Model development for nanotube-infused polyimides.

摘要

Polyimides are a class of polymers that are thermally and chemically stable and radiation resistant. In addition to their stability, polyimides possess a relatively large elastic modulus and are flexible. Their stability and stiffness make them good candidates for use in space applications. However, due to their insulating nature, static charge build-up can deteriorate the structure. This charge build-up can be mitigated by embedding single-wall nanotubes (SWNTs) into the polyimide. SWNTs are excellent conductors and have a high elastic modulus. Thus, embedding the SWNTs into the polyimide not only introduces conductivity but also increases the stiffness of the composite. SWNTs can also be added to create an active structure from inactive polyimides.Nanocomposites are being investigated for use in constructing large ultra-lightweight (gossamer) spacecraft. Since the gossamer spacecraft is folded and packed into the launch vehicle prior to launch, the materials need to withstand this process. The nanotube-infused polyimides are flexible enough to withstand the packaging process and strong enough to withstand the harsh space environment. Specific applications of the gossamer spacecraft include thin-film membrane mirrors and gossamer antennas.Nanotube composites have been modeled in the past using a variety of techniques. However, much of the previous work focused on modeling the elastic modulus at a set temperature. Since temperatures widely vary in space, a temperature-dependent model is required for the elastic modulus.In this work, we present a temperature-dependent continuum material model, based on phenomenological elasticity theory, which characterizes stiffness through the material as a function of varying concentrations of nano-inclusions. Attributes of the model are illustrated through comparison with experimental data for the polyimide (beta-CN)-APB/ODPA and LARC-CP2. In Chapters 5 and 6, system models are developed and implemented for 1D and 2D nanotube-infused membranes under tension.