Tuesday, March 15, :10p.m. Featheringill Hall Room 138 “Atomistic to continuum homogenization method And Bonding super-hard ceramics to polymers” DR. RANGANATHAN PARTHASARATHY Postdoctoral Researcher TSU Nanomaterials Research Lab Tennessee State University ABSTRACT Atomistic to continuum homogenization method The method of granular micromechanics involves discrete-to-continuum homogenization and has been used to incorporate the effects of micro-scale inter-particle interactions on the macro-scale deformation and failure of the material. These effects include inter-particle contact, grain interlock, fiber buckling, liquid bridge, fluid pressure, swelling, and viscoelasticity. Several of these are associated with interactions at atomic scale; thus potentials developed for use at this scale are highly beneficial for modeling. We present an extension of the granular micromechanics approach for homogenization from atomic to continuum scale, which enables direct incorporation of atomic-scale interactions in the granular micromechanics framework. The energetic contribution of the atomic vibration to the potential energy is captured using the second moment of atomic displacements as a continuum field in addition to first and higher spatial orders of strain. A local description is retained in contrast to the phonon gas approach for finite temperature atomistic to continuum homogenization methods, where the local mapping is lost due to diagonalization of the dynamical matrix. In addition, our approach also obviates the necessity for the canonical transformation generator function, which is used to derive the traditional form of the virial stress. The entropic contributions to the stress are calculated separately. The quasi-harmonic approximation is not necessary in this case since the moments of deformation can be extended up to any order using Taylor series. Such features make the method especially attractive for investigating high temperature deformation of anharmonic materials. We demonstrate our method on the results for room temperature uniaxial deformation of fcc Aluminum using molecular dynamics. We show anisotropy and symmetry of the vibrational moments with deformation and compare the stress with the canonical transformation approach. Bonding super-hard ceramics to polymers Super-hard ceramics are used to coat polymers for wear resistance. Bond-strength of the ceramic to the polymer substrate is a limiting factor in load-bearing applications. We use a modified version of ASTM D4541 to test the bond strength between Teflon substrate and Rhenium Diboride (ReB 2 ), a superhard coating prepared using confined-plume chemical deposition at room temperature and pressure at the Lukehart Lab. Results indicate a) increased bond-strength with chemical and mechanical surface treatment b) brittle failure and c) microstructure of deposited ReB 2. BIOGRAPHY Dr. Parthasarathy received his PhD in Bioengineering with honors from the University of Kansas (KU) in He earned his MS degree in Civil Engineering from the University of Missouri-Kansas City (UMKC) and B-Tech in Civil Engineering from the Indian Institute of Technology-Madras with a minor in Applied Mechanics. Dr. Parthasarathy’s research interests include micromechanics, molecular dynamics, multiscale modeling and experimental characterization.