Sudeshna Roy

• Manager at Daiichi Sankyo Deutschland GmbH

The packing behavior of powders is significantly influenced by various types of inter-particle attractive forces, including adhesion and non-bonded van der Waals forces [4, 7, 8, 19, 41, 43]. Alongside particle size and shape distributions, the inter-particle interactions, particularly frictional and adhesive forces, play a crucial role in determin...

The interplay between dilatancy and particle alignment in sheared granular materials composed of non-spherical particles leads to morphological inhomogeneity. Dilatancy, driven by interparticle friction, causes the packing to expand, while particle alignment tends to densify it. We examine the influence of friction, particle aspect ratio, and initi...

We perform Discrete Element Method simulations of wet granular matter in a split-bottom shear cell. To calculate the capillary forces from the liquid bridges between the grains, we used three different approximations. The simulations of the shear cell showed a linear increase in bulk cohesion with the surface tension of the liquid, consistently for...

We present the implementation of two advanced capillary bridge approximations within the Discrete Element Method (DEM) framework of the open-source code MercuryDPM. While MercuryDPM already includes a simplified version of the Willett approximation, our work involves implementing both the classical Willett approximation and the recently published B...

When granular materials of shape-anisotropic grains are sheared in a split-bottom shear cell, a localized shear band is formed with a depression at its center. This effect is closely related to the alignment of the particles with the increase in aspect ratio, which, in turn, influences the local packing density, the stress distribution, and the sys...

We present the implementation of two advanced capillary bridge approximations within the Discrete Element Method (DEM) framework of the open-source code MercuryDPM. While MercuryDPM already includes a simplified version of the Willett approximation, our work involves implementing both the classical Willett approximation and the recently published B...

The quality of the powder spread in additive manufacturing devices depends sensitively on the particles' shapes. Here, we study powder spreading for mixtures of spherical and irregularly shaped particles in Polyamide 12 powders. Using DEM simulations, including heat transfer, we find that spherical particles exhibit better flowability. Thus, the pa...

We consider a liquid bridge between identical spheres and present approximate expressions for the capillary force and the exposed surface area of the liquid bridge as functions of the liquid bridge’s total volume and the sphere separation distance. The radius of the spheres and the solid–liquid contact angle are parameters that enter the expression...

We introduce SPIRAL, a third-order integration algorithm for the rotational motion of extended bodies. It requires 91 only one force calculation per time step, does not require quaternion normalization at each time step, and can 92 be formulated for both leapfrog and synchronous integration schemes, making it compatible with many particle 93 simula...

Producing dense and homogeneous powder layers with smooth free surface is challenging in additive manufacturing, as interparticle cohesion can strongly affect the powder packing structure and therefore influence the quality of the end product. We use the Discrete Element Method to simulate the spreading process of spherical powders and examine how...

Granular materials show inhomogeneous flows characterized by strain localization. When strain is localized in a sheared granular material, rigid regions of a nearly undeformed state are separated by shear bands, where the material yields and flows. The characteristics of the shear bands are determined by the geometry of the system, the micromechani...

Producing a consistent layer quality for different raw-materials is a challenge for powder-based additive manufacturing. Interparticle cohesion plays a key role on the powder spreading process. In this work, we characterise the structure of deposited layers in the powder-base additive manufacturing process by numerical simulations using the discret...

Producing consistent and homogeneous packing structure in powder layer deposition for cohesive raw materials under varying thermal conditions is challenging for additive manufacturing. Interparticle cohesion and thermal parameters play key roles on the structure of powder layer deposited on the substrate in additive manufacturing. In this work, we...

We use a virtual Couette rheometer to study the behaviour of dry and wet granular materials in aerated bed. A typical fluidization curve for dry powders exhibits fixed bed characterized by linear increase in pressure drop with increasing air velocity. This is followed by a fluidized bed at a constant pressure drop with further increase in air veloc...

