Aluminum Rivets Research Articles

Microstructure and performance of joint of Al/Cu welded by resistance element welding with an auxiliary gasket

A 1060 commercial-purity aluminum and T2 pure copper plates with a thickness of 2 mm were welded by using resistance element welding with an aluminum rivet and auxiliary gasket. The interfacial microstructure was analyzed, and the tensile shear load of the joint was tested. In the joint welded, a layer of Al2Cu adjacent to the copper and the eutectic structure of Al2Cu + (Al) near the nugget region were formed at the interface of Al/Cu. The tensile shear load of the joint increased first and then decreased with the increase of welding current, and it reached the maximum of 2.24 kN when the welding current was 26 kA. The results reveal that the application of the auxiliary gasket not only promote the thickening of the nugget, but also achieve the joining between the rivet leg and the upper plate when resistance element welding of Al/Cu is performed.

Enhanced composite laminate fastening and delamination repair using hierarchical thermoplastic composite rivets

Aircraft require numerous composite parts, which are fastened with rivets. However, these rivet fastening processes have several disadvantages, including delamination during drilling, increased weight, galvanic corrosion with metallic rivets, and thermal expansion mismatch. Here, the authors develop a hierarchical carbon fiber reinforced thermoplastic (CFRTP) rivets using MWCNT for high strength and enhanced electrical/thermal conductivity, achieving 907 S/m and 0.750 W/m∙K, respectively. The conductive network of MWCNT and carbon fiber enabled the induction heating-assisted fastening process. The optimal hierarchical structure and fastening process condition were investigated using a development framework with numerical modeling and experiments. The fastened CFRTP rivets showed a maximum of 35 % higher bearing strength than conventional aluminum rivets, with a 43% weight reduction.

Design of aluminium solid self-piercing rivets for joining aluminium sheets by material and geometric modification

Because of their excellent lightweight properties, aluminium alloys are processed in industries across the mobility sector. A suitable and efficient process for joining structural components made of aluminium sheet metal is solid self-piercing riveting (SSPR). It eliminates the need for time-consuming preparatory work, such as the insertion of pilot holes, while making the joining process highly automatable.Due to the process technology, the rivet itself first acts as a punching tool and then as a fastener to transfer the load of the joint. This leads to high requirements for the rivet in terms of strength and ductility.In this paper, a new rivet design will be presented that focuses on adjusting the rivet geometry, as well as the material, to enable sufficient functionality in the installation and operational phase. Consequently, aluminium sheet metal can be joined in a wider range of applications using aluminium-based SSPR. With this newly developed aluminium rivet, it is possible to join the aluminium alloy EN AW-6111 PX, which is widely used in the automotive industry, up to a total sheet thickness of 3.1 mm for the first time. This development contributes to aluminium-based lightweight structures and ensures a good recyclability.

Improved Mechanical Properties of SUS304/AA5083 Dissimilar Joint by Laser Ablation Pretreatment in Vortex- Friction Stir Lap Welding

To obtain a high-quality Al/steel dissimilar joint, a micro-groove-assisted vortex-friction stir lap welding (MG-VFSLW) process was developed. Through prefabricating micro-grooves on the steel plate surface by laser ablation, high-quality mechanical interlock and metallurgical bonding were obtained simultaneously in the MG-VFSLW process. The weld formation, interface microstructure, mechanical properties, and failure mode in MG-VFSLW were studied by comparing them with those in VFSLW. The results showed that a line load of the AA5083/SUS304 dissimilar joint up to 485.9 N/mm was obtained by MG-VFSLW, which is 40.1% higher than that in VFSLW. Remarkable intermetallic compound layers and cracks were found in VFSLW. The cracks were closely related to the oxides on the interface. However, in MG-VFSLW, cross-riveting aluminum rivets and steel rivets were formed on the interface due to the micro-grooves and flashes made by the laser ablation. Good metallurgical bonding was also formed between AA5083 and SUS304. No remarkable intermetallic compound layers and cracks occurred. During the tensile shear tests, the aluminum rivets were cut off and some dimples and tear ridges existed on the fracture surface. In short, the high strength of the Al/steel lap joint in MG-VFSLW was attributed to the high-quality mechanical interlock and metallurgical bonding.

