Search

The aim to reduce pollutant emission has led to a trend towards lightweight construction in car body development during the last years. As a consequence of the resulting need for multi-material design, mechanical joining technologies become increasingly important. Mechanical joining allows for the combination of dissimilar materials, while thermic joining techniques reach their limits. Self-piercing riveting enables the joining of dissimilar materials by using semi-tubular rivets as mechanical fasteners. The rivet production, however, is costly and time-consuming, as the rivets generally have to be hardened, tempered and coated after forming, in order to achieve an adequate strength and corrosion resistance. A promising approach to improve the efficiency of the rivet manufacturing is the use of high-strength high nitrogen steel as rivet material because these additional process steps would not be necessary anymore. As a result of the comparatively high nitrogen content, such steels have various beneficial properties like higher strength, good ductility and improved corrosion resistance. By cold bulk forming of high nitrogen steels high-strength parts can be manufactured due to the strengthening which is caused by the high strain hardening. However, high tool loads thereby have to be expected and are a major challenge during the production process. Consequently, there is a need for appropriate forming strategies. This paper presents key aspects concerning the process design for the manufacturing of semi-tubular self-piercing rivets made of high-strength steel. The aim is to produce the rivets in several forming stages without intermediate heat treatment between the single stages. Due to the high strain hardening of the material, a two stage forming concept will be investigated. Cup-backward extrusion is chosen as the first process step in order to form the rivet shank without forming the rivet foot. Thus, the strain hardening effects in the area of the rivet foot are minimized and the tool loads during the following process step can be reduced. During the second and final forming stage the detailed geometry of the rivet foot and the rivet head is formed. In this context, the effect of different variations, for example concerning the final geometry of the rivet foot, on the tool load is investigated using multistage numerical analysis. Furthermore, the influence of the process temperature on occurring stresses is analysed. Based on the results of the investigations, an adequate forming strategy and a tool concept for the manufacturing of semi-tubular self-piercing rivets made of high-strength steel are presented.

Press hardened structural components are a key factor in lightweight car design and thus in reducing vehicle mass while increasing crash safety. The use of quenched 22MnB5 (Usibor 1500) has been established in hot sheet forming for the production of safety-relevant car body components. In order to expand the field of application for press-hardened components, a process-reliable joining technique is essential. Ultra-high-strength components can be joined with other parts in car bodies using the resistance spot welding process. Here, challenges like uneven welding lens formations with an incorrect connection in multi-sheet joints arise. Mechanical joining processes, for example self-pierce riveting, can only be used to a limited extent due to the high hardness of the hardened parts. For this purpose, an annealing treatment is often carried out in order to reduce the strength of the material after press hardening. Another possibility to create softened areas is the introduction of local deformation in the austenitic material. The phase areas in the continuous cooling transformation diagram are shifted to shorter cooling times, which enables the development of deformation-induced ferrite. The local thinning and softening improves joinability by means of mechanical and thermal joining processes but increases the forming force. Therefore, in this study the process of hot forming and local deformation is first pre-estimated using numerical simulation. The required force for the deformation and an optimal positioning, as well as the possible number of deformation punches, are investigated. Furthermore, the first experimental results of the feasibility of locally thinned and softened sheets are presented. In addition, joining tests by resistance spot welding and self-pierce riveting are carried out on the generated specimen to illustrate the practical effectiveness of the local thinning and the use of deformation-induced ferrite for critical joints.

This paper presents a new form of setting process monitoring for mechanical joining implemented into a human-robot collaboration. The used lightweight robot can be manipulated in an intuitive way. We developed an easy to use hand guiding opportunity for cobots from Universal Robots by providing an URCap. This way such a cobot can be manipulated quickly and precisely with ease by any operator new to the system within minutes. It enables an economic use of hand guiding with an additional hand guiding device. With this device the teach pendant is not needed during the regular operations which simplifies the usage of the cobot. The integrated sensors (primarily a force-torque sensor) collect data, which gives information about the setting process. Several errors (e.g. no rivet head support, angle offset, gap between the sheets) were carried out on a test setup while recording the data for evaluation. The resulting force/torque-time graphs give indication of the occurring error. As a result the classified error can be immediately displayed to the operator for recognizing the need for reworking. In combination with an error avoidance algorithm the overall quality of the product can be sustainably improved.

The applications of adhesive joints have grown in recent years in various industries, ranging from automotive to maritime. Compared to traditional joining techniques, such as bolts, welding or riveting, adhesive bonding has some advantages, namely, they are low weight, have high strength and have a more uniform stress distribution. However, they also have some disadvantages, many times they are impossible to disassemble, they have low peel strength and some adhesive require high curing temperatures. A particular advantage of using adhesives in composite joints is that they do not require holes in the composite to join the joint, which are associated with delamination failure. The present work aims at using radial point interpolation meshless methods to study the stress distributions and predict the strength of composite adhesive single lap joints (SLJ). To this effect, a brittle adhesive was tested in composite joints with varying overlap lengths (LO). The stress distribution obtained using meshless methods was compared to one obtained using the well-established Finite Element Method (FEM), resulting in a similar behaviour. The strength predictions, using the critical longitudinal strain (CLS) criterion, were similar to the experimental joint strength.

