This paper presents a micromechanical representation of deformation in 2D granular materials, based on the void-cell approach of M. Satake and a generalization of K. Bagi's work. The representation applies to a material region partitioned into polygonal subregions, allowing for a unique assignment of the contribution of each contact displacement to the average deformation of an assembly. The paper addresses the construction of the particle graph and appropriate data structures for use with the Discrete Element Method (DEM). A numerical simulation of a two-dimensional assembly of disks is performed, and results of the distributions of deformation and particle-group rotation are presented with a resolution of about a single particle diameter. Deformation was very nonuniform, even at low strains, and micro-bands, thin linear zones of intense rotation, were also observed. The paper discusses the deformation of granular materials, focusing on the movement of individual particles and the complex relationship between deformation and particle movement. Several methods have been used to measure and visualize deformation resulting from particle movements, including plotting particle movement or velocity vectors. These methods have been used to infer complex deformation structures within granular materials. The paper also discusses the development of a generalization of Rowe’s stress-dilatancy theory, viewing deformation as a mechanism that occurs along chains of particles. Deformation of an assembly produces compression or elongation of the chain by folding the branch vectors between pairs of adjacent particles. The paper presents a more recent means of visualizing and measuring deformation, one in which deformation occurs within the void space between particles. Such void-based methods require that an assembly be partitioned into a covering of non-overlapping subregions, so that the local effects of deforming the assembly can be measured within each subregion. The paper also discusses the implementation of the method with a dense assembly of multi-sized disks, presenting algorithms and data structures for use with the Discrete Element Method. Results of the simulation are presented, showing the distribution of deformation and particle-group rotation. The paper concludes that the method may be useful in revealing other deformation structures and lead to realistic constitutive descriptions based on the micromechanics of granular materials.This paper presents a micromechanical representation of deformation in 2D granular materials, based on the void-cell approach of M. Satake and a generalization of K. Bagi's work. The representation applies to a material region partitioned into polygonal subregions, allowing for a unique assignment of the contribution of each contact displacement to the average deformation of an assembly. The paper addresses the construction of the particle graph and appropriate data structures for use with the Discrete Element Method (DEM). A numerical simulation of a two-dimensional assembly of disks is performed, and results of the distributions of deformation and particle-group rotation are presented with a resolution of about a single particle diameter. Deformation was very nonuniform, even at low strains, and micro-bands, thin linear zones of intense rotation, were also observed. The paper discusses the deformation of granular materials, focusing on the movement of individual particles and the complex relationship between deformation and particle movement. Several methods have been used to measure and visualize deformation resulting from particle movements, including plotting particle movement or velocity vectors. These methods have been used to infer complex deformation structures within granular materials. The paper also discusses the development of a generalization of Rowe’s stress-dilatancy theory, viewing deformation as a mechanism that occurs along chains of particles. Deformation of an assembly produces compression or elongation of the chain by folding the branch vectors between pairs of adjacent particles. The paper presents a more recent means of visualizing and measuring deformation, one in which deformation occurs within the void space between particles. Such void-based methods require that an assembly be partitioned into a covering of non-overlapping subregions, so that the local effects of deforming the assembly can be measured within each subregion. The paper also discusses the implementation of the method with a dense assembly of multi-sized disks, presenting algorithms and data structures for use with the Discrete Element Method. Results of the simulation are presented, showing the distribution of deformation and particle-group rotation. The paper concludes that the method may be useful in revealing other deformation structures and lead to realistic constitutive descriptions based on the micromechanics of granular materials.