报告摘要：

Nearly all materials have one or more levels of spatial heterogeneity. Prediction of their mechanical response at the macroscale clearly depends on an understanding of the local behavior for which quantitative measurement approaches are needed. This presentation will review several different techniques that address specific microstructures of various materials. The first half of the presentation will focus on the propagation of ultrasound through polycrystalline media. The complex heterogeneous composition causes distortion in the amplitude and phase of the ultrasonic wave as it propagates. This distortion can limit nondestructive evaluation (NDE) of important defects if the signal-to-grain noise ratio drops below a critical value. On the contrary, the scattered waves contain information about the microstructure (e.g., grain size, grain elongation, multiple phases) which can be used to quantify it. In the second half of the presentation, synthetic polymers, bio-polymers, and concrete will be discussed with respect to their thermomechanical behavior at the micro- and nano-scales. Nanoindentation and atomic force microscope methods can help quantify this behavior, but knowledge of each measurement system requires careful calibration. The importance of such measurements for predictive plant growth models will be highlighted. Finally, prospects for future research associated with NDE, microstructure characterization and modeling will be discussed with respect to metal additive manufacturing (AM), concrete, and plant cell walls.

报告人简介：

Dr. Joseph A. Turner
Robert W. Brightfelt Professor of MME, Mechanical and Materials Engineering
University of Nebraska-Lincoln, Lincoln, NE 68502. E-mail: jaturner@unl.edu

Joseph A. Turner is currently the Robert W. Brightfelt Professor of Mechanical and Materials Engineering at the University of Nebraska-Lincoln (UNL). He received his B.S. (Eng. Sci.) and M.Engr. (Eng. Sci. Mech.) degrees from Iowa State University in 1988 and his Ph.D. (Theoretical and Appl. Mech.) from the University of Illinois at Urbana-Champaign (UIUC) in 1994. After a postdoctoral experience at UIUC, he served as an Alexander von Humboldt Postdoctoral Fellow at the Fraunhofer Institute for Nondestructive Testing (IZFP) in Saarbrücken, Germany before joining UNL in 1997. He is a Fellow of the Acoustical Society of America and recipient of the Wilhelm Bessel Forschungspreis from the Alexander von Humboldt Foundation (2014). His research interests are associated with characterization of a variety of materials and their microstructures using ultrasound/acoustics, nanoindentation, and atomic force microscopy with analytical, numerical and experimental components.

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