Mathias Simon Daniel Bechert
Dr. Bechert graduated at the Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU) with a diploma in Physics in 2011. He wrote his diploma thesis entitled "Heisenberg and Stabilizer Dynamics of Quantum Optical States" at the Max Planck Institute for the Science of Light under the supervision of Dr. Peter van Loock.
Afterwards, Dr. Bechert joined the Institute of Polymer Materials of the FAU, where he obtained in 2017 his PhD under the supervision of Prof. Dirk Schubert and Prof. Benoit Scheid of the Université Libre de Bruxelles on the "Influence of Process and Material Parameters on the Draw Resonance Instability".
Since then he is working as a postdoc at the EPFL in the Laboratory of Fluid Mechanics and Instabilities of Prof. François Gallaire.
1) Transport of Fibers in Microchannels
(in collaboration with Anke Lindner, Jean Cappello (ESPCI, Paris) and Camille Duprat (École Polytechnique, Paris))
The behavior of fibers transported by a flow in confined geometries is important for many applications, e.g., paper production, hydraulic fracturing, or biomedical technologies. The complex interactions between the fiber and the surrounding flow lead to various dynamical behavior, e.g. oscillatory movement between the channel walls or rotation of the fiber.
We are especially interested in effects induced by elasticity of the fibers, as well as geometrical asymmetries. For this purpose, we develop models of reduced dimensionality based on the so-called Brinkman equations, which enable a high flexibility for exploring the transport dynamics.
2) Thermal Drawing of Multimaterial Fibers
(in collaboration with Fabien Sorin, Alexis Page (FIMAP, EPFL))
With the process of thermal drawing, it is possible to produce multimaterial fibers with high accuracy down to diameters of 10-100 micrometers. Due to high control of the fiber architecture, the size of particular functional features in the fiber can reach tens of nanometers.
In general, a previously prepared preform consisting of a supporting material and one or several functional materials, e.g., conductive composites or semiconductors, is elongated by heating and cooling it in a furnace while pulling with a defined speed. The choice of the temperature profile is, apart from the preform architecture, one of the key parameters to tune the final product.
We investigate ways to analyze this process with models of reduced dimensionality in order to describe experimental observations as well as to reveal favorable processing conditions.
3) Draw Resonance
(in collaboration with Benoit Scheid (ULB))
In film casting and fiber spinning processes, liquid material is extruded through a die with predefined speed and taken up by a rotating chill roll in order to fabricate thin films and slender fibers. The main control parameter is the so-called draw ratio, defined as the ratio of the inlet to the take-up velocity. Exceeding a critical draw ratio results in steady oscillations of both the velocity field and film or, respectively, fiber geometry, which is commonly known as draw resonance and which leads to inhomogeneous product properties and possible breakdown of the process.
We analyze the influence of various effects like inertia, surface tension or viscoelasticity on the instability, with particular focus on the mechanism underlying possible (de-)stabilization.