Silicone

PADeMIS will be made from silicone due to two reasons:

A compliant material allowing large strains is needed

At the moment no allergic reactions with silicone are known

The biggest drawbacks of silicone are:

At the moment technology for manufacturing of thin, homogenous layers is not known and must therefore be developed.

The mechanical behavior -required for the simulations- of thin silicone layers is not well known and has to be studied.

A tension test apparatus is set up to investigate the mechanical properties of the silicone used. As constitutive law of silicone the Mooney-Rivlin law is used:

With the relative length change in direction i (current length, initial length)

and the modified invariants of the Cauchy Green deformation tensor

the stress energy density W can be expressed using the Mooney Rivlin constantsand the bulk modulus:


Assuming incompressibility

and uniaxial tension in direction 1

the invariants can be simplified to

and the true stress in direction 1 can be calculated as

The figure shows the Mooney Rivlin Fit of silicons with different Shore hardness SH. Prestreched silicone shows fatigue, the so called Mullins effect. For SH 50 a prestretched curve is shown too.

The Mooney - Rivlin constants are needed as input parameters for the FEM simulations of the deformation.

For questions or comments, please contact: pademis@tu-ilmenau.de