With the increasing applications of novel materials and structures in new-generation aircraft, conventional joining techniques in aircraft component assembly are greatly challenged. To meet those challenges, the electromagnetic riveting (EMR) technique was developed as an advanced joining tool, which exhibits obvious advantages in the assembly of new-generation aircraft. In this paper, the riveting principle of EMR was analyzed, and its development history and status were presented in detail. Then, equipment features of three typical EMR systems were given. Moreover, three important applications of EMR were covered, i.e., composite structure riveting, titanium rivet and large-size aluminum rivet riveting, and interference fit bolt installation. Specially, a novel strengthening method for mechanical linking holes based on EMR was also presented, which can significantly improve the fatigue behaviors of mechanical joints. Finally, open questions in the EMR field were discussed, and some recommendations for future work were also made. This paper can be useful for optimizing the joint designs of aircraft components and improving the level of aircraft maintenance. Keywords: Composite, Electromagnetic riveting, Hole strengthening, Interference fit, Titanium alloys

A method for creating a rivet connection using nitrogen cooling of rivets is considered. A rivet, cooled to a temperature of -196 C, is placed in a cylindrical hole in the plates at room temperature. When heated to room temperature, the rivet undergoes a thermal all-round expansion and creates a tight fit. The finite element method solves the contact termal-stress problem for such a connection in the COMSOL MULTIPHYSICS and APM Winmachine software complexes. The problem is solved in a three-dimensional statement. The first stage is the temperature distribution in the rivet-plate system. The resulting temperature field is used as a parameter at the second stage when solving the stress problem. The fields of residual stresses in the plate and rivet are obtained. It is shown that plastic deformations occur in a small part of one of the connected plates. Recommendations for calculating the strength of such compounds are given.

In the aerospace industry there is a constant search for lighter, better performing and economically beneficial solutions. To that effect, an alternative to the more common joining techniques such as riveting or screwing, Friction Stir Welding (FSW) emerged. This technique allows the manufacture of high-quality joints with complex geometry, reducing the production costs. This technique can be further improved if combined with adhesive application, forming hybrid joints, which exhibit better mechanical performance. However, in FSW welds, it is hard to monitor or inspect the integrity of the joint during its work-life and that unreliability factor is one of the main reasons why its application is not yet widely spread in the industry. Consequently, there is a need for a detailed analysis of the mechanical performance during the welding process and under a variety of loads. To achieve that goal, in this paper the application of Bragg sensors that allow the monitoring of deformations in both manufacturing and service moments is studied and results benchmarked against finite element models. This work aims to demonstrate the potential of a large-scale application of this technique in the aeronautical structures.

Mechanical joining techniques such as riveting and clinching are specifically designed on the basis of the joint’s properties i.e. the geometry, dimensions, loads and materials employed. These design guidelines result in an ever-greater variety of joining-technique versions and related components, such as rivets and fasteners, as increasing importance is attached to lightweight design and hence to the processing of various pre-products. This trend is resulting in a high cost for the engineering, tooling, machine and set-up time. SFB TRR 285, which is being funded by the DFG (German Research Foundation), is focusing on this issue in its research work. The research goal is the development of a methodology for versatile process chains for mechanical joining. The LUF (Chair of Forming and Machining Technology) is involved in this special research area and is investigating joining with versatile friction-spun joint connectors. This article presents an innovative joining technique employing versatile friction-spun joint connectors to bond a wide range of bulk sheet materials. Before being installed, the initial connector, which is wire/tubular-shaped at that point, is pre-shaped using the friction-spinning techniques. The forming operation as well as the joining process is performed/supported by friction-spinning. As kinematic process control characterizes friction-spinning, both ends of the connector can undergo in-process shaping to form versatile joint-specific heads employing same tools, initial connector materials and machinery. This joining technique thus includes the ability to bind different joint components with their individual dimensions, geometry and material. The method is accordingly a cost-effective solution for joining a wide range of components and significantly increases design flexibility.

Deep-learning architectures were developed for the self-piercing riveting (SPR) process to predict the cross-sectional shape from the scalar input of the punch force. Traditionally, the SPR process is studied using a physic-based approach, including finite element modeling, but in this study, a data-driven approach consisting of two supervised deep-learning models was proposed. The first model was used for data transformation from an optical microscopic image to a material segmentation map, which characterizes the shape and location of the two sheets and the rivet by applying a convolutional neural network (CNN)-based deep-learning structure. To validate the developed models, two types of sheet combinations were tested, namely, carbon-fiber-reinforced plastic (CFRP) and galvanized dual-phase steel (GA590DP) sheets, and steel alloy (SPFC590DP) and aluminum alloy (Al5052-H32) sheets. The transformation was performed with a mean intersection-over-union of 98.50% and a mean pixel accuracy of 99.78%. The next model, which was a novel generative model based on a CNN and conditional generative adversarial network with residual blocks, was then trained to predict the cross-sectional shape from the input punch force. The predicted cross-sectional shapes were compared with the experimental results of SPR. The overall accuracy was 94.20% for CFRP-GA590DP and 96.31% for SPFC590DP-Al5052, with respect to three key geometrical indexes, namely, rivet head height, interlock length, and bottom thickness.

