Rivet Head Research Articles

Effect of the countersunk rivet head dimensions on fatigue behavior of riveted specimens of 2024-T3 alloy

PurposeThis study aims to investigate the effect of countersunk rivet head dimensions on the fatigue performance of the riveted specimens of 2024-T3 alloy.Design/methodology/approachThe relationship between rivet head dimensions and fatigue behavior was investigated by finite element method and fatigue test. The fatigue fracture of the specimens was analyzed by scanning electron microscopy.FindingsA change of the rivet head dimensions will cause a change in the stress concentration and residual normal stress, the stress concentration near the rivet hole causes the fatigue crack source to be located on the straight section of the countersunk rivet hole and the residual normal stress can effectively restrain the initiation and expansion of fatigue cracks. The fatigue cycle will cause the rivet holes to produce different degrees of surface wear.Originality/valueThe fatigue life of the specimens with the height of the rivet head of 2.28 mm and 2.00 mm are similar, but the specimens with the height of the rivet head of 1.72 mm were far higher than the other specimens.

Investigation of the influence of the rivet geometry on joint formation for a versatile self-piercing riveting process

Climate change has led to a large number of countries deciding to reduce carbon dioxide (CO2) emissions significantly. As the mobility sector is a major contributor to CO2, various strategies are being pursued to achieve the climate targets set. An increasingly applied lightweight design method is the use of multi-material constructions. To join these structures, mechanical joining technologies such as self-pierce riveting are being used. As a result of the currently rigid tool systems, which cannot react to changing boundary conditions, a large number of rivet–die combinations is required to join the rising number of materials as well as material thickness combinations. Thus, new, versatile joining technologies are needed that can react to the described changes. The versatile self-piercing riveting (V-SPR) process is one possible approach. In this process, different material thicknesses can be joined by using a multi-range capable rivet which is set by a joining system with extended actuator technology. In this study, the V-SPR joining process is analysed numerically according to the influence of the geometrical rivet parameters on the joints characteristics as well as the resulting material flow. The investigations showed that the shank geometry has a decisive influence on the expansion of the rivet. Furthermore, the rivet length could be proven to be an influencing factor. By changing the head radii and the protrusion height, the forming behaviour of the rivet head onto the punch-sided joining part could be improved and thus the formation of air pockets was prevented. Based on the numerical investigations, a novel rivet geometry was developed and produced by machining. Subsequently, experimentally produced joints were analysed according to their joint formation and load-bearing capacity.

Non-destructive rapid defect testing around curved head rivets without displacement of eddy current sensors

In the field of aeronautics, it is essential to ensure the structural integrity of aircraft components. Non-destructive testing (NDT) plays a crucial role in ensuring the safety and reliability of structures used in aeronautics as it enables the detection of defects and imperfections without damaging the inspected parts. Domed head rivets are commonly used in aeronautics to assemble multilayer structures due to their strength and ability to maintain the structural integrity of aircraft. However, inspecting these assembly areas can be challenging and presents unique challenges in terms of non-destructive testing due to the curved surface of the rivet, resulting in lift-off variation during surface scanning and a modification of the trajectory of eddy currents near the rivet. This can lead to changes in the response of eddy currents, complicating the accurate interpretation of test results. In recent years, researchers have focused on developing advanced eddy current testing methods to detect defects in complex structures, such as those found in aeronautics. In this work, we propose a promising solution to address both the shape of the rivet and the probe displacement issue during testing. We have developed a model based on the finite element method (FEM) using COMSOL Multiphysics for non-destructive testing through 3D imaging using a matrix of multiplexed multi-element eddy current sensors distributed over multiple layers around the rivet without the need for the displacement of this matrix and capable of adapting to the variation in the diameter of the domed head rivet. The non-displacement of the sensors eliminates parasitic signals that can lead to errors in the interpretation of obtained signals, and the multiplexed powering of the sensors eliminates the mutual inductance effect between adjacent coils.

