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MacroPac - Simulating Particle Packing

If your materials include particulates, you'll know how difficult it can be to get information on how they pack, and how this affects microstructure and properties. Now you can add new understanding to your materials design and processing with MacroPac.

For research scientists and process engineers who want to understand how particle packing affects end-use properties, MacroPac brings new insights into orientation, packing fraction and percolation pathways. With its ability to model various particle shapes and mixed size distributions, MacroPac lets you model realistic structures such as short-fibre-filled composites, and paints and coatings.

MacroPac:

Explores the effects of changing and mixing different particle sizes and shapes - without needing to make and characterize the material

Lets you examine real issues such as pigment distribution in paints, free volume for resin-based composites, and fibre and filler orientation in composites

Incorporates a range of boundary conditions to let you simulate real situations - air interfaces, hard walls and bulk systems, for example

Provides visualization to give you a new perspective on the microstructure of your material.

MacroPac development is driven forward in collaboration with leading academic groups and a multinational client base, in areas including:

short-fibre reinforced composites
filled thermoplastic and thermoset systems

paints and coatings
formulation of personal care products

Defining the particles

Each particle in MacroPac is made up of spheres - this 'blackberry' model gives great flexibility, allowing shapes like rods, plates and rhomboids to be built up quickly. Because of this elegant representation, developed in the group of Professor Ken Evans at the University of Exeter, simulations can be performed quickly even for mixed systems with different shapes and sizes.

If your shapes are more complicated, the optional ShapeBuilder lets you create your own custom object shapes.

MacroPac representation of a typical 'chunk'

Different types of particle can be set up - for example, rods, spheres and chunks can be mixed in the same system. Select from uniform, Gaussian or log normal size distributions. Then choose whether you want to aim for maximum packing fraction, or whether you want the ratio of particles in the packed system to be exactly as specified.

Once the particles are set up, you then define the simulation box you want to use, selecting from

periodic boundaries
hard walls
soft walls

Hard walls model a solid surface - for example, a coating substrate or the inside of an injection mould. Soft walls - where the particle can 'stick out of the box' - are ideal for representing what happens at an air boundary, while periodic boundaries give the best model of a bulk system.

Either 2D or 3D simulations can be treated with MacroPac

Packing the particles

Most of MacroPac's packing modes use a Monte Carlo approach. For these, a particle is selected, and placed at random into the simulation box. Provided it does not overlap an existing particle, it is left where placed. If it would collide with a particle already in the box, another attempt is made to place it.

There are options to shake the box during or after packing, to achieve higher packing fractions. There is also a 'gravity pack' option, although this does not allow particles to roll past each other.

You may pause the simulation before it terminates, if you wish to examine intermediate results. It's a simple matter to restart a paused simulation, to let you take 'snapshots' of the system as packing progresses.

The location of all the particles is stored - the stored particles can provide the starting point for a later MacroPac simulation, or can be interfaced with another program (like Finite Element Analysis meshing, for example).

What does MacroPac tell you?

MacroPac integrates analysis and visualization to let you examine features of the packing system.

Visualization is especially useful. Both 2D and 3D representations can be obtained, and you can even define 'slabs' to visualize slices through the simulation box. And, since this is a Windows-based program, copied and pasted into your presentation graphics or word-processed reports. Visualization and analysis give powerful insights into local ordering, behaviour at boundaries, and overall packing densities.

Volume Fraction is shown on-screen as the simulation runs. This gives an easy calculation of the amount of free volume unfilled, and it correlates with the rheological behaviour. A very accurate calculation of the volume fraction can also be undertaken.

Orientation Analysis shows how the orientation changes across the simulation box. This relates directly to anisotropic behaviour of the system, and its mechanical properties.

Density Analysis shows how the particle density varies across the box. For example, the particle depletion near 'hard walls' can be calculated quickly. Both 'number density' and 'mass density' can be calculated.

Contacts Analysis show how many particles each particles touches, to enable thermal and electrical conductivity to be studied.

The Radial Distribution Function shows the degree of order or disorder in the system.

The Diffusion module lets you look at the random walk of a penetrant through the system - confined either to the matrix or to the particles. This is useful not only for looking at the migration of small molecules, but also gives information on thermal and electrical conductivity.

Porosity can also be investigated, using various options to correlate with different experimental techniques.

To view a PowerPoint presentation on MacroPac, follow this link.

To see some publications where MacroPac has been used, see here.

For some older Application Notes, in PDF format, see here.

Or, contact Intelligensys for more details.