Lap Joints Research Articles

A comprehensive investigation on tensile behavior of surface‐modified Kevlar hybrid nanocomposites for similar and dissimilar joints

AbstractThe main objective of this study is to enhance the interfacial adhesion between Kevlar fiber‐reinforced epoxy composite for a single lap joint. This has been achieved by performing various chemical treatments on Kevlar fiber. Moreover, the nanofiller‐added epoxy matrices were also used for investigating its potentiality in a single lap joint. A thorough comparison has been made among various chemical treatments based composite and modified epoxy matrix composite. The tensile strength of similar and dissimilar single lap joints was investigated through experiments and was analyzed by SEM, XRD, and Weibull model. It was perceived that the tensile shear strength and Weibull modulus of the treated similar Kevlar lap joint were 21.45% and 40.18% higher than the similar nanocomposite joint; also, it has been found that an increment of about 79.8% and 76.64% with that of untreated similar Kevlar joint. Furthermore, the failure progression of optimized joints was evaluated by acoustic emission (AE) monitoring.Highlights Interfacial adhesion study of Kevlar fiber with matrix in single lap joint. Kevlar surface modification and epoxy modified by nanocomposites were used. The lap shear strength of similar and dissimilar single lap joint composites. SEM, XRD, and Weibull analysis and AE monitoring were used for this research. Chemical treatments on Kevlar fiber have enhanced the interfacial adhesion.

Effect of laser beam incidence angle on weld formation mechanism and corrosion resistance of T2 copper/304 stainless steel

Over the last 20 years, industry interest in copper has increased. Its application in the petrochemical, automotive, and nuclear power industries highlights the need for new research directions especially in the joining of copper to other metals. In this work, lap joint of 304 stainless steel and T2 copper precoated with Cu–Mn–Ni filler metal was performed by laser brazing. The aim of this study is to characterize the influence of laser beam incidence angle on the welded joint forming mode, microstructure, elements diffusion and corrosion resistance. According to the findings, the joint is classified as a welded joint when the laser beam incidence angle is 80°, and as a welded-brazed joint when it’s 90°, 70°, or 60°. The microstructure is mainly composed of Cu-rich and Fe-rich phases, Mn in the Cu-rich phase aggregation and Cr in the Fe-rich phase aggregation. In the fusion zone (FZ) the content of less than 50% of the liquid will be in the form of supersaturated droplets in the matrix of the other side. The local corrosion pair that the copper steel matrix and liquid drop produce in the FZ speeds up the dissolution of the Cu-rich phase, which effected corrosion resistance of the joint.

Ultrasonic welding of lap joints of PEI plates with PEI/CF-fabric prepregs

In this study, ultrasonic welding (USW) of lap joints of polyetherimide (PEI) plates (adherends) with carbon fiber (CF) prepregs impregnated with PEI was investigated. No energy director (ED) was used, so binder contents were varied in the prepregs to compensate for the lack of the polymer in the fusion zone. In addition, the effect of the USW parameters on the structure and the mechanical properties of the lap-joints were analyzed. The most homogeneous macrostructure, the maintained structural integrity of both the CF-fabric in the prepregs and the lap-joined PEI adherends, as well as the maximum strength properties (tensile strength) were revealed for the USW joints with the minimum polymer content in the prepreg. In this case, rising the USW time from 400 up to 800 ms radically changed the macrostructure of the fusion zone, while the strength properties did not vary significantly (shear stresses were 42–48 MPa). Computer simulation of the influence of the PEI/CF-fabric ratios in the prepregs on the deformation response of the USW joints showed that the prepreg thicknesses and, accordingly, the PEI/CF ratios did not exert a noticeable effect on the strain–stress (tensile) diagrams, while the determining factor was the adhesion level.

