Progressive collapse of titanium alloy micro-lattice structures manufactured using selective laser melting

Hasan, Rafidah Progressive collapse of titanium alloy micro-lattice structures manufactured using selective laser melting. Doctor of Philosophy thesis, University of Liverpool.

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Abstract

The starting point for this research was the viability of the Selective Laser Melted (SLM) titanium alloy Ti-6Al-4V micro-lattice structure for applications in Foreign Object Impact (FOI) situations in aerospace sandwich constructions. To this end, the mechanical behaviour of single struts and the compression behaviour of micro-lattice blocks were studied. Detailed characterizations of dimensional accuracy, circularity and microstructure, as well as clarifications of deformation behaviour and failure of single manufactured struts under tensile loading were done. The variability in stress-strain curve of struts which was derived using compliance correction method was found to arise from the variations in strut diameters, due to outer surface roughness of the material. Post-manufacture heat-treatment processes improved the surface roughness and variations of strut diameters as well as the microstructure of the α/β titanium alloy, hence reduced the scatter in the stress-strain curve of single struts. The deformation of the SLM Ti-6Al-4V micro-lattice blocks with Body Centred Cubic (BCC) structure was elucidated using combined experimental studies and computational analysis. Detailed analysis of geometry and diameter variations in struts of the micro-lattice blocks were done and compared to that of single manufactured struts. Node formation and manufactured quality of the micro-lattice structure were revealed from a 45° angle diagonal plane of sectioned block. The compressive deformation behaviour of the BCC micro-lattice block structures was then studied. Effects of different manufacturing routes and parameters as well as post-manufacture treatments in the compressed micro-lattice structures were discussed. Finite element analysis was performed using a validated model of BCC micro-lattice unit cell. The progressive collapse of the micro-lattice block structure was shown to be comparable with the prediction from the finite element model of a unit cell. The numerical simulation was then used to quantify the effect of parent material properties on block collapse. In this way, the relations between SLM manufacturing route, material properties and structural performance are highlighted.

Item Type:	Thesis (Doctor of Philosophy)
Additional Information:	Date: 2013-02 (completed)
Uncontrolled Keywords:	micro-lattice structures, selective laser melting, titanium alloy
Divisions:	Faculty of Science and Engineering > School of Engineering
Depositing User:	Symplectic Admin
Date Deposited:	13 Aug 2013 09:13
Last Modified:	17 Dec 2022 01:07
DOI:	10.17638/00011933
Supervisors:	Mines, Bob
URI:	https://livrepository.liverpool.ac.uk/id/eprint/11933