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Residual stress analysis of riveting process using finite element method

Karasan, M Murat
Rivets are widely used as a means of fastening in airframe construction industry. There are various types of riveted joints on an aircraft fuselage or on a helicopter body. Among the other types of fasteners riveted joints are preferred in such applications due to; their permanence after installation and their economical advantages. In a riveted joint, it is known that residual stresses are present as a result of the installation process. Furthermore, during the flight of an aircraft, the fuselage is loaded in one cycle and such cycles are repeated throughout the service life. As a result, the panels and the rivets are subjected to fatigue type loading. The integrity of the joint must be maintained against this combination of service loads and the residual stresses. Hence, the riveting process parameters which influence the residual stresses are utmost critical in terms of fatigue life of the hole body. In this study it is aimed to obtain an accurate numerical model of a single-lap riveted joint which is widely used in airframes. 2-D axisymmetrical and 3-D numerical models are generated using commercial finite element code ABAQUS/CAE and subsequent parametric studies are carried out on these models. The Results of both models are compared with those found in the literature. Clearance between hole and rivet shank is selected as the primary parameter to be inspected. The effects of hole clearance on the final residual stress field are examined on 2-D and 3D models. Furthermore, a through the thickness, crack on the inner panel which is initiated after installation is modeled. The crack is perpendicular to the direction of loading. It is placed to the residual tensile stress zone that surrounds the rivet hole. Hence, the effects of residual stresses are also taken into account. For a riveted joint subjected to fatigue loading, such a macroscopic crack could eventually form. In this thesis, stress intensity factors (SIF’s) for this crack are calculated for various parameters such as clearance and crack length. These can be utilized in a subsequent fatigue crack growth analysis as the initial values or they can be used in a fracture analysis, to predict unstable crack growth due to overload (i.e. crack linking).