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This study investigates the impact of particle plasticity on the mechanical behaviour of a model granular system under plane stress conditions simulated with the Discrete Element Method. A contact model transitioning from nonlinear elasticity to linear plastic deformation is integrated to analyse its effects on a 576-ball-bearing assembly subjected to varying loads. Simulations were conducted using Yade, comparing them with experimental results and traditional elastic models. The findings show that incorporating plastic deformation improves the accuracy of simulated force distributions and the material’s frictional response, particularly under high external loads. These results underscore the need for plasticity-inclusive models in realistic granular simulations, providing valuable insights for practical applications in industries handling high-stress granular systems. [ABSTRACT FROM AUTHOR]

Aggregates consisting of submicron-sized cohesive dust grains are ubiquitous, and understanding the collisional behavior of dust aggregates is essential. It is known that low-speed collisions of dust aggregates result in either sticking or bouncing, and local and permanent compaction occurs near the contact area upon collision. In this study, we perform numerical simulations of collisions between two aggregates and investigate their compressive behavior. We find that the maximum compression length is proportional to the radius of aggregates and increases with the collision velocity. We also reveal that a theoretical model of contact between two elastoplastic spheres successfully reproduces the size- and velocity-dependence of the maximum compression length observed in our numerical simulations. Our findings on the plastic deformation of aggregates during collisional compression provide a clue to understanding the collisional growth process of aggregates. [ABSTRACT FROM AUTHOR]

Results from an experiment involving the measurement of individual particle stresses in a two-dimensional mono-disperse assembly of 579 ball bearings are presented. Using a combination of neutron radiography and strain scanning techniques, the full bi-axial stress state was obtained for each particle from which the full contact force network could be established. The evolution of this network was examined over a series of five monotonically increasing loads. Significant levels of inhomogeneity were observed in the form of prominent force chains that showed complex interaction with regions of order and disorder within the assembly. A reduction in the level of inhomogeneity with increasing load was also observed. [ABSTRACT FROM AUTHOR]

Fragmentation of granular clusters may be studied by experiments and by granular mechanics simulation. When comparing results, it is often assumed that results can be compared when scaled to the same value of E / E sep , where E denotes the collision energy and E sep is the energy needed to break every contact in the granular clusters. The ratio E / E sep ∝ v 2 depends on the collision velocity v but not on the number of grains per cluster, N. We test this hypothesis using granular-mechanics simulations on silica clusters containing a few thousand grains in the velocity range where fragmentation starts. We find that a good parameter to compare different systems is given by E / (N α E sep) , where α ∼ 2 / 3 . The occurrence of the extra factor N α is caused by energy dissipation during the collision such that large clusters request a higher impact energy for reaching the same level of fragmentation than small clusters. Energy is dissipated during the collision mainly by normal and tangential (sliding) forces between grains. For large values of the viscoelastic friction parameter, we find smaller cluster fragmentation, since fragment velocities are smaller and allow for fragment recombination. [ABSTRACT FROM AUTHOR]

Shear deformation of granular media leads to continual restructuring of particle contact network and mechanical interactions. These changes to the mechanical state include jamming of grains, collisions, and frictional slip of particles-all of which present abrupt perturbations of internal forces and release of strain energy. Such energy release events typically result in the generation of elastic waves in the kHz frequency range, termed acoustic emissions (AE). The close association between grain-scale mechanics and AE generation motivated the use of AE as surrogate observations to assess the mechanical state of complex materials and granular flows. The study characterizes AE generation mechanisms stemming from grain-scale mechanical interactions. Basic mechanisms are considered, including frictional slip between particles, and mechanical excitation of particle configurations during force network restructuring events. The intrinsic frequencies and energy content of generated AEs bear the signature of source mechanisms and of structural features of the grain network. Acoustic measurements in simple shear experiments of glass beads reveal distinct characteristics of AE associated with different source mechanisms. These findings offer new capabilities for non-invasive interrogation of micromechancial interactions and linkage to a stochastic model of shear zone mechanics. Certain statistical features of restructuring events and associated energy release during shearing were predicted with a conceptual fiber-bundle model (FBM). In the FBM the collective behavior of a large number of basic mechanical elements (representing e.g. grain contacts), termed fibers, reproduces the reaction of disordered materials to progressive loading. The failure of fibers at an individual threshold force corresponds to slipping of a particle contact or a single rearrangement event of the granular network. The energy release from model fiber breakage is the equivalent to elastic energy from abrupt grain rearrangement events and provides an estimate of the energy available for elastic wave generation. The coupled FBM-AE model was in reasonable agreement with direct shear experiments that were performed on large granular assemblies. The results underline the potential of using AE as a diagnostic tool to study micro-mechanical interactions, shear failure and mobilization in granular material. [ABSTRACT FROM AUTHOR]

Model validation remains a serious problem within the field of computational granular materials research. In all cases the rigor of the validation process is entirely dependent on the quality and depth of the experimental data that forms the point of comparison. Neutron and X-ray diffraction methods offer the only quantitative non-contact method for determining the spatially resolved triaxial stress field within granular materials under load. Measurements such as this can provide an unprecedented level of detail that will be invaluable in validating many models. In this paper the theoretical foundation underpinning diffraction-based strain measurements, their conversion to local stress in the particles and ultimately into the bulk stress field is developed. Effects such as elastic anisotropy within the particles of the granular material, particle plasticity and locally inhomogeneous stress distribution are shown to not offer any obstacles to the method and a detailed treatment of the calculation of the bulk stresses from the particle stresses is given. [ABSTRACT FROM AUTHOR]

Applying a method that is widely known in nonlinear structural mechanics, the paper offers an alternative approach for the jamming analysis of granular assemblies. The main advantage of the proposed approach is that deformable particles with general shapes can be handled with it, in contrast to the previous methods that are restricted to rigid grains with spherical shape. The paper first gives an overview on the existing concepts of jammed states. Then an alternative set of definitions is proposed; the definitions are based on the stability analysis of the considered assemblies. After that, a calculation method (restricted to elastic contacts) is introduced for the jamming analysis. The method is based on determining the eigenvalues of the stiffness matrix that contains the effect of the particle properties as well as the already existing contact forces that are present in the system. [ABSTRACT FROM AUTHOR]