Joy E. Gockel, Ph.D. (Advisor); Nathan W. Klingbeil, Ph.D. (Committee Member); Ahsan Mian, Ph.D. (Committee Member); Onome Scott-Emuakpor, Ph.D. (Committee Member); Anthony Rollett, Ph.D. (Committee Member)
Doctor of Philosophy (PhD)
In many structural applications void-like defects cause significant performance debits which call for component redesign or post-processing to account for or remove the defects. For laser powder bed fusion (LPBF) processes, it has been shown that many of these features and their size and shape characteristics are controllable through LPBF process parameter manipulation. For design efforts, however, it is necessary to understand the direct influences of processing on the formation of porosity and the role that individual pores and porosity distributions have on the properties and performance of AM components. Additionally, design criteria must be established to facilitate implementation of AM components into structurally critical applications. To this end, the investigations that have been performed here relate the AM material processing of alloy 718 to the pore structure, crack growth properties and fatigue performance. This dissertation first explores the influence of four key process parameters and scan strategies on the formation and characteristics of porosity distributions in AM material. Then, based on the porosity distributions observed via non-destructive inspection techniques, a crack-growth based life prediction method was developed to accurately predict fatigue lives of AM components. Additionally, fatigue limit models were modified based on experimental data to explore the interactions of defect size and applied stress with respect to both finite and "infinite" fatigue life which enables defect tolerant design for components manufactured via AM. Finally, a novel compliance-based method for crack initiation detection was developed and used to assess some of the assumptions made in the prior investigations. The connections made through the work presented herein link AM processing to potential design requirements which will facilitate faster, safer design efforts for implementation of AM components into structurally critical applications.
Department or Program
Ph.D. in Engineering
Year Degree Awarded
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