Abstract
Fracture toughness testing in a Ti-6Al-4V alloy with acicular micro-structure was carried out using 20 mm thickness compact tension specimens, hot-rolled in β-phase temperature range. During the test, the amplitude distribution of Acoustic Emission signals were monitored, and these detected signals were classified into small and large amplitude distributions. With the aid of light micro-photography and electron fractography, it was revealed that small amplitude emissions result from micro-cracking due to inclusions and α-β phase boundary, and large emissions from the coalescence of these micro-crackings, that is, micro pop-in, in the unit of blocking prior β grain. The onset of stable crack growth, therefore, can be defined by the appearence of large amplitude emissions, and it can be concluded that the dynamic fracture process can be understood by the measurement of AE amplitude distribution.