Mechanical Properties of Double-Layer Riveted Aluminum Roofing Panels with Curved Surfaces

In recent years, aluminum alloy has been increasingly used in building structures, becoming an important construction material for metal structures. Currently, aluminum alloy is commonly used in buildings as beam–column components, profiled roof panels, and door and window frames, among other forms. However, there is limited research on the mechanical properties of aluminum alloy roof panels with irregular curved surfaces. In this study, a full-scale curved double-layer anisotropic riveted aluminum alloy roof panel was subjected to a load test to analyze its deformation patterns and failure mechanisms. The results indicate that the load-bearing capacity of the roof panel meets the design requirements. During failure, neither the upper nor lower layers of the panel enter the plastic deformation stage, indicating sufficient safety redundancy. The failure mode observed is a ductile failure with noticeable deformation with the weak points of the component being the riveted connections of the stiffeners. A finite element model was established for numerical simulation and the results matched well with the experimental data. Finally, a theoretical calculation for the ultimate load-bearing capacity of the roof panel was derived, providing a reference for design purposes.

Resistance element welding of aluminium alloy and steel using an element of aluminium

Aluminium alloy AA6061 and mild steel Q235 were welded by resistance element using an aluminium rivet as the element. The microstructure and properties of the joints were characterised. The temperature distribution on the cross-section of the joints was calculated by using ABAQUS numerical simulation software. The observation results on the cross-section of the joints show a nugget formed at the interface between the rivet tip and steel of lower plate. The maximum tensile shear load of the joints reached 5.82 kN at the welding current of 26 kA. This study reveals that the bearing interface of the resistance element welded joint between aluminium alloy and mild steel is like-to-like interface of aluminium alloy which strengthens the joint.

Effect of edge riveting on the failure mechanism and mechanical properties of self-piercing riveted aluminium joints

In order to improve the use of aluminium alloys in lightweight automotive body panels, the failure mechanism and mechanical properties of AA5052 aluminium alloy sheets under different conditions were investigated by means of self-piercing riveting (SPR). The impact of riveting position on the structural strength, absorbed energy and instantaneous stiffness of self-piercing riveted connections was analyzed using the edge riveting method. Four edge distances of 1.65 mm, 2.65 mm, 3.65 mm and 4.65 mm were considered for the experimental study, and the riveted structure was analyzed and tensile shear tests were carried out by comparing the mechanical properties. The results indicated that this riveting method changed the failure mode of the joint, with the rivet pulling out from the lower sheet to a co-existence of rivet pull-out and riveted mouth sheet breakage; the maximum shear load, absorbed energy and deformation resistance decreased as the distance from the riveting point to the strip edge decreased; and the strength of the riveted joint based on the upper plate was significantly greater than that based on the bottom plate at the same edge pitch, and the stability of the joint is superior. This study provides a theoretical basis for the damage suppression of aluminium alloy edge riveted joints and the lightweight production of vehicles.

Static and Fatigue Strength and Failure Mechanisms of Riveted Lap Joints of CFRP Composites

The background of this work is the search for the most effective ways of joining composites, inter alia in aeronautical applications. The purpose of this study was to analyze the impact of mechanical fastener types on the static strength of lap joints of composite elements and the impact of fasteners on the mechanism of failure of such joints under fatigue load. The second objective was to check to what extent the hybridization of such joints, consisting of supplementing them with an adhesive joint, affects their strength and the mechanism of failure of such joints loaded with fatigue. Damage to composite joints was observed using computed tomography technology. The fasteners used in this study (aluminum rivets, Hi-lok and Jo-Bolt) differed not only in terms of the materials they were made of, but also in terms of the pressure forces they exerted on the joined parts. Finally, in order to check how a partially cracked adhesive joint affects the load on the fasteners, numerical calculations were carried out. Analyzing the results of the research, it was found that partial damage to the adhesive joint of the hybrid joint does not increase the load on the rivets and does not impair the fatigue life of the joint. An important advantage of hybrid joint is the two-stage destruction of the connection, which significantly increases the safety of aircraft structures and facilitates the process of supervising their technical condition.