Influence of local heat treatment of rivets on the joint formation of a versatile joining process

An efficient lightweight construction method is the combination of different materials in order to adapt the structure to the applied load. To join these multi-material structures mechanical joining technologies are applied. However, the rigid tooling systems cannot be adjusted to changing boundary conditions which is why new, versatile joining technologies are required. In the versatile self-piercing riveting (V-SPR) process presented in [1] different material combination are joined by using a multi-range capable rivet. The rivet head is formed onto the respective thickness of the joint by an outer punch. In order to punch thru the upper sheet a great rivet hardness is required whereas a lower hardness is required for the subsequent forming of the rivet head. To achieve a combination of these requirements, this study investigates a local heat treatment of the rivet. The aim is to determine the feasibility of such a heat treatment as well as to investigate the influence on the joint formation.

Research on aircraft skin rivet detection technology based on the normal vector-density clustering algorithm.

Riveting quality is crucial to an aircraft's overall aerodynamic performance and fatigue life. In order to effectively extract the point cloud of rivet heads and analyze the quality of riveting, this paper proposes a rivet flushness detection method based on the normal vector-density clustering algorithm. First, initial point cloud data sampling is based on normal vectors. Then, the density clustering algorithm is employed to cluster and extract the point cloud of rivet heads. Subsequently, the obtained point cloud of rivet heads is subjected to the random sample consensus algorithm for fitting the contour and obtaining the model parameters of the rivet head. The paper introduces a quality detection metric to describe the flushness of the rivet head. Finally, the proposed method is applied to analyze the skin and theoretical model point cloud data of rivets. The results demonstrate that the proposed method yields small errors and high accuracy compared to theoretical values. The method is further employed for quality detection and analysis of rivet flushness in practical aircraft engineering. A visualization system for rivet flushness quality detection is developed to represent the results visually. This system enhances the intuitive identification of rivet detection outcomes. Therefore, the proposed method holds significant engineering application value in rivet flushness detection.

Performance and failure analysis of perforated CFRP/aluminum alloy bonding and self-piercing riveting hybrid joints

This paper explores the new hybrid hole-drilled bonding and self-piercing riveting (HH-BR) connection technique to enhance the strength and overall performance of carbon fiber reinforced polymer (CFRP) and dissimilar metal materials at joint interfaces. The forming quality, mechanical performance, failure modes, and fracture characteristics of the CFRP and aluminum alloy joints utilizing the HH-BR procedure were analyzed in detail and compared with the joints of the hole-less adhesive-bonding self-piercing riveting (H-BR) and self-piercing riveting (SPR). At the same time, the effects of different rivet performance levels, overlap lengths, and various fiber orientation angles on joint performance were discussed. The results show that joints made by the HH-BR technique have a substantial advantage in terms of achieving superior mechanical performance and interlocking value. Firstly, HH-BR joints with bent rivets and torn fibers have connection strengths that are noticeably higher than those with CFRP laminate delamination or rivet pullout failure. The use of the HH-BR technique for joining CFRP/aluminum alloy culminated in reduced strength loss and higher energy absorption than H-BR and SPR joints, improving the joint's overall strength. Secondly, the interlock value between the rivet and the plate, is what essentially determines the strength of HH-BR joints, especially evident in connections with 0°/90° fiber orientation and more overlap lengths. The results also show that there is a strong relationship between the height of the rivet head and the joint's mode of failure, and the height of the rivet head is affected by the rivet force. Furthermore, the interlock value's magnitude, the joint's remaining bottom thickness, and the metal material's capacity for plastic deformation are all directly correlated.

Quasi-static tensile failure mechanism analysis of CFRP/Al countersunk electromagnetic riveted joints with different rivet-hole clearances

CFRP/Al countersunk riveting can meet the requirements of aircraft aerodynamic shape and lightweight joining. This paper reports an experimental study on the forming mechanism and quasi-static tensile failure of single-lap electromagnetic riveted joints with varying rivet-hole clearances. The aim is to quantitatively evaluate their deformation characteristics and mechanical properties. The failure process and fracture mechanism are revealed through the use of digital image correlation (DIC) and scanning electron microscope (SEM). The results demonstrate that the rivet-hole clearance has a significant impact on the initial damage and mechanical properties of riveted joints. The interference is not uniformly distributed in the Al sheet and the CFRP sheet. Increasing the clearance can delay the occurrence of damage of the laminate under external load. As the clearance increases, the riveted joint failure mode changes from rivet sheared off to manufactured head fracture and rivet pull-off, and the rivet fracture shows a brittle- ductile mixed fracture mode. Additionally, the initial riveting damage of the joint does not determine the final extent of damage to the laminate after failure, and the bearing damage of CFRP laminates increases with the increase in the load-carrying capacity of the joint.

