Archives: Events

Title:

Gel Mechanics: A Thermo-Mechanically Coupled Theory for Fluid Permeation in Elastomeric Materials

 

Abstract:

An elastomeric gel is a cross-linked polymer network swollen with a solvent, and certain gels can undergo large reversible volume changes as they are cycled about a critical temperature. We have developed a continuum-level theory to describe the coupled mechanical deformation, fluid permeation, and heat transfer  of  such thermally-responsive gels.  In discussing special constitutive equations we limit our attention to isotropic materials, and consider a model based on a Flory-Huggins model for the free energy change due to mixing of the fluid with the polymer network, coupled with a  non-Gaussian statistical-mechanical model for the change in configurational entropy — a model which accounts for the limited extensibility of polymer chains. We have numerically implemented our theory in a finite element program. We show that our theory is capable of simulating swelling, squeezing of fluid by applied mechanical forces, and thermally-responsive swelling/deswelling of such materials.

 

About the Speaker:

Dr. Lallit Anand, is the Warren and Towneley Rohsenow Professor of Mechanical Engineering at MIT. He teaches subjects related to Solid Mechanics, Mechanics of Materials, and Continuum Mechanics. He has recently co-authored a book titled The Mechanics and Thermodynamics of Continua with Morton Gurtin and Eliot Fried. The honors he has received include: Eric Reissner Medal, 1992, for outstanding contributions to the field of Mechanics of Materials in the past decade from the International Society for Computational Engineering & Sciences, Khan International Plasticity Medal, 2007, for outstanding life-long contributions to the field of Plasticity from the International Journal of Plasticity.

Faculty Host: Prof. Somnath Ghosh, 203 Latrobe, 410-516-7833, [email protected]

For more information, please contact Jae Hong, 410-516-5033, [email protected]

Title:

Modeling Ductile Fracture Toughness and Fracture Surface Roughness

Abstract:

Two fundamental questions in the mechanics and physics of fracture are: (i) What is the relation between observable features of a material’s microstructure and its resistance to crack growth? (ii) What is the relation between observable features of a material’s microstructure and the roughness of the fracture surface? An obvious corollary question is: What is the relation, if any, between a material’s crack growth resistance and the roughness of the corresponding fracture surface? I will report on recent calculations of mode I ductile crack growth aimed at addressing these questions. At room temperature, ductile fracture of structural metals generally occurs by the nucleation, growth and coalescence of micron scale voids. In the calculations, an elastic-viscoplastic constitutive relation for a progressively cavitating plastic solid is used to model the material. A characteristic length is needed, if only from dimensional considerations, to predict fracture toughness and in the calculations this is introduced via a discretely modeled microstructural feature such as the spacing of inclusions that nucleate voids. The crack growth resistance is quantified in terms of JIC and the tearing modulus, TR. The Hurst exponent of the correlation function of the fracture surface height distribution, a quantity typically used to characterize the fracture surface roughness, is also calculated. In addition, we go beyond the characterization of fracture surface roughness by the correlation function and investigate the full statistics of the fracture surface roughness. Possible connections between quantitative measures of crack growth resistance and quantitative measures of fracture surface roughness are explored and related to the nature of the ductile crack growth process.

 

About the Speaker

Alan Needleman completed his Ph.D. in Engineering at Harvard University in 1970. He then spent five years in Applied Mathematics at MIT before moving to Brown University where he became Florence Pirce Grant University Professor in 1996. He retired from Brown in June 2009 and is now Professor of Materials Science and Engineering at the University of North Texas. His contributions include the development of a ductile fracture computational methodology, the development of cohesive surface methods for fracture analysis and creation of a framework that enables using discrete dislocation plasticity to solve general boundary value problems. Professor Needleman was awarded a Guggenheim Fellowship in 1977, and is a member of the National Academy of Engineering and of the American Academy of Arts and Sciences.  He has been awarded the Prager Medal by the Society of Engineering Science, the Drucker and Timoshenko Medals by the American Society of Mechanical Engineers and has been recognized by ISI as a Highly Cited Author in both the fields of Engineering and Materials Science. Professor Needleman also holds honorary doctorates from the Technical University of Denmark and Ecole Normale Superior de Cachan (France).

Faculty Host: Prof. Somnath Ghosh, 203 Latrobe, 410-516-7833, [email protected]

For more information, please contact Jae Hong, 410-516-5033, [email protected]

Title:

Guide to Use of ASCE 7-10 Wind Load Provisions

 

Abstract:

The talk aims at assisting undergraduate students in the use of the wind load provisions of ASCE/SEI Standard 7-10, Minimum Design Loads for Buildings and Other Structures, published by the American Society of Civil Engineers (ASCE). It will introduce a brief history of the wind load provisions, design approaches specified by ASCE 7-10, and the associated fundamentals in wind engineering. A design example of a low-rise building for wind will be presented to illustrate how wind loads are determined using the design procedure described in ASCE 7-10.

 

About the Speaker:

Dr. DongHun Yeo’s current research interests are in the area of structural wind engineering with particular emphasis on structural response to wind and computational wind engineering. Dr. Yeo obtained a B.S. (1994) and M.S. (1998) degree in Civil Engineering at Yonsei University, and a Ph.D. in Civil Engineering from the University of Illinois at Urbana-Champaign (2008). In 2008 he became a post-doctoral fellow in Civil Engineering, The Johns Hopkins University. Before pursuing his doctoral degree, he was involved in many design and consulting projects of steel and reinforced concrete structures in Hyundai Construction and Engineering Company, Korea. Dr. Yeo is a member of the Task Committee on Computer-Aided Wind Engineering of the Structural Wind Engineering Committee, American Society of Civil Engineers (ASCE). He is also a graduate-level lecturer in Civil Engineering, The Johns Hopkins University, and a registered professional engineer in Virginia

Faculty Host: Prof. Somnath Ghosh, 203 Latrobe, 410-516-7833, [email protected]

For more information, please contact Jae Hong, 410-516-5033, [email protected]