Riv-Bonding of Aluminum Alloys with High-Strength Steels against the Favorable Joining Direction

In order to exploit the advantages offered by multi-material design, this work studies the feasibility of joining aluminum alloys with high-strength steels (HSS) against the favorable joining direction by using self-piercing riveting (SPR) combined with adhesive bonding, so-called riv-bonding. Therefore, riv-bonding of four joint configurations including different aluminum alloy sheets (AW-6014-PX, AW-6451-T4), HSS sheets (HC420LA, HC450X) and rivet types (C5.3×8.0-H4, U5.5×5.0-H6) was experimentally investigated. Moreover, riv-bonding of two joint configurations was exemplarily modeled using the Simufact Forming finite element (FE) software. The viscoelastic properties of the liquid adhesive layer between the sheets were substituted with “equivalent” elastoplastic properties to model the adhesive as solid with strain rate-dependent flow behavior. Good agreement of joint cross sections and force-displacement curves between experiments and simulations confirms that the presented numerical model of riv-bonding is suitable for predicting both the joinability of aluminum alloys with HSS and the final quality of hybrid joints.

Design of Self-Piercing Aluminium Rivets by Material and Geometric Modification for Joining Aluminium Sheets

Design of Self-Piercing Aluminium Rivets by Material and Geometric Modification for Joining Aluminium Sheets

Metallurgical analyses on Al-Mg alloy pop rivets used in the electric cabinet

One of the rivets connecting the frame and cover plate was broken unexpected in use. To analyze the fracture mode of this Al-Mg alloy pop rivet and prevent the similar events, scanning electron microscopy observation and chemical composition tests were carried out. Fatigue tests were performed to further find out the cause of failure of the Al-Mg alloy pop rivets. The failed rivets showed obvious fatigue fracture characteristics, whereas no corrosive medium could be tracked. The fatigue limit of Al-Mg alloy pop rivets was about 400 N. The stress concentration generated during riveting process and the maximum external forces beyond fatigue limit of aluminum rivets led to the initiation of plastic deformation zone. The low content of Mn and the possible existence of crevice between rivet core and rivet body may promote the initiation of plastic deformation zone. Under the action of continuous external load, the fatigue crack continued to expand, and finally caused the fracture of pop rivet. The effect of corrosive medium on cracking can be eliminated.

Microstructural evolution in friction self-piercing riveted aluminum alloy AA7075-T6 joints

Friction self-piercing riveting (F-SPR) is an emerging technique for low ductility materials joining, which creates a mechanical and solid-state hybrid joint with a semi-hollow rivet. The severe plastic deformation of work materials and localized elevated temperatures during the F-SPR process yield complex and heterogeneous microstructures. The cut-off action of the work materials by the rivet further complicates the material flow during joint formation. This study employed the F-SPR process to join AA7075-T6 aluminum alloy sheets and systematically investigated the microstructural evolutions using electron backscatter diffraction (EBSD) techniques. The results suggested that as the base material approached the rivet, grains were deformed and recrystallized, forming two distinct fine grain zones (FGZs) surrounding the rivet and in the rivet cavity, respectively. Solid-state bonding of aluminum sheets occurred in the FGZs. The formation of FGZ outside the rivet is due to dynamic recrystallization (DRX) triggered by the sliding-to-sticking transition at the rivet/sheet interface. The FGZ in the rivet cavity was caused by the rotation of the trapped aluminum, which created a sticking affected zone at the trapped aluminum/lower sheet interface and led to DRX. Strain rate gradient in the trapped aluminum drove the further expansion of the sticking affected zone and resulted in grain refinement in a larger span.

Joint quality of self-piercing riveting (SPR) and mechanical behavior under the frictional effect of various rivet coatings

