induced by geometric eccentricity. Because these eccentricity moments are the key elements of this analysis, a general relationship between the eccentricity moments and simple geometric moments has been determined with the aid of finite element analysis (FEA). Example calculations show that the shear- and peel-stress profiles from the closed-form model are well matched to FEA results except in the small regions near the free ends of the joints, because of the shear lag basis of the model. For asymmetric joints, the model predictions are more accurate for the case of modulus eccentricity than thickness eccentricity. Elastic-limit load predictions accounting for both shear and peel stress in the adhesive have been used to find optimal joint configurations between asymmetric adherends.     

Adhesively bonded steel tubes — Part I: Experimental investigations

Circular hollow sections (CHS) represent a class of tubular structural steel elements that enjoy great popularity among architects, and civil engineers. Connections thereof, however, remain complicated, despite significant developments in welding procedures. The first part of this series of two articles summarises research on adhesive bonding as a substitute to traditional joining techniques for tubular sections on a large scale. For that purpose, suitable adhesives have been selected and fully characterised, their adequacy for the required strength in combination with steel verified on lap shear samples, and finally corresponding adhesively bonded tubular joints tested in quasi-static loading with diameters from 42 mm (joint capacities from 55 kN) up to 300 mm (joint capacities up to 1’800 kN). Additionally to various diameters and overlap lengths considered, effects resulting from different types of imperfections, as axial and angular misalignment, on joint strength were experimentally investigated. Presented results clearly indicate that adhesive bonding is a joining technique adapted for civil engineering applications. The second part of this series presents a design methodology for adhesively bonded tubular joints that fits into the conceptual framework of civil engineering practice.     

Elasto-Plastic Analysis of Adhesively Bonded Symmetric Single Lap Joints Under In-Plane Tension and Edge Moments

An analysis is presented that predicts adhesive shear and peel stresses and strains in an adhesively bonded single lap joint having symmetric configuration with adhesive behavior. The single lap joint is under tension loading together with moments induced by the interactions of the geometric eccentricity and the boundary conditions of the joint. The von Mises yielding criterion is used to relate the adhesive stress components within the yielded region. The adhesive strains are computed from the relative displacements of the adherends and can be considered as an average of the strain variation through the adhesive thickness direction. Example calculations show that the predicted adhesive shear and peel stress and strain profiles are well matched to detailed finite element analysis results. Generally, the analytical model predictions are found to be more accurate when the adhesive thickness is small.     

Elasto-Plastic Analysis of Adhesively Bonded Symmetric Single Lap Joints Under In-Plane Tension and Edge Moments

An analysis is presented that predicts adhesive shear and peel stresses and strains in an adhesively bonded single lap joint having symmetric configuration with adhesive behavior. The single lap joint is under tension loading together with moments induced by the interactions of the geometric eccentricity and the boundary conditions of the joint. The von Mises yielding criterion is used to relate the adhesive stress components within the yielded region. The adhesive strains are computed from the relative displacements of the adherends and can be considered as an average of the strain variation through the adhesive thickness direction. Example calculations show that the predicted adhesive shear and peel stress and strain profiles are well matched to detailed finite element analysis results. Generally, the analytical model predictions are found to be more accurate when the adhesive thickness is small.