Overlap Joints Research Articles

SY7-3. Trials of IT based-telemonitoring of blood pressure for pregnant women at higher risk: an overview of the BUMP trials

The overlap joints of 6061 aluminium alloy and galvanized DP590 steel were made by the laser welding-brazing technology. Effects of Si contents in filler wires on weld appearances, microstructure and mechanical properties of the welding-brazing joints were studied. The well-formed joints could be obtained under the optimized welding-brazing parameters. The interfacial intermetallic compounds (IMCs) could divided into five zones from the steel side to the Al side: the R-IMCs and G-IMCs mainly composed by Fe(Al,Si) phases, the S-IMCs mainly consisted of Fe2(Al,Si)5 phases, the P-IMCs mainly made up of Fe(Al,Si)3 phases and the Fe2Al8Si phases formed at edges of the P-IMCs. Various ranges and morphologies of IMCs within different zones were attributed to the element diffusion and microstructure evolution affected by thermal interactions. Formation of the Fe–Al–Si ternary compounds softened the hardness of interfacial zones compared to the Fe–Al binary compounds. Harness of the Fe2(Al,Si)5 phase was highest, followed by the Fe(Al,Si)3 phase and then the Fe(Al,Si) phase. Addition of Si element significantly improved tensile properties of the welding-brazing joints, optimal tensile strength and ductility could be achieved when the AlSi10 wire was adopted, owing to the dispersion strengthening of the soft G-IMCs distributed discretely within S-IMCs.

A new design model for welded joints

AbstractIn the AiF‐FOSTA research project P1020 [1], a new design model for welded joints was developed. In this context, a small scale test on flat tensile specimens was designed, with the help of which various influences on the strength and ductility of the welds were investigated. Furthermore, extensive tests were carried out on overlap joints, cruciform joints with double fillet welds as well as partially and fully penetrated butt joints. This was done to calibrate the weld construction factor αw, which takes into account the influence of the type of joint on the load‐bearing capacity. In the following article, after a short summary of the current state of research, the design model, and the results from the parameter studies on flat tensile tests are described in more detail in [2–4]. Subsequently, the test program on welded joints and the calibration of the weld construction factor αw are presented. Finally, the results of the design model and the tests carried out are compared with test results from other research projects and the design model of prEN 1993‐1‐8 [5].

Microstructure, mechanical and functional properties of refill friction stir spot welds on multilayered aluminum foils for battery application

The production of batteries often involves the joining of multilayered foils to a conductive tab. In the present study, a solid state spot welding method, the refill friction stir spot welding (refill FSSW), was employed for welding multilayered commercially pure aluminum (CP–Al) foils to 2024-T3 Al alloy sheets (tab). Defect-free welds with high lap shear strength (LSS) are obtained. In the stirred zone (SZ), 2024 Al alloy is only found within the shoulder refill region, which is greatly refined due to dynamic recrystallization. Unlike overlap joints in thicker sheets, a thermo-mechanically affected zone also forms above the SZ in the probe refill region. “Stop-action” experiments have been conducted to describe joint formation. The presence of the 2024 Al alloy tabs resulted in significant changes to material follow behavior and the formation of microstructural zones not previously observed in conventional refill FSSW overlap welds in thicker sheets. Most welds failed in SZ pull-out mode during LSS test. The cracks initiate at the interface between the upper sheet and the first layer of the multilayered foils and then propagate upward and circumferentially outside the SZ. Welds of multilayered Al foils produced by refill FSSW show low contact resistance. The decomposition of electrochemically active materials in batteries can be avoided by maintaining a minimum distance from the spot-weld. The produced welds with flat appearance, high mechanical properties, and potential to meet industry requirements imply that refill FSSW is a promising welding technique for battery production.

