Self-piercing Riveting Joining Research Articles

Self-Piercing rivet joining of multi-material including CFRP: Experiments and FE modeling

In this study, finite element (FE) analyses based on the arbitrary Lagrangian–Eulerian technique were used to investigate the complex deformation behavior and numerous process variables that arise during the self-piercing riveting (SPR) joining of multi-materials, including carbon-fiber-reinforced polymer, GA590DP, and Al5052-H32 sheets in two- and three-layer combinations. Tensile tests and inverse analysis were conducted to determine the mechanical responses of each joining material, including the rivet, and equivalent strain-based fracture modeling approaches were adopted for a simple but effective crack initiation prediction during the mechanical joining process. The damage distribution and joining characteristics during the SPR joining were then numerically investigated by considering different die profiles. The high predictability of the proposed FE modeling approach in terms of the cross-sectional profile with joint quality indicators, such as the interlock, residual distance between the rivet leg and die, minimum thickness of the bottom sheet, load history, and peak load during mechanical joining, was validated through comparisons between the experiments and FE simulations.

Assessment of Self-Piercing Riveted Joints Using the Analytic Hierarchy Process

Self-piercing riveting (SPR) as a solid-state joining technology has recently found extensive applications in the automotive industry, mostly in the joining of car body aluminium sheets. To achieve an acceptable joint, key operation and tooling parameters, including set force, die profile, and rivet shape and hardness, should be selected appropriately. To evaluate joint performance, the interlocking parameters and joint strength have to be determined. In the current laboratory and industrial practices, joint quality is assessed according to requirements of individual applications, lacking a systematic assessment method. The goal of the present study is to develop a method to determine the SPR conditions that produce a joint of the best quality, based on an analytic hierarchy process (AHP), which is a methodology for relative measurement. A general AHP model was proposed for analysing SPR and joint performance in different conditions and with an unlimited number of criteria and alternatives. Joints of two layers of 2.5 mm thick AA6082 aluminium sheets in T6 condition were produced using various dies, rivets, and SPR processing conditions. A selection of seven joints, which achieved minimum requirements in terms of interlocking parameters and strength, was nominated for AHP assessment. With the application of six criteria, including head height, bottom thickness, minimum bottom thickness, deformed rivet diameter, shear strength, and peel strength, the AHP assessment was able to define the best conditions for the SPR joining of the aluminium alloy sheets.

Residual stress distribution in self-piercing rivet joint of high strength steel

Abstract Manufacturing industries throughout the world are constantly facing the pressure to reduce carbon emissions. The automobile industries strategy for reducing carbon emissions are targeted at reducing the overall weight of the car body. Efforts to accomplish this haven been based on clever materials selection that suggests using materials like aluminium and magnesium with high strength to weight ratio in place of the traditional steel. However, these lightweight alloys are difficult or sometimes impossible to join by the traditional joining methods such as welding. As a result, self-piercing riveting (SPR) is increasingly used for joining required for assembly of components in automobile industries. In SPR, a mechanical interlock is created by the rivet. However, the rivet material should have enough hardness to pierce the top sheet and have enough ductility to deform plastically in the bottom sheet. Due to the rapid introduction of lightweight high strength alloys, joining ability of a rivet becomes more limited. It is necessary to understand the residual stress in SPR joints. Residual stress was measured in rivets of two different SPR joints using neutron diffraction technique. It was observed that the stresses that developed inside the SPR joints was compressive and the magnitude of the residual stress was low in the softer material in comparison with the harder material. It was also evident that the neutron diffraction can detect a crack in the rivet tip which was not evident from a cross-section. The results are discussed based on the physical movements of materials in SPR joining process.

Investigation of self-pierce riveting (SPR) process data and specific joining events

This paper describes a methodical study of the self-piercing riveting (SPR) process. The force-displacement curve is typically used in most investigations of SPR, but in this study, additional SPR process data are examined in details. Specifically, the characteristic pressure-displacement, displacement-time, force-pressure as well as force-displacement curves are analysed and correlated with cross-sections of interrupted joints obtained at different positions to determine the key different physical events that occur during SPR joining. The study shows that it is possible to identify the exact point when the rivet starts piercing the top sheet, finishes piercing the top sheet and starts flaring in the bottom sheet. It was found that all of the characteristic curves can be segmented into three distinctive stages (bending, piercing and flaring). However, the die filling event which is embedded within the piercing stage can be identified only by examining the pressure-displacement and force-displacement curves. This study also shows that it is possible to identify when the bottom sheet touches the die bottom surface.

