CMMI-EPSRC: Quantitative Characterization of Mission Critical Microstructures of Engineering Metals with Diffusive Ultrasound

This award is funded through the NSF Directorate for Engineering - UKRI Engineering and Physical Sciences Research Council Lead Agency (ENG-EPSRC) Opportunity, a collaborative solicitation between NSF and the Engineering and Physical Sciences Research Council (EPSRC) of United Kingdom Research and Innovation (UKRI). It will fund research that enables reliable assurance of safety-critical metal components, for example those used in the aerospace and nuclear power industries, thereby promoting the progress of science, and advancing the national prosperity and welfare. Thermomechanical processes that occur during manufacturing of metal parts result in grain microstructures that dictate strength, fatigue life, and creep and corrosion resistance. It is essential that these microstructures be carefully controlled during production and non-destructively characterized once a component is finished. Although ultrasound technology is the only practical means to access internal material properties, it has seen very limited industrial usage, as accurate interpretation of ultrasonic signals in terms of such microstructure remains an unsolved problem. Alternative techniques that rely on destructive testing of sacrificial samples after elaborate preparation are recognized as inadequate, as evidenced for example by failures of aircraft engines. This project will overcome these shortcomings by advancing a new method of interpreting ultrasonic wave scattering due to microstructural texture and inhomogeneities, potentially revolutionizing the use of non-destructive, contactless, ultrasonic characterization throughout production and in service, at elevated temperatures and on complex shapes. This capability will support the growth of new advanced manufacturing processes, whose vital need of quality control and assurance on complex geometries is currently only partially met. Collaboration with Dr. Bo Lan of Imperial College London will provide opportunities for international research exchange and training of postdoctoral scientists, as well as routes for industry outreach facilitated through the United Kingdom Research Centre in Nondestructive Evaluation.This research aims to make fundamental contributions to the development of an ultrasonic diffuse wave field method that enables volumetric characterization of mission critical microstructure of engineering metals. It will achieve this objective by designing and calibrating experimental transduction mechanisms and signal processing techniques for extracting the full Green’s tensor from the diffuse wave field on different sample geometries, and relating properties of diffusivity, attenuation, and scattering to microstructure-related properties. Further, a general multiple scattering theory will be derived in combination with radiative transfer theory, to account for the effects of texture and microstructures on coherent waves and to describe the incoherent wave diffusion. Computational models of such wave diffusion will be validated against experimental results and used to construct a knowledge database of quantitative linkages between the diffuse wave field and material microstructures. Finally, a robust inversion method will be developed for deducing critical microstructural properties from the diffuse wave field data.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.