Self-piercing Riveted Joints Research Articles

Experimental and numerical investigation on the effect of process parameters on joint strength and failure behavior of self-piercing riveted steel/aluminium hybrid joints

To further improve the joint strength and identify the potential failure behavior of self-piercing riveted (SPR) steel/aluminium hybrid joints under shear and cross-tension loading conditions, a simplified 2D-to-3D simulation process chain is proposed. The finite element models (FEM) for the failure process of SPR joints are established in LS-DYNA and verified against experimental results. The effects of rivet strength, sheet material and thickness, and riveting direction on the joint strength and failure behavior of SPR joints are investigated. The results show that when the rivet strength is less than 1.3 GPa, increasing the rivet strength can improve the joint strength of AS joints under shear load and SA joints under cross-tension load. The joint strength of two types of SPR joints increases gradually and then decreases with an increase in thickness ratio Rt. When the steel/aluminium sheet thickness ratio Rsa exceeds 1.47, the aluminium-to-steel direction should be chosen. Increasing material strength can improve the joint strength of two types of SPR joints, while their sensitivities to the material strength vary under different loading conditions. The sheet material, sheet thickness, and riveting direction can change the failure behavior of the joints, while the rivet strength does not alter the failure behavior. This work contributes to understanding the mechanism of joint strength improvement and enhances riveting quality in industrial practice.

Study on the fatigue properties of SPR-bonded aluminum-steel sheet joints

This study deals mainly with the influence of adhesive layer on the fatigue behavior and fretting of self-piercing riveted (SPR) joint joining differing thicknesses of AlSi10MnMg aluminum and DP590 steel sheets in lap shear geometry. Fatigue life, failure modes, crack propagation and fretting behaviors of the SPR and SPR-bonded joints were investigated and compared. The results showed that the static strength and fatigue life of SPR-bonded joints were significantly enhanced than that of SPR joints, but the fatigue failure mode of SPR-bonded and SPR joints differed. The SPR-bonded joints all failed in a rivet tail pull-out mode at all tested loads, which accompanied with small cracking in the aluminum sheet in contact with the rivet tail at lower test load. However, the failure mode of the SPR joints shifted from the aluminum sheet cracking to rivet tail pull-out as the fatigue test load increased. And during the aluminum sheet cracking failure, the fatigue crack originated from the faying interface of aluminum and steel sheet at the vicinity of the rivet shank and propagated along the width direction of aluminum sheet. Fretting wear analysis showed that the overall extent of fretting decreased and the location of fretting areas varied due to the adhesive bonding. Fretting of SPR joints mostly existed at the faying interface between aluminum and steel about 1.5mm away from the rivet shank and resulted in fatigue crack initiation, while the fretting region of SPR-bonded joints shifted to the faying interface between rivet tail and aluminum sheet.

A comparative study of self pierceing riveting and mechanical clinch of DP590-Al5754 high-strength steel and aluminum alloys

This paper presents a comparative study of two joining processes, self piercing riveting (SPR) and mechanical clinch, used to join DP590 high-strength steel and Al5754 aluminum alloy. A comparative study of microhardness, tensile shear properties, fatigue properties, and economics of joints from both processes was conducted. The findings indicate that the highest hardness levels are observed in the rivet leg region for SPR joints and in the neck region for mechanical clinch joints. The maximum failure load and energy absorption values of SPR joints were found to be 1.46 and 9.07 times higher, respectively, than those of mechanical clinch joints. The static tensile test results demonstrate that the strength and hardness of SPR joints in aluminum sheets subjected to cold work hardening are significantly lower than those of steel sheets. Therefore, the failure of SPR joints is primarily attributed to the deformation and fracture of the lower aluminum sheet. Mechanical clinch joints fail by neck fracture because the steel sheet neck becomes brittle by cold work hardening and the neck thickness is small. The fatigue behavior of SPR joints was observed to be superior to that of mechanical clinch joints. The findings of the scanning electron microscopy and energy spectrum analysis suggest that fretting wear between the upper and lower sheets results in fatigue fracture of the lower sheet in the joints. When joining the same material on a large scale, the selection of mechanical clinch over SPR can prove an effective method of reducing costs. Furthermore, the selection of a set of dies with an extended life can contribute to the reduction of joining costs.

