Determination of strain during hot tearing by image correlation

The evolution of strain and strain at the onset of localization resulting in a hot tear has been determined for alloys AA6111, AA3104, CA31218, and Al-0.5 wt pct Cu during solidification. A bar constrained at both ends was solidified with a window above the hot spot region to allow observation of hot tear formation and growth. A high-resolution camera was used to capture images of the surface during solidification. In addition, a thermocouple cast into the sample was used to acquire temperature data in proximity to the hot tear. The images were analyzed using digital image correlation software to measure the evolution of displacement and strain based on tracking the motion of discrete features on the as-cast surface of the sample. Strain data was determined starting from the point immediately after solidification shrinkage ends (the metal pulls away from the glass) and finishing when the first sign of a crack or hot tear is visible to the eye. The minimum strain at which strain localization occurs was found to be > 0.0069 in AA6111, > 0.0123 for AA3104, > 0.0047 for CA31218, and > 0.0021 for Al-0.5 pct Cu.