ON THE FORMATION OF NECKS IN AN AL-13-PERCENT-SI EUTECTIC ALLOY

An Al-13%Si eutectic alloy was tested at an elevated temperature of 55 7 degrees C at constant strain rate. Marked deviations from uniform de formation occurred in the specimens tested at three different strain r ates of 1 x 10(-5), 5 x 10(-4) and 1 x 10(-2) s(-1) at elongations as low as approximately 50%. At a strain rate of 1 x 10(-2) s(-1), a diff use neck formed up to an elongation of 100%. Thereafter, the neck beca me sharp and catastrophic. At strain rates of 5 x 10(-4) and 1 x 10(-5 ) s(-1), failure occurred by the formation and subsequent growth of sh arp necks within the gauge length. These results are consistent with a genuine decrease in the value of the strain rate sensitivity index m with a decrease in strain rate.