New Weldable Steel for Rebars

A new steel grade, developed at the CELSA steelworks in Ostrowiec Świętokrzyski and used in the production of rebars, contributes greatly to the development of industrial and civil engineering. Steel B600B is characterised by yield point fyk = 600 MPa and immediate tensile strength ftk = 700 MPa. Tests revealed that the steel satisfies all requirements of related standards, both in terms of strength and processing properties. The mechanical properties of the new steel grade are higher by 20% than those of currently produced steels characterised by the highest mechanical properties (characteristic yield point Re= 500 MPa). As a result, the application of the new steel provides notable technical and economic advantages. The new steel grade meets requirements concerning technical class C in accordance with PN-EN 1992-1-1, which indicates that the steel has a significant yield point margin (being an important advantage in terms of limit state design). Plastic steels are easier to weld and less susceptible to welding crack formation. Technological (research-related) tests revealed the favourable welding properties of the new steel. Welding tests were performed using the manual metal arc welding method, i.e. the most common welding process used when making structural reinforcements. The welding tests involved the making of butt, overlap and cruciform joints. The strength and technological tests revealed that the steel satisfied the requirements specified in the PN-EN ISO 17660-1 standard.

Design of adhesively bonded lap joints with laminated CFRP adherends: Review, challenges and new opportunities for aerospace structures

Adhesive bonding is one of the most suitable joining technologies in terms of weight and mechanical performance for current carbon fiber reinforced polymer aircraft fuselage structures. However, traditional joint topologies such as single overlap joints induce high peel stresses, resulting in sudden failure and low joint strength when compared to metal adherends. This drawback in using carbon fiber reinforced polymer is hindering their performance and efficiency in full-scale structures where joints are essential.The goal of this paper is to review how the joint design can help to improve the lap shear strength of composite bonded joints, to recognize the challenges that still need to be understood and to give insight into new opportunities. The focus is thereby on means to increase the matrix-dominated out-of-plane strength of the adherend in order to postpone delamination failure, as it is known to be the most prone type of failure of composite bonded joints. The paper is divided in two main parts: firstly, a review of topology-related and material-related design parameters is given and secondly, future opportunities to improve out-of-plane strength of CFRP bonded joints yet to be explored are discussed.

Fatigue assessment of laser beam and friction stir welded joints made of aluminium

Available fatigue recommendations are typically developed for arc-welded joints. Some of them may need to be adjusted to fit fatigue life of joints manufactured with non-conventional welding techniques since they show different mechanical properties. Laser beam and friction stir welded butt and overlap joints made from aluminium are addressed in this paper focused on a comparison between different fatigue assessment methods. For an evaluation, S-N data from published papers was collected. Additionally, fatigue tests on laser beam and friction stir welded overlap joints were carried out. For a fatigue assessment, the nominal stress, notch stress and effective stress approach were applied. The comparison of the endurable nominal stresses showed a comparatively high fatigue strength of the tested friction stir welded overlap joints in comparison to literature data. The notches at the interface of the overlap joints were observed to have an asymmetric geometry compared to the common symmetric one, frequently found in literature, leading to a lower stress concentration. A comparison between endurable nominal stresses and the classes FAT 28 for butt welded and FAT 12 for overlap welded joints resulted in a conservative design for the majority of specimens. An evaluation based on notch stresses lead to partly non-conservative results that could be explained by the mild notches present at the laser-beam welded butt joints. For the effective stress approach, an evaluation of the micro-structural length was performed and a FAT-value is proposed.

Effect of electrode pressing force on the amount of energy supplied to interelectrode space in resistance projection welding with constant current welding machine

The paper describes the procedure for theoretical and experimental determination of the graphical regularity of the effect of the electrode pressing force on the amount of energy supplied to the interelectrode space when producing overlap joints of plates with equal thicknesses by using resistance projection welding. The regularity reflects a sufficiently strong connection between the parameters of the welding mode with the heat balance equation of the interelectrode space and the Joule-Lenz law.