Finite Element Analysis of Self-Pierce Riveting in Magnesium Alloys Sheets

Conventional fusion joining methods, such as resistance spot welding (RSW), have been demonstrated to be ineffective for magnesium alloys. However, self-pierce riveting (SPR) has recently been shown as an attractive joining technique for lightweight metals, including magnesium alloys. While the SPR joining process has been experimentally established on magnesium alloys through trial and error, this joining process is not fully developed. As such, in this work, we explore simulation techniques for modeling the SPR process that could be used to optimize this joining method for magnesium alloys. Due to the process conditions needed to rivet the magnesium sheets, high strain rates and adiabatic heat generation are developed that require a robust material model. Thus, we employ an internal state variable (ISV) plasticity material model that captures strain-rate and temperature dependent deformation. In addition, we explore various damage modeling techniques needed to capture the piercing process observed in the joining of magnesium alloys. The simulations were performed using a two-dimensional axisymmetric model with various element deletion criterions resulting in good agreement with experimental data. The simulations results of this study show that the ISV material model is ideally suited for capturing the complex physics of the plasticity and damage observed in the SPR of magnesium alloys.

SPR 접합법을 이용한 Al-5052 인장-전단 시험편의 피로강도

Self-piercing riveting(SPR) is a mechanical fastening technique which is put pressure on the rivet for joining the sheets. Unlike a spot welding, SPR joining does not make the harmful gas and <TEX>$CO_2$</TEX> and needs less energy consumption. In this study, static and fatigue tests were conducted using tensile-shear specimens with Al-5052 plates for evaluation of fatigue strength of the SPR joints. During SPR joining process for the specimen, using the current sheet thickness and a rivet, the optimal applied punching force was found to be 21 kN. And, the maximum static strength of the specimen produced at the optimal punching force was 3430 N. During the fatigue tests for the specimens, interface failure mode occurred on the top substrate close to the rivet head in the most high-loading range region, but on the bottom substrate close to the rivet tail in the low -loading range region. There was a relationship between applied load amplitude <TEX>$P_{amp}$</TEX> and lifetime of cycle N for the tensile-shear, <TEX>$P_{amp}=3395.5{\times}N^{-0.078}$</TEX>. Using the stress-strain curve of the Al-5052 from tensile test, the simulations for fatigue specimens have been carried out using the implicit finite element code ABAQUS. The relation between von-Mises equivalent stress amplitude and number of cycles was found to be <TEX>${\sigma}_{eq}=514.7{\times}N^{-0.033}$</TEX>.

その場加熱SPRプロセスで締結したAM50マグネシウム合金板材の接合強度

Self pierce riveting (SPR) as mechanical joining is widely used for aluminum alloy, high strength steel or dissimilar materials such as polymer and metal in vehicle structures. The purpose of this study is to evaluate the tensile-shear strength of AM50 magnesium sheets jointed by a newly developed in-situ heating SPR joining system. It is difficult to joint magnesium sheets by riveting due to less ductility from a limitation of slip at room temperature, although there are few studies. In-situ heating SPR joining process has been developed to improve reliability of the joining sheet of magnesium, and to prevent occurrence of cracks which are initiated at beginning of riveting process. AM50 magnesium alloy sheet has 0.8 mm in thickness, and commercial aluminum rivet with 3.3 mm in diameter of the leg and 4 mm in height was used in this process. Cracks occurred in a lower sheet in both as-rolled and annealed AM50 sheet when conventional SPR joining process was applied at room temperature. No cracks are observed during in-situ heating SPR joining process at 250°C. The tensile-shear test was carried out at room temperature in order to estimate an effect of in-situ heating on reliability of the joint. The tensile-shear strength of AM50 joint heated at 250°C is higher than that of the joint from 5052 aluminum alloy with the conventional equipment.

Mechanical Behaviors of Self-Piercing Riveting Joining Dissimilar Sheets

This paper summarizes riveting tests and mechanical behaviors of Self-piercing Riveting (SPR) with semi-tubular rivet joining dissimilar metal sheets. The tests joining 2A12 aluminum sheet and DC01 steel sheet are carried out in lap-shear, coach-peel and cross-tension joint styles. The results show that SPR joining dissimilar materials of steel and aluminum alloy is feasible and riveting joints take on high mechanical behavior.