Download Failure Behaviour of Selectively Laser Melted Ti-6Al-4V

Failure Behaviour of Selectively Laser Melted Ti-6Al-4V
I. Ullah1,2, W. Xu1, M. Brandt1 and S. Feih1,2
1Advanced Manufacturing Precinct, RMIT University, GPO Box 2476, Melbourne,
Australia, 3001.
2Sir Lawrence Wackett Aerospace Research Centre, School of Aerospace,
Mechanical & Manufacturing Engineering, RMIT University, GPO Box 2476,
Melbourne, Australia, 3001.
Metallic core designs for sandwich composites play an important structural role in
high performance light-weight structural applications for aerospace and automotive
structures. For impact events, the failure strain of the core material defines the
structure’s energy absorption capacity. In this research Ti-6Al-4V alloy structures
produced by Selective Laser Melting (SLM) are evaluated for their failure
characteristics. Because of the faster cooling rate in this unique manufacturing
process, the titanium alloy develops a martensitic microstructure and exibits different
mechanical properties when compared to a conventionally produced Ti-6Al-4V. To
understand the static and dynamic failure behaviour of complex SLM built structures,
the failure curve of stress triaxiality versus plastic failure strain needs to be
evaluated. There are three distinct modes of failure defined based on the value of
stress triaxiality in ductile metals: (1) ductile failure, (2) shear failure and (3) mixed
mode failure. Mechanical testing has been performed on several conventional
material test specimens and micro-truss structures in order to generate a wide range
of stress states during the failure initiation process. Finite element models are
utilized to evaluate the internal state of stress and establish a failure model for SLM
built Ti-6Al-4V material. The numerical model was validated for a wide range of
truss-based core structures under various loading conditions of compression and
shear and was found to predict the mechanical test results accurately. The plastic
failure strain for the SLM alloy is found to reduce significantly for the range of stress
triaxiliaty values investigated when compared to forged Ti-6Al-4V alloys with the
conventional - microstructure.