Civil, Environmental and Architectural Engineering Department
The University of Kansas, Lawrence
Granular materials take a variety of forms, spanning the spectrum from highly consolidated dense solids formed of particulate precursors to confined packing of non-cohesive particles. In all their forms, these materials are characterized by complex structures and compositions. More importantly, they share the common trait that their behavior at the macro-scale, that contains large numbers of grains (>106), is profoundly affected by the grain-scale interactions. For many important problems in engineering and science, continuum description of their mechanical behavior is desired. Discrete atomic or coarse-grained models often pose insurmountable challenges. Granular micromechanics method is a practical approach for continuum modeling these materials. In this approach, the material representative volume element (RVE) is modeled as a collection of grains which are interacting with each other through different inter-granular mechanisms. The resultant models offer the versatility of investigating the influence of both the macro-scale parameters and the grain-scale parameters on the overall stress-strain response by incorporating the effect of nearest neighbor grain interactions through the inter-granular force-displacement relationship and orientation vector. We have been developing the granular micromechanics approaches since 1980s. In their earlier formats, the models based upon granular micromechanics were successful in describing the elastic small strain behavior. In recent years, these models have undergone further refinement and have been applied to model a number of phenomena exhibited by granular geomaterials. In particular, the models have been shown to describe the damage and softening in cementitious materials . The approach also leads to a 2nd gradient continuum theory involving strain gradient and its conjugated double stresses useful for modeling shear bands . The method has also been extended to include rate effects , incorporate thermomechanical consistency [3,4] and develop efficient numerical scheme  that can be implemented into finite element formulation. The model predictions have shown both quantitative and qualitative consistency with the observed behavior for asphalts and cementitious materials [3-5, 9]. Recently, the method has been extended to include non-classical terms which lead to micromorphic models [6,10]. The derived model has been applied to study the wave dispersion relationships and topology optimization . Method for identifying elastic constants for the derived model has been demonstrated for regular and irregular grain assemblies by performing discrete simulations . In the proposed presentation, we will describe some of the recent developments in granular micromechanics.
 Misra, A. and Yang, Y., (2010) “Micromechanical model for cohesive materials based upon pseudo-granular structure,” International Journal of Solids and Structures, Vol. 47, No. 21, 2970-2981.
 Yang, Y. and Misra, A., (2012) “Micromechanics based second gradient continuum theory for shear band modeling in cohesive granular materials following damage elasticity,” International Journal of Solids and Structures, 49(18) 2500-2514.
 Misra, A. and Singh, V, (2014) “Thermomechanics based nonlinear rate-dependent coupled damage-plasticity granular micromechanics model,” Continuum Mechanics and Thermodynamics, (doi: 10.1007/s00161-014-0360-y).
 Misra, A., and Poorsolhjouy, P. (2015). "Granular Micromechanics Model for Damage and Plasticity of Cementitious Materials Based upon Thermomechanics." Mathematics and Mechanics of Solids, (doi:10.1177/1081286515576821).
 Misra, A. and Singh, V, (2014) “Nonlinear granular micromechanics model for multi-axial rate-dependent behavior,” International Journal of Solids and Structures, Vol. 51, 2272-2282.
 Misra, A., and Poorsolhjouy, P. (2015). "Granular Micromechanics Based Micromorphic Model Predicts Frequency Band Gaps." Continuum Mechanics and Thermodynamics, (doi: 10.1007/s00161-015-0420-y).
 Misra, A., and Poorsolhjouy, P. (2015) “Identification of Higher-Order Elastic Constants for Grain Assemblies based upon Granular Micromechanics,” Mathematics and Mechanics of Complex Systems; 3(3):285-308.
 Jia, H., Misra, A., Poorsolhjouy, P., Liu, C., (2017) “Optimal structural topology of materials with micro-scale tension-compression asymmetry simulated using granular micromechanics”. Materials & Design 115, 422-432.
 Poorsolhjouy, P. and Misra, A., (2017) “Effect of Intermediate Principal Stress and Loading-Path on Failure of Cementitious Materials Using Granular Micromechanics,” International Journal of Solids and Structures, 108, 139–152.
 Misra, A., and Poorsolhjouy, P. (2017) “Grain- and Macro-scale Kinematics for Granular Micromechanics based Small Deformation Micromorphic Continuum Model,” Mechanics Research Communications, 81, 1–6.
Anil Misra received his bachelor’s degree in civil engineering from the Indian Institute of Technology, Kanpur, India, and his M.S. and Ph.D. degrees from the University of Massachusetts at Amherst. He is currently a Professor in the Civil, Environmental and Architectural Engineering Department of the University of Kansas, Lawrence. He also serves as Associate Director of the University of Kansas Institute for Bioengineering Research (KU-IBER). Dr. Misra has a broad research interest that spans topics covering both basic and applied aspects of mechanics of geomaterials, interfaces and biomaterials, including analytical, computational and experimental granular micromechanics, particle and atomistic methods, multi-scale modeling, constitutive behavior, micro-macro correlations, and multi-modal material characterization using high resolution techniques. He has co-edited three books; guest edited three journal special issues; and authored more than 250 papers in journals, edited books and conference proceedings. He has made more than 150 presentations of his research results at national and international fora. His research has been funded by a variety of sources, including the United States National Science Foundation, National Institute of Health, and private industry. He is active in various professional societies and serves as reviewer and editorial board member of a number of journals.
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