Analysis of TB2 rivet forming quality and mechanical properties of thin sheet riveted joints based on different riveting methods

The riveting of high-strength rivets (such as TB2 (Ti-5Mo-5V-8Cr-3Al)) faces difficulties in forming. This article compares the electromagnetic riveting (EMR) and the hot riveting (HR) joints of two typical TB2 rivets (the flat cone head rivet and the countersunk head rivet). The interference and hardness distributions of the rivets were measured, and the strength of the joints was tested. Moreover, the microstructures of rivets after riveting and the fractured surfaces after the shear and pull-out tests were both observed. The results indicate that the interference of the EMR joints is greater and more uniform than that of the HR joints. The deformation of the EMR driven head is more severe than that of the HR. Higher hardness is measured in the driven head and the rivet shank at the positions of severe deformation. The hardness of the EMR driven head and rivet shank is higher than that of the HR. Additionally, it will not cause a decrease and even slightly improve in the mechanical properties of the joint when using the EMR riveting TB2. The pull-out strength of flat cone head rivet joints is significantly higher than that of countersunk rivet joints due to the influence of the structure strength of the manufactured head. The fracture mode of all joints is mixed fracture. However, the failure mode of joint varies greatly due to the influence of rivet structure and riveting method. When using the EMR instead of the HR to rivet the TB2 rivets, it will not cause a decrease in the mechanical properties of the joint. Therefore, it is indicated that the EMR can be used to replace the HR.

Fatigue failure mechanism and estimation of aluminum alloy self-piercing riveting at different load levels

In order to investigate the mechanical properties of self-piercing riveting (SPR) joints in low ductility aluminum alloys, the study utilized three different types of aluminum alloy sheets: 7075, 6061, and 5754. These sheets were joined together using self-piercing riveting technology. The research compared the geometric parameters, microhardness, quasi-static mechanical properties, and fatigue properties formed with the joints of the three aluminum alloys. Additionally, the fatigue life of the self-piercing riveting joint in the 7075 aluminum alloy was analyzed using the Paris law and its corollary. The findings revealed that effective connections were established in all three aluminum alloys, although the expansion of the rivet was comparatively lower in the 7075 alloy. Plastic deformation resulted in an increase in microhardness of joined sheets. The hardness of the joined sheets followed the order: 7075 > 5754 > 6061. Furthermore, the 7075 alloy exhibited superior static mechanical and fatigue properties due to its inherent material. However, despite its lower material strength, the 5754 alloy outperformed the 6061 alloy at low fatigue load levels as a result of work hardening. The failed joints exhibited black oxide, and fretting damage under fatigue loading exacerbated the fatigue failure of the joint, serving as the primary cause. In the case of the 7075 alloy, three types of failure occurred due to fretting damage, which was influenced by the unique nature of the lower die. Fretting between the lower sheet and the rivet leg primarily caused lower sheet fracture and rivet failure, while fretting wear between the rivet head and the upper sheet or between the two sheets mainly led to upper sheet fracture failure. The fatigue life estimation method employed in the study, based on the Paris law, demonstrated good agreement with the experimental results.

