RHEOLOGY

From the 17th century onwards, up to the beginning of this century, materials were divided into solids, which behave according to the theory of linear elasticity (i.e. Hooke's law), and liquids which exhibit viscous flow, described by the Navier-Stokes equations.

But this simple division excludes an increasingly number of modern materials, whose properties lie between the above two extremes. Foams are examples of such viscoelastic materials.

The actual behaviour of the material depends on the circumstances and parameters under which an experiment (or application) is carried out (time scale, applied force etc.).

An example of a viscoelastic material is shaving foam, which sticks onto the face until being made to flow under the action of the razor. The foam exhibits a certain yield-stress below which it behaves as a solid (with a corresponding shear modulus) and above which it flows as a liquid.

Modelling of solid foams

We have developed a simple mechanical model of a 2-dimensional solid foam, which tells us how a foam buckles under stress. Here you can see one of our results on an eight cell system:

Relevant Publications