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ACS AMA: We’re James Patterson and Shawn Averett from Brigham Young University. Ask us anything about using lasers for non-destructive testing of structures.
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ACS AMA Hello, Reddit! I’m Prof. James E. Patterson of Brigham Young University. I completed my B.S. and M.S. degrees in chemistry at BYU, and my Ph.D. in physical chemistry at the University of Illinois at Urbana-Champaign. After a postdoctoral fellowship at the Institute for Shock Physics at Washington State University, I began my appointment at BYU in 2007. Most of my work has focused on the use of nonlinear optics (sum-frequency generation and second harmonic generation) to the molecular-level investigation of materials and interfaces. A common theme has been to understand the molecular response of materials, such as polymers and metals, to mechanical, thermal and chemical stress. Hi Reddit! My name is Shawn Averett, and I am finishing a Ph.D. in physical chemistry at BYU. As a graduate student I use sum frequency generation spectroscopy to investigate the surface response of materials to mechanical deformation. I am also working to better understand the nature and origin of nonresonant sum frequency generation. Prior to graduate school I taught high school science and engineering for four years. Our team recently presented research about a new laser-based technique we’ve developed to reveal hidden damage in metals at the 253rd American Chemical Society National Meeting & Exposition. Non-destructive testing (or NDT) offers the ability to check the structural integrity of an airplane, ship, or bridge without having to dismantle it or remove any material for testing, which could further compromise the structure. Current NDT techniques include X-ray imaging, which can detect microscopic cracks in metals. This method is expensive, requires shielding from the X-rays, and is difficult to use in the field. Other NDT techniques give less precise results and require highly trained technicians. Our approach uses a spectroscopic method known as second harmonic generation (SHG), which alters the wavelength of the light. We start with shining green laser light onto a metal sample. Through SHG, the metal converts some of the incoming light into ultraviolet light, which bounces back from the metal along with the remaining green light. By measuring this conversion, we can detect if the metals have been changed by some form of stress. We’ve found this technique can distinguish between metal samples that are still sound and those that have been irreversibly damaged and require replacing. Our method can detect damage invisible to current NDT, and because SHG is extremely sensitive to material changes it may give earlier warning of danger for damage that current NDT can detect. You can learn more about this research in this video. Ask us anything about our new approach for non-destructive testing and its applications for detecting damage. We’ll be back at 11am EDT (8am PDT, 3pm UTC) to answer your questions! -acs edit