MacroCrack from Intelligensys - crack propagation software

Developing better products faster

MacroCrack

Crack Propagation in Viscoelastic Materials

Sometimes, if your polymer coating or material has inclusions like pigments - or even if there are simply holes arising from a formation process - cracking can be a real problem. For film-coated tablets, cracks make it impossible to control the release of a drug, for example. Understanding how the formulation variables affect crack propagation can be an important part of avoiding these problems.

For research scientists and formulators who want to understand crack propagation in filled viscoelastic materials, MacroCrack gives a rapid calculation of the crack velocity with different mixes of inclusions and polymer properties. MacroCrack has been tested for materials as diverse as compacted aspirin, pigmented cellulose derivatives, PMMA and even steels. As long as the material is capable of viscous flow, MacroCrack is relevant.

Models crack propagation in compacted porous materials as well as for filled polymer systems - so you can look at cracking of tablets as well as of tablet film coatings

Lets you try out 'what if' changes to see if modifying polymer properties (e.g. by changing molecular weights, or adding plasticizers) would give better performance

Models several different inclusions, with different sizes and size distributions, in a single simulation. See what happens if you change the size of the particles, or the amount used.

Visualization of the cracking process and prediction of crack propagation velocity obtained in seconds on a PC

MacroCrackhas been developed in collaboration with Professor Ray Rowe, author of the acclaimed book Intelligent Software for Product Formulation and of many papers in which modelling techniques are applied to formulations.

How does MacroCrack work?

MacroCrack uses a model developed by K B Broberg (Int. J Fracture 42, 277 (1990)) for modelling crack propagation in viscous materials like steels. The method has been adapted by Rowe and coworkers for organic materials.

You input information about the particles - their size and size distribution, and the amount (weight or volume) which is present. These particles are assumed to be spherical and are randomly distributed in the simulation box, to fulfil the required volume/weight fractions. The inclusions can be real particles (pigments or fillers, for example) or can be holes (in the case of compacted porous materials).

You also input information about the polymer - the Young's modulus, the yield stress, the density and the critical stress intensity factor - and these are used to calculate the stress.

In the model, holes are opened when the stress reaches a critical value, dependent on the size of the inclusion. Holes coalesce when the distance between them - or between a hole and the main crack - falls below a certain critical value. Hole opening and growth causes a reduction in the stress of the neighbourhood of the crack.

What does MacroCrack tell you?

By seeing how fast the crack propagates across the simulation box, the crack propagation velocity can be calculated. If the crack cannot propagate, then MacroCrack informs you of this.

Optional visualization shows how the crack propagates, so that you can see how far and fast it progresses. These have been validated against electron micrographs of real materials in a number of cases.

In pigmented hydroxypropyl methycellulose films, for example, the simulation predicts (1) radial propagation of cracks from the inclusions linking to form a major crack, (2) the tendency for minor cracks to diverge from the main crack, and (3) the formation of small cracks independent of the main crack - all of which can be found in real tablet film coatings.

Applications

MacroCrack has been tried out for a variety of materials, including PMMA and steels. Published applications primarily focus on issues important in drug formulation, and include:

Crack propagation in porous compacted specimens of aspirin - R C Rowe and R J Roberts, J Materials Science 28 3385 (1993)

Crack propagation in porous compacted specimens of microcrystalline cellulose - R C Rowe and R J Roberts, Eur. J Pharm. Biopharm. 40 9 (1994)

Crack propagation in tablet film coatings containing pigments - R C Rowe and R J Roberts, International Journal of Pharmaceutics 78 49 (1992)

Hardware requirements

Windows 2000 or Win XP operating system.

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

Customised versions of MacroCrack, incorporating your own materials, can be produced upon request. Contact Intelligensys for more details.