MCE Ph.D. Thesis Seminar
Shock waves are typically generated in a material when it is subjected to a high velocity impact or a blast. These waves are characterized as propagating discontinuities across which material properties and states jump. They can cause the material to achieve very high stress states, and if transmitted without mitigation, it can lead to failure of key components. An important question here is 'Can we design materials which can successfully mitigate damage?' Another important question is 'Can we exploit the energy associated with shock waves for other applications?'.
In this talk, I will discuss my work on shock propagation in composites and ferroelectric materials. We try to understand the interplay between the length scale of the heterogeneities and the length scale associated with the wave front thickness. We study the phenomenon of scattering by solving an impact problem on a layered (not-necessarily periodic) material. We obtain analytic solution to the impact problem by looking at individual fundamental interactions and solving those Riemann problems. The individual solutions are then stitched together to obtain a complete picture of the impact process. Using the knowledge from the individual interactions. we comment on optimal design parameters for the composite. Next, we study shock induced phase transitions, depolarization and energy harvesting through current generation in ferroelectric materials. The nonlinear electro-thermomechanical coupling of the material plays a central role in this process. We develop a continuum framework to explain the physics behind pulsed power generators and shock induced phase transitions. We obtain current profiles from the analysis and compare them with experiments. Finally we comment on the shape of the current pulses obtained, and the influence of various experimental and material parameters on the pulse shape.