FR3095023A1 - METAMATERIAU FOR VIBRATION FILTERING AND INSULATING PART MADE WITH LEDIT METAMATERIAU - Google Patents

Abstract

The invention relates to a metamaterial for filtering vibratory waves, the structure of which comprises at least one auxetic modular element (1), characterized in that said auxetic modular element (1) comprises at least one cell (10) carrying bridges (11). ) elastically deformable peripherals and enclosing a rigid resonator insert as well as an insulating part made with said metamaterial. Figure 1A

Description

METAMATERIAL FOR VIBRATION FILTERING AND INSULATING PART MADE WITH SUCH METAMATERIAL

The invention relates to a metamaterial intended for filtering vibrations as well as an insulating part made with said metamaterial.

More precisely, the invention is concerned with a metamaterial making it possible to provide insulation with regard to vibrations at the interface of the internal connections of a complex structure and, in particular, with respect to the vibratory phenomena generated by the rotating members of motor vehicles and/or by external stresses applied to said vehicles.

There are already many means intended to ensure filtering of the vibration waves and/or insulation with respect to the vibrations.

Among these means, mention may be made, in particular, of shims made of elastomeric material, hydraulic shims, damping devices.

Generally, these traditional means are intended, in the presence of vibrations, either to provide stiffening at high frequencies, or to process only low frequencies.

Their operating frequency bands are therefore narrow, in particular for masses of the “Tuned Mass Damper” (TMD) type on board, which restricts the field of their use and limits their effectiveness.

Moreover, at the crossroads of the vibration and acoustic domains, other insulation solutions have been found using materials with so-called auxetic properties.

These auxetic materials have a negative Poisson's ratio and generally have a structure made up of geometric shapes which under the action of a tensile stress in the longitudinal direction will extend in the transverse direction.

Such structures, including the one developed in particular by Cui and Harne, comprise a polyurethane foam block with rotating squares, each polygon of which contains a metal cylinder.

This material with double porosity can thus, depending on its compression, significantly improve vibration isolation and sound absorption.

However, this material was not developed with a view to dynamic optimization and its design (both in profile and in geometry) is therefore not suitable for the automotive field.

In addition, the use of a foam as a constituent element modifies the behavior of the material and restricts its applications in a non-negligible way.

In addition, patent FR3016945B1 describes a cellular material allowing shock absorption. This material comprises a base plate supporting an auxetic structure. The cross section of this material has a plurality of through holes which are filled with a damping material.

It therefore turns out that there is currently no insulating material with an openwork composite structure allowing a highly non-linear mechanical behavior.

Metamaterials are synthetic materials suitable and intended to process wave phenomena such as vibrations. The structure of metamaterials is generally composite and consists of a base integrating resonators. The profile and geometry of the resonators vary according to the type of waves to be processed, but they are generally arranged periodically on the base and thus make it possible to guide the waves through the metamaterial.

The present invention proposes a metamaterial whose specific structural geometry is developed with a view to solving the technical problems posed by traditional insulation and/or filtering solutions.

This object is achieved by means of an insulating metamaterial for filtering vibratory waves, the structure of which comprises at least one auxetic modular element, characterized in that the said auxetic modular element comprises at least one cell carrying elastically deformable peripheral bridges and containing a rigid resonator insert.

According to a preferred embodiment, the auxetic modular element comprises four cells interconnected by bridges so as to form a closed loop.

According to an advantageous characteristic, the walls of the cell and of the intercellular bridges are made in one piece and in the same elastomeric material and in that the rigid resonator insert is made of metal.

According to a specific characteristic, the thickness of the bridges is at least equal to that of the wall of the cell.

According to another characteristic, the bridges extend perpendicular to each other at the periphery of the cell.

According to yet another feature, the cell has a substantially circular cross-section, the interior volume of which is entirely occupied by the rigid resonator insert.

According to a first variant, the cell is cylindrical and carries four bridges which extend radially and diametrically opposite two by two.

According to another variant, the cell is spherical and carries six bridges.

Another object of the invention is an insulating part made of metamaterial for filtering vibrations in motor vehicles comprising a periodic series of modular auxetic elements as defined above, connected to each other by bridges.

According to a variant embodiment, this insulating part is in the form of a plate or a block.

Equipped with a specific composite and perforated structure, the metamaterial of the invention, by its static and dynamic characteristics, makes it possible to obtain a compact vibration isolation system affecting a widened frequency range.

In statics, the system presents a plate of stiffness (zone of null stiffness) after compression. A state of stress close to this plateau allows a more extensive dynamic filtering of vibrations. In practice, this state would be reached via the recovery of the mass of the system to be isolated (static stress).

In dynamics, the material has frequency zones in which the waves cannot propagate.

In addition, the metamaterial of the invention while having a low cost, offers better performance compared to traditional insulation materials and without increasing the size because it can be implanted in the existing interlayer space or equivalent.

Therefore, the insulation material of the invention presents an excellent compromise between cost, performance, reliability and quality.