Nowadays industries are taking strength enhancement and weight reduction its main criteria’s for selecting any material. This paper analyses the process of slow speed, shape heading forging where the initially circular porous aluminum powder specimen fixed by one of its ends, is headed into a circular shaped head rivet by appropriate yield criterion, friction law and using an upper bound approach. For the relative average forging pressure of the specimen for different strain intensity, a mathematical model was formulated. The specimens were prepared and subjected to upset rivet head forging process for strain rates of 1.5, 50, 100 and 150 mm/min under lubricated end conditions. Parametric analysis showing deviation of the average forging pressure with percentage reduction in height during rivet head forging process was done graphically. Theoretically and experimentally obtained values of forging load versus percentage reduction in height of the specimen during the process were plotted and a satisfactory equivalence was perceived. Effects of strain rate on load forging during the process of forming the circular rivet head versus percentage height reduction were analyzed and critically addressed.

The method for analyzing of stress-strain state characteristics of unloaded riveted joints performed with OST 1 11781-74 rivets has been developed using Coupled Euler-Lagrange finite element approach implemented in the CAD / CAE system Abaqus. A comparative analysis of the stress-strain state characteristics of the examined riveted joint’s finite element models using the Lagrangian and the Coupled Lagrangian-Eulerian finite element approaches has been conducted. A three- dimensional finite element model based on the CLE method has been proposed for further study of fatigue strength and durability of the loaded riveted joints.

This paper discusses a find of a falchion from the neighbourhood of Gieczno in the Łodzkie Voivodeship. This artefact comes from a sequestration of the collection of an illegal treasure hunter. This 15th century falchion with a conventional blade form stands out with its hilt which is provided with a cap-like pommel, and first of all with a scales rivet which is shaped as an ornamental rosette.

The parameters of heating and cooling of rivets made of steel and aluminum alloy, as well as data of fi lling holes with these rivets during hot and cold riveting are compared. The features of the process of performing cold impact riveting by direct and reverse methods, as well as the possibility of reducing the force of this riveting by improving the closing heads and constructive transformation of the rivets themselves are considered. Features of physiological infl uence of cold shock riveting on hands, elbows and shoulders of workers are determined. Describes the construction of riveting hammers and supports with spring shock absorbers that prevent the disease of workers vibration disease, portable riveting presses of pneumatic and hydraulic action. A description of the press equipment and technology of bolt-riveting connections, allowing mechanizing the process of cold riveting is given.

An introduction to the structural layout of conventional GA aircraft is provided. Special mentioning of aircraft loads is made to help the student understand how different parts of the aircraft structure are designed to react a specific type of load. Then, information on the characteristics and properties of typical materials used for the construction of the modern GA aircraft. This includes aluminum, steel, titanium, and composite materials. The last section of the chapter presents a description of the fabrication of and installation of various structural components for aircraft, such as the fuselage, wing, and stabilizing surfaces.

By combining experimental SPR tests with a finite element (FE) model, the influences of top sheet thickness (Tt), bottom sheet thickness (Tb) and rivet length (L) on the joint formation mechanisms were systematically investigated in this study. Single factor experiments were firstly conducted to uncover the three joining parameters' effects on the joining results. Interrupted SPR tests were also performed to confirm the prediction accuracy of the FE model on the joint formation process. Then, the joint formation mechanisms were analyzed by numerically inspecting the events during the riveting process, including the sheet deformation behaviors, rivet shank flare behavior and formation of quality indicators. The results revealed that the joining parameters affected the interlock formation by directly altering the positions of two interlock boundaries. The rivet shank flare behavior was apparently affected by the Tt and Tb, but less influenced by the L. The formation of remaining bottom sheet thickness at the joint center (Tc) was significantly affected by the Tt and Tb. Rapid reduction of the Tc occurred before the top sheet was penetrated and after the rivet cavity was fully filled. Meanwhile, it is highlighted that the FE model is an excellent tool to analyze SPR joint formation.

This work measures the contact area between an anti-rotation rivet and an aluminum plate under different riveting loads based on the regional scanning of ultrasound. The contact image is a novel disclosure for the anti-rotation rivet contact. The 2D maps show an apparent change not only in area sizes but also in contact shapes under various normal forces applied. The 3D contact images also provide useful information to show the intensity of contact. The contact area between the anti-rotation rivet and the aluminum is calculated using an image analysis software package. The range of contact areas varies from 6.3 mm2 to 57.2 mm2, depending on the applied forces and the definition of the contrast ratio. Furthermore, a calibration of data fitting is performed to provide a useful polynomial equation for contact area estimation. In addition, maps of both a reflection coefficient and a pressure contour distribution are presented. The range of peak contact pressure varies from 7.1 MPa to 11.2 MPa.