Investigating friction spin welding of thermoplastics in shear joint configuration

The welding of thermoplastic pipes under a shear joint configuration using friction spin welding is investigated. The shear joint configuration consists of two cylindrical and concentric polypropylene plastic parts joined with each other at their interfacing cylindrical surfaces through frictional heat generation. The effects of welding pressure and rotational velocity on the joint overlap distance and joint strength between the parts of polypropylene plastic are evaluated. The study is of a specific application in making plastic pressure vessels and joining of pipes. The joint strength is tested by conducting the hydraulic pressure burst test. The burst test is conducted for welded specimens manufactured using different values of rotational velocity and welding pressure. It is observed that at the constant spin velocities, the welding pressure in the range 64.8 to 65.2 kPa produced better joint strength than the other values of welding pressure in the overall range 64–76 kPa. It is concluded that the suitable welding pressure range to manufacture polypropylene plastic pressure vessels in the shear joint configuration using friction spin welding is 64.5 to 65.2 kPa. Further, it is established that the user can control the joint overlap distance at 64.8 kPa welding pressure by selectively controlling the rotational velocity in the range of 700 to 2500 rpm.

Investigations on the material flow and the role of the resulting hooks on the mechanical behaviour of dissimilar friction stir welded Al2024-T3 to Ti-6Al-4V overlap joints

During friction stir lap joint welding, hooks are systematically formed at the interface of dissimilar Al2024/Ti-6Al-4V plates. Various hooks dimensions and shapes are observed according to the welding parameters (welding speed, rotational speed and double-pass). Based on digital image correlation (DIC) during tensile shear tests, it is found that hooks features govern the fracture behaviours and, hence, the mechanical properties of the overall welds. In particular, three fracture behaviours are obtained: at the interface, in the Al2024 and across the Ti-6Al-4V plate, which was never reported in dissimilar Al/Ti studies. The aims of this work are (i) to study the influence of FSW parameters on the mechanisms of hooks formation and (ii) to understand the role of both AS and RS hooks on the mechanical behaviour of the welds, by the means of two new approaches. First, hooks are investigated by X-ray tomography which provided some innovative insight into the material flow (3D viewing). Based on these qualitative and quantitative results, hooks are used as tracers and two new scenarios of AS and RS generation are proposed. Then, the contribution of both hooks on the stress distribution is clearly revealed by some calculations of the stresses reached around AS and RS hooks. Contrary to RS hook, AS hook is sharp and, hence, the stress reached at the top of AS hook is characterized by a stress concentration. The results showed that the fracture behaviours are greatly influenced by hooks size and the formation of microstructural defects inside the Ti-6Al-4V, which depend on the welding parameters. In conclusions, this work revealed the relationship between the achievable parameters, the resulting hooks dimensions and the fracture behaviours. In addition, based on the understanding of the material flow, another FSW parameters are proposed to optimize the mechanical properties.

Epoxy-Based Structural Self-Adhesive Tapes Modified with Acrylic Syrups Prepared via a Free Radical Photopolymerization Process

New modifiers (i.e., acrylic syrups; ASs) of epoxy-resin-based thermally curable structural self-adhesive tapes (SATs) were prepared via a free radical bulk polymerization (FRBP) of n-butyl acrylate, butyl methacrylate, glycidyl methacrylate, and hydroxybutyl acrylate. In the process, two kinds of UV-photoinitiators (i.e., monoacylphosphine oxide/Omnirad TPO and bisacylphosphine oxide/Omnirad 819) and various mixing speed of the monomers mixture (200–1000 rpm) were applied. The TPO-based syrups exhibited a lower copolymers content (10–24 wt%), dynamic viscosity (<0.1 Pa·s), molecular weights (Mn and Mw, and polydispersity (1.9–2.5) than these with Omnirad 819. Additionally, the higher mixing speed significantly reduced monomers conversion and viscosity of ASs as well as molecular weights of the acrylate copolymers. These parameters influenced the properties of thermally uncured (e.g., adhesion) and thermally cured SATs (shear strength of aluminum/SAT/aluminum overlap joints). Better self-adhesive features were observed for SATs-TPO (based on ASs with lower monomers conversion, Mn and Mw); however, a slightly higher shear strength was noted for the thermally cured SAT-819 (ASs with higher monomers conversion, Mn and Mw). An impact of polydispersity of the acrylate copolymers as well as crosslinking degree of thermally cured SATs on the mechanical strength was also revealed.

