CHIPFoam Modification to Allow for Modelling SWIFT Foams

Abstract

SWIFT (Silicon-water in Familiar Template) foams are silicone foams that have a continuous porosity without having any obvious spherical or ellipsoidal pore shapes. Like other foamed rubber, SWIFT foams can experience large reversible deformations. Because of their microstructure, SWIFT foams have a stiffering behavior in compression that is very abrupt compared to most other foamed rubbers. Work by Benedikt reported by Miller showed that fitting compressive test data with the CHIPFoam model in its current form is impractical and inaccurate. This report describes an extension made to CHIPFoam to allow the modeling of SWIFT foams. While the extension allows the modeling of SWIFT foams, it also extends the range of porosity of foams that can be modelled with CHIPFoam to include very high porosity (>99%) foamed rubber. The previous model was unstable for porosities greater than 70%. The changes made to CHIPFoam include the introduction of a critical porosity at which the compressible Danielsson strain energy function that couples volumetric and deviatoric mechanical behavior begins to increase with compression. This new feature also required the introduction of a third term in the multiplicative decomposition of the relative volume, J . The organization of this report is described here. The first section, SWIFT Foam Structure and Mechanical Behavior, describes the structure of SWIFT foams as contrasted to other foamed rubbers. It also contrasts the mechanical behavior of SWIFT foams to other more traditional foamed rubbers. The second section, CHIPFoam Modifications, describes the specific modifications done to be able to modify the delayed rapid compressive stiffening seen in SWIFT foams. The third section, Results, demonstrates the use of the modified model to fit compressive loading response data from a SWIFT foam sample. The fourth section, Conclusions and Further Work, puts the work in perspective and presents likely further work.