Characterization of the Stress-Softening and Permanent Set Effects of Elastomeric Materials

In this work, the application of a phenomenological constitutive model able to predict residual strains of isotropic, incompressible hyperelastic rubberlike materials is studied. It consists in a form of the strain energy which accounts for the microstructural damage developed during loading and unloading deformation process. Along with the study of the application of the model, two new strain energy damage functions are proposed; the first one is based on an exponential form that depends in a single material parameter to predict the inelastic behavior of rubberlike materials; the second one is a simple function with two fitting positive constants that characterize residual strain. Theoretical models for the representation of uniaxial and equibiaxial extension are presented using non-Gaussian constitutive models affected by a phenomenological function to account for the Mullins effect. Also a comparison of the derived models with experimental data of different materials is presented. Also, an experimental set up has been designed to obtain data for equibiaxial deformation state membrane inflation. the test consists in monitoring the evolution of a rubberlike material membrane as inflated by steps of uniform static pressure. A non-contact measuring system is used to obtain the stretch information from the material for each inflation step. At the end of the present work, we discuss the nanomanufacturing process of thermosetting panels reinforced with carbon fibers and carbon nanotubes used in the lab facilities of the Mechanical Engineering and Materials Science (MEMS) at Rice University. A review of the main processing stages, the generation of the nanotubes, the purification process, separation, embedding them into the composite, as well as the technology and methodology employed for the qualitative characterization of the different processing steps of the material was carried out. Finally, a description of the Vacuum Assisted Resin Transfer Molding process is presented; it is the method currently employed in the facilities of the MEMS department for manufacturing polymeric reinforced panels.