Structural factors influence on strength properties of S235JR steel welded joints

The paper presents the results of strength tests of welded joints of S235JR structural steel. Welded joints of various geometries were made: butt joints, overlap joints with a single weld, overlap joints with double welds, overlap joints with spot welds, overlap joints with hole welds, and double-flanged seam. The strength tests carried out made it possible to determine the destructive force. Eight joints of each type were made. Based on the results obtained, a statistical analysis was carried out to determine the influence of structural factors on the strength of welded joints and to assess the repeatability of the process of making joints of a given type. This analysis allows verifying which of the tested geometries of welded joints are the most strength and stability, which is especially important when designing new structures or planning renovation of existing structures. The analysis showed that the highest strength as well as the highest repeatability was obtained in the case of overlapped joints with double welds – destructive force at 37 367 MPa. The lowest strength was characterised by double-flanged seam – destructive force 8 603 MPa.

Load Controlled Fatigue Behaviour of Microplasma Arc Welded Thin Titanium Grade 5 (6Al-4V) Sheets.

The current study investigates the load controlled fatigue properties of the microplasma arc welded thin titanium Grade 5 (6Al-4V) sheets. In order to explore the effect of weld geometry on the fatigue, two different welded joints were used in the experimental studies. Load controlled fatigue test results were evaluated to present an outlook on the behaviour of microplasma welded titanium alloy Grade 5 sheets under cyclic loading. Even though the previously published monotonic tests showed successful use of microplasma arc welding to join thin titanium Grade 5 sheets with mechanical properties comparable to the base metal, fatigue life of the welded joints was lower than the lives of samples without welds. In particular, the fatigue performance of overlap joints was very poor. This was presumed to be due to the changed material properties of the heat affected zone which was formed by the excess heat of the welding process as fractures often occurred at such locations. Based on experimental findings and fractographic observations, a clear adverse effect of welding process in material behaviour was discovered. Despite the concentrated heat of microplasma arc welding, post-weld heat treatment of the weld area is recommended to improve the mechanical behaviour of the welded joints.

Experimental study of welding torch positioning parameters influence on overlap joint formation

The article presents the experimental results demonstrating the influence of welding torch positioning parameters on the overlap joint formation. Effect of welding torch tilt angle and its displacement relative to joint and lap joint assembly gap on joint formation quality was evaluated. The general recommendations for choosing the welding torch positioning parameters depending on joint gap size were established.

Numerical and Experimental Investigation of Controlled Weld Pool Displacement by Electromagnetic Forces for Joining Dissimilar Materials

In order to reduce CO2 emissions, an increasing interest in lightweight construction exists in the automotive industry, especially the multi-material-design approach. The main construction materials here are steels and aluminium alloys. Due to their different physical material properties and limited mutual solubility, these two materials cannot be joined thermally without difficulty. This paper presents a new joining approach for dissimilar materials. It uses electromagnetic displacement of a laser-generated melt pool to produce overlap joints between 1 mm steel (1.0330) and 2 mm aluminium alloy (EN AW 5754). Contactless induced Lorentz forces are generated by an alternating current (AC) magnet system. The controlled displacement of the aluminium alloy melt into the hole of the overlying steel sheet is investigated through numerical and experimental studies. The numerical results are compared with cross sections and thermocouple measurements. For the first time, it is possible to achieve a reproducible controlled melt pool displacement on thin sheets to produce overlap joints between dissimilar materials.

