1. 일 시 : 2007년 9월 19일(수) 13:30-14:30

2. 장 소 : 신공학관 301동 117호 세미나실( Starbucks coffee is served. )

3. 제목 및 연사
◎ 제 목 : Mechanochemical Aspects of Shock-Induced Chemical Reactions in Powders:
Time-Resolved Impact Experiments and Meso-Scale Numerical Simulations

◎ 연 사 : Professor Naresh Thadhani, Associate Chair, School of Materials Science and Engineering,Georgia Institute of Technology(Joint Appointment in Woodruff School of Mechanical Eng.)

4. 내 용 :
The dynamic application of high pressure via impact loading, or more appropriately shock-compression, generates unique and non-equilibrium states that allow studies of materials in thermodynamic regimes not accessible by any other method. Most intriguing is the possibility of shock-wave initiation of highly-exothermic chemical reactions in powder mixtures in the microsecond time-scale of the high-pressure shock state. Time-resolved impact experiments performed on intermetallic-forming mixtures of powders of varying initial packing densities and particle morphologies have indeed shown evidence of shock-initiation of chemical reactions. Occurrence of reaction has been inferred on the basis of compressibility changes and shock-velocity increases corresponding to those calculated based on assumed kinetics, and constant volume or constant pressure approximations to account for the heat of reaction. The influence of the characteristics of starting powder mixtures on their densification response, and the type and extent of configurational changes between reactants has also been revealed by experiments. However, the mechanisms responsible for reaction initiation and product formation, and the correlation of the extent of reaction and type(s) and amount(s) of reaction products formed with measured changes in shock velocity and/or shock compressibility, have not been conclusively demonstrated. Meso-scale numerical simulations of shock-wave propagation through discretely represented powder mixtures can be used to approximate the configuration of reactants participating in the reaction based on a pre-defined stress, strain, or temperature criterion, and therefore, determine the product and its extent under a given set of loading conditions. We have used such meso-scale numerical analysis performed on actual micrographs to probe configurational changes and reaction mechanisms, considering processes such as forced or turbulent flow and/or fracture and dispersion of reactant powders of dissimilar properties or morphologies. The understanding being developed can be used for influencing the reaction initiation thresholds and energy release characteristics for the design of advanced energetic materials. In this presentation, mechanochemical aspects of shock-compression of reactive powder mixtures leading to “shock-induced” chemical reactions will be discussed on the basis of time-resolved impact experiments and meso-scale discrete particle simulations.

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5. 약 력 :
He joined the faculty at Georgia Tech, in 1992, after completing two years of postdoctoral research at Caltech, and spending 6 years at his alma mater at New Mexico Tech. His current research is in high-pressure shock-induced phase transformations, high-strain-rate mechanical properties, deformation and strengthening mechanisms, and processing of nanocrystalline and metastable materials with structural, energetic, and functional properties. Dr. Thadhani is author of about two hundred publications in journals and proceedings, including several authoritative reviews and book articles. He is key reader for Metallurgical and Materials Transactions, Associate Editor of Shock Waves Journal, President of the Alpha Sigma Mu, a Materials Honor Society, and a fellow of ASM International.

6. 문 의 : 기계항공공학부 여재익 교수 (☏ 880-9334)