Design and Implementation of a Force Dynamometer for Friction Stir Welding

The locations of the strain nodes on the extended octagonal ring force transducer (EOR) have been examined by many studies in the literature. However, there is a considerable lack of agreement between the different studies due to different assumptions and approaches used to define nodal locations. Because an exact solution for the stress and strain distributions in the octagonal ring does not exist, some researchers used the solution of the classical circular ring as a first approximation. Others used the finite element method to obtain a solution. But very few studies attempted to investigate the effect of geometry of the ring itself on the solution. In this work, the stress and strain distributions in an EOR transducers of varying geometries have been investigated by the finite element method and the locations of strain nodes and those of maximum sensitivity were determined and compared with the literature. It was found that strain node locations vary with ring geometry, but do not generally coincide with the classical solution of the circular ring. The strain node locations are also not coinciding with maximum sensitivity locations for horizontal force measurement. An EOR dynamometer was fabricated based on the results of this study. The dynamometer was calibrated and tested in friction stir welding. It was shown that the dynamometer response is highly linear and with very small cross talk.