Abstract This study investigates the frictional influence of different rivet coatings on the joint quality and strength of self-piercing riveted aluminum alloys. A mechanically plated Zn-Sn-Al (Almac®) and an electroplated Zn–Ni coating were applied to the steel rivets to examine the frictional effect of rivet coatings. The friction properties of the rivet coatings were evaluated using a micro-mechanical surface tester. The results demonstrated that the friction properties of the rivet coatings remarkably influenced both the joint quality after riveting and the mechanical behavior of the joints. Under a similar riveting condition, owing to the lower friction coefficient, the Zn-Ni-coated rivets experienced deeper rivet head penetration and larger interlocking in terms of joint quality compared to those of Almac®-coated rivets with a higher friction coefficient. However, under a similar joint quality with respect to the appropriate riveting parameters, the joints with Almac®-coated rivets exhibited higher lap-shear and cross-tensile loads owing to the higher frictional force at the rivet/sheet interface compared to the joints with Zn-Ni-coated rivets. The surface profiles of the coatings after applying an external load using a micro-mechanical surface tester revealed a larger plastic deformation and subsequently higher delamination of the Almac® coating during the riveting process, which altered the friction properties at the rivet/sheet interface and thereby contributed to the higher lap-shear and cross-tensile loads. A numerical analysis also elucidated a significant effect of the friction coefficient at the rivet/sheet interface on the joint quality and lap-shear behavior, which is consistent with the experimental results.

Low-speed friction riveting: a new method for joining polymer/metal hybrid structures for aerospace applications

Low-speed friction riveting, a novel method of joining hybrid structures, is a promising technology for joining polymer with metallic structures in automotive and aerospace industries. It offers unique advantages such as weight reduction, reduced consumption of fuel and its cost without compromising the required mechanical properties. The present work deals with riveting of polymethyl methacrylate (PMMA) to aluminium (AA 1100) rivets using low-speed friction riveting technique. It reports the possibility of friction riveting at lower speed and its influence on the integrity of the hybrid joints. The performance evaluation of the low-speed-friction-riveted components is done by carrying out a series of mechanical tests. Microstructural investigation reveals the formation of distinct zones on the riveted components and modes of failure identified during the tensile and bending tests. Besides, numerical simulation of the low-speed friction riveting process has been carried out using ABAQUS 6.14-1 for better understanding of the process. The developed numerical model could be used as a tool to predict the temperature distribution. Validation shows that there is a good agreement between experimental and numerical results.

Shock absorber with inward-folding composite tube and its application in legged landing gear

A shock absorber based on the progressive failure of a composite tube was developed. The composite tube is subjected to axial compression from the pressing cap at one end and folds inward at the other end under the effect of the crush cap without debris overflow. The crushed composite is compacted into a hollow tube and increases the resisting force once it reaches the pressing cap. For larger strokes without a load increase, a hole is made in the pressing cap for the crushed composite. Three crush caps with different curvatures of the inward-folding surface and two composite tubes were evaluated through static and dynamic tests. The crush cap lowered the initial peak load and varied the specific energy absorption (SEA). We also investigated the effects of connection rivets. Aluminum rivets were severed and had little effect on the load curve while steel rivets did not shear but cut the composite tube into strips, resulting in a lower sustained load because failure was induced. A set of shock absorbers with larger strokes was tested for use in the legged landing gear of a drone assumed to crash with a speed of 10 m/s, energy of 5000 J, and overload of less than 25 g. The maximum SEA of the absorbers, including the two caps, was 20 kJ/kg.

Effect of mechanical and solid-state joining characteristics on tensile-shear performance of friction self-piercing riveted aluminum alloy AA7075-T6 joints

Friction self-piercing riveting (F-SPR), as a combination of traditional self-piercing riveting and friction stir spot welding processes, has been proposed to solve the cracking issues in riveting low ductility materials. The F-SPR process creates mechanical and solid-state hybrid joints, which are quite different from existing spot welding/joining methods. However, the roles that mechanical interlocking and solid-state bonding play upon the mechanical behavior of the joints are unknown. To fill in this gap, the current body of work investigated the tensile-shear behavior and fracture mechanism of the F-SPRed AA7075-T6 aluminum alloy sheets. The results reveal that the ring-shaped solid-state bonding between aluminum sheets enhances the overall stiffness of the joints but shows a minor contribution to the tensile-shear performance. The solid-state bonding formed between the captured aluminum in the rivet shank and the lower sheet serves as an “anchor” to hinder the rotation of the rivet, which delays the action of rivet pull-out from the lower sheet and thus strengthens the joints significantly. The combination of a hard rivet, large rivet flaring and solid-state bonding inside the rivet shank is necessary to achieve the preferred rivet pull-out fracture mode, which shows a higher peak load and larger energy absorption compared to other fracture modes.