Metallurgical analysis of laser welded AZ31/5A06 lap joints with Ti–Ni interlayer

The presence of brittle Mg–Al intermetallic compounds (IMCs) in Mg/Al welded joints significantly degrades their mechanical properties. Understanding of the joint interfacial metallurgical reactions is essential for improving the performance of Mg/Al joints. Various single element interlayers, such as Ti, Ni, Zn, Fe, Ce and Cu, have been introduced to improve the joint performance, and the Miedema model has been applied to analyze the priority of phase generations in binary systems. However, the metallurgical reactions in the Mg/Al interface with bi-alloy interlayers cannot be fully explained using only a binary system. In this study, laser welding of AZ31-5A06 using a Ti–Ni interlayer was comprehensively investigated Then, the aggregation tendency of the elements in the Mg–Ni–Ti–Al system was explained using the Toop model and the ternary phase diagram was used to analyze the solidification process in the interlayer. With the increasing of laser power, the interlayer became from intact to incomplete, and finally completely destroyed. As a result, the Mg–Al IMCs with a thickness of 4.5 μm (1617 W) increased to 17–21 μm (1815 W) and 130 μm (2013 W) respectively. The distribution of Mg–Al IMCs also changed from being distributed between Mg-interlayer (1617 W) to being discontinuously distributed within the joint (1815 W) and continuously distributed within the joint (2013 W). When the interlayer remained intact at 1617 W, the maximum shear strength of the joint was 145.76 MPa, and the fracture exhibited a mixed fracture pattern consisting of brittle and ductile fracture. At 1617 W, the distribution of elements at the joint interface revealed that the interlayer was composed of Al, Ni, and Ti without Mg, which successfully blocked the diffusion between Mg and Al. The Gibbs free energy calculated from the Toop model indicated that the minimum Gibbs free energy of an Al–Ni–Ti system was −59.3 kJ/mol, which is lower than that of a Mg–Ni–Ti system (−48.1 kJ/mol); therefore, the Al–Ni–Ti system would be preferentially generated in the joint. The composition of the interlayer was mainly concentrated in the α-Ti and β-Ti phase region of the liquid-phase projection phase diagram and in the TiAl+τ3-Al3NiTi2 and Ti3Al+τ3-Al3NiTi2 phase regions of the isothermal cross-section phase diagram. Consequently, the interlayer consists of multiple phases such as Ti3Al, TiAl, and Al3NiTi2. The Ti3Al and TiAl with superior strength and deformability in the interlayer inhibited the generation of Mg–Al IMC, and the partially melted Ni layer facilitated the connection between Mg/Ni/Ti, thus improving the strength of Mg–Al dissimilar alloy joints.

Improving mechanical behavior of adhesively bonded composite joints by incorporating reduced graphene oxide added polyamide 6,6 electrospun nanofibers

Adhesive joining of fiber-reinforced polymer (FRP) composites requires adequate interface tailoring and careful surface preparation to obtain a strong bond between components. This study aimed to improve the mechanical performance of adhesively bonded unidirectional carbon fiber-based (CFRP) composite parts by modifying joint surfaces with graphene-added electrospun Polyamide 6,6 (PA66) nanofibers. Reduced graphene oxide (rGO) was dispersed at 10 % wt/v PA66 solution at three different concentrations below rGO saturation limits. Bead-free nanofibers with homogenous graphene distribution were obtained on a prepreg by electrospinning. Addition of up to 2 % rGO yielded complete dispersion through the nanofiber network while the higher values created local agglomerations. Surface wetting experiments showed conversion of slightly hydrophobic surfaces to complete hydrophilic with electrospun nanofiber coating and the lowest contact angle was obtained at 2 % wt/v rGO addition (26.18°±2.03°). Composite plates were produced in a hot press keeping the modified prepregs on top. Plates with different surface treatments joined by secondary bonding using 3 plies of FM 300 K film adhesive. Mechanical properties of adhesively bonded composites were tested by Single lap joint and Charpy impact tests. We achieved an 18 % increase in shear strength and 31 % increase in impact strength by adding 2 % wt/v ratio rGO into PA66 electrospun nanofiber.

