Session: 02-09-03: Computational Modeling and Simulation for Advanced Manufacturing-III

Paper Number: 71800

Start Time: Tuesday, 03:30 PM

71800 - Numerical Study of the Percussive Riveting Process: Analysis Validation 

This effort represents the continuation of percussive riveting work that has been performed by this University of Washington research group and presented at this event in the past. Percussive riveting is an assembly method that is used ubiquitously in the aerospace industry, especially in the fuselage final assembly phase. It is a dynamic assembly process that requires two entities opearting simultaneously in order to form a rivet. One entity operates with a riveting gun on the exterior of the fuselage. The rivet gun provides the energy input to carry out the assembly process. The other entity operates with a bucking bar on the interior of the fuselage. This entity is responsible for forming the rivet from the shank end. 

In previous work undertaken by this research group, an axisymmetric thermomechanical finite element model (FEM) framework implementing actual boundary conditions was developed to understand the effect of geometric factors on the residual stress and strain distributions within the riveting stackup. A countersunk rivet and two skins are part of the riveting stackup. The countersunk rivet is widely used in the aerospace industry because of flushness requirements. Because no further joint finishing processes are required after the countersunk rivet has been formed, it is an economically viable final assembly method. 

Residual stress and strain distributions within the rivet stackup affect the fatigue performance of the assembled joint. The percussive riveting process is different from the conventional squeeze riveting process because of the dynamic and adiabatic nature of the percussive riveting process. Strain rate effects and thermal effects are negligible in the squeeze riveting process because of the low velocities and strain rates involved. But, these two effects along with large strain magnitude play an influential role in the percussive riveting process.

To help capture the strain, strain rate and thermal effects, Johnson-Cook material model for flow stress calculation is utilized in the FEM framework. Because of the dynamic nature of the percussive assembly process, framework validation is important. A three-dimensional FEM (3DFEM) was constructed with asymmetric motion of the bucking bar, also known as the forming tool. The results of the 3DFEM simulation are compared with previously presented axisymmetric FEM and are presented in this study. A 3DFEM with asymmetric bucking bar motion more closely represents the percussive riveting process. The percussive riveting axisymmetric FEM and 3DFEM results will be compared with classical hand analysis of the squeeze riveting process and with few experimental observations derived from workshop fabricated joints to help validate the FEM framework implemented in this study. 

Presenting Author: Sai C. Krovvidi University of Washington

Authors:

Sai C. Krovvidi University of Washington
M. Ramulu University of Washington
Per G. Reinhall University of Washington