The de-icing of a wing leading edge using an electro-impulse method benefits from its very low energy requirement and high efficiency. The high-frequency mechanical vibration activated by an electromagnetic pulse coil linked to an impulse circuit fractures the ice accumulating on the leading edge, and the ice is removed very rapidly when flying. An improved de-icing criterion based transient dynamics method is employed to accurately simulate the electro-impulse de-icing (EIDI) process. To reduce computational expenses in modelling all the rivet joints, a simplified model of leading edge structure ignoring all rivets is established using tie-constraints to identify high-stress areas or critical areas of leading edge structure during the EIDI process. Afterwards, a local detailed model of leading edge structure modelling rivets, rivet holes and their surfaces in critical areas, is set up to accurately describe the impact response and stress configuration of leading edge structure during the EIDI process. According to the EIDI local detailed model for leading edge structure, the fatigue life of critical rivet holes is predicted based on the local maximum stresses. Consequently, the endurance strength of the leading edge structure is estimated and a safe assembling scheme of the EIDI system is suggested.

Multi-material design offers cost-efficient lightweight solutions for automotive body-in-white production. Ultra-high strength steels remain an essential part of the lightweight construction and are increasingly used in combination with components made of aluminum alloys in multi-material body designs. For these applications, the commonly used joining processes (riveting, clinching, resistance spot welding, etc.) have been pushed to their technological limits and a further technological development is needed. The present research describes a new joining technology based on resistance welding process for joining ultra-high strength steel 22MnB5 (AS150) with aluminum sheets AW 6016. The technology consists of a two-stage resistance spot welding process with an additional simple cost-effective joining element. Its implementation allows joining aluminum and steel on extremely short flanges of 10 mm using short time projection welding with high-energy concentration. Joining elements—cylinders made of Cu- and Fe-based wires with diameter 1.6 mm and length 10 mm - were welded using the common resistance spot welding equipment. Experimental results have shown that all tested materials for joining dissimilar steel-aluminum compounds can be successfully used and the weld current ranges are sufficient for industrial application.

As there are increasing demands for efficiency and quality in airframe assembly, automation integration is required to replace manual operation. This paper presents a design of a robotic riveting cell for wedge part riveting, which is used on the trailing edge of airfoil. To complete the continuous riveting in a row of rivets at the trailing edge, a robotic riveting cell is designed to realize a set of process actions including rivet feeding/injection/cutting and press riveting. Based on the visual compensation of the hole position, a forceless feedback spiral track rivet injection compensation method is proposed. The stress feedback-based riveting process control method is introduced after rivet injection and cutting. The proposed approach is applied to the robotic riveting cell and the rivet injector works stably. No indentation has been detected using the force-controlled riveting method. The prototype can achieve the riveting task well on the wedge part. The proposed design and approach can be applied on both wedge parts and flat parts. This will give a new way to solve the automation integration problem in airframe assembly. A robotic riveting cell is designed to realize a set of process actions. A forceless feedback spiral track rivet injection compensation method is proposed. The stress feedback-based riveting process control method is employed after rivet injection and cutting.

In order to improve the joint performance of a titanium alloy rivet connecting aircraft CFRP structure and promote the wide application of ordinary titanium alloy rivets in the aviation field, the ductility of a Ti45Nb rivet was improved using a current-assisted method in this paper. Through experiments, the mechanical behavior and temperature during the riveting process were monitored, and the variation rules of interference and damage were studied in detail. The results show that a current within 16.5 A/mm2 can effectively reduce the riveting pressure requirement, and the maximum engineering stress is reduced by nearly 22%. As the current density increases, the softening effect is obvious, but as the processing time increases, the softening effect has an upper threshold. The current-assisted method can significantly increase the interference fit level, and the uniformity of riveting can be improved by nearly 30%. The outlet burr height of a joint obtained by new technology meets the relevant standards. When the current density is too large or the action time is long, the damage pattern and mechanism at different depths of hole have obvious regional differences.

In recent years, the application of fiber-reinforced plastics (FRPs) as structural members has been promoted. Metallic bolts and rivets are often used for the connection of FRP structures, but there are some problems caused by corrosion and stress concentration at the bearing position. Fiber-reinforced thermoplastics (FRTPs) have attracted attention in composite material fields because they can be remolded by heating and manufactured with excellent speed compared with thermosetting plastics. In this paper, we propose and evaluate the connection method using rivets produced of FRTPs for FRP members. It was confirmed through material tests that an FRTP rivet provides stable tensile, shear, and bending strength. Then, it was clarified that non-clearance connection could be achieved by the proposed connection method, so initial sliding was not observed, and connection strength linearly increased as the number of FRTP rivets increased through the double-lapped tensile shear tests. Furthermore, the joint strength of the beam using FRTP rivets could be calculated with high accuracy using the method for bolt joints in steel structures through a four-point beam bending test.

In modern constructions, especially aircraft, the aim is to minimize the weight of the components used. This necessitates the use of innovative construction materials, or the production of these parts with ever-decreasing wall thicknesses. To simplify assembly and improve strength properties, so-called structural elements are being used in the form of monolithic elements, which are replacing the assemblies of parts joined by, for example, riveting. These structures often have a complex, thin-walled geometry with deep pockets. This paper attempts to assess the accuracy of manufacturing thin-walled elements, in the shape of walls with different geometries, made of various aluminum alloys. Machining tests were conducted at different cutting speeds, which allowed comparisons of the geometric accuracy of parts manufactured under conventional and high-speed cutting conditions. Based on the result obtained, it was found that the elements made of EN AW-7075 T651 alloy underwent the greatest deformations during machining in comparison to other two materials (EN AW-6082 T651 and EN AC-43000). An increase in the geometrical accuracy of the manufactured elements was also observed with the increase in the cutting speed for the HSC range. Hence, to minimize the postmachining deformation of thin-walled elements, the use of high-speed cutting is justified.

