A SEMI-IMPLICIT MICROPLAR DISCRETE-TO-CONTINUUM METHOD FOR GRANULAR MATERIALS

Kun Wang, WaiChing Sun

Department of Civil Engineering and Engineering Mechanics, Columbia University
614 SW Mudd, Mail Code: 4709, New York, NY 10027
e-mail: {kw2534,wsun}@columbia.edu

Keywords: Micropolar Continua, Discrete-to-Continuum, Granular Matters, Length Scale, Strain Localization.

Abstract. A micropolar discrete-continuum coupling model is proposed to link the collectively particulate mechanical simulations at high-order representative elementary volume to field-scale boundary value problems. By incorporating high-order kinematics to the homogenization procedure, contact moment and force exerted on grain contacts are homogenized into a non-symmetric Cauchy stress and higher-order couple stress. These stress measures in return become the constitutive updates for the macroscopic finite element model for micropolar continua. Unlike the non-lcoal weighted averaging models in which the intrinsic length scale must be a prior knowledge to compute the nonlocal damage or strain measures, the proposed model introduces the physical length scale directly through the higher-order kinematics. As a result, there is no need to tune or adjust the intrinsic length scale. Furthermore, since constitutive updates are provided directly from micro-structures, there is also no need to calibrate any high-order material parameters that are difficult to infer from experiments. These salient features are demonstrated by numerical examples. The classical result from Mindlin is used as a benchmark to verify the proposed model. 

URL: https://www.seas.harvard.edu/calendar/event/86486

Some remarks on modeling fluid-infiltrating, thermal-sensitive, and partially-frozen porous media across length scales
23MAR
Applied Mechanics Colloquia
Steve WaiChing Sun, Columbia University
Wednesday, March 23, 2016 - 4:00pm to 5:00pm
MD G115

​Many engineering applications, such as geological disposal of nuclear waste, require reliable predictions on how porous media responds to extreme environments. This presentation will discuss the relevant modeling techniques designed specific for porous media subjected to such harsh environments. In particular, we will discuss (1) a finite strain finite element model that captures the freeze-thaw action of frozen soil, (2) the stability and dispersion analyses that reveals the vanishing of physical length scale of thermal-sensitive porous media at short wavelength limit, (3) the usage of multiscale techniques to link grain-scale simulations to macroscopic predictions and hence bypass the usage of any macroscopic phenomenological law. Spurious pathological predictions by previous DEM-FEM models are examined and the remedies are proposed. 

Speaker Bio: WaiChing Sun is an assistant professor in the Department of Civil Engineering and Engineering Mechanics at Columbia University. Prior to joining the Columbia faculty, he is a senior member of technical staff at Sandia National Laboratories. Professor Sun works in the fields of theoretical and computational poromechanics with a special emphasis on geomechanical applications. His research includes multiscale modeling porous media, multiscale verification and validation with CT images, digital rock and granular physics, applications of mathematical tools, such as graph theory, Lie algebra for modern engineering problems. He received the Dresden Junior Fellowship in 2016, Army Young Investigator Program Award in 2015, and the Caterpillar Best Paper Prize in 2013. He holds BS degree from UC Davis, MS degrees from Stanford and Princeton and PhD degrees from Northwestern. 

Host: 
Chris Rycroft
Contact: 
Rebekah Stiles
Email: 
rstiles@seas.harvard.edu