Riveted Lap Joints Research Articles

Physics-based digital twin updating and twin-based explainable crack identification of mechanical lap joint

The mechanical joints, including the lap joint, weld, bolt, and pin, are vulnerable to fatigue failure because of stress concentration and internal flaws. Digital twin (DTw) strategies were proposed to prevent catastrophic system failure by fatigue damage in mechanical joints. In previous studies, the data-driven approach, such as deep learning and machine learning were utilized to estimate severity of the damage. However, it needs to improve its prediction accuracy because of insufficient data and physical interpretability. In this study, the physics-based digital twin model updating and twin-based crack identification of fatigue damage in riveted lap joints were proposed using lamb waves with consideration of uncertain crack growth path. The proposed approach is based on three techniques; (i) Data pre-processing, including filtering and optimization-based signal synchronization, (ii) Lamb-wave propagation analysis with sensor dynamics model and uncertain crack path, and (iii) Optimization based physics-based model updating and inference. In data pre-processing, the excitation frequency magnitude and truncation time are estimated using the observed actuator signal in the Lamb-wave test. The sensor dynamic model and model parameters are updated using the Bayesian optimization method to minimize both the errors in the predicted (y^t) and observed (yt) wave signal and the errors in the inferred (l*) and observed (l) crack length. The crack growth path is sampled based on angular and spline schemes to consider uncertain crack propagation paths. The validity of the proposed method is demonstrated using an open data set (2019 PHM society data challenge). The results conclude that the proposed digital twin approach can improve estimation accuracy considering both the crack growth path and sensor dynamics model.

نمذجة ومحاكاة لوحين متصلين عبر مفصل حضني مفرد البرشمة

Rivets and riveted lap joints are important mechanical fasteners that are used in a large variety of applications, and their performance depends on many parameters. The goal of this study is to model and simulate two plates joined together by a riveted lap joint. Four configurations were used, which are 2-vertical, 2-horizontal, 4-inline and 4-staggered configurations, and diameters of 0.2 cm to 0.4 cm were also used. The plate was subjected to forces ranging between 2000 N to 8000 N. Results have shown that the 4-inline configuration was the best due to its lower stresses than the other configurations, followed by the 2-vertical configuration. The 2-horizontal and 4-staggered configurations had the worst performance and had similar performance. Stresses produced by the forces had a linear relationship with the magnitude of force. Finally, the results showed that the best rivet design was the 4-inline configuration with a diameter of 0.4 cm, since increasing the diameter beyond that had a much lower benefit.

Effect of ultrasonic amplitude and riveting speed on mechanical properties of Ti-45Nb riveted lap joints

Ultrasonic vibration-assisted machining has been introduced as a new process in riveting aircraft components. In this paper, the effects of different ultrasonic amplitudes and riveting speeds on the quality, shear properties, and cross-tension properties of riveted joints are investigated. The failure sample fracture was characterized using a scanning electron microscope and the cause of the fracture was discussed. The results show that the ultrasonic amplitude is negatively correlated with the height of the riveted joint and positively correlated with the diameter of the riveted joint. The maximum shear failure load was obtained at a riveting speed of 5 mm/s with an ultrasonic amplitude of 35.3 μm, and the maximum cross tensile failure load was obtained at an ultrasonic amplitude of 23.3 μm. All shear fractures occurred in the rivet shanks and all cross fractures occurred in the rivet manufactured head, and the failure modes of both shear and cross-tension fracture were mixed brittle and plastic fracture modes.

Artificial neural network based fatigue life assessment of riveted joints in AA2024 aluminum alloy plates and optimization of riveted joints parameters

The objective of this paper is to provide the fatigue life of riveted joints in AA2024 aluminum alloy plates and optimization of riveted joints parameters. At first, the fatigue life of the riveted joints in AA2024 aluminum alloy plates is obtained by experimental tests. Then, an artificial neural network is applied to estimate the fatigue life of riveted lap joints based on the number of lateral and longitudinal holes, punch pressure, gap between the edge of hole and rivet, rivet shank diameter, and rivet shank length. Also, meta heuristic optimization algorithm is applied to calculate the riveting process parameters. Finally, sensitivity analysis is used to obtain the influence of parameters affecting the riveting process on the fatigue life.

