Ph.D Thesis

Ph.D StudentGalich Pavel
SubjectManipulating Elastic Wave Propagation in Non-Linear Flexible
Materials via External Stimuli
DepartmentDepartment of Aerospace Engineering
Supervisors PROFESSOR EMERITUS Itzchak Frankel
DR. Stephan Rudykh
Full Thesis textFull thesis text - English Version


Understanding of wave propagation phenomena in solids is pivotal for numerous engineering applications in healthcare, petroleum, military, and aerospace industries. Among them nondestructive material testing, vibration protection of sensitive electronics, unwanted noise mitigation, earthquake forecasting, and medical ultrasound diagnostics. The ability of flexible materials to sustain large deformations opens rich prospects for manipulating elastic wave characteristics by deformation. Moreover, elastic waves can be tuned through designing micro- or macro-structures, which can be further actively controlled by external stimuli, such as mechanical loading, electric or magnetic fields. Understanding of how large deformations affect relatively simple isotropic and more complex anisotropic materials is essential for this task. Therefore, in my thesis, I investigated the acoustic properties of the relatively simple initially isotropic non-linear materials and then proceeded with the periodic layered and fiber composites made of these materials. Firstly, I studied the influence of the deformation induced stiffening (intrinsic feature of most soft materials) on the propagation of small-amplitude elastic plane waves. Secondly, I showed that electroelastic isotropic materials (i.e. dielectric elastomers) can be utilized to achieve acoustic functionalities such as decoupling of pressure and shear waves by application of an electric field. Thirdly, I analyzed wave propagation in non-linear elastic and electroelastic laminates. In particular, I derived the long wave estimates of the phase and group velocities for the waves propagating in the laminates subject to external mechanical or electrical stimuli. Moreover, I found the material compositions and loading conditions producing wide complete band gaps (frequency ranges where neither pressure nor shear waves can propagate) at desired low frequency ranges. Finally, I investigated the anisotropy of elastic wave propagation in finitely deformed fiber composites (FCs). Specifically, by employing rigorous analytical methods of non-linear mechanics, I derived long wave estimates for phase and group velocities of shear waves propagating in non-linear FCs. Next, by utilizing Bloch-Floquet approach in a finite element code, I calculated dispersion relations for shear waves propagating along the fibers in FCs with square arrays of fibers.