Forming quality and static properties of self-piercing riveted joints of hot-rolled steel and aluminum alloy sheets

The self-piercing riveting (SPR) Forming and tensile tests of hot-rolled steel sheet BR1200HS and aluminum alloy sheet AA 6082-T6 were simulated by Simufact Forming software. The test results show that the diameter of the rivet leg opening, which is the most important parameter affecting the mechanical properties of the joints, shows a first increase and a second decrease with the increase of rivet length, and the Max. tensile loads of the joints have the same variation law. The larger the diameter of the rivet leg opening, the greater the Max. tensile load of the joint, and the greater the effective plastic strain of the rivet of the joint. The rivet length of the joints in the five preferred SPR formation schemes obtained were all 6.5 mm, and only one scheme had a rivet hardness of H4, the rest were H5. The SPR experiment is used to verify the current finite element simulation data can get the final research conclusion. The finite element simulation (FEM) would greatly reduce the test times of the SPR test, save the test consumables and save the test cost.

Evaluation of Corrosion and Its Impact on the Mechanical Performance of Al-Steel Joints.

Aluminum-steel joints are increasingly used in the automotive industry to meet the requirements for energy saving and emission reduction. Among various joining technologies, self-pierce riveting (SPR) and resistance spot welding (RSW) are two well-established technologies for fabricating dissimilar joints with stable and high mechanical performance. However, corrosion will occur in these joints inevitably due to different electrochemical properties, which can degrade the surface quality and the mechanical performance, such as strength. This paper presents a method of understanding the corrosion mechanisms in joining aluminum and steel. For this understanding, a hybrid method combining experimental observations, mechanical properties identification, and analytical approaches was used to assess the evolution of the impact of corrosion on the joining performance, such as traction separation curves. The study was conducted on common combinations used in the vehicles, e.g., a 1.2 mm thickness aluminum alloy (AA 6022) and 2.0 mm thickness hot deep galvanized steel (HDG HSLA 340) joined by SPR and RSW. After the fabrication of these joints, accelerated cyclic corrosion tests of up to 104 cycles were performed, which reproduced the environmental conditions to which a vehicle was exposed. By investigating the microstructural evolution within the joints, the corrosion mechanisms of SPR and RSW joints were revealed, including the initiation and propagation. Moreover, the intrinsic impact of the corrosion on the mechanical performance, including the strength, axial stiffness, and crashworthiness, was analyzed by performing a lap-shear test. It showed that as corrosion proceeds, the fracture modes and mechanical performance are affected significantly.

A data-driven approach for predicting the fatigue life and failure mode of self-piercing rivet joints

A data-driven approach for predicting the fatigue life and failure mode of self-piercing rivet joints

Effects of Hole Sizes and Stack Thicknesses on Mechanical Properties and Failure Behavior of Pre-holed Self-piercing Riveted Steel-Aluminum Joints

Effects of Hole Sizes and Stack Thicknesses on Mechanical Properties and Failure Behavior of Pre-holed Self-piercing Riveted Steel-Aluminum Joints

A machine learning-based calibration method for strength simulation of self-piercing riveted joints

A machine learning-based calibration method for strength simulation of self-piercing riveted joints

Static mechanical properties and failure behaviors of self-piercing riveted joints in aluminum alloy 5A06 after aging

This paper conducts an investigation on the static mechanical properties and failure behavior of self-piercing riveted joints in aluminum alloy 5A06 after being subjected to the aging process. The study involves three distinct categories of joint specimens: original specimens, 1-year aged specimens and 1-year aged specimens that have been additionally heat-treated at 200 °C. The research findings affirm that strain aging is responsible for a reduction in the peak strength of the joints. Furthermore, the weakest failure chain within the self-piercing riveted joint shifts towards the upper sheet due to a more significant reduction in internal stress experienced by the upper plate. This leads to a failure model characterized by upper sheet pull-off. Through Weibull distribution analysis, it has been established that the 5 % lower limit value for the strength of the SPR joint experiences an 86 % decline following 1-year aging. In practical terms, this means that for a vehicle structure with 7000 riveting points will lose an overall structural strength equivalent to the initial strength of 1000 riveting points within one year.

