Dr. Dasgupta's Talk

Aug 08, 2013 - 17:00

Aug 08, 2013 - 18:00

Creativity Hall (Room 118) Chemical Engineering

Seminars

Ratul Dasgupta Dept. Chemical Physics Weizmann Institute of Science Rehovot Israel

Abstract: A large class of amorphous or disordered materials ranging f rom “hard” bulk-metallic glasses to “soft” foams exhibit strain localisation when s ubject to a sufficiently large defor- mation. This particular phenomenon often leads to material failure and thus obtaining a microscopic understanding of this process becomes very imp ortant. In recent work we have studied the instability responsible for this process from a microscopic point of view using athermal quasi-static simulations of binary Lennard-Jon es glasses and continuum solid me- chanics. The talk will start with an introduction to some of t he basic ideas in amorphous elasticity & plasticity. The importance of non-affine motion the notion of elementary plastic instabilities in the stress-strain response and the connec tion between non-affine response and eigenvalues & eigen-modes of the Hessian matrix will be disc ussed briefly. Data obtained from numerical simulations show that the non-affine displacement field associated with a plastic instability undergoes a qualitative shift changing from a quadrupolar field to a shear band as we strain the material. We will understand this transitio n using the theoretical formalism of Eshelby inclusion(s). An expression for the elastic ener gy of N inclusions dispersed and oriented randomly in an elastic medium subject to a global lo ading will be obtained. It will then be proven analytically that at sufficiently large values of strain a state of minimal energy is when each of these N inclusions are equi-aligned and lie on a line oriented at 45 ◦ to the global compressive axes. It will be seen that this highly cor related arrangement of inclusions is responsible for organising the non-affine flow into a shear b and. A formula for yield-strain obtained from this calculation will be presented. Extensi on of these ideas to account for finite temperature and finite strain-rates will also be discussed. In a second and shorter part of the talk I will also present so me of my Ph.D. work on laminar hydraulic jumps and the connection to non-linear w aves. Results from free-surface Navier-Stokes simulations of hydraulic jumps in both plana r and circular geometries will be discussed and some interesting theoretical analysis will b e presented in brief.    Bio of the speaker: Ratul Dasgupta obtained his B.E. in Mechanical Engineering from Reg ional Engineering College (N.I.T.) Rourkela in 2001. After this he spent a few years in the indus try working with var- ious organisations like Financial Engineering Solutions Mumbai and In fosys Technologies Ltd. Bangalore. He joined the Jawaharlal Nehru Centre for Advanced S cientific Research (JNCASR) Bangalore in 2005 at the Engineering Mechanics Unit where he worked on hydraulic jumps and non-linear waves for his Ph.D. He completed his Ph.D. in November 201 0 and moved to the Dept. of Chemical Physics at the Weizmann Institute of Science Is rael where he is currently a Post-Doctoral Research Fellow. His Post-Doctoral work has be en on understanding plasticity and shear-banding in amorphous materials. Ratul’s research intere sts lie in the general areas of continuum mechanics involving fluid and solid mechanics with possible con nection(s) to statistical mechanics. He likes to use a combination of numerical and analytical tools and techniques in his reaserch.