Riveted aircraft structures are susceptible to fatigue cracking at fastener locations. Inspection for second layer cracking can be performed by bolt hole eddy current, but requires rivet removal. Pulsed eddy current was adapted for the inspection of aircraft structures in the vicinity of aluminum rivets, without requiring rivet removal. A pulsed eddy current probe was used in combination with modified principle component analysis and cluster analysis to detect notches that simulated cracks. The notches were located in the first and second layer of aluminum structures representative of aircraft skin and underlying structure that was held together by bucked aluminum rivets with universal heads. The technique can detect notches smaller than the overhang of the fastener head. When the aluminum layers were very thin (

This paper presents a robotic automatic drilling and riveting system for single-sided fasteners composed of a robot, an end effector including an intelligent camera and normal measurement cells, a rivet feeder, and some auxiliary system. The control system is designed with the functions of normal adjustment, drilling and riveting position adjustment, compaction, drilling, rivets feeding, glue spread, workstation conversion, and riveting. In order to meet the design needs, communication networks including EtherCAT bus, TCP/IP, serial communication, Automation Device Specification (ADS) communication, and digital IO communication are implemented. The laser sensors and intelligent camera assist to realize algorithms of the normal adjustment and the drilling and riveting positioning. The drilling and riveting system is verified by experiments of flat plate and curved surface. At last, a conclusion is made based on the experiment results which show drilling accuracy the maxi-mum aperture accuracy is 0.016 mm, the maximum deviation of dimple depth is 0.025 mm and the maximum deviation of normal is 0.151°. Aperture accuracy can reach H9 and the efficiency of drilling and riveting in this system can be 5/min.

Refill friction stir spot welding (RFSSW) is an innovative solid-state welding technology for aluminum structures. The presented study aimed to evaluate the mechanical properties of refill spot welds and their failure mechanisms with the use of industrial test standards. The mechanical properties of refill spot welds were compared with those of rivet joints with comparable joint sizes. Static load tests indicated that RFSSW coupons demonstrate higher ultimate shear strengths but slightly lower ultimate tension strengths than those of rivet coupons. Fatigue test results indicated that both RFSSW coupons and rivet coupons demonstrate comparable performances during low-load-level fatigue lap shear tests but RFSSW coupons outperform rivet coupons during high-load-level fatigue lap shear tests. The failure mechanisms of refill spot welds were characterized in terms of external loading, parent metal properties, and weld properties. Refill spot weld failures included parent metal tensile failures, nugget pullouts, and interfacial failures. A refill spot weld may demonstrate one or a combination of these mechanical failures. Although the mechanical tests of refill spot welds demonstrated promising results with predictable failure mechanisms, the metallurgical evolution involved in RFSSW remains a subject to study.

Self-pierce riveting (SPR) is a complex joining process where multiple layers of material are joined by creating a mechanical interlock via the simultaneous deformation of the inserted rivet and surrounding material. Due to the large number of variables which influence the resulting joint, finding the optimum process parameters has traditionally posed a challenge in the design of the process. Furthermore, there is a gap in knowledge regarding how changes made to the system may affect the produced joint. In this paper, a new system-level model of an inertia-based SPR system is proposed, consisting of a physics-based model of the riveting machine and an empirically-derived model of the joint. Model predictions are validated against extensive experimental data for multiple sets of input conditions, defined by the setting velocity, motor current limit and support frame type. The dynamics of the system and resulting head height of the joint are predicted to a high level of accuracy. Via a model-based case study, changes to the system are identified, which enable either the cycle time or energy consumption to be substantially reduced without compromising the overall quality of the produced joint. The predictive capabilities of the model may be leveraged to reduce the costs involved in the design and validation of SPR systems and processes.

This paper concerns the influence of the material modeling method on the results of strength analyses. The research object was a single lap joint with a blind rivet (ISO 12996). The results of numerical strength analysis for various configurations of material models with material and contact nonlinearity were compared not only with the experimental results of such a connection but also with the values estimated using classical analytical tools (pressure stress and Hertz stress). The research aimed to determine how the results of numerical analyses (FEMs) were influenced by the method of modeling the material model and how it relates to the experimental results. As part of the analyses, a discrete riveted model and material models were constructed. The analyses took into account various load cases (from 10 to 90% of the connection capacity) to better illustrate the relationship between the numerical and experimental results. As a result of the conducted analyses, it was determined that the linear-elastic model was an acceptable and suggested solution (with a load of up to 90% of the load capacity of the joint connection) for further tests. The work was summarized with general and specific conclusions relating to all cases of numerical modeling. In addition, the summary includes suggestions for future works.

