Chapter 5 Fatigue Assessment of Porosity in Electron Beam Melted Ti-6Al-4V Justin Warner, Dino Celli, Jacob Rindler, M. Herman Shen, Onome Scott-Emuakpor, and Tommy George Abstract Additive manufacturing (AM) has proven itself to be an effective and versatile solution in replacing aircraft structures and components. However, the AM process still requires the necessary structural reliability as well as the technology to assess operational longevity. In this work, a fatigue performance and damage progression assessment framework is proposed to achieve a fundamental understanding of the fatigue damage mechanisms and its progression in as-built treated electron beam melted (EBM) Ti-6Al-4V at the macroscopic structural scale as well as at the microscopic constituent scale. The work presented utilizes digital image correlation (DIC), an optical strain measurement technique, as a method to detect crack initiation sites occurring on the material’s surface and propagating throughout the specimen. A comprehensive testing framework and experimental procedure is developed to generate fatigue data for AM material Ti-6Al4V as-built specimens. Characterization and simulation of the fatigue progress due to AM process defects (voids, surface roughness, etc.) are also performed using damaging energy progress and damage evaluation. Keywords Fatigue · Porosity · Computed tomography · Defect damage criterion · Digital image correlation Many research efforts, within the engineering community, have been focused on the improvement of additive manufactured (AM) materials. Specifically, the fatigue life characterization is of great interest to the aerospace industry due to high standards for the fatigue performance of materials in flight critical components. Powder bed fusion(PBF) is a commonly used AM process to produce components within a small region (200–350 mm) of space by using thermal energy to fuse powder and build a product [1]. There are various options when considering which PBF method to use (i.e., electron beam melting, direct metal laser sintering, selective laser sintering/melting). Electron beam melting (EBM) is an accepted method that is relatively inexpensive and has a small footprint by recycling the unused powder [1]. EBM uses an electron beam source, which can create internal stress-concentrating defects, such as porosity, and significantly reduces fatigue life. This becomes significantly more important for the aerospace industry as fatigue of engineering components made up 25% of all failures and 55% in aircraft components [2]. Therefore, to utilize AM materials for aerospace components, characterizing and ultimately reducing defects within AM materials such as Ti-6Al-4V, Inconel 718, and Aluminum 7075 are demanded to ensure proper safety standards. Various parameterized defect detriment criterions are investigated to identify the crack initiation site which ultimately leads to fatigue failure. 3D computed tomography (CT) scan data was completed to use identified individual defects characteristics to distinguish fatigue life performance. This was conducted in effort to develop a cycle to failure fatigue life prediction and locates the area of interest of crack initiation prior to destructive testing. Detecting the initiation site can aid in the AM process by informing, via in situ (QM meltpool) or post-CT scans, defect attributes without destructive testing. In addition to determining actual cycles to failure, defect attributes were identified for life prediction with CDM or fracture mechanic fatigue life approaches. Digital image correlation (DIC), an optical strain measurement technique, was used to aid in detection of the location of failure and strains fields. DIC data was utilized to cross-examine the dog bone specimen’s regions of interest and evaluate defect detriment criterions’ validity. Ti-6Al-4V was analyzed due to its wide application J. Warner · D. Celli ( ) · J. Rindler · M. H. Shen The Ohio State University, Columbus, OH, USA e-mail: warner.799@osu.edu; warner.799@buckeyemail.osu.edu; celli.6@osu.edu; rindler.115@osu.edu; shen.1@osu.edu O. Scott-Emuakpor · T. George Air Force Research Laboratory, Wright-Patterson AFB, OH, USA e-mail: onome.scott-emuakpor.1@us.af.mil; tommy.george@us.af.mil © The Society for Experimental Mechanics, Inc. 2021 S. Xia et al. (eds.), Fracture, Fatigue, Failure and Damage Evolution, Volume 3, Conference Proceedings of the Society for Experimental Mechanics Series, https://doi.org/10.1007/978-3-030-60959-7_5 37
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