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Negri Christopher_A_Master_of_Science_2021.pdf (10.68 MB)
ETD Abstract Container
Abstract Header
Ductile Fracture of Laser Powder Bed Fusion Additively Manufactured Ti-6Al-4V
Author Info
Negri, Christopher Anthony
Permalink:
http://rave.ohiolink.edu/etdc/view?acc_num=dayton1627570434852405
Abstract Details
Year and Degree
2021, Master of Science (M.S.), University of Dayton, Mechanical Engineering.
Abstract
Understanding the mechanical performance of additively manufactured aerospace metals is of paramount importance for the development of new structural materials and next-generation aerospace components. Of particular interest in this investigation is the titanium alloy Ti-6Al-4V produced using laser powder bed fusion (LPBF), and its structural integrity in the event of sudden aerospace-related impacts. These impacts, known as foreign/domestic object damage, can cause catastrophic damage to aircraft components and serious injuries to passengers. To enable simulation-aided design and analysis for foreign/domestic object damage survival, the overarching goal of this project is to develop a stress-state-dependent ductile fracture model for LPBF Ti-6Al- 4V that is representative of the material’s behavior across a broad range of loading conditions. The foundational steps presented in this thesis include the design of an experimental program to calibrate the LPBF Ti-6Al-4V fracture locus, a three-dimensional representation of the variation of equivalent plastic strain at fracture with stress triaxiality and Lode parameter, commonly utilized in continuum damage models. The proposed experimental program provides a family of mechanical tests that employ different specimen geometries (e.g., notched plane stress, plane strain, axisymmetric, and thin-walled tube specimens) and loading conditions (e.g., tension and torsion) to access a broad window of stress states (triaxiality and Lode parameter combinations). Six axisymmetric tension specimens were chosen from the aforementioned family of candidate specimen designs for subsequent mechanical testing and stress state analysis. The grain morphology and porosity of the LPBF-printed Ti-6Al-4V material was characterized using electron backscatter diffraction (EBSD) and X-ray computed tomography (XCT), respectively. Quasi-static mechanical testing was performed on a servo-hydraulic load frame, with full-field surface strains measured using three-dimensional digital image correlation (DIC). The effective plastic strain (EPS) at fracture for each test (thirty total, with five runs for each of the six specimen geometries) was obtained through direct DIC measurements and the customary plastic incompressibility assumption. Traces and weighted average values of the stress state parameters (triaxiality and Lode parameter) over the plastic deformation history were obtained from parallel numerical simulations of each test. Acceptable agreement between simulation and experiment – as quantified by comparing force-displacement and principal strain-displacement curves – was observed across the majority of the test series. However, a general trend was noticed across the force-displacement plots where the simulations predicted sometimes meaningfully higher yield stresses and ultimate tensile stresses than the experiments. This discrepancy is attributed to the material constitutive modeling and/or specimen metrology. Arithmetic averages of the stress state parameters and EPS at fracture were reported across the five tests performed for each specimen geometry. A trend of the EPS at fracture (ductility) decreasing with an increasingly negative (tensile) triaxiality is observed, consistent with a significant body of previous literature in the ductile fracture community, including previously published results on wrought Ti-6Al-4V. The research presented in this thesis complements the few existing studies on ductile fracture of LPBF Ti-6Al-4V, providing additional fracture data that can be used to calibrate tabulated or parameterized ductile fracture models used in predictive simulations of aerospace-related structural impacts.
Committee
Robert Lowe, PhD (Advisor)
Dennis Buchanan, PhD (Committee Member)
Luke Sheridan, PhD (Committee Member)
Jeremy Seidt, PhD (Committee Member)
Pages
161 p.
Subject Headings
Aerospace Engineering
;
Aerospace Materials
;
Engineering
;
Mechanical Engineering
;
Mechanics
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Citations
Negri, C. A. (2021).
Ductile Fracture of Laser Powder Bed Fusion Additively Manufactured Ti-6Al-4V
[Master's thesis, University of Dayton]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=dayton1627570434852405
APA Style (7th edition)
Negri, Christopher.
Ductile Fracture of Laser Powder Bed Fusion Additively Manufactured Ti-6Al-4V .
2021. University of Dayton, Master's thesis.
OhioLINK Electronic Theses and Dissertations Center
, http://rave.ohiolink.edu/etdc/view?acc_num=dayton1627570434852405.
MLA Style (8th edition)
Negri, Christopher. "Ductile Fracture of Laser Powder Bed Fusion Additively Manufactured Ti-6Al-4V ." Master's thesis, University of Dayton, 2021. http://rave.ohiolink.edu/etdc/view?acc_num=dayton1627570434852405
Chicago Manual of Style (17th edition)
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Document number:
dayton1627570434852405
Download Count:
677
Copyright Info
© 2021, all rights reserved.
This open access ETD is published by University of Dayton and OhioLINK.