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ESR6: Periodic inclusions in auxetic media PhD Position at UFC (Université de Franche-Comté, Besançon, France) and UoB (University of Bristol, UK)
Ecole Centrale de Lyon, Ecully
Full Description:


In this work we plan to investigate further the ability of auxetic composites to maximize energy dissipation by combining Bragg effect at several scales, resonant inclusions and negative Poisson’s ratio effect. The two main auxetic effects that will be investigated are the auxetic character of the core and of the foam that can fill the free spaces of the core. The auxetic periodic base structure that will be considered in this work will be defined according to the partners’ previous works on this topic, in coherence with ESR3. The work will be focused on the design of the inclusions that will be used in the free spaces of the core. We plan to investigate the following concepts:
1- As a starting point, the classical solution which uses a covering plate that is opened with necks constituting Helmholtz resonators will be considered. This will constitute a basis for comparison, while being almost directly applicable for industrial applications.
2- In the next step, we plan to investigate the use of a second scale periodicity inside the free space of the cores. For improvement of the LF behavior, the scale separation must be such as the period of the inclusions is much larger than the specific size of the core. This can be achieved in several ways: using acoustic resonators or using mechanical single resonators made of polymer/metal, which can be tuned by blocks in a large-scale arrangement. This double scale approach has been found to be effective in several works for porous materials and could be very efficient to improve the behavior of the package. Dedicated double-scale homogenization approaches will be used to design the system and obtain a numerically efficient model of the concept. An alternative strategy based on auxetics properties will be the use of auxetic foams to fill the spaces of the core. This particular material has been found to exhibit interesting acoustic properties and is a good candidate for sound attenuation.
3- The last investigation will be focused on the combination of the Bragg effect associated to the geometry of the core to gradient properties of inclusions. The inclusions will be tuned in a spatially continuous way to achieve ultimate absorption in a target frequency range. Here again, the scale separation will be probably necessary to avoid lowering of the performances that would be due to the coupling between Bragg effect and gradient effect. Manufacturing of demonstrators will be an integral part of this workpackage. We will use combinations of laser cutting, injection moulding for the polymer/metal resonators and thermoforming processes patented at UoB to produce the auxetic foams at industrial scale for higher technology readiness levels.

Expected Results
All the designs will be model-based, using dedicated homogenization tools, and practical realizations will be tested in labs, both in terms of structural and acoustic behaviors.

Posted on: 30 May 2016Deadline to apply: 01 September 2016Start Date: 01 October 2016 Duration: 36 months
The Fund category is Mixed Funding and the salary is 35-40k€ annual gross
Doctoral School is Doctoral program in physical and engineering sciences in the Rhône-Alpes Region.

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