Influence of Impact Speed on the Quality of Riveted Lap Joints of Composite/Metal Stacks

Riveting is the most important method for joining two sheets of different materials. In order to promote electromagnetic pulse riveting (EMR), the influence of the impact velocity will be studied in this paper in order to correctly model the electromagnetic field of the riveting process. There are many parameters associated to the riveting process, however, the interference fit is considered as the most important criterion to measure the riveting quality, which consequently will be associated to the impact velocity, being this the most important parameter. The use of the washer will be studied to guarantee the optimal flow of the material and to restrict the expansion of the rivet shaft, thus minimizing damage to the composite material. The interference generated between the rivet shaft and the hole of the sheets and the flow of the material will be developed by finite elements which will later be validated by means of experimental tests analyzing its final microstructure. Finally, the relationship between the impact velocity on the rivet head will be directly related to the distribution of the interference generated in the deformation, verifying that the impact velocity.

Numerical Analysis of Double Riveted Lap Joints

In a previous work, the fatigue behaviour of different hot riveted joints under fatigue loadings were experimentally calculated. In particular, the experimental data showed a Wöhler curve slope close to five against the slope of three proposed by Eurocode 3. However, two series of shear splice riveted joints showed, at two million cycles, a stress range very close to the value suggested by Eurocode for shear splices that use non-preloaded high-strength bolts. In order to clarify the fatigue behaviour of riveted joints at high- and medium-fatigue regimes, this paper presents a preliminary three-dimensional non-linear FE analysis of a double-riveted lap joint previously analysed experimentally. Different friction coefficients and rivet clamping stress have been taken Into account, as well as the elastoplastic behaviours of the main plate subjected to tensile loadings. The numerical analysis shows that the friction force tends to reduce the range of stresses at the net section during fatigue loadings, and the force distribution or the stress concentration on the rivets is always critical for the external rivet, which is also the case regarding the non-linear behaviour of the material.

Double-flush riveting by punching and compression

This paper presents a new double-flush riveting process to fabricate flat lap joints that can be easily integrated in progressive or transfer multistage tool systems. The process is based on a punching-compression sequence and the design methodology combines experimentation and finite element modeling followed by destructive peel testing. Special emphasis is placed on the identification and selection of punch-to-die clearances to produce tapered cut surfaces that are appropriate for subsequent compression of the solid rivets into double-flush riveted lap joints. Results confirm that rivet materials with lower mechanical resistance than the sheet materials allow fabricating double-flush riveted lap joints with flat surfaces on both sides in which the mechanical interlocking in the undercut area is obtained by plastic deformation of the rivets instead of the sheets. The utilization of aluminum sheets and copper rivets allows extending the process scope of application from structural to energy distribution parts in which the electrical resistance of joints is a critical design parameter.

Experimental investigation and quantitative prediction in interference-fit size of CFRP riveted joints under a transversal ultrasonic vibration-assisted riveting

In this study, a transversal ultrasonic vibration-assisted riveting (TUVAR) process was developed to improve the uniformity of CFRP riveted lap joint interference-fit size, which provided a possibility for the quantization of riveted joint interference-fit sizes. The relationship between the process parameters of vibration amplitude, vibration duration, and roughness with interference-fit sizes by algorithms, through the minimum coefficient variance of interference-fit size (ICV-min) to confirm the riveting process parameters of the quantized average interference-fit sizes (IA). The experimental verification results showed that the mean absolute percentage error of measured IA and predicted IA is less than 10%. Furthermore, the tensile tests were carried out to investigate the effect of interference-fit size {1.4%, 1.6%, 1.8%, and 2.0%} on mechanical performances of CFRP riveted lap joints by TUVAR, and the tensile strength presents first-up then down with the interference-fit size increase, the maximum ultimate tensile strength is the riveted lap joint with the interference-fit size of 2.0%. Hence, the quantitative optimization method can well predict the riveting process parameters corresponding to the most uniform interference-fit size.

Fretting Fatigue of Riveted Lap Joints in Aircraft Fuselage

Failure of riveted lap joints originating from fretting fatigue has been responsible for a number of structural failures of aircraft in midflight. Using a combination of extended finite element method analysis and experimental data, this paper investigates the formation and propagation of cracks initiated by fretting, and how it is influenced by rivet squeeze force and by the applied fatigue stresses. It is found that fretting and plain fatigue crack growth life increase with the increase of rivet squeeze force. However, the rise of applied fatigue stress reduces fretting and plain fatigue crack growth life. Moreover, enhancing rivet squeeze force or applied fatigue stress decreases the ratio of fretting to total fatigue crack growth life.

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.

