Dr Kyriakos Kourousis from UL discusses his current research into metal additive manufacturing and the work of the Metal Plasticity and Additive Manufacturing Group at UL.
Dr Kyriakos Kourusis is associate professor of aeronautical engineering at the University of Limerick (UL), and director of postgraduate research and education in the university’s Faculty of Science & Engineering. He also leads UL’s Metal Plasticity and Additive Manufacturing Group.
Kourusis joined UL’s School of Engineering 12 years ago, and prior to his academic career, he spent more than a decade as an aeronautical engineer in the Hellenic Air Force working on aircraft maintenance, airworthiness and structural integrity – experience he says now shapes his research and teaching.
At UL, he teaches topics on aircraft systems, airworthiness and operational engineering.
Regarding his current research, Kourousis says that his work focuses on two things: how metals behave when they are repeatedly loaded, which leads to permanent deformation – “what engineers call plastic plasticity” – and how to make and trust 3D printed metal parts (metal additive manufacturing), “especially in those loading conditions that cause plasticity”.
“In simple terms, we test metals, study their microstructure, build computer models that predict how they will perform over time, and use those models to predict how permanent corrosion builds up during their operation,” he told SiliconRepublic.com.
“Localized permanent deformation (plasticity) is the source of fatigue in metals. My work is in traditional and 3D printed metals.”
Here, Kourusis tells us about his work and offers a glimpse into the world of 3D printed materials and aerospace engineering.
Why is your research important?
As 3D printed metal parts move from prototypes to actual aircraft and machines, we need to predict their behavior with confidence. Test data and models help engineers design components that won’t crack or fail prematurely, and help industry and regulators build the evidence needed to obtain certification. In short, better predictions mean safer, simpler, more effective products.
Also, from a sustainability point of view, the use and reuse of powder in additive manufacturing of steel offers a significant advantage over other (traditional) manufacturing processes. However, with each recycling cycle, the recycled powder changes its composition and overall ‘quality’, which can affect the manufactured parts, especially regarding their plastic behavior.
What was the most surprising/interesting observation or discovery you made as part of this research?
Another important finding is how 3D printed metals can be oriented and what causes this orientation. For example, we have shown that changing the shape of the construction and the processing of post-3D printing of metal parts through heat treatment can significantly change how they stretch and how they are produced. We have seen similar results in 3D-printed titanium, specifically Ti‑6Al-4V, which is widely used in the aerospace and biomedical industries.
We also found that even low-cost metal 3D printing routes (such as material/composite filament fabrication) show clear links between print settings and machine performance, useful for small/medium-sized companies exploring affordable metal additive manufacturing.
What are some common misconceptions about your research area?
3D printed metals are not ‘just like’ traditional (fabricated) metals. The layer-by-layer process creates a directional ‘character’, so the properties change with the construction process, which is clearly shown in our steel and titanium work. The signing process is important. Printing can leave small pores (lack of integration or keyhole) and lock in residual stress; A scanning strategy for repair and strength is helpful, but these factors still drive plasticity and fatigue if not controlled.
An interesting debate I have with colleagues working in material science is that a 3D printed material may appear to have the same characteristics at the microscale, but high-scale errors caused by solid melting and re-melting can lead to a non-homogeneous part with different mechanical properties at different loading points (mechanical anisotropy).
Post processing can close the loop. Aging/reducing pressure and especially isostatic pressure (HIP) homogenises the microstructure and pores of the sealant, increasing ductility and fatigue, although the results depend on the built quality and available budget. The main goal of the manufacturing industry is to make 3D printing not only accurate and consistent but also affordable, and we realize that there is a lot of work to be done there.
What has been the most important development in your field since you began your academic career?
The biggest change is the convergence of accessible metal 3D printing machines with advanced, physics-based modeling.
At UL, a milestone was receiving the GE Concept Laser Mlab Cusing R metal 3D printer with a GE Additive award. Unlike other facilities in Ireland, our 3D printer is hosted on an industrial site, through a partnership agreement with our partner, Croom Medical. Our students and researchers can test ideas under real-world conditions, while both UL and Croom Medical take advantage of this strategic partnership.
Can you tell me a little about the Metal Plasticity and Additive Manufacturing Group at UL?
Our research group leads the research work on metal additive manufacturing at UL.
Our work is built around two main strands: metal plasticity modelling, where we turn lab data into reliable models of how metals actually bend; and the production of metal additives, where we study and develop metals such as titanium and steel, translating the results into practical construction and treatment guidelines. Current projects and predictions of informed yield of the physics of 316L, laser powder bed fusion (a widely used additive manufacturing method for metals) process development, and corrosion-cyclic plasticity topics for aerospace grade alloys.
Interesting recent work involved showing that, by carefully resetting the laser power, scan speed and hatch spacing, we can go from normal thin layer settings to thick layers in laser powder bed fusion of aerospace grade titanium, while keeping the process stable with dense parts. Led by one of our medical researchers who also works with Croom Medical, research has shown that those thick structures bring strength and ductility on par with conventional settings, showing that productivity can be increased without automatically compromising the performance of the material.
Most importantly, after standard vacuum heat treatment and hot isostatic pressure, the components satisfy the relevant industry standards, which point to a practical approach to high output that still meets certification expectations.
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