Effect of welding parameters on weld surface roughness, hardness, and microstructure in laser-welded 340BH-steel and pure vanadium

This study delves into the influence of laser welding parameters on the microstructural evolution, surface roughness, and hardness of dissimilar lap joints formed by welding 340BH steel (upper) to cold-rolled pure vanadium (bottom) in an attempt to successfully develop metal membranes by adopting a novel technological route. Specifically, we examined power levels of 0.3 kW and 0.4 kW combined with varying welding speeds (40 mm/s, 50 mm/s, and 60 mm/s). The results indicate that defect-free joints were achievable at the higher welding speed of 60 mm/s. This conclusion is supported by the observed surface roughness profile. Elemental interdiffusion and temperature play pivotal roles in the formation of these dissimilar joints. These factors determine the dimensions of the heat-affected zone (HAZ) and the fusion zone (FZ) under all welding conditions. Notably, the high cooling rates during laser welding hindered the formation of intermetallic phases both in the FZ and at the interface between the metals. Microstructural examination of the HAZ/FZ on the Fe side showed a coarser microstructure when using a power of 0.4 kW, in contrast to the lath martensite observed at 0.3 kW. These observations align with the cooling curve derived from finite element analysis (FEA). FEA was also used to estimate temperature profiles throughout the welded area, and the results were consistent with experimental data. Further microstructural analysis using electron backscattered diffraction (EBSD) revealed a significant phenomenon: the formation of recrystallized grains of vanadium in the HAZ near the FZ on the vanadium side. Microhardness tests, conducted to gauge joint quality, displayed varying hardness levels across the base metal (BM), HAZ, and FZ interfaces. At a power of 0.3 kW, the HAZ displayed greater hardness than the FZ and BM due to the formation of lath martensite. Conversely, at a power setting of 0.4 kW, a reduction in hardness was observed within the HAZ, attributable to coarser ferrite formation.

Enhancing the reliability of laser welded-brazed aluminum/stainless steel joints via laser-chemical hybrid surface texturing

Surface microtexture is a promising technique for enhancing the quality of heterogeneous joints. This study developed a novel surface texturing method to improve the reliability of laser welded-brazed aluminum/stainless steel joints. The method combined laser etching and chemical etching to create high-quality multi-scale surfaces with large grooves and small wrinkles. The designed microtexture promoted atomic transfer and induced the generation of nanoscale η-Fe2(Al,Si)5 phases during the welding-brazing process. It reduced the spreading activation energy along the groove direction, which enlarged the joining area. It also optimized the strain-stress distribution to enhance the deformation tolerance of the bonding interface throughout the structural strengthening mechanism. Through the synergistic regulation, the joint achieved a maximum line load of 495.9 N/mm, which was 61 % higher than the untextured joint of 307.5 N/mm. The joint performance reached 95 % of the Al/Al lap joint (519.3 N/mm) with the same welding parameters. This study provided new insights into the high-quality joining of aluminum/steel systems or other heterogeneous materials.

Impact of Welding Parameters in the Porosity of a Dissimilar Welded Lap Joint of CP800-XPF1000 Steel Weldment by GMAW-P

The use of the orthogonal array L4 allows a determination of the effect between the welding parameters peak current (Ip), background current (Ib) and frequency (f) on the porosities in a dissimilar welded lap joint of CP800 and XPF1000 steel weldment by the gas metal arc welding process with the transfer pulsed mode. According to the results, modifications in the welding parameters affect the heat input during welding. A heat input higher than 0.30 KJ/mm generates up to 0.32% porosity in the weld metal, while a heat input lower than 0.25 KJ/mm generates up to 28% porosity in the weld metal. The variation in heat input generated by the process allowed the observation of the final microstructure of the welded joints and the effect of mechanical properties such as hardness because the results show values of hardness from 300 Hv to 400 Hv in the heat affected zone (HAZ).

Fatigue strength of single-sided fillet welds in overlapping ultra-high-strength steel sheets

