Summary:

In the field of underwater acoustics, the detection of vessels is now a widely studied subject. Hull coatings can be used to avoid detection, but their performance needs to be improved to keep pace with the development of SONAR systems, particularly at low frequencies. Metamaterials are used for this purpose because of their frequency filtering and local resonance properties. However, another strategy is to look at metamaterials with unusual mechanical properties, such as an anti-auxetic Poisson's ratio, i.e. greater than 0.5. In this thesis, a structure making it possible to obtain such Poisson's ratios is studied, in the case of infinite volumes and then adapted to the case of plates of finite thickness, using numerical tools based on finite element simulation. A homogenisation method in the long wavelength limit is developed from the numerical tools by exploiting the dispersion curves and is used to obtain the effective properties of the structure both in volume and in plate. In the case of the plate, the model is adapted to take into account a matrix density. The plate structure is then characterised statically by tensile tests and dynamically by the identification of bending modes. These tests highlight the limits of validity of the homogenisation model. Finally, coatings are designed on the basis of the architectural structure to meet the performance targets set, particularly at low frequencies, for underwater stealth. Several panels are then proposed.

Abstract:

In the context of underwater acoustics, the detection of vessels is now a widely studied subject. Hull coatings allow to avoid this detection but it is necessary to improve their performances to follow the development of SONAR systems, in particular for low frequencies. Metamaterials are used for this purpose for their frequency filtering and local resonance properties. However, another strategy is to focus on metamaterials with unusual mechanical properties, such as an anti-auxium Poisson's ratio, i.e. greater than 0.5. In this thesis, a structure allowing to obtain such Poisson's ratio is studied, in the case of infinite volumes and then adapted to the case of plates of finite thickness, by numerical tools based on finite element simulation. A homogenization method in the long wavelength limit is developed from the numerical tools by exploiting the dispersion curves and is used to obtain the effective properties of the structure both in volume and in plate. In the case of the plate, the model is adapted to take into account a matrix density. The plate structure is then characterized statically by tensile tests and dynamically by the identification of bending modes. These tests allow to highlight the limits of validity of the homogenization model. Finally, coatings are designed from the architectural structure to meet the performance objectives set, especially in low frequencies, for underwater stealth. Several panels are then proposed.