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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.