From the manufacturing viewpoint, overlapping thin sheets can provide a substantial geometrical improvement in welded hollow sections compared to butt-welded cross-sectional details. However, the plate eccentricity and non-penetrating fillet welds make the joints susceptible to fatigue failures under transversal cyclic loads. This work experimentally investigates the fatigue strength of overlap joints prepared with gas metal arc welding in the single-sided fillet weld configuration. Fatigue tests were carried out on the lap joints made of S960 ultra-high-strength steel (UHSS) grade under uniaxial constant amplitude axial loading employing both pulsating tension (applied stress ratio of R ≈ 0) and pulsating compression (R ≈ -∞). In addition, the lap joints were prepared with both straight welds (the welds transverse to the loading direction) and inclined welds (the welds with a 30° inclement angle from the transversal direction) to investigate the shear stress effects on the joints’ fatigue performance. Plasma butt-welded samples were tested as a reference join type. For the plasma butt-welded joints, the recommended detail category of FAT71 in the nominal stress system for weld root failures in single-sided butt welds was observed clearly conservative—a mean fatigue strength of Δσc,50% = 130 MPa with a fixed slope parameter of m = 3 was obtained. Compared to the butt-welded joints, a significant decrease in fatigue strength capacity was found in the lap joint specimens with misalignment factors of km > 3.0. The failure locations were also different in joints subjected to the tension and compression loads. The shear load did not majorly contribute to the changes in the fatigue strength capacity compared to the joints subjected to the transversal normal stress.

Resistance of thin sheets lap joints connected by spot welding and brazing

AbstractThe results of an experimental program on lap joints of thin gauge sheets connected by spot welding and MIG brazing are compared to the design code provisions. The results show the dependency of the spot weld lap joints resistance on the thickness of the connected sheets, while the MIG brazed lap joints resistance depends on the minimum thickness of the steel sheets connected. A statistical interpretation of the results shows the accuracy of the joint resistance. The coefficient of variation of the spot weld specimen is smaller than the one for the MIG brazed specimen, while the resistance of the spot weld is higher than the MIG brazed specimen when compared to the nominal resistances.

Evaluating structural strength and vibrational characteristics of silicon carbide incorporated adhesively bonded single lap joints

The adhesive bonding approach is widely used in assembling of spars, stringers, ailerons, flaps, and rudders in aircraft. The present research investigated the impact of silicon carbide (SiC) nanoparticle inclusion on the shear and free vibrational behaviour of adhesively bonded single lap joints (SLJ). The shear test results showed that the inclusion of 1.5 wt.% SiC in the epoxy resin enhanced the shear behaviour of adhesively bonded SLJ. Furthermore, the failure surfaces of adhesively bonded SiC-reinforced SLJ were examined using a field emission scanning electron microscope (FESEM). The microstructural investigation of the failure surface demonstrated that the development of rougher surfaces, plastic void enlargement, and formation of shear bands in the joint region had improved adhesion among GFRP adherends. Thus, the SiC-incorporated adhesively bonded SLJ had predominant cohesive failures. Meanwhile, the SiC-free lap joint had an adhesive failure due to lower adhesion. The vibrational results avowed that 1.5 wt.% SiC-incorporated adhesively bonded SLJ has higher natural frequencies. Results also affirmed that higher wt.% SiC-incorporated joint had better modal damping values due to nanoparticle accumulation, which increased the interaction between glass fiber reinforced polymer (GFRP) adherends.

A new deformable self-clinching fastener

This work proposes a novel deformable self-clinching fastener for producing hidden lap joints suitable for both structural and electric power distribution applications. The fastener, characterized by an axisymmetric concave shape, is employed to fabricate hybrid busbar joints between electrically conductive strips of different materials and thicknesses. The self-clinching process with the new deformable fastener involves machining dovetail holes in both conductors and applying a squeezing force to the fastener to create a form-closed mechanical joint. The work encompasses both experimental investigations and numerical modeling using finite element analysis and is carried out on unit cells made from aluminum and copper conductors, which are representative of the joining process. The investigation evaluates force requirements, conducts destructive testing, and performs thermo-electric characterization of the new joints to conclude on the suitability of the new deformable self-clinching fastener for electric power distribution applications. Results indicate that while copper fasteners necessitate greater squeezing forces, they offer superior mechanical and thermo-electrical performance compared to aluminum fasteners in hybrid busbar joints.