Investigation of Mechanical Properties of Overlap Joint Form in CMT-Brazed Joints of DP800 Thin Zinc Coated Steel Plates Using Different Torch Feed Rates

Bu &amp;amp;ccedil;alışmada,1 mm kalınlığındaki DP800 (&amp;amp;Ccedil;ift Fazlı) &amp;amp;ccedil;elik plakalar bakır esaslı (CuAl8) ilave tel kullanılarak CMT-lehimleme (Soğuk Metal Transferi) tekniği ile birleştirilmiştir. Numuneler bindirme birleştirme formunda hazırlanmıştır. CMT-lehimleme işlemi, tor&amp;amp;ccedil; ilerleme hızları 21, 24, 27, 34 ve 39 cm/dk olmak &amp;amp;uuml;zere 5 farklı değerde yapılmıştır. Dolgu metali olarak b&amp;amp;uuml;y&amp;amp;uuml;k oranda bakırdan oluşan CuAl8 teli kullanılmıştır. CMT-lehimleme işlemi ger&amp;amp;ccedil;ekleştirildikten sonra; numunelerin gerilme &amp;amp;ouml;zellikleri saptanmış ve DP800 &amp;amp;ccedil;elik sacının CMT-lehimleme tekniği ile birleştirilebilirliğini g&amp;amp;ouml;rmek i&amp;amp;ccedil;in birleşme noktalarının mikro ve makro g&amp;amp;ouml;r&amp;amp;uuml;nt&amp;amp;uuml;leri incelenmiştir.

Investigation of the Mechanical Properties of Overlap Joint Combined Crash Boxes Joint Area by the Cold Metal Transfer Method

Bu &amp;amp;ccedil;alışmada, otomotiv sekt&amp;amp;ouml;r&amp;amp;uuml;nde &amp;amp;ccedil;arpışma s&amp;amp;ouml;n&amp;amp;uuml;mleyici g&amp;amp;ouml;revini &amp;amp;uuml;stlenen &amp;amp;ccedil;arpışma kutularının &amp;amp;uuml;retiminde kullanılan galvaniz kaplı 2 mm kalınlığındaki SCGA440 (&amp;amp;Ccedil;ift Faz) &amp;amp;ccedil;elik levhalar birleştirilmiştir. Birleştirme işlemi CMT y&amp;amp;ouml;ntemi uygulaması ile yapılmıştır. Bu uygulamada kaynak hızı 60 cm/dk&amp;amp;rsquo;da sabit tutularak yapılan bindirme birleştirmeleri CuAl8, SG2 dolgu telleri ile ger&amp;amp;ccedil;ekleştirilmiştir. CMT birleştirme işlemleri yapıldıktan sonra, bağlantı b&amp;amp;ouml;lgelerindeki &amp;amp;ccedil;ekme mukavemeti (Mpa), &amp;amp;ccedil;entik darbe enerjisi (J), sertlik değerleri (HV) makro ve mikro testleri yapılarak incelenmiştir.

A fully coupled thermo-mechanical numerical modelling of the refill friction stir spot welding process in Alclad 7075-T6 aluminium alloy sheets

Refill friction stir spot welding (RFSSW) is a solid state joining technology that has the potential to replace processes such as the open-air fusion bonding technique and rivet technology in aerospace applications. Selection of proper RFSSW parameters is a crucial task which is important to ensure the mechanical strength of the joint. The aim of this paper is to undertake numerical modelling of the RFSSW process to understand the physics of the welding process, which involves large deformations, complex contact conditions and steep temperature gradients. Three-dimensional fully coupled thermo-mechanical models of RFSSW joints between Alclad 7075-T6 aluminium alloy sheets have been built in the finite-element-based program Simufact Forming. The simulation results included the temperature distribution and the stress and strain distributions in the overlap joint. The results of numerical computations have been compared with experimental ones. The numerical model was able to predict the mechanics of material flow during the joining of sheets of Alclad aluminium alloys using RFSSW. The predictions of the temperature gradient in the weld zone were in good agreement with the temperature measured experimentally. The numerical models that have been built are capable of simulating RFSSW to reduce the number of experiments required to set optimal welding parameters.

Evaluation of Usefulness of AlCrN Coatings for Increased Life of Tools Used in Friction Stir Welding (FSW) of Sheet Aluminum Alloy.

