Mechanics of Polymer Nanocomposites

This area of research deals with the finite deformation mechanics of polymeric (plastic) materials and their composites, which are inherently non-linear viscoelastic materials. (Non-linearity means that the stress response at 20% strain will not be twice that at 10% strain. Viscoelasticity means the response depends on how quickly the polymer is loaded.  It also means the response depends on the temperature of loading.) I conduct experiments, develop mathematical models and use numerical approaches to understand how these materials will behave under extreme environments such as high strain rates of loading. I use the same approaches to determine how to make design improvements for the next generation of materials. Applications for this work include automotive crash worthiness and improved armors. Polymers and polymer composites are capable of dissipating energy via several mechanisms, all of which are not fully understood, and dissipation is important because the energy dissipated prior to interaction with a human is not available to cause injury to the human.  When riding in an automobile for example, the first thing your various body parts will interact with in the event of a crash is usually a rapidly deforming polymeric material. The challenge in this work is that we cannot predict the high strain rate response of polymers from an understanding of the low strain rate response, even if we understand the strain rate dependence at low strain rates because it changes at high strain rates. At high strain rates of loading the polymer heats up as it deforms because strain energy is dissipated as heat and there is insufficient time for this heat to transfer from the polymer. Therefore we design and conduct experiments and simulations at high strain rates and consider the entire non-linear, thermomechanically coupled response of the materials. Another challenge, especially in extreme rates of loading such as a blast or impact, is to find a way to dissipate the impulse associated with an impact before it reaches the body. Our soldiers and marines are currently surviving encounters with various explosions thanks to current improvements in armor technology, but they often suffer losses of limbs and/or traumatic brain injury as a result. Our goal is to develop the next generation of body and vehicle armor technologies to reduce the effects of blasts and ballistics encounters. The nanocomposites we work with may be applied as tough, clear coatings and interface layers to glasses, and to mitigate the effects of blasts on vehicle and body armors. These same materials will also work to dissipate energy in crash applications.