Flow visualization and estimation of strain and strain-rate during friction stir process

A soft and ductile aluminum foil is embedded within a workpiece undergoing friction stir processing (FSP) to observe the deformation zone. A whirlpool of material is detected in the stir zone which consumes the foil over time. Among different approaches to estimate material strain, a logarithmic thickness strain is defined and experimentally measured by observing the gradual change in thickness of ductile aluminum foil. Additionally a strain-rate is numerically evaluated from the FSP process parameters and the deformed foil geometry using finite-element analysis. It is believed that this method provides reliable strain-rates in the friction stir process.