In this paper, the mechanical properties and corrosion behavior of steel/Al electromagnetic self-pieced riveting, adhesive and hybrid riveted and adhesive joints in the salt-spray environment were compared. These joints were firstly placed in the neutral salt spray environment, and then surface observation, weighting, mechanical properties tests and fractographic analysis were conducted. Results showed that with the increase of ageing time, the peak load of the single riveted joints firstly increased and then decreased, while the peak loads of the other two joints continued to decline. This was because the corrosion products formed in the sheet clearance of the single riveted joint, increasing the frictional resistance during the shear process after a short ageing time (before 20 days). For adhesive and hybrid joints, adhesives prevented the formation of corrosion products in the clearance, but it was vulnerable to damage by chloride ions, which would result in the continuous strength degradation of the joints. Specifically, after ageing for a long time (25 days), the peak load of the riveting, adhesive and hybrid joints, respectively, decreased by 11.2%, 26.3% and 14.4% comparing with the uncorroded joint, which showed the adhesive joint had the worst corrosion resistance. This indicated that the adhesive joint was more affected by environmental factors than the riveted and hybrid joint.

With the continuous progress of modern industry, the traditional nondestructive testing methods cannot meet the growing demand. At present, as a novel approach, the thermography non-destructive testing (TNDT) technology has been widely used in various industrial fields. In this paper, we present the study of a three-layer "metal-air-metal" structure, firstly through the modeling by finite element analysis software COMSOL Multiphysics, and then under the laboratory conditions using flash lamp as excitation methods for TNDT. Based on the preliminary simulation and experimental results , it is proved that it is possible to detect the bottom layer defects with a certain aspect ratio in the multilayer structure. It has practical significance in many scenarios, such as the locating the rivet holes under aircraft skin, the detection of defects below insulation layer and tomographic inspection of post-impact multilayer composites.

In the automatic drilling and riveting process, the perpendicular error of the hole is inevitable, which has a great influence on the assembly quality. In the current research, the shear and pull-out behaviors of riveted joints under different perpendicularity errors and squeeze forces were investigated and compared by the quasi-static tests. The fracture of the failed samples was characterized by a scanning electron microscope and the formation process of fracture was discussed. The failure mechanisms of riveted joints were analyzed in detail to guide engineering applications. The test results demonstrated that the shear load and pull-out load of riveted joints increased slightly with the increase of the tilt angle from 0° to 4°. The perpendicularity error did not affect the shear and pull-out failure modes of the riveted joints. However, the squeeze force had a significant effect on the failure modes of the pull-out samples. Fracture analysis showed that the failure of all shear samples occurred at the rivet shaft. Besides, when the squeeze force increased from 15 kN to 23 kN, the failure modes of the pull-out samples changed from the sheet to the rivet itself.

In the present study, an integrated material and structure (IMAS) design approach is proposed for fabrication of a multifunctional grille composite sandwich plate. It consists of two panels made of carbon fiber/resin polymer (CFRP) and one grille functional core that includes several grid frame beams (GFBs) and grille functional units (GFUs) via falcon riveting connections to achieve vibration sensing and damping control functions. In each GFU, it is composed of a rectangular grille (RG) and several embedded functional materials with 4-layer laminates, including a piezoelectric sensing layer, an upper copper wire layer, a magnetorheological elastomer (MRE) layer and a lower copper wire layer. To investigate the free vibration and damping characteristics of such a highly integrated sandwich structure, an analytical model is proposed that is based on the complex modulus method, the polynomial expansion approach, the improved Rayleigh-Ritz method, etc. After the natural frequencies, modal shapes and damping parameters are successfully solved, with results from literature being employed to roughly validate the model developed. Meanwhile, the dynamic experiments with different internal magnetic field distribution patterns and intensities of MRE are undertaken to give a further validation of the present model. Finally, the parameter analysis is carried out and some important conclusions are summarized to better exert active and passive vibration suppression performance of the CFRP-GFB-GFU plate.

Mechanical joints are commonly required in structures made of fiber metal laminate (FML), which pose a threat due to multi-site stress concentrations at rivet or bolt holes. Thus, for a reasonably designed FML joint, it is essential to characterize the failure mechanism of multiple-hole FML, however, little information about this has been found in open literature. In the present work, influences of hole arrangement and loading strategy (on-axis or off-axis) on the failure mechanism of multiple-hole FML were investigated, by performing finite element analyses and energy dissipation analyses with elastoplastic progressive damage models that took curing stress into account. Six types of specimens with holes arranged in parallel and staggered forms were designed, whose geometrical parameters were in strict accordance with those specified for composites joints. It indicated that the stress distribution, gross/net notched strength, critical fracture path, and damage evaluation process were only slightly influenced by the hole number and hole arrangement. On the other hand, they were strongly influenced by the loading strategy, due to the transition of failure domination. Results presented here can provide evidence for introducing design regulations of composite joints into the more hybrid FML, and for reasonably determining its multiple-hole strength merely based on the sing-hole specimen.

