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SUMMARY:MechE Colloquium: Deciphering Shock-Induced Amorphization in Ultra
 hard Ceramics
DTSTART:20210921T121500
DTEND:20210921T131500
DTSTAMP:20260508T053606Z
UID:be23c7c63a9ce0076d8a82daafe3d1aa33b0feb50a0322d93fbedb8e
CATEGORIES:Conferences - Seminars
DESCRIPTION:Prof. Ghatu Subhash\, Laboratory for Dynamic Response of Advan
 ced Materials (LDRAM)\, Mechanical and Aerospace Engineering\, University 
 of Florida\nAbstract:\nThe hardest materials for engineering applications 
 include diamond (HV>100 GPa)\, cubic-boron nitride (HV=60-75 GPa)\, boron 
 carbide (HV>30 GPa)\, and boron suboxide (HV>40 GPa). While the former two
  have diamond structure with a density of 3.5 g/cm^3\, the latter two have
  icosahedral structure with a density of 2.5 g/cm^3. These icosahedral sol
 ids exhibit high compressive strength (in excess of 5 GPa) and better ther
 mal and chemical stability than diamond-like structures. These properties 
 favor them in applications including protective armor\, abrasives and wear
  resistant materials\, machine tool bits\, etc. However\, under high-press
 ure deformation\, such as those encountered in indentation and ballistic i
 mpact\, these boron-rich solids undergo a deleterious deformation mechanis
 m referred to as ‘amorphization’ (loss of crystalline order). Mystery 
 has surrounded the appearance of new peaks in Raman spectrum of amorphized
  boron carbide (B4C)\, but to-date\, no convincing explanation exists on i
 ts origins. This mechanism has been responsible for reduced hardness and n
 onrealization of the intrinsic potential of B4C. In this research\, the pr
 essure-dependent response of the amorphized B4C is investigated using expe
 riments\, microscopy\, Raman spectroscopy\, and molecular dynamics simulat
 ions. We propose a new rationale towards deciphering the amorphization beh
 avior centered on atomic interactions in the amorphous islands. Quantum me
 chanical simulations (DFT and DFPT) are utilized to understand the stress 
 dependence of Raman spectra\, while results from molecular dynamics (MD) s
 imulations of volumetric compression and shock loading are used to underst
 and thermodynamic aspects of amorphization. The derived pressure-volume re
 lationship (Hugoniot) has been found to match well with reported experimen
 tal data. The consequences of amorphization are addressed in relation to v
 olumetric change in the nanosized amorphized islands and the stress state 
 in the surrounding regions. Finally\, new insight into quasi-longitudinal 
 and quasi-transverse wave propagation in single crystal B4C are investigat
 ed through MD simulations to further unravel the relationship between temp
 erature rise\, amorphization and Hugoniot behaviors up to a pressure level
  of 100 GPa. These investigations underline the power of computational met
 hods to unravel the physics in complex shock experiments.\n\nBio:\nProfess
 or Ghatu Subhash obtained his PhD from University of California San Diego 
 in 1991 and conducted his post-doctoral research at California Institute o
 f Technology during 1992-93. He is currently Newton C Ebaugh Professor in 
 Mechanical and Aerospace Engineering department at University of Florida (
 UF). His research focusses on dynamic multiaxial behavior of advanced cera
 mics\, metals\, composites\, gels and biological materials. He has develop
 ed novel experimental methods which have been patented and widely used amo
 ng the high strain rate experimental mechanics community. He has coauthore
 d 205 peer reviewed journal articles (>8600 citations in Google Scholar\, 
 h-index=49)\, 85 conference proceedings\, 2-books\, and 6 patents. He has 
 poneered the concept of ‘Dynamic Hardness’ which is patented in US and
  Canada\, and widely used by researchers to quickly evaluate the material 
 resistance to dynamic loads. Most recently\, he has developed a novel ‘m
 illipede bar’ which has many applications in construction and machine to
 ol industry. Dr. Subhash has graduated 35-PhD students. For his exceptiona
 l dedication to graduate education he was awarded 2020-2021 Doctoral Disse
 rtation Advisor/Mentoring Award by the University of Florida. He is a Fell
 ow of three societies: ASME\, Society for Experimental Mechanics (SEM)\, a
 nd the American Ceramic Society. He serves as the Co-Editor-in-Chief of Me
 chanics of Materials journal. Dr. Subhash has received numerous awards fro
 m professional societies: SEM Lazan Award (2021) for innovative contributi
 ons to experimental mechanics\, SEM ‘Frocht Award’ (2018) for outstand
 ing achievements as an educator\, ‘Best Paper’ award - ASME Journal of
  Engineering Materials and Technology\, ‘Significant Contribution Award
 ’ from the American Nuclear Society\, ‘Technology Innovator Award’ f
 rom UF\, ASME Student Section Advisor Award\, ‘SAE Ralph R. Teetor Educa
 tional Award’\, and ‘ASEE Outstanding New Mechanics Educator’ award.
  He is currently on sabbatical at EPFL and enjoying the beautiful Lausanne
  and Switzerland.
LOCATION:BM 5202 https://plan.epfl.ch/?room==BM%205202 https://epfl.zoom.u
 s/j/65093257313
STATUS:CONFIRMED
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