In this document, we present a methodology for predicting the transport and distortion of foil markers used to study the flow of material during friction stir welding (FSW). The governing equations are summarized for modeling viscoplastic flow and heat transfer using an Eulerian framework. A streamline integration method is used to track material particles (differential volumes) along their trajectories through the flow field and to compute the evolution of the state variables. This method is also used to compute how differential volumes distort during the flow. Tracking several two-dimensional patches, which model the foil markers used experimentally, allows us to illustrate how the markers move and distort during a friction welding process. Two animations of the marker histories (fsw-centerline.mov and fsw-inlet.mov) are included in this collection and are the subject of this the document.