D.H. Lammlein PhD Dissertation - Vanderbilt University

Figure 12: Horizontal cross-section taken at mid-plane of AA5083 plate with embedded
pin after break test(v=2mm/s, ω =750, head tilt =3°), figure from [66].
It can be seen that shear layers are deposited sequentially along the trailing edge of the
weld from the retreating side to the advancing side. The author uses the rotational speed
of the tool, the travel speed, and the distance traveled by each successive shear layer to
calculate the shear velocity. The shear velocity is calculated to be ~16mm/s while the
periphery of the pin is traveling at ~235mm/s. This results in a shear/pin periphery
velocity of 0.07 (where 0.0 is pure slip and 1.0 is pure stick). The authors, therefore,
conclude a slip condition to be dominant in this situation. It is mentioned that this ratio
compares well with results obtained by Schmidt et al. [24] who arrive at a values in the
range of 0.1-0.3. The authors of [66] further contend that a liquid film exists at the shear
interface which facilitates the slip condition.
Computational Modeling Studies
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