Finite element modeling and analysis of the self-piercing riveting forming process with the ball-shaped die

Self-Piercing Riveting (SPR) technique faces challenges as it expands to low ductile materials. In this paper, the ball-shaped die is suggested to prevent the formation of cracks in sheets during the SPR process. The SPR model with the ball-shaped die was developed using the finite element method, and simulations of the joint forming process and tensile test were conducted. The influence of die depth and diameter on SPR forming process and quality was analysed. The simulation results showed that as the die diameter increases, the undercut decreases, and the remaining thickness of bottom increases. The undercut and the remaining thickness of bottom decreases with the increase of the depth of the die. When employing a ball-shaped die with a 1 mm depth and 10 mm diameter, the SPR joint with tight interlock and excellent mechanical properties can be obtained. The results of the simulation and experimental tests are consistent.

Fatigue behaviour and life prediction of self-piercing riveted joints in DP590/AA5754 dissimilar sheets

This paper investigates the fatigue properties of self-piercing riveted joints made by DP590 steel and AA5754 aluminium alloy. The fatigue failure mechanism and fatigue fretting mechanism of the joint were well revealed by analysing the microstructure features of fracture surfaces of sheets and rivets as well as viewing and measuring the distribution and chemical composition of fretting debris. The fatigue life of the joint was also predicted based on the stress intensity factor of the kinked crack of the lower sheet. The results confirmed that two failure modes occurred during fatigue: lower sheet fracture and rivet fracture. During the fatigue failure, cracks appeared in both the lower sheet and the rivets, indicating a competitive relationship between the propagation of cracks in the lower sheet and the rivets. In the range of 40 % and 50 % load level, fatigue crack propagation of the lower sheet is dominant and fracture failure of the lower sheet occurs. Rivet fatigue crack propagation has a significant advantage in the 60 % load range and rivet fracture failure often occurs. It was found that the fatigue failure of the lower sheet is mainly influenced by the main crack, which produces two different morphological sections. Fretting wear of the contact surface was the source of crack initiation, and the fretting debris promoted crack initiation and propagation. Cracks propagate along the width and thickness of the plate, as well as the thickness of the rivet neck. The stress intensity factor range can properly predict the fatigue life of joints.

Evaluating the joinability of thin-walled high pressure die cast aluminium for automotive structures using self-piercing rivets

This paper is the first to report successful application of self-pierce riveting (SPR) in thin-walled high pressure die cast (HPDC) aluminium for use in automotive applications. HPDC fabricated AA356x coupons were joined to conventional rolled RC5754 material. A set of industry-relevant joint stacks were created. Priority stacks included cast material as the upper layer. More challenging joints were also fabricated with cast material as the lower layer. Automotive industry key performance indicators were used to assess joint integrity. The key results and recommendations were:•HPDC aluminium was revealed to be able to be joined to rolled aluminium according to vehicle manufacturer automotive standards.•Process boundaries were established for satisfactory SPR joints across a range of material thicknesses and stack types.•SPR joint solutions were proven in the most challenging stacks with cast material as a bottom layer.•Greater variability in the joint key performance indicators was observed in stacks where the cast alloy is the top layer.•Microstructural analysis of both AA356x and RC5754 revealed differences in grain structure and hardness and it is proposed that this accounts for the increased variability.•Strength testing of lap shear joints demonstrated the mechanical effectiveness of an SPR joint including cast material. Under normal vehicle operating conditions, the performance of joints including cast material was equivalent to that of rolled material only joints. Following yielding, joints including cast material suffered a more brittle failure mode leading to differences in performance under crash scenarios.

Material-structure-process-performance integrated optimization method of steel/aluminum self-piercing riveted joint

Material-structure-process-performance integrated optimization method of steel/aluminum self-piercing riveted joint

Mechanical properties of ultrasonic welded and self-piercing riveted joints in a 5A06 aluminum alloy and a TA1 titanium alloy

Abstract The self-piercing riveting (SPR) experiences problems of poor forming qualities and mechanical properties during joining aviation alloy sheet materials. To address this issue, a novel combined process nominated ultrasonic self-piercing riveting (USPR) is carried out to join a 5A06 aluminium alloy and a TA1 titanium alloy sheets. The forming qualities, mechanical properties, failure modes, and mechanisms of USPR and SPR joints are comprehensively investigated. The results showed that the mechanical properties of the USPR joints were enhanced due to the welding formation of a solid phase between the specimen sheets and the degree of solid phase. The investigation showed that the welding was mainly affected by the material of the upper sheet. However, the welding also increased the brittleness of the rivet to some extent. The failure modes of the joints are affected by the welding process. The results determined that APL, AFD, and AEA of USAA joints were improved by 25.6 %, 31.3 %, and 88.8 %, respectively. The performance of the USPR joints with 5A06 aluminum alloy as the upper sheet is improved more than 88.8 % after the welding process. The combined method can be advantageous and supportive for automotive and spacecraft applications.