International audience; In the last decades, the use of structural adhesives has increased. Indeed, they are able to replace advantageously traditional assembly techniques such as riveting or bolting, and generally tend to reduce the global weight of the structure and/or improve the strength of the structure thanks to more homogeneous stress distribution. In addition, it allows the assembly of composite materials or materials having different nature, which is of great interest in the aeronautic industry. However, to be used for structural joining and critical application, reliable non-destructive testing techniques are compulsory for evident safety reasons, be it after fabrication or during the whole life of the structure. While linear ultrasounds have demonstrated their capability to detect easily decohesion or voids in a structure, their use for bond strength inspection is less straightforward. Another approach relies on the analysis of nonlinear signature of a bond defect inspected by high amplitude ultrasound. In the present paper, a Chaotic Cavity Transducer is used to inspect various metallic bonded plates (titanium or aluminum) with several bond defects. The defects were introduced by depositing localized surface pollution (introduction of PTFE spray, release agent, or fingerprints) before the adhesive is deposited on top of the surface. Combined with the pulse inversion technique, high amplitude plane waves were sent in the structure, leading to harmonic components observed in the defect region. Mechanical destructive tests were performed and display a good agreement with nondestructive tests.

Riveting is widely used in aircraft manufacturing. The strap butt joint is often used in the aircraft’s main bearing area such as the aircraft docking area. The connection quality affects the reliability and safety of the aircraft directly. To study the effect of the rivet position on the connection quality of the strap butt joints, this paper analyzed the distribution of stress around the rivet hole at different positions by the finite element method, and then further analyzed the influence of the different rivet layouts on the connection quality of the strap butt joints by experiments. The static load tensile failure test of the joints was carried out, and the obtained tensile strength and failure mode of the strap butt joints showed that the main static tensile failure form of the single strap butt joint is that the whole rivets is sheared and the connecting sheets are separated. By changing the layout of different rivets, the connection strength can be maximized by reducing the outer row spacing (ORSD) of rivets. The results can be used for reference in the design of the riveting structure of aircraft panels.

Aircraft panel assembly mainly includes the pre-joining process and the riveting process. In addition, the traditional pre-joining process is mainly executed by bolts, which has problems such as the large tightening torque, inconvenient bilateral tightening, heavy workload, and inconvenient loading and unloading. To solve the above-mentioned problems, a research of new temporary fastener is performed deeply from three levels of quick installation, labor-saving, and reversible ability. This involves (a) employing the lever mechanism and the rapid expansion anchor to implement the rapid clamping and disassembly of working processes by labor-saving, (b) integrating the adjusting spring to overcome the tolerances of parts, and (c) building up the space-cross slide rails to provide the axial clamping forces and the reversible forces. The application of designed fasteners was employed into the production of aircraft panel, and the error between theoretical and experimental values was less than 10%. Besides this, the result showed the good effect in panel clamping and the reliable processes of loading and unloading installation, and will greatly reduce the complexity of pre-joining process, the difficulty of installation, and the comprehensive cost.

One of the most important processes in the structural design is the joining techniques. Adhesive bonded joints have various advantages over the riveted joints. These advantages include high strength to weight ratio, low stress concentration and large bond area for load transfer. However, adhesive bonded joints have few disadvantages as well, some of them are; (1) their disassembly may lead to the component damage (2) they have low peel strength. Due to the aforementioned disadvantages, ensuring the bondage quality is a challenge. A relatively new approach is to use adhesive bonded riveted joints which are also known as hybrid joints. Hybrid joints actually integrate of both adhesive and riveted joints. Stress concentration will be less in adhesive joints as compared to the riveted joints if number of rivets are reduced in hybrid joints and adhesive is used to overcome the strength. This study focuses on the static strength of the adhesive, riveted and the hybrid joints. Experimental and analytical results are available and numerical analysis is to be done using ANSYS®software using tensile testing and models will be made in CATIA®. All work is performed on aluminum alloy 2024-T3 commonly used in aircraft structures. Only single lap joint is studied in this paper to examine joint behaviour.

Mechanical connections such as bolts and rivets are inevitable in most engineering structures and may significantly affect the dynamic behavior of the structures. Therefore, modeling a joint simply and accurately is essential for assembled structures. On the other hand, the most important step is the determination of these joint model parameters which will be used in the calculation of dynamic response of assembled structures. For this purpose, in this paper, FRF Decoupling Method (FRF-DM), proposed in an earlier study for bolted beam connections is extended in two ways: Firstly, the bolt model proposed for 2D beam elements is extended to 3D finite element models of structural systems, and thus the dynamics of a bolted connection is modeled as an equivalent 6 × 6 complex stiffness matrix including linear and torsional stiffnesses. Secondly, FRF-DM is extended to include measurements at connection degrees of freedoms, which improves the accuracy in identification. Several equations for the identification of joint parameters are derived utilizing FRF-DM. Joint parameters are calculated by using developed FRF decoupling relations, as well as by employing a recently developed method called Inverse Structural Modification Method (ISMM) in a case study consisting of two beams connected by a 6 × 6 stiffness and viscous damping matrices. The accuracy and the advantages of each method/formulation are discussed by using the case study based on simulated experiments.

