Matlack uses ultrasonic NDE to analyze additively manufactured metal
New research from Assistant Professor Katie Matlack and graduate student Changgong Kim, published in Additive Manufacturing, focuses on ultrasonic non-destructive evaluation of additively manufactured metal. The journal addresses advancements and contributions to additive manufacturing, which is a highly multidisciplinary field.
Their paper, “Ultrasonic nondestructive evaluation of laser powder bed fusion 316 L stainless steel,” was published in collaboration with mechanical engineering colleagues at Auburn University. The goal of the study was to relate microstructures, mechanical properties, and print settings of laser powder fusion additively manufactured materials using non-destructive evaluation (NDE) techniques.
Matlack, who runs the Wave Propagation and Metamaterials Laboratory in MechSE, initiated the project with collaborator Professor Xiaoyuan Lou at Auburn. “He's an expert in additive manufacturing and our group’s expertise is on ultrasound and ultrasonic characterization. So we came up with this idea of using ultrasound to look at some of the samples that they have been printing, because we were interested in understanding how ultrasonic waves propagate in these samples, and developing an NDE method for these parts,” she said.
The researchers at Auburn printed the blocks out of steel using laser powder bed fusion techniques. Additively manufactured metals have unique microstructures that vary depending on the printing processes. By varying different printing parameters and using X-ray computed tomography to create a 3D reconstruction of the microstructure of the additively manufactured part, the microstructure and defect properties, like texture and porosity, of the printed parts can be assessed.
The printed blocks and their models were then sent to UIUC where Kim evaluated the microstructure using ultrasonic NDE. “Ultrasound interacts with those unique microstructures and the result of those interactions can be related to mechanical properties,” said Kim.
Ultrasonic NDE uses ultrasonic waves that travel throughout a material; these waves are affected by the microstructure of the material, for example their propagation speed changes, and can be used to detect defects or discontinuities. The results in their paper showed that the ultrasonic velocity is sensitive to changes in texture and porosity in the additively manufactured samples, suggesting that this NDE method could be used to characterize the initial printed state of these materials.
Many current methods of evaluating additively manufactured parts are destructive, which can be costly and wasteful. Using non-destructive methods like ultrasonic measurements allows for a strong analysis of the parts without destroying them. “The properties [in additively manufactured parts] are very sensitive to different parameters that you use in the printing process, so it becomes cost-prohibitive to just print all these parts and destructively test them,” said Matlack.
Kim and Matlack hope to continue this research in the future, looking at the effects of variation in more printing parameters as well as other types of additive manufacturing.