Corrosion behaviour of self-piercing riveted joints with uncoated rivets in high nitrogen steel

AbstractSelf-piercing riveting is an established joining technique for lightweight materials. To increase the sustainability of the rivet manufacturing process, the authors of the present paper have developed an approach for shortening the process chain by omitting the heat treatment and rivet coating. To do this, use is made of high nitrogen steel as the rivet material. Successful joining with these rivets has already been proven, and it has also been shown that a competitive joint strength can be achieved with these rivets. Up until now, no studies have been conducted of the corrosion behaviour of uncoated rivets in high nitrogen steel compared to conventional rivets made of heat-treatable steel with a coating of Almac® or zinc-nickel with topcoat, and the corrosion behaviour of joints manufactured with these rivets has also not been investigated. Furthermore, the suitability of rivets in high nitrogen steel for structures undergoing cathodic dip painting has not been evaluated to date. These are therefore the aims of the research work presented in this paper. Corrosion behaviour is tested by exposing rivets and joints to a salt spray atmosphere. Cross-cut tests are conducted in order to classify the adhesion of cathodic dip paint to the different rivet surfaces and materials. The results of the experimental test show that the cathodic dip paint has sufficient adhesion to the uncoated rivets in high nitrogen steel and that these rivets can therefore be used in the manufacture of car bodies. Due to the stainless properties of the high nitrogen steel, better corrosion resistance is seen by comparison to the commonly used coatings of Almac® and zinc-nickel with topcoat. A study of the corrosion behaviour of the joints shows that the rivet head diameter and rivet head position, in particular, are decisive for preventing crevice corrosion under the rivet head and contact corrosion within the joint.

Corrosion behavior of riveted joints with electrophoretic treatment in neutral salt spray environment

AbstractThis study delves into the corrosion behavior of riveted joints with electrophoretic treatment in a neutral salt spray environment using tensile test and surface analysis. The results showed that the open‐circuit potentials of the dual‐phase steels (590DP and 780DP) exceeded those of the AlSi10MnMg‐T7 and JDA1b die‐casting aluminum alloys by 100 mV, and exceeded that of the AA6063‐T6 extruded aluminum alloy by 50 mV. AlSi10MnMg‐T7 and JDA1b die‐casting aluminum alloys were more susceptible to corrosion in contrast to the AA6063‐T6 extruded aluminum alloy. The corrosion mechanism of the steel/aluminum riveted joints was not only galvanic corrosion but also oxygen concentration polarization. Over the 720‐h corrosion period, the failure loads of the riveted joints were not reduced at all. On the contrary, they increased at least 17% for the two‐sheet self‐piercing riveting (SPR) joints, 6% for the three‐sheet SPR joints, and 4% for the flow drill screw joints.

Comparative Analysis of SPR and SPR-Bonded Joints of Hot Press Forming Steel and AA5052 under Corrosive Conditions

The increasing demand for effective joining techniques in dissimilar materials has led to the widespread use of self-piercing rivet (SPR) mechanical joints, particularly in aluminum combinations. Studies in this field aim to enhance joint strength by optimizing process conditions, including the use of SPR-bonded processes with structural adhesives. Structural adhesives in SPR-bonded processes introduce different corrosion behavior owing to galvanic corrosion caused by potential differences between sheets over time. In this study, we utilize SORPAS® simulation to optimize SPR conditions and analyze stress and deformation. A tensile shear test was performed on a hot pressforming steel/AA5052-H32 combination for SPR and SPR-bonded processes. The experimental results indicated die sticking during SPR optimization, increased tensile strength through AA5052-H32 surface cleaning in the SPR-bonded process, varying corrosion conditions, and consistent SPR-bonded strength after salt spray exposure. The difference in failure modes between the processes concerning corrosion time can be attributed to the corrosion- mitigating effect of structural adhesive within the galvanic coupling region formed by potential differences. Additionally, adhesive and rivet failure modes were observed. Moreover, adhesive failure occurred in the SPR-bonded process after shear tensile tests, characterized by a fracture between the lower AA5052-H32 interface and adhesive. Furthermore, we found a linear relationship between the remaining adhesive area and shear tensile strength.