The Effect of Rivet Arrangement on the Strengths of Lap Joints and Lap Joint Design Methods

To address the impact of rivet arrangement on the strengths of riveted lap joints, the failure modes and failure mechanisms of riveted lap joints were first studied using finite element analysis software. Next, the effects of the number of rivets, rivet rows, rivet arrangement, and row spacing on the lap joint strength were studied using the peak load as the evaluation index. Then, we proposed the concept of line load density to solve the problem that a varying rivet spacing and rivet edge distance will change the width of the sheet and thus the maximum load capacity, which is used as an index to study the effect of rivet spacing and rivet edge distance on the lap strength. Finally, a spring–mass model was developed to study the forces present in multi-row riveting. The model could accurately calculate the force–displacement curves during tensioning. The results show that when multiple rivet rows are used, higher stress concentrations cause the plate to first fracture at an outer rivet row with more rivets; therefore, the rivets should be arranged such that there are more rivets in the middle and fewer rivets on both sides. When the total rivet strength is greater than the remaining strength of the plate, the numbers of rivets and rivet rows have limited effects on the lap joint strength; however, this primarily affects the damaged form of the lap joint member. When the rivet spacing is less than 5d, the lap strength increases with increases in the rivet spacing, and when the rivet spacing is greater than 5d, the lap strength does not change significantly with increases in the rivet spacing. When the rivet edge distance is less than 3d, the lap joint strength increases with increases in the rivet edge distance, and when the rivet edge distance is greater than 3d, it has a limited effect on the lap joint strength. The rivet row spacing has no significant effect on the lap joint strength. The results of this study are valuable for improving the strengths of riveted structures in aircraft.

Investigation of microstructure of fretting wear behavior in 6061-T6 aluminum alloy

PurposeThe purpose of this study is to investigate the microstructure of fretting wear behavior in 6061-T6 aluminum alloy. The fretting wear of blind riveted lap joints of 6061-T6 aluminum alloy plates, which are widely used in aircraft construction, was investigated. Fretting damages were investigated between the contact surface of the plates and between the plate and the rivet contact surface.Design/methodology/approachExperiments were carried out using a computer controlled Instron testing machine with 200 kN static and 100 kN dynamic load capacity. Max package computer program was used for the control of the experiments. Fretting scars, width of wear scars, microstructure was investigated by metallographic techniques and scanning electron microscopy.FindingsIt was found that fretting damages were occurred between the plates contacting surface and between the plate and rivet contact surface. As load and cycles increased, fretting scars increased. Fretting wear initially begins with metal-to-metal contact. Then, the formed metallic wear particles are hardened by oxidation. These hard particles spread between surfaces, causing three-body fretting wear. Fretting wear surface width increases with increasing load and number of cycles.Originality/valueThe useful life of many tribological joints is limited by wear or deterioration of the fretting components due to fretting by oscillating relative displacements of the friction surfaces. Such displacements are caused by vibrations, reciprocating motion, periodic bending or twisting of the mating component, etc. Fretting also tangibly reduces the surface layer quality and produces increased surface roughness, micropits, subsurface microphone.

A Non-Uniform Interference-Fit Size Investigation of CFRP/Al Alloys by Riveting Mold Design

The interference-fit size has a significant effect on the riveted lap joints of CFRP/Al alloy laminates. The requirements for the interference-fit size are different because of the strengthening of heterogeneous materials. However, in the riveting process of CFRP/Al alloys, the heterogeneous laminates lead to poor structural strength because of the different interference-fit size requirements. Therefore, differently assembled riveting molds are designed to acquire a novel interference-fit size, and the tensile test is adopted to evaluate their tensile properties. In addition, the fracture failure of CFRP/Al alloy laminate riveted lap joints is observed with an ultra-depth-of-field microscope. Finally, the best assembly type is identified as the trapezoid riveting mold combined with an arc riveting die, and the sidewall intersection angle of the trapezoid riveting mold is 66°, which could achieve a suitable interference-fit size and a better mechanical performance.

Automatic Detection and Imaging of Rivet Hole Defects for Aircraft Structures With Optimized Sensor Array Using Eddy Current Method and Image Analysis

Fatigue cracking in riveted lap joints on aircraft could cause severe safety consequences in flight. The prior inspection for the integrity of the second layer of aircraft structure with rivet removed is necessary due to the priority of safety. Methods such as radiographic and ultrasonic testing are widely applied but require relatively expensive equipment, mechanical scanning or professional operators. Eddy current method can be adopted for non-destructive testing (NDT) inspection, which is safe and low-cost. In this paper, a hand-held eddy current (EC) sensor array was optimised based on sensitivity map analysis. The EC sensor array was used with a multi-channel EM instrument, which was capable of inspecting defects around the fastener locations covered by the head of rivets. A simulated sample of riveted joint with defects was examined with the eddy current sensing system and the collected data was processed by Hough Circle Transformation (HCT) and texture analysis. The analysis results could detect and locate fatigue cracks on the sample. The presented eddy current sensing system in this paper achieved an automatic, real-time, portable, convenient and accurate inspection method for defects in riveted joints.

