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Title: Enhancing fracture toughness of ultrahigh strength aerospace components made by additive manufacturing
Author: Alsalla, Hamza Hassn Ramadan
ISNI:       0000 0004 7226 0821
Awarding Body: University of Exeter
Current Institution: University of Exeter
Date of Award: 2017
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Direct Metal Laser Sintering (DMLS) and Selective Laser Melting (SLM) are an Additive Manufacturing (AM) technique that produces complex three-dimensional parts by adding layer upon layer of powder materials from bottom to top. Recently, AM has received a significant amount of press and is set to have an enormous impact such as decreasing the cost of production, fast and flexible, design freedom and increase the innovation opportunities. The powder base nature allows these techniques to process a variant of materials as well as produce complex composite parts and develop new materials system for Aerospace industries. The biggest problems in the process are limited surface quality and residual porosity in SLM and DMLS parts that are undesirable for some applications where fatigue resistance and high strength are essential. This research aims to improve the fracture toughness, ductility and fatigue of the metallic components, which is essential to be able to exploit the potential of the SLM and DMLS of these alloys for aerospace applications. In an additional development of the AM technology is not only limited to new machines but also processes, new materials, and methods, as it offers high mechanical properties and performance. This research focuses on DMLS and SLM of titanium and stainless steel alloys to investigate the effect of processes parameter and different build direction on toughness and fatigue crack growth property to change the physical and mechanical properties. Also, manipulate the process parameters and their effect on strength, fracture toughness and quality for both bulk and cellular lattice structure parts. The novelty in this study lies in using additive manufacturing process to evaluate the local failure mechanism of 316L bulk and cellular lattice structures made by SLM under uniaxial tension and three-point bending load. The effect of different build directions of the 316L lattice structure on the fracture toughness properties is compared to the Ashby and Gibson models. The findings demonstrate that the build direction does have an effect on the microstructure of parts, which subsequently has an effect upon mechanical properties and the surface quality of manufactured parts. Results found in this study will enable the designer to understand the important factors which affect the SLM and DMLS process and quality of final parts at different build direction. The comparison between micromechanics model and experimental results will help the designer to predict fracture toughness of AM cellular structures without the need of experimental tests. Finally, the results of mechanical properties of these bulk and lightweight parts will give a confidence to the designer to use and tailor their properties to specific applications.
Supervisor: Smith, Christopher ; Eichhron, Steve Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available