Author

Megan Ryan

Date of Award

Spring 2020

Document Type

Open Access Dissertation

Department

Mechanical Engineering

First Advisor

Anthony Reynolds

Abstract

Friction stir extrusion is a solid state process that uses a rotating die to perform extrusions. This process can be used to directly recycle waste from machining processes and has been shown to produce wires with desirable mechanical properties. In order to better understand the friction stir extrusion process, the effect of the process parameters on the strain distribution in the wires needs to be understood. The process parameters evaluated in this work are die advance rate, die rotational seed, and die geometry. A total of 16 wires were extruded using different combinations of these process parameters. Marker wires were inserted into the billets prior to extrusion to observe material flow throughout the process. After the extrusion, transvers cross sections were taken at multiple locations along the wires in order to evaluate the strain distribution in each wire. Longitudinal, circumferential, and radial strain were calculated using the change in dimension of the marker wire.

The longitudinal strain was consistent across all wires and was close to the expected value in a conventual extrusion with the same reduction ratio, showing it is not dependent on the process parameters. The radial and circumferential strain were dependent on the process parameters and varied from wire to wire. As the die advance rate per revolution increased, the radial and circumferential strain values began to converge on the expected value for a conventional extrusion with the same reduction ratio. The samples produced with the scroll die had very similar strain distributions when compared to the samples produced with a flat die and the same process parameters. While the images of the cross sections showed that the scroll die changed the marker wire shape, it did not alter the strain distribution. The sum of the strain components was very close to zero for all cross sections, which is expected in a controlled volume plastic deformation process. This shows that the method used produced accurate strain results.

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