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

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

Effect of aircraft rivet installation process and production variables on residual stress, clamping force and fatigue behaviour of thin sheet riveted lap joints

This paper presents research on the effect of riveting process parameters on residual stresses, clamping stresses and clamping force in thin sheet riveted joints, as well as the fractographic observations of riveted lap joints. The following variables were considered in the study: riveting force, sheet thickness, sheet material and rivet material, rivet hole tolerance and rivet diameter tolerance. The research was carried out for 2024-T3 aluminium alloy sheets with a thickness of 1.6 mm and 1 mm and universal head MS20470-AD (2117-T4 aluminium alloy) rivets with shank diameters of 3.96 mm and 3.18 mm. The results obtained from finite element (FE) analyses were linked with observations of the fatigue crack initiation site, crack path and fretting phenomenon in real three-row riveted lap joints. The results show that the crack initiation site depends on the zone of compressive residual hoop stress in the sheets and the clamping force. The location of the crack path can be related to the location of the largest favourable residual normal stress in the sheets (acting in the direction of the joint loading), the value of the clamping force and the range of the residual clamping stress zone. Large fretting wear regions on the contact surface of sheets for joints with more severely squeezed rivets are associated with a larger zone and a higher value of clamping stresses, which during fatigue loading through friction intensify the harmful phenomenon of fretting.

Effect of riveting parameters on the forming quality of riveted lap joints with reduced countersunk head half-crown rivet

Effect of riveting parameters on the forming quality of riveted lap joints with reduced countersunk head half-crown rivet

Numerical Analysis of Single Riveted lap joint Panels Under Tension load

Numerical Analysis of Single Riveted lap joint Panels Under Tension load

Residual fatigue lives assessment of riveted lap joints based on a crack growth model

Many riveted joints bear the action of out-of-plane bending moments in steel truss bridges. The fatigue resistance of these joints isn’t stipulated in the current design criteria. Ensuring the safety of structures necessitates analysing the fatigue process of such riveted joints. This paper attempts to evaluate the fatigue life of riveted lap joints from the perspective of engineering applications. The study first found through fatigue tests with two types of fatigue details in riveted lap joints: plate surface cracking and rivet hole edge cracking. Then, the fatigue progression is divided into three stages: the microstructure short crack (MSC) stage, the physical short crack (PSC) stage and the long crack stage. The crack propagation model in the short crack stage is established by combining a scanning electron microscope test of the material and an empirical formula. The crack propagation model of the long crack stage is established by the crack propagation test and considering the crack closure effect. Results show that the fatigue life corresponding to the hole edge crack fatigue detail category is shorter than that to the plate surface crack. In each crack propagation stage, the crack propagation life decreases with increasing load and decreasing load ratio RL. For the two fatigue detail categories, the proportion of the long crack stage to the whole fatigue life is small, and the effect of the crack closure on the overall fatigue life is limited; therefore the effect of the load ratio RL on the fatigue life can be ignored.

Tensile Load Distribution Improvement of Three-Row Riveted Lap Joint Based on Different Squeezing Displacement Combinations

Many previous studies have mainly focused on the effects of riveting parameters on single-row riveted lap joints. Little attention has been paid to multi-row riveted lap joints. The outer rows of a normal multi-row riveted lap joint usually bear a larger part of the tensile load. However, none of the studies relate the phenomenon to the squeezing displacement combination of a multi-row riveted lap joint. To improve the performance of a three-row riveted lap joint, this paper aims to reveal the internal relation between tensile load distribution, structural deformation and squeezing displacement combination. Theoretical discussion, numerical simulation and an experimental test have been conducted. Four different squeezing displacement combinations have been studied. The result indicates that an appropriate squeezing displacement combination can effectively make tensile load distribution more homogeneous. Each rivet can take approximately 33% tensile load. Structural deformation magnitude can be reduced as well. Compared with the worst situation, at the region most sensitive to tensile load, the max strain value can reduce about 53.22–79.76%. A suitable squeeze displacement combination is a simple approach for the performance enhancement of a three-row riveted lap joint. It can be practically applied in aircraft manufacturing without any additional equipment or skill learning.