Design and Development of Orbital Riveting Machine

Orbital Spin riveting is a relatively new technology for bearing locking in which parts are joined by specific movement of tools. Special incremental motion enables smaller contact area between tool and cage and therefore, lower forming load and friction. Hence, orbital spin riveting makes it possible to join a desired part in lower forming force in the operation, whereas in conventional locking more force would be required. The angle of the riveting tool held in the riveting head plays a significant role in the reduction in forming force, whereas the table motion will determine the accurate positioning of the rivet in to tool profile, resulting into exact shape and size of rivet head formed. This project presents a brief overview of Design and Development of Orbital Riveting machine for Bearing Assembly which leads to improve the product quality and its Productivity. Keywords: Orbital Riveting, Design, Development, Cost TRIZ, SPM, Productivity

Fretting wear behaviour in 6061-T6 aluminium alloy

Abstract In this study, fretting wear in riveted lap joints of aluminium alloy plates was investigated. For the fretting test, 6061-T6 aluminium alloy plates, which are widely used in aircraft construction, and blind rivets were used. Experiments were carried out using a computer controlled Instron testing machine. Fretting surface roughness, microhardness was investigated by metallographic techniques and scanning electron microscopy. Tensile load cycles in the riveted lap joint were found to cause damage to all surfaces. Two contact surfaces where friction occurs were investigated. The contact surface of the lower plate with the upper plate, and the contact surface of the lower plate with the rivet head. As load and cycles increased, fretting scars and surface roughness increased. Consequently, it has been determined that fretting damages occur between the contact surface of the plates and between the plate and the rivet contact surface.

Aviation Rivet Classification and Anomaly Detection Based on Deep Learning

The shortage of personnel and the high cost have become a major pain point in the current safety supervision work of the inspectors. Aiming at the problem that the aircraft maintenance inspector could not visit the scene in person during the epidemic, a remote safety supervision platform was built based on intelligent glasses and 5G network, and the real-time monitoring of the aircraft skin rivet status was realized. And a method of aviation rivet classification and anomaly detection based on deep learning algorithm was proposed. Firstly, according to the appearance of rivet head, the aviation rivet is classified, the data set of aviation rivet is made, and the aviation rivet classification and anomaly detection model are constructed. Evaluate the detection results from such indicators as confidence, precision, recall rate, and mAP and compare the algorithm with the detection results of Yolox-s, Yolox-m, Yolov5-s, Yolov5-m, and Yolov4. The results show that (1) the algorithm proposed in this paper can realize the classification of aviation rivets and the detection of abnormal conditions, the confidence of the detection results is more than 90%, and the average precision, recall, and AP value are above 95%, 85%, and 88%, respectively. (2) The order of rivet classification and abnormal detection effect from good to bad is Philips screws, round head rivets, flat head rivets, countersunk head rivets, blind rivets, and abnormal condition. (3) Compared with other algorithms, the aviation rivet classification abnormal target detection based on deep learning has absolute advantages in accuracy and speed.

Effect of repeated impacts on the mechanical properties of nickel foam composite plate/AA5052 self-piercing riveted joints

Due to their good impact resistance, foam metal composite plates are widely used in the lightweight multi-structure design of cars, and nickel foam is one of the commonly used foam metals. In this paper, the nickel foam composite plates were manufactured, and the self-piercing riveting was used to join the nickel foam composite plates with AA5052 aluminum alloy. The impacts of different energies and times ont the joints were investigated, and the mechanical properties and failure forms of the impacted joints were analyzed. The results show that self-piercing riveting can realize the connection between the composite plate and AA5052 aluminum alloy, and the variation of impact force with displacement is different at various impact energies and times. The higher the impact energy, the deeper the damage to the joint. At 5 J, the impact times have no significant effect on the residual strength, while at 10 J and 15 J, the residual strength decreases with the increased impact times. The failures are all manifested by tearing the lower panel of the composite plate and the rivet head is pulled out from the composite plate, and the impacts do not affect the tensile failure forms of the joints. The aluminum alloy panel shows a ductile fracture, and mixed damage occurs for the adhesive layer.

