On the existence of a friction stress for high–temperature creep

Abstract
Strain transients following small stress decrements during creep of high–purity poly crystalline copper at 673 K indicate that delay times of zero creep rate do not occur, except when the reduced stress level is equal to the average internal stress. Similar measurements on aluminium and a zirconium alloy have failed to detect Buch delay times. Thus, the existence of a friction stress in the creep of these materials is questioned.