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.

Experimental Investigation of Single Lap Joint on Composite Materials

To improve the efficiency and performance can be achieved by decreasing the aircraft weight through considerable usage of composite material in primary aircraft structures. In fuselage construction it consist of various structural members such as skin, stringers, frames, bulkheads etc., all fastened together by rivets and bolts. The failure of riveted joint take place when tearing of the plate, shearing of rivets and plate under the action of over load. This project deals with the tensile strength analysis of riveted lap joints of three different composite materials such as Glass fiber, Basalt fiber and Carbon fiber are reinforced with epoxy resins. By using universal testing machine the tensile strength of the riveted single lap joint of three different composite materials are tested experimentally.

Study on shear properties of riveted lap joints of aircraft fuselage with different hole diameters

Riveting is the most important way to connect metal sheets, which is widely used in the connection of aircraft components. In this paper, the effect of different hole diameters on the shear properties of riveted lap joints were studied from the perspective of practical application. Considering the symmetry and the calculation time of the model, a 2D axisymmetric finite element method is established with the help of ABAQUS commercial finite element software, the validity of the finite element model is verified by experiment tests. Because the interference distribution has an important influence on the mechanical properties of riveted lap joints, the interference distribution and material flow characteristics in riveting process are analyzed in detail by using finite element method, and the shear characteristics of riveted lap joints in tensile process are explained. The variation of hole diameter with shear force under different squeeze force was obtained by shear test in order to explain the effect of hole diameter on the shear mechanical properties of riveted lap joint. In addition, the fracture mode and microstructure of the rivet shank were characterized by SEM and the formation process of brittleness and plastic fracture is discussed. Finally, the shear failure mechanism of riveted lap joint is analyzed in detail to provide guidance for engineering application. The test results show that all the specimens are both brittle and plastic mixed fracture modes of rivet shank, and the shear strength of the rivet increases with the increase of the hole diameter. Compared with increasing the squeeze force, increasing the hole diameter can effectively improve the shear strength of the riveted lap joint.

A Test Rig for the Experimental Investigation on the Nonlinear Dynamics in the Presence of Large Contact Interfaces and Numerical Models Validation

The simulation of the coupling between components modeled by finite elements (FEs) plays an important role for the prediction of the forced response of the assembly in terms of resonant frequencies, vibration amplitudes, and damping. This is particularly critical when the time-varying stress distribution must be limited for vibrating components with thin thickness coupled with large contacts. Typical examples can be found in aeronautical structures (plates, panels, and bladed disk components) assembled with bolted flanges, riveted lap joints, or joints without hole discontinuities like rail-hook joints, lace wire sealings, and strip dampers. In this paper, a new test rig is introduced for the experimental validation of a reduced-order model (ROM) based on the Gram–Schmidt Interface (GSI) modes applied to a friction contact whose dimensions are not negligible with respect to the size of the substructures. In this case, classical approaches like Craig–Bampton technique might be not effective in reducing the size of the problem when many contact nodes subjected to nonlinear contact loads cannot be omitted. The technique is implemented in a solution scheme in the frequency domain using penalty contact elements and the harmonic balance method. The preload on the joint is produced by permanent magnets to enhance the friction contact without introducing uncertainties due to bolting. Measurements are compared with the ROM simulations and with standard time-domain integration of the full FE model. The advantage of using the GSI technique is shown in terms of time computation and accuracy of the simulation.

Influence of Rivet Diameter and Pitch on the Fatigue Performance of Riveted Lap Joints Based on Stress Distribution Analysis

Interference-fit riveting is one of the most widely used mechanical joining ways in aircraft assembly. The fatigue performance of riveted joints has a significant impact on the service life and reliability of aircraft. In this paper, the fatigue performance of the riveted lap joints with various rivet diameters and pitches are studied based on stress distribution analysis under tensile load. First, a theoretical model of the riveted lap joint under tensile load is developed by using the spring-mass model. The rivet-load stress, bypass stress, and interference stress around the riveted hole are analyzed. Then, the finite element (FE) model of riveted lap joints are established. The influence of rivet diameter and pitch on stress distribution around the riveted hole are discussed. Finally, the fatigue tests are conducted with riveted lap joint specimens to verify the theoretical model and FE results, and a good agreement is observed. Based on the simulation and experimental results, a good combination of structural parameters of the riveted lap joint is found which can optimize the stress distribution around the riveted hole and improve the fatigue life of the riveted lap joint.

Residual stress and fatigue behavior of riveted lap joints with various riveting sequences, rivet patterns, and pitches

The residual stress of multi-rivet structures is related with the riveting sequence, the rivet pattern, and the pitch due to the deformation interaction of different rivets. The stress amplitude of riveted structures subjected to the cyclic loads is affected by the residual stress, which increases the difficulty in the prediction of fatigue life. In this article, the riveting processes for single-row and triple-row riveted lap joints with various riveting sequences, rivet patterns, and pitches are studied numerically and experimentally. The residual stresses for both types of riveted structures are verified by the testing data. Significant difference appears in the residual stress field for riveted lap joints with various riveting sequences and rivet patterns. The decrease in the rivet pitch increases the compressive residual stress at the edge of the rivet hole. Furthermore, the fatigue life prediction model is developed for multi-rivet structures, in which the coupling effect of residual stress and cyclic load is considered. The fatigue experiments are conducted for riveted lap joints with various riveting sequences, rivet patterns, and pitches. The accuracies of the numerical results obtained from the Homan model and the developed model are compared with the experimental data. The proposed fatigue model shows better performance to predict fatigue life for multiple rivet structures.