Significance There is not yet a robust theoretical framework predicting the dynamics of dense active matter, where energy is injected at the scale of constituent particles. Previous work has shown that some features of dense active matter are similar to those in dense disordered materials that are sheared globally from the boundaries. Using analyti...

The similarity in mechanical properties of dense active matter and sheared amorphous solids has been noted in recent years without a rigorous examination of the underlying mechanism. We develop a mean-field model that predicts that their critical behavior should be equivalent in infinite dimensions, up to a rescaling factor that depends on the corr...

This paper aims to understand the effect of different particle/contact properties like friction, softness and cohesion on the compression/dilation of sheared granular materials. We focus on the local volume fraction in steady state of various non-cohesive, dry cohesive and moderate to strong wet cohesive, frictionless-to-frictional soft granular ma...

We introduce the open-source package MercuryDPM, which we have been developing over the last few years. MercuryDPM is a code for discrete particle simulations. It simulates the motion of particles by applying forces and torques that stem either from external body forces, (gravity, magnetic fields, etc.) or particle interactions. The code has been d...

We focus on the main new developments underway in MercuryDPM. New features include deformable clusters (agglomerates), experimental coarse-graining, melting particles, particle-solid interactions, multi-resolution particle-fluid coupling, pressure-controlled Lees-Edwards boundaries, better hybrid openMP-MPI parallelisation, and more advanced STL/ST...

Two-dimensional Particle Tracking Velocimetry (PTV) is a promising technique to study the behaviour of granular flows. The aim is to experimentally determine the free surface width and position of the shear band from the velocity profile to validate simulations in a split-bottom shear cell geometry. The position and velocities of scattered tracer p...

Two-dimensional Particle Tracking Velocimetry (PTV) is a promising technique to study the behaviour of granular flows. The aim is to experimentally determine the free surface width and position of the shear band from the velocity profile to validate simulations in a split-bottom shear cell geometry. The position and velocities of scattered tracer p...

Shearing wet granular systems causes a redistribution of the interstitial liquid, which can affect the material's bulk behavior. Using the discrete-element method, we study the early rapid transients, the intermediate states, and the slow long-term evolution of liquid redistribution for various material parameters and different initial wetting cond...

MercuryDPM is a particle-simulation software developed open-source by a global network of researchers. It was designed ab initio to simulate realistic geometries and materials, thus it contains several unique features not found in any other particle simulation software. These features have been discussed in a companion paper published in the DEM7 c...

We study the rheology of dry and wet granular materials in the steady quasistatic regime using the discrete element method in a split-bottom ring shear cell with focus on the macroscopic friction. The aim of our study is to understand the local rheology of bulk flow at various positions in the shear band, where the system is in critical state. We d...

This paper results from an ongoing investigation of the effect of cohesion on the compaction of sheared soft wet granular materials. We compare dry non-cohesive and wet moderately-to-strongly cohesive soft almost frictionless granular materials and report the effect of cohesion between the grains on the local volume fraction. We study this in a thr...

We study the rheology of dry and wet granular materials in the steady quasistatic regime using the Discrete Element Method (DEM) in a split-bottom ring shear cell with focus on the macroscopic friction. The aim of our study is to understand the local rheology of bulk flow at various positions in the shear band, where the system is in critical state...

Particulate systems and granular matter are discrete systems made of many particles; they display interesting dynamic or static, fluid- or solid-like states, respectively, or both together. The challenge of bridging the gap between the particulate, microscopic picture towards their continuum description (via the so-called micro-macro transition) is...

This paper presents the rheology of weakly wetted granular materials in the slow frictional regime, using Discrete Element Method (DEM) simulations. In a split-bottom ring shear cell geometry a slow, quasi-static deformation leads to wide shear bands away from the walls. Dry non-cohesive and cohesive materials are compared in order to understand th...

Wet granular materials in a quasi-static steady state shear flow have been studied with discrete particle simulations. Macroscopic quantities, consistent with the conservation laws of continuum theory, are obtained by time averaging and spatial coarse-graining. Initial studies involve understanding the effect of liquid content and liquid properties...