Effect of thermal-mechanical conditions on strength of silanized Al alloy/CFRTP hybrid joint made by thinning-controlled hot pressing

The strength of thermal-assisted joined metal and carbon fiber-reinforced thermoplastics (CFRTP) is dependent on physical and chemical interactions at the joining interface, which are strongly influenced by heat and pressure. Currently, there is a lack in deep research on effect mechanism of changeable pressure on the joining quality, limiting the joining condition optimization of the thermal-assisted joining process. In this study, an improved hot-pressing joining process with added thinning displacement control was adopted to study the effect of the joining pressure on the structure and strength of the interface between a silane-treated Al alloy and three CF-Polyamide-6 (CF/PA6). A high-strength, thinning-controlled lapped joint of Al and CF/PA6 could be realized by the proposed process, regardless of the fiber volume fractions in CF/PA6. At temperatures above the melting point of PA6, higher pressure typically resulted in higher interface strength. However, as the temperature approached the decomposition temperature, the joints under higher pressure tended to exhibit lower strength. The underlying mechanism of the interface strength variation with pressure was investigated by analyzing the effects of the joining conditions on the chemical reaction conditions, the resolidified-resin structure near the interlayer, and the existence of defects. These findings lay the foundational groundwork for future endeavors in metal/composite joining, offering potential benefits for industrial applications and environmental sustainability in the automotive sector.

Improved Interface Morphology and Failure Load of Ultrasonic-Assisted Friction Stir Lap Welding Joint of 2024 Aluminum Alloy to 304 Stainless Steel

Achieving high-strength welding joint of aluminum to steel is a highly pressing and challenging task in the manufacturing industries, and friction stir lap welding (FSLW) has advantages for joining these two metals. To further heighten the strength of dissimilar aluminum and steel metals (Al/steel) FSLW joint, the ultrasonic-assisted FSLW (UAFSLW) process was used, and the upper 2024-T4 aluminum alloy and the lower 304 stainless steel were chosen as research object. The results show that the addition of ultrasound eliminates the micro pores, changes the aluminum-rich intermetallic compounds (IMCs) into the iron-rich IMCs and enhances the micro and macro mechanical interlocking structures along the Al/steel lap interface. Under the rational IMCs layer thickness lower than 1.5 μm, the UAFSLW joint has the failure load higher than the traditional FSLW joint. The maximum failure load of UAFSLW joint reaches 7.06 kN, and the loading capacity of this joint is higher than that of reported Al/steel traditional FSLW joint. The UAFSLW process is an effective way to fabricate the high-strength Al/steel lap joint.

Hybrid Single Lap Joints between 3D Printed Titanium Lattices and CFRP Composites: Experimental and Numerical Insights

In the contemporary emphasis on weight reduction, the utilization of advanced materials like Carbon Fiber Reinforced Polymers (CFRPs) and cutting-edge technologies such as 3D printing of metal is increasingly crucial. This study delves into the junction of CFRP and titanium, aiming to conduct Single Lap shear tests on specimens featuring a co-lamination of long fiber composite onto a metal lattice structure. Different specimens with different dimensions of the Simple Cubic (SC) unit cell were subjected to testing. A microscope investigation facilitated an exploration of junction failure and epoxy resin infiltration into the lattice substrate. Employing an efficient 2D Finite Element Model, the homogenization process yielded theoretical models underestimating the Young Modulus by approximately 10% compared to real specimens. Despite the challenges in bonding titanium and CFRP, the novel junction exhibited a shear stress of 17.25 MPa, which is nearly equivalent to those of a co-lamination between sandblasted steel and CFRP, that is 17.15 MPa.

Evaluation of Welded Lap Joints Using Ultrasonic Guided Waves.

Welded lap joints play a vital role in a wide range of engineering structures such as pipelines, storage tanks, pressure vessels, and ship hulls. This study aims to investigate the propagation of ultrasonic guided waves in steel welded lap joints for the baseline-free inspection of joint defects using the mode conversion of Lamb waves. The finite element method was used to simulate a single lap joint with common defects such as corrosion and disbonding. To identify the propagating wave modes, a wavenumber-frequency analysis was conducted using the 2D fast Fourier transform. The power loss of the transmitted modes was also determined to identify damage in the lap joints. The results indicate that the A0 incident in pristine conditions experienced significant transmission losses of about 9.5 dB compared to an attenuation of 2.8 dB for the S0 incident. The presence of corrosion was found to reduce these transmission losses by more than 28%. In contrast, introducing disbonding in the lap joint increased the transmission loss of the S0 incident, while a negligible loss was observed for the A0 incident. The mode-converted S0 (MC-S) and mode-converted A0 (MC-A0) incidents were found to exhibit a unique sensitivity to the presence of corrosion and disbonding. The results indicate that MC-S0 and MC-A0 as well as Lamb mode incidents interact differently in terms of corrosion and disbonding, providing a means to identify damage without relying on baseline signals.

