Papers by Keyword: Riveted Joints

Abstract: In this paper are described fatigue physical tests that were performed on a great number of riveted specimens with different constructive and technological parameters. Some of the purposes of the experimental tests, they were: determining the number of load cycles at which cracks by fatigue occurred, determining the moment of initiation, the location and propagation speed of the fatigue crack. For fatigue crack evolution study numerical models were designed. A simplified model for FEM analysis was proposed that reduced considerable the calculus effort and allows models for complex riveted joints. From the described experiments on specimens and numerical simulations there are some important conclusions regarding the fatigue phenomenon in riveted joints such as: important peculiarity of damage by multiple cracks is the cracks junction of adjacent rivet holes, which contributes, by jumping, to increase the degradation rate of assembly; the riveted joint model can be applied with good accuracy to estimate the durability of the structures inclusively to identify and prevent the cases of widespread fatigue damage.

Abstract: The aim of this paper is to assess the impact of the rivet hole sizing process on the fatigue life based on the example of the structural connections characteristic for riveted joints used in aviation industry. Test specimens reflected the structural connection consisting in a riveted lap joint of an airplane plating stiffened with a T-bar. Connected plates and the T-bar are made of D16CzATW aluminum alloy. 3 mm diameter oval head solid rivets for aviation-related purposes were made of PA24 aluminum. During fatigue tests, individual specimens with non-sized holes and with sized holes were subjected to uniaxial, one-sided, fixed-amplitude loading (R = 0). It can be concluded from the fatigue life comparison that introduction of an additional operation in the riveting process, i.e. the hole sizing, results in significant, about two-fold increase of the fatigue life of the riveted structural connection, even at slight sizing degree. The difference of the specimen damage nature was observed between specimens with sized and non-sized holes.

Abstract: Effects of variables related to design and production of riveted lap joints representative of longitudinal sheet connections for a pressurized transport aircraft fuselage were experimentally investigated. The specimens from an aircraft Al alloy D16 Alclad sheets of three different thicknesses (1.9, 1.2 and 0.8 mm) were assembled under load control using round head rivets and rivets with the compensator from a P24 Al alloy. For the joints from 1.9 mm thick sheets fatigue tests indicated a dependency of the crack initiation site and crack path on the squeeze force level and on the rivet type. At the same time, increasing the squeeze force led to improved fatigue properties of the joints, specimens assembled using the rivets with the compensator showing fatigue lives consistently longer than joints with the round head rivets. All observed trends have been explained based on hole expansion and load transfer measurements. For thin sheets connected using the round head rivets, local deformations and indentations under the driven rivet head promoted crack initiation and failure in the adjacent sheet. Fatigue test results indicated that the detrimental effect of this type imperfections could outweigh the benefits associated with a decrease in secondary bending due to thinning the sheets. The rivets with the compensator were observed to cause significant local imperfections beneath the manufactured head, which adversely affected the joint fatigue performance.

Abstract: A very large number of variables affect the response of bolted or riveted joints typically used in aerospace applications: geometry of the joint, characteristics of the sheets, friction between sheets, geometry of head and kind of fastener, amplitude of clearance before assembly, mounting axial load, pressure effects after manufacture. It must be also recalled that these parameters influence the many failure modes existing for such joints, among which a relevant importance is attributed to bearing. The present paper deals with the study of the influence of assembly parameters on the joint operational behaviour and in particular with the analysis, performed through numerical simulations, of the influence of the residual stress-strain state coming from the riveting operation on the bearing resistance of an aluminium alloy joint. This work has been developed within the FP6 research project called MUSCA (Non linear static multiscale analysis of large aero-structures).

Abstract: A new interest has been increasingly directed in recent years to study the behaviour of joints provided with various kinds of fasteners and the mechanism of load transfer; profiting of the present capabilities of computing systems and analysis codes, which appear such as to deal with models built with more than one million elements, thanks to new numerical techniques which can solve huge systems of equations. However, the main interest has been limited to the case of bolted joints, for which several models are now available, while a few results are known for the case of riveted joints, where more complex mechanisms are involved. In the present paper a full set of analyses has been reported, with reference to both normal and blind rivets, where the manufacturing operation has been simulated through Ls-Dyna to evaluate the stress and strain states induced into the jointed sheets, varying the dimensional and riveting load characteristics of the joint. A subsequent investigation is presented, which aims to evaluate the effects of the compressed zone over the behaviour of an approaching crack.