Arutyun Arutyunyan

Analyst, Elixirr

Arutyun worked on small scale ultrasonic fatigue testing and its application to Ti. The testing is based around an ultrasonic actuator at 20 kHz which provides a significant acceleration of the test allow 10^6 cycles to be applied in less than a minute and even the giga-cycle regime can be achieved within a day. In (very) high cycle fatigue the initiation and growth of a microstructurally short crack tends to dominate the fatigue lifetime but is a difficult process to study since initiation is localised both spatially and temporally. Using small test pieces in which the stress is raised over a ~100x100 µm patch allows the entirety of the test region to be monitored using in situ optical microscopy, and characterised using EBSD before and after testing.

Arutyun has been using this new testing methodology to study fundamental aspects of fatigue in commercially pure titanium. Of interest are basic S-N fatigue lifetime data, but more importantly trying to identify if crack initiation is linked to particular grain types (size, orientation), and understanding crack paths and associated growth rates as the crack propagates from grain to grain.