Currtently, the chair Mechanics of Materials has the following vacancies for PhD students:
The performance, and in particular the frequency response and output pressure, of MEMS ultra-sound transducers, critically relies on the mechanical properties of the ultra-thin free-standing multi-layer membranes that generate the ultrasonic waves. Currently, fundamental manufacturing challenges arise for frequencies above 40 MHz. Due to the high voltage driving conditions, reaching the fracture strength is not exceptional. This results in an undesired loss of functionality. In addition, residual stresses arise during manufacturing and result in performance changes as well as premature cracking or buckling of the films, which compromises the manufacturability and device performance. It has become clear that these multi-layer membranes push our understanding of ultra-thin film behavior to the limits. In order to enable the manufacturability of the next generation ultra-high frequency MEMS ultra-sound transducers, the micro-mechanics of the ultra-thin free-standing multi-layer membranes need to be better understood and controlled. To this end, this PhD project will establish the relation between the manufacturing of the free-standing membranes and the resulting residual stresses and thermo-mechanical properties, by means of a combined numerical/experimental multi-scale approach that incorporates the development of numerical models including size effects, and the experimental testing of dedicated in-line test structures that are processed by the project partners.
For more information, or to apply, click here.
During processing of a polymer, the material is subjected to conditions that often result in an oriented microstructure, leading to anisotropic properties. In semicrystalline polymers, structural features such as the degree of crystallinity and crystal type, size and orientation strongly influence their mechanical properties. This project will focus on the development of a macroscopic constitutive model describing the anisotropic yield behaviour of oriented polyethylene films, based on a combination of experimental characterization and micromechanical modelling and of which the parameters depend on morphological characteristics.
For more information or to apply, click here