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SUMMARY:Molecular Deformation of Polycarbonate: from Atomistic to Continuu
 m Characterization -   Dr Lili Zhang\, CUED  
DTSTART:20180202T143000Z
DTEND:20180202T150000Z
UID:TALK99877@talks.cam.ac.uk
CONTACT:Hilde Hambro
DESCRIPTION:Transparent amorphous polymers such as polycarbonate (PC) have
  been widely used in structural applications and have been a topic of theo
 retical\, experimental and computational study for several decades. Recent
 ly\, with the rapidly increasing capacity of numerical computing\, molecul
 ar dynamics (MD) simulation has become a powerful tool for the further stu
 dy of material behavior in full atomistic detail. In most cases molecular 
 level motions are key contributors to the observed macroscopic response\, 
 but are not easily obtained experimentally. MD simulation can be used to p
 rovide a picture of these motions\, and thus help elucidate the underpinni
 ng molecular mechanisms during deformation and can\, in some cases\, provi
 de insight into how a material may behave under complex loading conditions
 .\nA relatively large all-atom MD system (containing 198365 atoms) of PC w
 ith a realistic molecular distribution (polydispersity) was built and stud
 ied. The MD system was constructed using the PCFF force field\, which was 
 initially developed for PC. The model was validated and evaluated by compa
 ring the stress-strain responses with a large number of existing experimen
 tal results under various loading conditions. To capture and analyze the m
 olecular motions\, the molecular deformation gradient (using the “MinD m
 ethod”) was calculated for the individual molecules and compared to the 
 bulk deformation. The difference between volumetric\, principal\, and devi
 atoric molecular and bulk deformations was used to illustrate the molecula
 r motions during the different stages of deformation (e.g.\, elastic loadi
 ng\, plastic flow\, and hardening).\nThis work employs our newly developed
  tools to quantify and characterize the molecular mechanisms underlying th
 e response of PC to various loadings. The procedures can easily be adapted
  to study other polymers and systems with different microstructures.\n\nRe
 ferences\n[1] L. Zhang\, J. Jasa\, G. Gazonas\, A. Jérusalem and M. Negah
 ban. Extracting continuum-like deformation and stress from Molecular Dynam
 ics simulations. Computer Methods in Applied Mechanics and Engineering\, 2
 83:1010-1031\, 2015. \n[2] Z. Zhang\, L. Zhang\, J. Jasa\, W. Li\, G. Gazo
 nas\, M. Negahban. High Fidelity Computational Characterization of the Mec
 hanical Response of Thermally Aged Polycarbonate. Modelling and Simulation
  in Materials Science and Engineering\, vol. 25\, number 5\, pages 055012\
 , 2017.\n[3] L. Zhang et al. Software for Extracting Continuum-Like Deform
 ation Gradient\, Internal and Interaction Stresses from Molecular Dynamics
  Simulations. http://digitalcommons.unl.edu/mechengfacpub/207/\, 2017. \n\
 n\n
LOCATION:Oatley Seminar Room\, Department of Engineering
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