The present work deals with the transferability of Friction Riveting joining technology from laboratory equipment to adapted in-house, low-cost machinery. A G13 drilling machine was modified for the requirements of the selected joining technique, and joints were performed using polyethermide plates and AA2024 aluminum alloy rivets of 6 mm diameter. This diameter was not previously reported for Friction Riveting. The produced joints were mechanically tested under tensile loading (pullout tests) with ultimate tensile forces of 9500 ± 900 N. All tested specimens failed through full-rivet pullout, which is the weakest reported joint in Friction Riveting. In order to understand this behavior, FE models were created and analyzed. The models produced were in agreement with the experimental results, with failure initiated within the polymer under stress concentrations in the polymeric material above the deformed metallic anchor at an ultimate value of the stress of 878 MPa at the surface of the joint. Stresses decreased to less than half of the maximum value around the anchoring zone while the rivet was removed and towards the surface. The paper thus demonstrates the potential ease of applying and reproducing Friction Riveting with simple machinery, while contributing to an understanding of the mechanical behavior (initialization of failure) of joints.

Electromagnetic riveting process (EMR) is a high-speed impact connection technology with the advantages of fast loading speed, large impact force and stable rivet deformation. In this work, the axisymmetric sequential and loose electromagnetic-structural coupling simulation models were conducted to perform the electromagnetic riveting process of a Ti-6Al-4V titanium rivet, and the parameter analysis of the riveting setup was performed based on the sequential coupled simulation results. In addition, the single-objective optimization problem of punch displacement was conducted using the Hooke–Jeeves algorithm. Based on the adaptive remeshing technology adopted in air meshes, the deformation calculated in the structural field was well transferred to the electromagnetic field in the sequential coupled model. Thus, the sequential coupling simulation results presented higher accuracy on the punch speed and rivet deformation than the loose coupling numerical model. The maximum relative difference of electromagnetic force (EMF) on driver plate and radial displacement in the rivet shaft was 34.86% and 13.43%, respectively. The parameter analysis results showed that the outer diameter and the height of the driver plate had a significant first-order effect on the response of displacement, while the platform height, transition zone height, angle, and transition zone width of the amplifier presented a strong interaction effect. Using the obtained results on the optimal structural parameters, the punch speed was effectively improved from 6.13 to 8.12 m/s with a 32.46% increase. Furthermore, the displacement of the punch increasing from 3.38 to 3.81 mm would lead to an 80.55% increase in the maximum radial displacement of the rivet shaft. This indicated that the deformation of the rivet was efficiently improved by using the optimal rivet model.

A simplified finite element model of riveted joints for structural analyses which effectively incorporates nonlinear response of riveted joints is proposed. Load-transfer characteristics of riveted joints were experimentally and numerically studied. First, a detailed finite element analysis for the process of a tensile test of a single-row joint which consists of squeezing of the rivet and tensile loading to the joint was conducted to confirm the validity of a conventional method of analysis. The load–relative displacement behaviors of single-row joints observed in the detailed finite element analysis and previously conducted experiments agreed well. Then, a simplified method of the analysis was developed based on the detailed analysis and the experiments and was applied to analyses of multiple-row joints. A nonlinear relationship between load and relative displacement in the simplified analyses had good agreement with the detailed one. Distributed loads to the multiple rivets in the simplified analysis coincided with those of the detailed analysis under the maximum load. Memory and CPU time required to run the simplified analyses were reduced to about 1/4 and 1/6 compared to those of the detailed analysis, respectively.

There is a significant number of old metallic bridges with high levels of structural degradation due to their long service period. Fatigue problems are especially important in these structures since the majority of them were not designed taking into account this phenomenon. Several investigations showed that riveted joints are critical details since several fatigue cracks were found in these joints. In this sense, strengthening methodologies need to be studied. The strategy that has been considered a good solution is the implementation of injection bolts to replace faulty rivets. The structural performance of injection bolts has been demonstrated essentially under quasi-static conditions presenting good results. This paper intends to contribute to the scientific knowledge regarding the fatigue behavior of connections with preloaded injection bolts in the context of a bridge strengthening scenario. An experimental investigation was conducted to compare the fatigue performance of connections with preloaded injection bolts and preloaded standard bolts. Single and double shear connections were tested. New S–N design curves were proposed based on a statistical analysis of the results and compared with the S–N curves proposed in EC3-1–9. The obtained results showed that the use of injection bolts lead to lower scatter and improvement of fatigue life. It was verified that the Eurocode 3 is not able to represent the fatigue strength of connections whose performance is influenced by old metallic materials. Additionally, the fatigue behavior of these connections was assessed by numerical analysis. The relevance of the fatigue crack initiation was evident.

Construction of electric arc welded railway bridges developed in France with the work of Chief Engineer Louis Eugene Cambournac (1886–1973) within the Compagnie des Chemins de fer du Nord from 1935 onwards, then within the SNCF (French Railways) from 1938. Under the impetus of this Chief Engineer, about ten railway bridges were built, including only one truss bridge, the Joncherolles Bridge, put into service on 15 May 1939. During this period, the electric arc welding process was used to reinforce riveted bridges not strong enough to support the increase in loads and frequency of railway traffic. It was also used for repairing corroded riveted railway bridges, and occasionally following destructions that occurred during the Second World War. This study shows, in this transition period, how the electric arc welding process quickly – but quite lately – became established for the construction of French railway bridges, replacing the hot riveting process.