Progressive Failure Analysis of Composite/Aluminum Riveted Joints Subjected to Pull-Through Loading

Out-of-plane mechanical properties of the riveted joints restrict the performance of the wing box assembly of airplane. It is necessary to investigate the pull-through performance of the composite/metal riveted joints in order to guide the riveting design and ensure the safety of the wing box assembly. The progressive failure mechanism of composite/aluminum riveted joint subjected to pull-through loading was investigated by experiments and finite element method. A progressive damage model based on the Hashin-type criteria and zero-thickness cohesive zone method was developed by VUMAT subroutine, which was validated by both open-hole tensile test and three-point bending test. Predicted load-displacement response, failure modes and damage propagation were analysed and compared with the results of the pull-through tests. There are 4 obvious characteristic stages on the load-displacement curve of the pull-through test and that of the finite element model: first load take-up stage, damage stage, second load take-up stage and failure stage. Relative error of stiffness, first load peak and second load peak between finite element method and experiments were 8.1%, − 3.3% and 10.6%, respectively. It was found that the specimen was mainly broken by rivet-penetration fracture and delamination of plies of the composite laminate. And the material within the scope of the rivet head is more dangerous with more serious tensile damages than other regions, especially for 90° plies. This study proposes a numerical method for damage prediction and reveals the progressive failure mechanism of the hybrid material riveted joints subjected to the pull-through loading.

Effect of Top Sheet Materials on Joint Performance of Self-Piercing Riveting

Three types of self-piercing riveting (SPR) joints, i.e., steel/aluminum, carbon fiber reinforced polymer (CFRP)/ aluminum, and aluminum/aluminum, were constructed using three different top sheet materials with the same aluminum alloy as the bottom sheet. The effects of the top sheet material on the joint quality and mechanical behavior were evaluated. The top sheet materials’ characteristics dominate the rivet piercing process and the consequent interlock distance. The high-strength steel top sheet requires a comparatively higher rivet setting force and induces early flaring of the rivet tail, resulting in a larger interlock distance. Though the CFRP needs the highest rivet setting force to penetrate the rivet through the CFRP fibers, the CFRP/aluminum joint exhibits the smallest interlock distance because of the SPR process-induced damages to the CFRP and subsequently less flaring of the rivet tail. In strength tests, the damaged CFRP sheet resulted in rivet head pullout of the CFRP/aluminum joints, which exhibited the lowest lap-shear and cross-tension strengths. In contrast, the steel/aluminum joints demonstrated the highest strengths because of their comparatively larger interlock distances. In addition to the experimental analysis, simulations revealed the rivet penetration and flaring mechanisms with various top sheet materials, and their respective joint quality and strengths.

The Effect of Thickness on Strength of Single Lap Orbital Riveted Aluminum/Composite Joints Used in Marine Environments

In an innovative vision of manufacturing, orbital riveting is a joining technique characterized by high efficiency, energy saving, low costs and low noise. It is a cold forming process where a tool rotates at a fixed angle (i.e., typically 3° to 6°) to create a sweeping line of pressure around a rivet. This movement progressively promotes, with each rotation, the collapse of the rivet shank down onto the upper substrate of a joint, permanently forming a rivet head. The aim of this research is to make and test multi-material joints between an aluminum AA5083 H111 sheet and a glass fiber reinforced laminate. Specifically, nine configurations of single lap joints were studied by investigating the effect of the thickness (i.e., 2.5, 3.0 and 4.0 mm for the aluminum and 2.5, 3.0 and 4.0 mm for the composite laminate) both on the mechanical characteristics and on the failure modes.

Mechanical and geometrical characterisation of tumbling self-piercing riveting joints in multi-material-systems

Increasing requirements on lightweight construction to preserve resources necessitate new processes and methods in the production of weight-optimised multi-material-systems. Common joining processes such as the conventional semi-tubular self-piercing riveting are reaching their limits because of the rigid process designs. To extend this process, the linear punch movement is superimposed by an orbital forming process with a tumbling kinematic and provides new possibilities to influence the joining process. The configuration of the tumbling strategy consisting of the parameters tumbling angle and tumbling kinematics enables a targeted control of the material flow for the production of tailored joints. Within the scope of the investigations, the influence of the two parameters is examined both for the joining process and for the resulting joint formation. Force-displacement diagrams, micrographs and rivet head geometries are analysed to determine the influence on the process itself. Further, shear tensile tests and cross section tests are carried out to characterise the load-bearing capacities of tumbled joints and to identify the effects of the tumbling strategy on the mechanical properties. The tested materials in form of a dual-phase steel HCT590X+Z and a precipitation-hardening aluminium alloy EN AW-6014 have widely varying mechanical properties to represent multi-material-systems.