Fatigue of 1.5 Single-Shear Lap Joints with Sealant and Corrosion-Inhibiting Compounds

Corrosion-inhibiting compounds (CICs) are a secondary protection method used with aircraft that can reduce the rate of corrosion development. However, CICs can also affect the fatigue life of fastened lap joints. This study uses a 1.5 single-shear lap joint design to investigate fatigue life changes with CIC application. Hi-Lok and rivet fastener types are compared, along with the inclusion of faying surface sealant. It was found that without sealant, the application of CICs increased the fatigue life due to prolonging the crack initiation process. The presence of faying surface sealant led to a reduction in fatigue life for the rivet samples. The Hi-Lok samples saw no change in life due to the squeeze-out of the sealant around the fastener holes. This study provides a foundational understanding of the mechanisms and significance of the change in fatigue life with the presence of CICs and faying surface sealant in a fastened lap joint.

Plasma Arc Welding of 780CP High Strength Steel Sheet Lap Joint for Tensile Strength of 100% Compared to Base Metal

Plasma Arc Welding of 780CP High Strength Steel Sheet Lap Joint for Tensile Strength of 100% Compared to Base Metal

Surface modification strategies of 304 austenitic stainless steel plate with different micromorphology and composition for improved mechanical interlocking and chemical bonding in metal–epoxy joints

304 austenitic stainless-steel (SS) strip-based carbon fiber metal laminates (CFMLs) have raised significant concerns, in terms of their mechanical performance. On top of that, the hybrid laminates’ interlamination performance is vital in regulating their failure patterns. Along these lines, in this work, SS strips with regulatable micromorphology and composition were obtained by using physical and chemical surface modification strategies, including polishing, acid etching, anodization, and thermal treatment. The shear strength of the treated-SS/epoxy single lap joints (two treated-SS strips bonded by the epoxy resin via hot curing process) was systematically explored, and the origins of the enhancement mechanism were attributed to the resulting surface microstructure, as well as the possible chemical reactions between the treated surface and the curing agent. The etching-anodizing-thermally treated-SS (EAT-SS)/epoxy joint exhibited the maximum shear strength (16.04 MPa) and work of fracture (5.85 kJ·m−2) due to the substantial cohesive failure pattern of the epoxy. The encouraging enhancement was mainly attributed to the synergistic effect of the micro-annular pit and the nanoporous array structure of the EAT-SS surface. These effects induced a significant mechanical interlock and a plausible chemical reaction at the interface, which led to improved bonding strength between the epoxy and treated-SS surface. Overall, in this work, it was demonstrated that the combination of the anodization and thermal treatment can effectively improve the interlamination bonding properties between the SS strip and the epoxy resin due to the combination effect of mechanical interlocking and chemical bonding.

Delamination prevention of composite joints with asymmetric carbon-fiber reinforced plastic adherends

The use of adhesive bonding in aeronautical applications has gained popularity due to its numerous advantages over traditional mechanical fastening methods. However, the issue of delamination still poses a significant challenge in fully embracing this technology in the industry. This study proposes a unique approach to optimize carbon fiber reinforced polymer (CFRP) single lap joints (SLJ) by introducing a curved joint design with varying adhesive thickness. The curvature is achieved through the intentional warpage caused by residual stresses resulting from an asymmetrical composite layup. While these residual stresses can potentially lead to cracks and distortions, this research aims to leverage their presence to enhance joint performance and mitigate delamination risks. A comprehensive analysis, involving both numerical simulations and experimental testing was conducted to compare the performance of the curved joint design with traditional configurations. The findings indicate that the curved joint design effectively prevents delamination while maintaining comparable joint strength. This demonstrates the potential benefits of employing curved joints for aeronautical components with curved geometries, affirming the feasibility and advantages of this approach. However, further optimization of the curved joint configuration is warranted to enhance its performance and expand its applicability to a broader range of applications.