The study presents the results of examinations of wear in tools made of 1.2344 steel without and with an anti-wear coating in the process of welding overlap joints of sheet metal made of 7075-T6 aluminum alloy using friction stir welding (FSW) technology. A commercial anti-wear AlCrN coating (Balinit® Alcrona Pro by Oerlikon Balzers Coating Poland Sp. z o.o., Polkowice, Poland) was examined, applied using physical vapor deposition (PVD) and used to improve tool life in metalworking processes. Wear tests for the tools were conducted in industrial conditions at specific parameters of the friction stir welding process. Tool wear was evaluated through examination of the tool working surface. The results of the static tensile strength tests and metallographic examinations of the joints were used to evaluate the effect of tool wear and the coating impact on joint quality. The results obtained in the study show that the tool made of 1.2344 steel was intensively worn after the welding of a joint with the length of 200 m, increasing the risk associated with further use of the tool and suggesting the tool’s low durability. The use of the AlCrN coating led to an increase in tool life. The coating limits the process of tool wear and can be used as an anti-wear coating for tools used in the FSW of aluminum alloys.

Thermomechanical laser welding simulation of dissimilar steel-aluminum overlap joints

Mixing of steel and aluminum within the weld pool during keyhole laser welding results in a complex dissimilar microstructure, which in turn, initiates a shift in weld metal mechanical properties. In this study, a numerical model for computation of distortions in laser-welded dissimilar overlap joints (austenitic stainless steel 304 – 6082-T6 aluminum alloy), which considers properties of the mixed steel-aluminum weld metal was developed. The required yield strength, Young's modulus, and strain hardening exponent of the weld metal were experimentally determined using the indentation technique coupled with energy-dispersive X-ray spectroscopy. The designed material model calculates the weld elastic-plastic properties as a function of the aluminum concentration. The softening of the alloys in the heat-affected zone was determined by physical simulations and considered as a function of maximum temperature. Computed and measured distortions showed good agreement for various welding regimes with an average deviation of 18.4%. The sensitivity analyses indicated that the application of the developed weld material model significantly improves the accuracy of the thermomechanical simulations.

On the influence of overlap topology on the tensile strength of composite bonded joints: Single overlap versus overlap stacking

The goal of this study is to explore new topologies for adhesively bonded composite overlap joints in order to improve their strength under tensile loading. Multiple stacked overlaps, also referred as finger joints, are compared with single overlap topologies. The quasi-static tensile behaviour of single lap joints with two overlap lengths 12.7 mm and 25.4 mm are compared to finger joints with 1 and 2 stacked overlaps through thickness with constant 12.7 mm overlap length. Two composite adherend stacking sequences are tested for each topology [0/90]4s and [90/0]4s.A non-linear FE-analysis is performed to analyse the shear and peel stresses along the adhesive bond line. A difference in peak shear and peel stress, at the tip of the bonded region could be observed: (i) for 1 finger, the peak peel stress is higher than in the single lap joint configurations because the beneficial effect of avoiding eccentricity in the finger joint is outperformed by the detrimental effect of reducing to half the adherend stiffness at the overlap; (ii) for 2 fingers, the stress field changes significantly leads to a 23% decrease in peak shear and 33% in peak peel stress, compared to the single lap joint topologies.In addition, experimental lap shear tests are performed and monitored using acoustic emission technique, to follow the damage events. Different trends at damage initation and at maximum load are believed to result from how the damage propagates inside the joint. A topology with 2 fingers and layup [90/0]4s, which fails entirely inside the adherend, provides the lowest peak shear and peel stress and the highest load at damage initiation. It is however outperformed in maximum load by a single lap joint topology with layup [0/90]4s, with mostly cohesive failure. It is further found that, unlike in single overlap topologies, the most dominant stress component for damage initiation inside the finger joints is the in-plane tensile stress, at the butt joint resin pockets, rather than peel stresses at the overlap region. Lastly, if weight efficiency is the main requirement, a finger joint design can effectively replace a single overlap joint design. However, for absolute maximum joint strength, the single overlap joint is a better choice than the finger joint.