Two Early Career Awards for Investigating Fracking

image: Microstructural features of laser powder bed fused 316L stainless steel specimens: (a) Specimen design for crack propagation test and its relation to construction, (b) crystallographic planes and (c) orientation of the subgrain dislocation lattice on three coordinate planes. Model courtesy of Yao Fu.
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Credit: Virginia Tech

Watching a 3D printer at work can be fascinating. Guided by a digital data file, the machinery moves rhythmically back and forth, steadily adding layer after layer of material until a custom three-dimensional shape begins to take shape.

Additive manufacturing technology is booming, and it’s easy to see why. The process produces geometrically and compositionally complex parts using less energy and material waste than traditional manufacturing processes. Prototyping is much cheaper and small series are faster and cheaper. The technology is capable of providing on-demand manufacturing and repair capabilities whether the user is on land, at sea or even in space.

As with any new technology, there is still much to learn about its potential uses and opportunities for innovation. This material, whether it is based on polymer or metal, undergoes a lot of stress during the manufacturing process. As each new layer is applied, the material quickly solidifies and undergoes complex thermal cycles throughout the process. These factors can lead to unique microstructural features and defects in the final part.

Yao “Yolanda” Fu of Virginia Tech is interested in learning more about these unique microstructural characteristics and their effects on fracture and cracking in a corrosive environment throughout the life of the material.

Fu, assistant professor at Kevin T. Crofton Department of Aerospace and Ocean Engineering, is the recipient of two prestigious research grants to study the environment-related behaviors of additively manufactured metals. This year, she received an award from the National Science Foundation’s Early Career Development Program (CAREER), as well as an award from the Young Investigator Program (YIP) from the Office of Naval Research.

“Corrosion Fatigue Behavior of Additive Treated Metal Alloys”

With his $594,948 CAREER grant from the National Science Foundation, Fu seeks to answer two relevant unknowns about additively fabricated metals: how the fatigue behavior of these alloys differs from that of their conventional counterparts in normal and corrosives and how the additive-made alloy is unique. the microstructures contribute to these behavioral differences.

Using both experimental and computational methods, Fu and his research team will examine the behavior of additive manufactured metals under various conditions in the new Materials and Manufacturing Design Laboratory and the Aerospace Structures and Materials Laboratory at Randolph Hall.

To better understand the strengths and weaknesses of the material compared to traditional metal alloys, the team will study how the material reacts during tensile/compression tests and high-cycle fatigue tests. After the initial round of experimentation, the team will then perform similar tests in corrosive environments and take a closer look at environmental factors, such as variations in temperature, humidity or salinity.

Knowledge gained from Fu’s research will guide the design and manufacture of additively manufactured parts, helping to extend their life by limiting causes of fatigue failure and reducing financial losses from corrosion damage.

“Microstructural Effects on Environmentally Assisted Cracking of Advanced Manufactured Stainless Steels in the Marine Environment”

Fu also received a $509,878 grant from the YIP of the Office of Naval Research. While this project also focuses on additively manufactured alloys, Fu will specifically look at stainless steels often used in marine environments. It will also delve into the performance of hybrid structures composed of partly printed and partly conventionally processed parts.

Additive-made 316L stainless steel is particularly attractive for naval engineering and marine applications. Significant exposure to salt water can be unforgiving on metals as corrosion is inevitable. Fu and his team will take a closer look at hybrid conventional and printed stainless steel structures that contain a number of varied printed layers and evaluate how their environmentally assisted cracking behavior differs from that of their conventional or bulk counterparts. In addition, Fu will investigate how material solidification texture and grain directionality have a direct effect on corrosion-related properties over a wide range of temperatures.

Fu will study corrosive behaviors in sodium chloride solutions with concentrations close to that of seawater. She plans to perform electrochemical analysis of corrosion characteristics, stress corrosion cracking, polycyclic fatigue and crack propagation tests in a corrosive environment. Fu will also characterize the microstructural characteristics before and after cracking, as well as carry out multiphysical modeling of mechanical electrochemical processes to understand the link between microstructure and electrochemical/mechanical properties.

By understanding the underlying mechanisms that lead to corrosion, cracking and failure of alloys made with additives, in normal, humid or saltwater environments, researchers will be better equipped to control the characteristics and most critical defects during the manufacturing process. As an added benefit, the multiphysics computational framework established by Fu and his team will help to reduce the cost of designing and manufacturing corrosion-aware materials, and will make a significant contribution to the corrosion control of the Office of Naval Research and related technology.

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