Double-layer sheets SPR-bonded hybrid joining method of an extendable die

To further improve the strength and quality of the Sheet connection and increase the traditional self-piercing riveted (SPR) interlocking, a self-piercing riveted-bonded (SPR-bonded) hybrid joining method for double-layer sheets based on an extendable die was proposed. Three kinds of heterogeneous sheets expandable die SPR-bonded hybrid forming rules were investigated. The mechanical properties and failure mechanisms of SPR, adhesive, and hybrid joints were compared. Results show that compared with the traditional SPR die, the expandable die can increase the joint interlocking value to a certain extent and thus improve the strength of the connection by delaying the deformation of the lower plate and guiding the rivets to flare twice. The forming load is low when magnesium alloy is used as the upper sheet. Joint stress concentration, strain concentration, and thinning of the lower sheet are light. From the point of view of the shear strength of each joint, the hybrid joints of the three types of sheet materials increased the shear strength of the joints by 11 %, 36 %, and 30 %, respectively, compared with their respective SPR joints. The existence of the adhesive layer in the hybrid joint can improve the overall strength of the hybrid joint on the one hand and delay the destruction of the interlocking structure in the hybrid joint on the other hand. In general, the combination of an extendable die and SPR-bonded hybrid could improve the overall strength and safety of the joint and can be used for joining heterogeneous sheets.

A Deep Convolutional Neural Network-Based Method for Self-Piercing Rivet Joint Defect Detection

Abstract The self-pierce riveting process for alloy materials has a wide range of applications in the automotive manufacturing industry. This will not only affect the operation performance but also cause accidents in severe cases when there are defects in the riveted parts. A deep learning detection model is proposed that integrates atrous convolution and dynamic convolution to identify defects of self-piercing riveting parts efficiently to overcome the problem in quality inspection after the body self-piercing riveting process. First, a backbone network for extracting riveting defect features is constructed based on the ResNet network. Second, the center area of each riveting defect is located preferentially by the center point detection algorithm. Finally, the bounding box of riveting defects is regressed to achieve defect detection based on this central region. Among them, atrous convolution is used in the external network to increase the receptive field of the model, which combined with an active convolution so that a dynamic atrous convolution module is designed. This module is used to enhance the correlation between feature points of individual pixel in the image, which helps to identify defects with incomplete image edges and suppress background interference. Ablation experiments show that the proposed method achieves the highest accuracy of 96.3%, which is 3.9% higher than the original method. It is found that the proposed method is less affected by the background interference from the qualitative comparison. Moreover, it can also effectively identify the riveting defects on the surface of each area.

An improved simplified model of self-piercing riveted joints for predicting quasi-static mechanical behavior of steel–aluminum hybrid components

The problem that the existing models could not accurately predict sheet deformation modes in the riveting area led to low prediction accuracy in crash simulations for steel-aluminum hybrid structural components in vehicle bodies. An improved simplified model with rigid and washer-processed elements (CONSTRAINED_SPR4_RIGWE) is proposed to calibrate the mechanical behavior of self-piercing riveted (SPR) joints based on the *CONSTRAINED_SPR4 model. The diameters of rigid and washer-processed elements in the upper and lower sheets were based on the diameters of the rivet and bottom of the SPR joint, respectively; the influence domain in the joint was determined by the diameter of the rivet cap. The parameters of the two models were calibrated using the experimental results of the lap shear, pull-out, mixed tension–shear, and peeling tests, as well as the parameters from the detailed three-dimensional model. Compared with the *CONSTRAINED_SPR4 model, the CONSTRAINED_SPR4_RIGWE model had a higher stiffness value for pull-out and peeling specimens, which was closer to the experimental result. T-shaped and C-shaped structural components of DP590 high-strength steel and AC43500-T7 cast aluminum sheets were prepared using SPR joints. For the T-R4 component, the absolute prediction error of the CONSTRAINED_SPR4_RIGWE model in terms of the energy absorption was lower than that of the *CONSTRAINED_SPR4 model, with the former being 2.48 % and the latter being 16.53 %. For the C-R8 component, the absolute maximum prediction errors of the CONSTRAINED_SPR4_RIGWE model in terms of peak force, failure displacement, and energy absorption increased from 16.82 % to 149.42 %, as compared with those of the *CONSTRAINED_SPR4 model.