A NIST co-organized workshop identified the current needs for metal AM fatigue and fracture (F&F), which helped create the focus of this project. During the workshop, specific variables within processing-structure-properties-performance (PSPP) were identified and in some cases prioritized. More detail can be found in the workshop findings report (https://doi.org/10.6028/NIST.AMS.100-4). Processing includes not just machine settings (e.g. layer thickness) and melt parameters (e.g. energy beam power and scan speed) but also powder characteristics (e.g. particle size distribution, flowability, spreadability) and post-processing (e.g. heat treatment, machining). Structure includes chemical composition, crystallographic microstructure (e.g. phase composition, grain size and shape, texture, dislocations), residual stress, internal defects (e.g. entrapped gas porosity, lack-of-fusion voids), and external defects (e.g. surface roughness from sintered powder and melt flow). F&F properties of interest identified during the workshop include high-cycle fatigue (HCF), low-cycle fatigue (LCF), linear elastic fracture toughness (KIc), elastic-plastic fracture toughness (J-int), fatigue crack growth rate (FCGR), and impact toughness (Charpy).
In addition to the investigation of PSPP relationships in metal AM F&F, another need identified during the workshop that will be addressed in this project is evaluation of F&F mechanical test methods. This work will start with determining applicability of standard-sized test specimens and existing F&F test methods for metal AM. However, it is likely that this work will include development of sub-size specimen F&F test methods to address the known anisotropy in metal AM.
Additional needs identified during the workshop may provide areas for future expansion of the scope of the current metal AM F&F project. Participation in Integrated Computational Materials Engineering (ICME) efforts building toward rapid qualification is one potential area of future work for this project. Another strong candidate is development of predictive design tools (e.g. exceedance curves informed by critical flaw size measurements).
- Organized AM F&F workshop to identify AM metal fatigue and fracture needs and published workshop findings
- First measurements of residual stress for electron beam melted (EBM) titanium alloy (Ti-6Al-4V)
- Contributions toward traditional AM qualification framework
- Nikolas Hrabe, Thomas Gnäupel-Herold, Timothy Quinn. Fatigue properties of a titanium alloy (Ti–6Al–4V) fabricated via electron beam melting (EBM): Effects of internal defects and residual stress. Int. J. Fat. 94 (2017) 202-210
- Nikolas Hrabe, Nicholas Barbosa, Steve Daniewicz, Nima Shamsaei. Findings from the NIST/ASTM Workshop on Mechanical Behavior of Additive Manufacturing Components. NIST Advanced Manufacturing Series 100-4. (2016) (https://doi.org/10.6028/NIST.AMS.100-4)
- Mohsen Seifi, Michael Gorelik, Jess Waller, Nik Hrabe, Nima Shamsaei, Steve Daniewicz, John J. Lewandowski. Progress Towards Metal Additive Manufacturing Standardization to Support Qualification and Certification. accepted by JOM (2017)
- Enrico Lucon, Nik Hrabe. Instrumented impact tests on miniaturized Charpy specimens of additively manufactured (AM) Ti6Al4V. NIST Tech Note 1936 (2016) (https://dx.doi.org/10.6028/NIST.TN.1936)
- Edward Garboczi, Enrico Lucon, William Grell, Z Loftus, Maciej Kumosa, E Solis-Ramos, Paul Predecki, E Clark. Effects of Powder Oxidation on Impact Toughness of Electron Beam Melt Ti-6Al-4V. submitted to Acta Mater. (2017)
- Nikolas Hrabe, Timothy Quinn. Effects of processing on microstructure and mechanical properties of a titanium alloy (Ti-6Al-4V) fabricated using electron beam melting (EBM), part 1: Distance from build plate and part size. Mat. Sci. & Eng. A. 573 (2013) 264-270
- Nikolas Hrabe, Timothy Quinn. Effects of processing on microstructure and mechanical properties of a titanium alloy (Ti-6Al-4V) fabricated using electron beam melting (EBM), part 2: Energy input, orientation, and location. Mat. Sci. & Eng. A. 573 (2013) 264-270
NRC Post-Doc OPPORTUNITIES (you will leave NIST site when selecting these links)
Fatigue and Fracture of Metallic Materials Processed via Additive Manufacturing