Non-linear response of materials

In the past few years a new class of materials has emerged, where chemistry and electrostatic work together to generate large deformation. Both the phenomena and the engineering applications have motivated the development of theories of diverse soft active materials, including dielectric elastomers, elastomeric gels, polyelectrolytes and pH-sensitive hydrogels.

To design structures and devices made by soft active materials, the theories must be implemented within software. While the Finite Element framework is specially suitable for the analysis of the non-linear behavior of  structures made of such compliant materials, the implementation of theories of soft active materials is not straightforward  within commercial FE packages since additional nodal degrees of freedom (such as  chemical potential and electric field) are required. To overcome this issue and investigate instabilities in structures responsive to diverse stimuli we  are implementing the required theory within a widely available commercial Finite Element package as ABAQUS, taking full advantage of the possibility to actively interact with the software through user-defined subroutines. Both user subroutines to define material behavior (UMAT and UHYPER) and elements (UEL) are developed. Because a commercial software like ABAQUS is widely available, this will facilitate interactions with industry and collaborators. Moreover, the developed user-defined subroutines will be posted online,  enabling other people to analyze complex phenomena in soft active materials  without spending much time on coding. Although this approach is very appealing, we are aware of the fact that for certain analysis the commercial software may not offer enough flexibility.  In that case we will develop  in-house numerical tools.