Residual Stress Measurements for Studying Ingot Cracking

High strength aluminum alloy ingots are subject to cracking due to residual stresses developed during casting. Previously, casting variables have been correlated to ingot cracking frequency. In addition to this go, no-go type of information, techniques were sought to provide data concerning the magnitude of residual stresses present in uncracked ingots. Such numerical data are more amenable for use in multiple regression correlations to the numerous process variables. Initial work involved strain gaging and sawing of laboratory sized ingots. Magnitudes and signs of the various stresses were determined both by deflection calculations and strain gage readings. A third technique involved a non-destructive strain gaging and precision hole drilling procedure. The latter technique has been used to monitor full sized production ingots. The various experimental measurement techniques and the current state of knowledge concerning the origin and distribution of stresses will be discussed in detail.