Strain mapping and stability in nanomaterials by synchrotron probe
Professor Thomas Tsakalakos
Materials Science and Engineering Department Rutgers University, Piscataway, NJ
Nanotechnology is widely agreed to be the research focus that will lead to the next generation of breakthroughs in science and engineering. While the general principles are clear, systematic and comprehensive studies of the effects of processing and the resultant evolution of structure on the overall mechanical properties, performance and thermal stability, under complex loading conditions, have not been performed in sufficient depth. In this presentation, Prof. Tsakalakos will discuss advanced techniques to measure the residual stress tensor in nanostructured materials as a function of depth, directly and accurately, using synchrotron light source, i.e. energy-dispersive x-ray diffraction (EDXRD) methods. The residual stress profile will be correlated to deformation and fracture processes of nanomaterials and coatings. Systematic and well-controlled experiments aimed at investigating monotonic-cyclic deformation and failure across nanometer to macroscopic length scales are discussed in carefully chosen model systems. Specific questions to be resolved include – What is the role of processing-induced and mismatch-induced residual/internal stresses on the overall mechanical stability of nanomaterials? How do diffusion or grain boundary processes determine the elastic, plastic, creep and superplastic behavior of nanomaterials? What are the essential ingredients of a unified approach to life prediction of nanomaterials by strain mapping at the macro-, meso-, and nano-scale? It will be shown that the EDXRD mapping of a three-dimensional space distribution of local residual stresses at the crack tip, mapping of the plastic zone, as influenced by the combined chemical and stress effects, is a promising step toward life predictions of alloys. Understanding the stress distribution about the environmental stress crack tip is critical to modeling fatigue crack growth in a hydrogen embrittlement environment. The phase field microelasticity theory in conjunction with the time-dependent Ginzburg–Landau equation will be introduced for assessing the long-range strain- induced interaction in stress corrosion cracking. This work is supported of the Office of Naval Research under ONR Grants N000140410194 and N00014-02-1-0772.
Dr. Thomas Tsakalakos is a (Distinguished) Professor II in the Department of Materials Science and Engineering at Rutgers University. He joined Rutgers in 1977 after receiving his Ph.D. from Northwestern University. His research has focused on nanostructured and multilayer materials with an emphasis on interfacial phenomena in magnetic superlattices, mechanical behaviors, phase transformations, phenomena such as nonlinear diffusion and spinodal decomposition, processing of magnetic nano-powders, and ceramic nano-composites. He has used molecular dynamics for modeling the role of solid interfaces on physical properties, and micro mechanics to assess stress induced transformation in ceramic systems. Recent efforts use advanced characterization methods such as synchrotron energy dispersive x-ray diffraction in the National Synchrotron Light Source at Brookhaven National Laboratory to determine microscopic and macroscopic strain distribution in inhomogeneous solids for the analysis of fatigue, fracture, and stress corrosion cracking. Professor Tsakalakos has published over 130 archival articles, edited more than a dozen conference proceedings, and received several research grants including the NSF research creativity award and is currently supported by ONR and DARPA. He is a member of eight professional societies and has held offices in several, including the executive committees of the Materials Research Society, and AIME. He has received NATO awards and organized ten international conferences. He served as the Editor for the journal of Nanostructured Materials (Elsevier), serves on the New Jersey Commission on Science and Technology, and is the Director of the Laboratory for Nanostructured Materials Research (LNMR) at Rutgers-AIMS.