Residual stress creep relaxation around cold expanded holes in an aluminum alloy

Residual stress distributions were measured in aluminum-alloy 2650 disks after cold expansion and after exposure to creep at 150degreesC for various times. Strains measured as a result of boring out the hole after cold expansion were found to exhibit significant angular variations around the hole. However, after exposure to 150degreesC residual strains and stresses showed less angular variation. To take account of the angular variation, the Garcia-Sachs technique for measuring residual stresses was employed. Surface residual stresses on the entrance and exit faces of the disks were measured using the x-ray method. The most significant relaxation of the residual stresses occurred within the first 100 h. Two simple models were used to predict residual stress relaxation, one using a uniaxial creep relaxation model and a second using tensile and isochronous stress-strain curves. A good comparison between predictions and experiments was observed.