Research Seminar: Statistical Elastodynamics and Real-Time Ultrasonic Characterization of Laser Generated Melt Pools

Abstract:

In heterogeneous materials, the local displacement on the scale of the heterogeneity can be much different from the global displacement requiring careful consideration of length scales. The same consideration is required when an ultrasonic wave generates the displacement in the heterogeneous material. In this case, it is common to model the statistics of the wave displacement, i.e., the mean displacement field and higher-order statistical moments of the mean field. Both quantities provide invaluable information about the material heterogeneity for characterization purposes. In the first part of this seminar, the solutions for the mean field and its covariance are derived for the case of ultrasonic propagation in polycrystalline media. Instead of highlighting the results from the perspective of traditional ultrasonic nondestructive evaluation, it will be shown that the derivation is unified with the traditional elastic homogenization theories in the quasi-static limit including the Hashin-Shtrikman bounds and self-consistent theory. From this perspective, the elastodynamic theory and associated ultrasonic measurements can be linked to recent advances in microstructural sensitive material design. Future breakthroughs in this research could enable both microstructural sensitive quality and process control along with microstructural customization capabilities in advanced manufacturing processes including additive manufacturing (AM). The second part of the seminar will experimentally consider the scattering of ultrasound from a laser-generated melt pool on the surface of a stainless steel AM build plate. Pitch-catch measurements that capture out-of-plane scattering components from the solid-melt pool interface were conducted in real-time during melt pool formation and resolidification. The results demonstrate the potential of ultrasound to: (1) track and characterize laser generated melt pools and (2) measure the temperature distribution in a plate heated by a laser. Future research plans involving characterization of melt pools generated from a non-stationary laser and integration of ultrasound technology into an AM system will be discussed.

Biography:

Chris is an Additive Manufacturing & Nondestructive Evaluation Research Engineer of Bennett Aerospace and the U.S. Army Research Laboratory at the Aberdeen Proving Ground where he focuses on developing nondestructive characterization tools to enable Army-specific additive manufacturing capabilities aimed at enhancing Army agility and readiness. His interests surround the theme of ultrasonic wave propagation in heterogeneous materials, which include nondestructive evaluation, scattering theory, elasticity, homogenization theory, metamaterials, nonlinear ultrasound, diffusion, resonant ultrasound, correlation functions, anisotropy, and fractional calculus. He has authored or co-authored 23 articles since 2015 on these topics. He obtained a PhD in Mechanical Engineering and Applied Mechanics from the University of Nebraska-Lincoln under the advisement of Prof. Joseph A. Turner in 2014.

For additional details, call Diane K. Bierly at 814-863-6491.

 

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