Material flow and mechanical properties of aluminum-to-steel self-riveting friction stir lap joints

High-quality aluminum /steel joint was achieved via self-riveting friction stir lap welding (SRFSLW) characterized by the prefabricated holes in steel sheet. According to the origination of filling materials, the prefabricated holes were filled with the plasticized aluminum materials in this order: the deformed aluminum ahead of a pin firstly, the stirred aluminum by the pin body secondly and the driven aluminum by the pin tip finally. The strength of the SRFSLW joint reached maximum value of 317 N/mm at the hole diameter of 3 mm, which was 23% higher than that by conventional friction stir welding (FSW). The optimized joints failed at both the aluminum/steel interface and the formed aluminum rivets. The synergistic effect of mechanical bonding induced by the riveting and metallurgical bonding induced by the Al/Fe IMC layer contributed to high strength of the SRFSLW joint.

Modeling and experimental validation of friction self-piercing riveted aluminum alloy to magnesium alloy

Friction self-piercing riveting (F-SPR) process has been proposed to achieve crack-free joining of low-ductility materials by combining SPR process with the concept of friction stir processing. The inhibition of cracking in an F-SPR joint is related to the in-process temperature as well as plastic deformation of materials, which are controlled by the process parameters, i.e., spindle speed and feed rate. However, the relationship between F-SPR process parameters and the temperature characteristics within the joint has not been established. In the current study, a coupled thermal-mechanical model based on solid mechanics was setup to study the F-SPR process of aluminum alloy and magnesium alloy. Temperature and strain rate-dependent material models and preset crack surface method were integrated in the model and geometry comparisons were conducted for model validation. Based on this model, the evolutions of temperature and plastic deformation in the rivet and the sheets of an F-SPR joint were obtained to reveal the formation mechanism of the joint. The temperature distribution and evolution of the sheet materials were correlated with F-SPR process parameters, and a critical spinning speed of 2000 rpm at a feed rate of 1.35 mm/s was determined capable of inhibiting cracking in the magnesium sheet.

Application of electrical impedance tomography to an anisotropic carbon fiber-reinforced polymer composite laminate for damage localization

Electrical impedance tomography (EIT) is an emerging method for assessing the structural condition of composite structures. In this work, EIT's damage localization capability is investigated through its application upon a commercial laminated anisotropic carbon fiber reinforced polymer plate. Aluminum rivets were used as electrodes. EIT reconstructs the spatial conductivity within a defined space by using its boundary voltage response. The algorithm starts with a forward simulation of the voltage distributions within the boundary, hence the orthotropic conductivity of the CFRP plate was first characterized experimentally. It was found that the inhomogeneous fiber contacts through the thickness are influencing the reconstruction results. A detailed 3D finite element simulation was built to model the conductivity distribution. Different current injection patterns were attempted with their reconstruction results being evaluated via four criteria. It was found that the diagonal current injection and the difference evaluation lead to the best results.

Impact of specimen configuration on fatigue properties of self-piercing riveted aluminum to carbon fiber reinforced polymer composite

In this study, the fatigue properties of SPR joints in CFRP-to-AA6111 aluminum alloy in lap-shear and cross-tension specimens are presented. The test specimens were produced with two distinctive targeted rivet head heights separated by 0.3 mm. The tensile failure load and fatigue life of the lap-shear joints in particular was highly influenced by the flushness of the rivet head against the top sheet of CFRP. The lap-shear SPR joints produced with a proud head height exhibited higher tensile failure load and slightly longer fatigue life than SPR joints produced with a flush head height. In cross-tension joints, the flushness of the rivet had no significant influence on the quasi-static failure load and fatigue life of the SPR joints. Two distinctive failure modes were observed, in quasi-static loading, the lap-shear and cross-tension joints failed due to rivet pullout of the bottom aluminum sheet. In cyclic loading, the lap-shear joints failed due to kinked crack growth in the bottom aluminum sheet, while the cross-tension joints failed due to rivet pulling out of the top CFRP sheet. Finally, an analytical based, structural stress model was used to generate a master curve to predict the fatigue life of the SPR joints for both specimen types. The study shows, the flared rivet diameter as a controlling parameter in evaluating the fatigue life of the SPR joints.