Acoustic emission from a SiC reinforced Al-2618 metal matrix composite during straining

Abstract

Acoustic emissions can be detected from Al-2618 alloys in the peak aged condition prior to its tensile failure. These events are associated with the nucleation of voids by the brittle fracture of the FeNiAl{sub 9} dispersoid phase. When 10{micro}m SiC reinforcements are incorporated into the alloy the rupture of the dispersoids is suppressed and fracture of the SiC reinforcing particles begins at a plastic strain of 0.5--1.0%. The rate of acoustic emissions as a function of strain increases rapidly to a peak of about 10{sup {minus}3} m{sup {minus}3} s{sup {minus}1} at about 2.0--2.5% strain in both the quenched and peak aged particle reinforced metal matrix composites (PRMMCs). The rate of emissions appears to be a little greater in the case of the quenched PRMMC but the difference is not sufficient to be outside potential experimental scatter. When tests are interrupted and the specimens are held under constant load the rate of AE events still continue under a static load. The rate per second at which these static AE events occur decays rapidly over a few seconds. The reason for this time dependent behavior is unclear. However, it indicates that any constitutive law developed to predict particle fracture as a functionmore » of strain will also be strain rate dependent.« less