Research on the Simplified Method of Nonlinear Finite Element Analysis for CFS-SPR Connections

This study reviewed some simplified methods of finite element analysis (FEA) for connections in cold-formed steel (CFS) structure, and summarized eight simplified methods divided into three categories. Shear performance tests were performed for six groups of self-piercing riveted (SPR) connection in CFS. A constitutive model of shear behavior for SPR connections was proposed, which was simplified from the load–displacement curve of shear performance test results. The models of SPR connection were established in ABAQUS by the eight simplified methods, and then the FEA results and the test results were compared. The applicable scope of each simplified model was explored, and a simplified method of FEA that was most suitable for the shear behavior of the CFS-SPR connection was proposed. Moreover, the shear performance test of the CFS shear wall with SPR was conducted by considering the rivet spacing, and failure modes and load–deformation curves were obtained. On this basis, numerical models of the CFS-SPR connection shear wall were established. By comparing the test results and the FEA results for the CFS-SPR connection shear wall, the feasibility of a simplified method of FEA applied to the CFS-SPR connection was verified. The main failure modes of the CFS-SPR connection were that the rivet tail pulled out from the bottom sheet and the rivet head pulled over from the top sheet. The SPR connection of the CFS frame could be simplified with a pin or a fastener element, and the SPR connection between the steel frame and the sheathing could be simulated by a Cartesian connector or a Spring2 element. The FEA results were highly similar to the test results for the CFS-SPR shear wall.

Geometric and mechanical joint characterization of conventionally and tumbled self-piercing riveting joints

In view of economic and ecological trends, the concepts for lightweight construction in transport systems are becoming increasingly important. These are frequently applied in the form of multi-material systems, which are characterized by the selective use of materials and geometries. One major challenge in the manufacturing of multi-material systems is the joining of the individual components to form a complete system. Mechanical joining processes such as semi-tubular self-piercing riveting are frequently used for this application but reach their limits concerning the number of combinations of geometry and material. In order to react to the requirements and to increase the versatility of semi-tubular self-pierce riveting, a process combination consisting of a tumbling process and a self-pierce riveting process has been presented previously. This process combination is used in this work to investigate the versatility and to identify the influencing parameters on it. For this purpose, experiments are conducted to identify process-side influence possibilities. The tests are performed with a dual-phase steel aluminum alloy to represent the varying mechanical characteristics of multi-material systems. Furthermore, the initial sheet thicknesses of the joining partners are varied in several steps. In addition to the geometric joint formation used to describe the undercut, the rivet head end position and the residual sheet thickness, the joining process, is also analyzed during the investigations. Further, the innovative joining process is evaluated by comparing it with a conventional self-piercing riveting process. The knowledge obtained represents a basis for the identification and evaluation of the versatility of the process combination.

Joining mechanism and damage of self-piercing riveted joints in carbon fibre reinforced polymer composites and aluminium alloy

The joining mechanism and damage of self-piercing riveted joints in carbon fibre reinforced polymer (CFRP) composites and aluminium alloy were investigated. The damage constitutive model for composite materials, considering the shear effect, was proposed to predict the mechanical behaviour and damage evolution of the CFRP. Self-piercing riveting (SPR) tests were performed to determine the damage patterns of joints with different laminate structures. Furthermore, numerical simulations of the SPR process were performed to understand the joining mechanism and analyse the damage evolution process of the joints. The results show that matrix cracks and fibre cracks existed in the SPR joints in the CFRP and aluminium alloy, located around the rivet head. With the increase in CFRP thickness, the damage degree of the joint surface decreases. Therefore, the proposed constitutive model can predict the complex damage behaviours of a CFRP subjected to large deformations. The matrix cracks are mainly caused by the matrix tensile damage, with the ply angle influencing the damage evolution trend. In addition, delamination exists between each ply of the SPR joint; the propagation direction of delamination damage is consistent with the fibre direction of the lower layer, especially for the joints with [0/90/0]s CFRP or [45/-45/45]s CFRP.