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We introduce a novel numerical method for the simulation of soft granular materials, in which the particles can undergo large strains under load without rupture. The proposed approach combines an explicit total Lagrangian formulation of Material Point Method (TLMPM) with the Contact Dynamics (CD) method. The TLMPM resolves particle bulk deformations whereas the CD treats contact interactions between soft particles. The efficiency and accuracy of this approach are illustrated by analyzing diametral compression of a soft circular particle and the compaction of an assembly of soft particles up to very high levels of packing fraction. We show that although the assembly undergoes a jamming transition, the particles continue to rearrange as they get increasingly distorted under load. Interestingly, as the packing fraction increases, a transition occurs to a regime fully governed by particle shape change. The evolution of the global stress as well as the connectivity of the particles as a function of the packing fraction are discussed and a predictive model relating stress to packing fraction beyond jamming transition is proposed. [ABSTRACT FROM AUTHOR]

This paper revisits the modeling of compressive failure of long fiber composite materials by considering a multiscale finite element approach. It is well known that this failure follows from a fiber microbuckling phenomenon. Fiber microbuckling is governed by both material and geometrical quantities: the elastoplastic shear behavior of the matrix and the fiber misalignment. Although all these parameters are easily accounted by a finite element analysis at the local level, the failure is also influenced by macrostructural quantities. That is why a multilevel finite element model (FE 2 ) is relevant to describe the compressive failure of composite. Furthermore, fiber local buckling leads to a loss of ellipticity of the macroscopic model, which can be a criterion of failure. [ABSTRACT FROM AUTHOR]

Abstract: This paper presents a multiscale numerical technique for vibration analysis of heterogeneous materials. In this procedure, the unknown macroscopic constitutive relationship is searched by solving a local finite element problem at the microscale. Since the inertia effects are neglected at the microscopic level, this approach is limited to problems in which microstructure characteristic length is smaller than the wavelength. Numerical examples are limited to free vibration analysis of viscoelastic materials with a constant complex modulus. These examples allow one to validate the multiscale approach and to study the influence of different parameters on the passive damping of the structure. These parameters concern the morphology, the stiffness ratio and the inclusion volume fraction. [Copyright &y& Elsevier]

This paper presents a numerical algorithm based on a perturbation technique named asymptotic numerical method (ANM) to solve nonlinear problems with hyperelastic constitutive behaviors. The main advantages of this technique compared to Newton-Raphson are: (a) a large reduction of the number of tangent matrix decompositions; (b) in presence of instabilities or limit points no special treatment such as arc-length algorithms is necessary. The ANM uses high order series approximation with auto-adaptive step length and without need of any iteration. Introduction of this expansion into the set of nonlinear equations results into a sequence of linear problems with the same linear operator. The present work aims at providing algorithms for applying the ANM to the special case of compressible and incompressible hyperelastic materials. The efficiency and accuracy of the method are examined by comparing this algorithm with Newton-Raphson method for problems involving hyperelastic structures with large strains and instabilities. [ABSTRACT FROM AUTHOR]

Highlights • Agglomerates of wet particles undergo plastic deformation before breaking. • The plastic strength is proportional to the characteristic capillary stress. • The effect of particle size span is mainly included in the characteristic stress. • The amount of liquid affects the strength through the wet coordination number. Abstract Using particle dynamics simulations, we investigate the strength and microstructure of agglomerates of wet frictional particles subjected to axial compression. The numerical model accounts for the cohesive and viscous effects of the binding liquid up to a debonding distance with the liquid assumed to be distributed homogeneously inside the agglomerate. We show that wet agglomerates undergo plastic deformation due to the rearrangements of primary particles during compression. The compressive strength is thus characterized by the plastic threshold before the onset of failure by the irreversible loss of wet contacts between primary particles. We find that the agglomerate plastic threshold is proportional to the characteristic cohesive stress defined from the liquid-vapor surface tension and the mean diameter of primary particles, with a prefactor that is a nearly linear function of the debonding distance and increases with size span. We analyze the agglomerate microstructure and, considering only the cohesive capillary forces at all bonds between primary particles, we propose an expression of the plastic strength as a function of the texture parameters such as the wet coordination number and packing fraction. This expression is shown to be consistent with our simulations up to a multiplicative factor reflecting the distribution of the capillary bridges. [ABSTRACT FROM AUTHOR]

Pellets are spherical agglomerated particles used to produce multiparticulate pharmaceutical dosage forms. This study aims to develop a new approach that evaluates the deformation behavior of pellets under compression, by combining tableting data and compression models with X-ray micro computed tomography (XMT) image analysis. The deformation of Microcrystalline cellulose (MCC) and sugar pellets known to have different deformation behavior under compression was investigated. Compression data and modeling confirmed the plastic and brittle behavior for MCC and sugar pellets respectively. Image analysis of the XMT showed a different evolution of the morphometric parameters: structure thickness diameter (St Th) and volume equivalent sphere diameter (ESDv). The brittle sugar pellets showed a decrease in both ESDv and St Th parameters while plastic MCC pellets showed a decrease in ST Th and a constant ESDv which is coherent with ductile and brittle material deformation. This study shows that XMT can be used as a tool to characterize the mechanical behavior of pellet particles during compression. [Display omitted] • Pharmaceutical pellet mechanical behavior upon compaction. • Deformation mechanism of ductile and brittle pharmaceutical pellets. • Nondestructive X-Ray micro-computed tomography for pellet deformation. • Structure thickness and equivalent sphere diameters as morphometric parameters. [ABSTRACT FROM AUTHOR]

We use particle dynamics simulations to investigate the evolution of a wet agglomerate inside homogeneous shear flows of dry particles. The agglomerate is modeled by introducing approximate analytical expressions of capillary and viscous forces between particles in addition to frictional contacts. During shear flow, the agglomerate may elongate, break, or be eroded by loss of its capillary bonds and primary particles. By systematically varying the shear rate and surface tension of the binding liquid, we characterize the rates of these dispersion modes. All the rates increase with increasing inertial number of the flow and decreasing cohesion index of the agglomerate. We show that the data points for each mode collapse on a master curve for a dimensionless scaling parameter that combines the inertial number and the cohesion index. The erosion rate vanishes below a cutoff value of the scaling parameter. This leads to a power-law borderline between the vanishing erosion states and erosion states in the phase space defined by the inertial number and the cohesion index. [ABSTRACT FROM AUTHOR]

Using the contact dymanics method together with the finite element method, we simulate the uniaxial compression of assemblies of elastic cylinders. The numerical model accounts for finite deformations of the particles through the neo-Hookean constitutive equation and solid friction between the particles. A quantitative comparison with experiments carried out with centimetric rubberlike cylinders, with local deformations of the particles determined by image correlation, is proposed. We show that the simulations accurately capture the details of both the microstructure and the macroscopic behavior of the real granular system, demonstrating the relevancy of the numerical approach. [ABSTRACT FROM AUTHOR]