This is a Materials Engineering-based Microstructure Seminar Series, co-hosted with the Mechanical Engineering Department.

The seminar will split into two – with the first half presented by Dr. Rikesh Patel, focusing on what SRAS is, how it works physically and electronically/optically, and how we can get orientation images. The second half presented by Dr. Wenqi Li, who will put emphasis on the materials and shares about how we can get elasticity information from our measurements (SRAS+).

Seminar Abstract:

Advancing Spatially Resolved Acoustic Spectroscopy (SRAS) from Microstructure to Elasticity Imaging

Spatially Resolved Acoustic Spectroscopy has established itself as a powerful material characterization technique capable of imaging the microstructure of a number of engineering alloys and semiconductor materials. The technique non-destructively utilizes laser ultrasonics to robustly, rapidly, and repeatably measure controlled surface acoustic wave velocities – these can be mapped to image material grain contrasts (SRAS). This velocity is linked to the materials’ elastic constants and local crystallographic orientation – as such, by establishing the wave phase velocity through multiple measurements at different directions and utilizing published elastic constants values, the technique is able to extract the crystallographic orientation and map them as inverse pole figures (SRAS+). The cutting-edge research currently being undertaken is in utilizing these measurements, an inverse solver and physical material limitations to determine the elastic constants themselves of both established and newly developed materials (SRAS++). We present our work on the development of the technique over the last few years, and how we have put efforts into improving the image resolution and data capture rate on rough surface specimens.

Dr. Rikesh Patel is an Assistant Professor in the Optics and Photonics Research Group at the University of Nottingham. His research focuses on the design and interfacing of optical sensors and systems for real-world applications. He is developing innovative laser ultrasonic systems for inspecting components made in pioneering advanced manufacturing processes. He has authored 25+ peer-reviewed journal articles and 60+ conference presentations. He has contributed towards awards totalling £4M+.

Harnessing Spatially Resolved Acoustic Spectroscopy (SRAS) ++ for Elasticity Imaging of Materials

Measuring the single-crystal elastic stiffness matrix of polycrystalline materials has important engineering applications. A new method for measuring the single-crystal elastic stiffness matrix of polycrystalline materials is presented in this paper. It builds on the capabilities of SRAS, a laser ultrasound technique for measuring the surface acoustic wave velocity of a material. Combining measurements from multiple acoustic propagation directions it is possible to determine the crystal orientation of the grains. The recent work also determines the elastic constants of polycrystalline materials from the same measurements. The proposed method combines SRAS with an inverse solver to extract both the orientation and elasticity from the SAW measurements. The ability of the solver to extract Cij without a-prior knowledge of the crystallographic orientation comes from solving Cij globally for a multitude of (initially) unknown crystal orientations. The technique demonstrates its capability of measuring the elastic constants of materials with varies crystal structures including Nickel alloy, Titanium, and Tin.

Dr. Wenqi Li is a Senior Research Fellow in the Optics and Photonics Group. She primarily focused on the development of SRAS and has given award-winning talks at international conferences on this subject since 2007. With over a decade of experience in laser ultrasonics, her interests in materials characterisation and acoustic inversion led to the development of orientation imaging functionality of SRAS.