Other characteristics and advantages of the invention will become apparent on reading the description which follows, with reference to the appended figures detailed below.

is a front view of a first embodiment of the auxetic metamaterial of the invention in the free state (unconstrained).

is a front view of the embodiment of Figure 1A in the pre-stressed condition under compression.

is a front view of the embodiment of Figures 1A and 1B deformed under stress.

is a front view of an auxetic metamaterial according to the invention produced by assembling several modular elements according to the embodiment of FIG. 1A.

is a front view of the auxetic metamaterial of Figure 2A in the deformed state under compression.

is a graph representing the stiffness curve of the metamaterial of FIG. 2A.

is a graph representing the frequency zones of the forbidden bands of the vibratory waves as a function of the dimensions of local resonators.

is a graph representing the effects of deformation on the frequencies of the band gaps of vibrational waves.

is a perspective view of a second embodiment of the auxetic metamaterial of the invention in the free state (unconstrained).

For greater clarity, identical or similar elements are identified by identical reference signs in all the figures.

Naturally, the modes of implementation of the method of the invention illustrated by the figures presented above and described below, are given only by way of non-limiting examples. It is explicitly provided that it is possible to propose and combine different modes to propose others.

The invention relates to an improved auxetic metamaterial, intended for the filtering of vibration waves and whose structure comprises at least one cellular modular element. In particular, the invention concerns the filtering and/or the absorption of vibrations at the connection interface between various components mounted in a mechanical assembly.

The auxetic metamaterial of the invention finds a specific application in the filtering of vibrations generated by rotating machines and/or external stresses.

A field of application specifically targeted by the insulation metamaterial of the invention is in the automotive sector where the metamaterial is used for the manufacture of insulating parts.

In general, a material with auxetic properties is characterized by a negative Poisson's ratio.

The Poisson's ratio corresponds, in absolute value, to the ratio between the transverse stress of a material and its longitudinal stress. This coefficient therefore translates the transverse deformation capacity of a material.

When a material with a positive Poisson's ratio is subjected to tension in the longitudinal direction, then it contracts in the transverse direction as is the case for most materials.

On the other hand, there are materials which, when subjected to longitudinal tension, see their transverse dimension increase. Their Poisson's ratio is then negative and such materials are said to be auxetic.

In general, the modular auxetic element of the metamaterial of the invention comprises at least one cell carrying elastically deformable peripheral bridges and containing a rigid resonator insert.

In the embodiment represented in particular in FIGS. 1A and 2A, the modular auxetic element 1 constituting the vibration isolation metamaterial of the invention comprises here only four cells 10 (respectively 10a, 10b, 10c and 10d) connected between they by elastically deformable bridges 11 forming a closed loop 1a. Each cell contains a rigid resonator insert 12.

In another embodiment illustrated by FIG. 2A, the insulation metamaterial of the invention may comprise a periodic series of auxetic modular elements 1 connected to each other by the intercellular bridges 11 by forming a plate P of thickness uniform or variable. The structure of the metamaterial of the invention then consists of a regular arrangement of composite cells 10 in space.

However, the preferred embodiment of the metamaterial of the invention consists in assembling several auxetic elements 1 in closed loops 1a each formed of four cells 10.

The walls of the cells 10 and of the bridges 11 are made in one piece and in the same very elastic material, for example, an elastomer with a low dissipation coefficient. The thickness of the bridges 11 and at least equal to the thickness of the wall of the cells 10.

The elastomeric material constituting the wall of the cells 10 and that of the bridges 11 is preferably chosen from the group comprising; silicone, TPU, ... while the resonator insert 12 is made with a high density material, for example, a metal chosen from the group comprising steel, lead, ...

As illustrated by FIGS. 1A, 1B and 1C, the wall of each cell 10 is extended radially by four bridges 11 which project from the periphery of the cell and in a diametrically opposite way. In the embodiment represented here, the bridges 11 are arranged on perpendicular diameters of the cell 10.

The cells 10 have a substantially circular or polygonal cross-section, the interior volume of which is entirely occupied by the rigid resonator 12 which is encapsulated and secured to the wall of the cell. As a result, under stress, the wall of the cells 10 undergoes little or no deformation, unlike the bridges 11.

Indeed and as illustrated by the figures, the metamaterial of the invention is produced by means of a modular element 1 in a loop 1a (FIG. 1A) with four cells 10, either in the form of a plate P formed from the union of several modular elements 1 (FIG. 2A) extending in the same plane.

Of course, the metamaterial of the invention can be used to manufacture insulating parts having all profiles and all geometries provided that the modular elements 1 are periodically repeated in a closed loop 1a.

When a metamaterial part is fixed on a support R to be insulated and is under stress, for example, by the action of a source of vibrations S (shown above the plate P of insulating material in FIG. 2A ), the intercellular bridges 11 buckle and the cells 10 pivot (in the direction of the arrows in FIGS. 1B/1C and FIG. 2B) while gradually approaching (FIG. 1B) which leads to flattening the recess located in the center of the loop 1a.

The state of deformation of the plate P of insulating metamaterial as it results from a compression is illustrated by figure 2B (with 5% deformation) while figure 3 represents the curve of stiffness of the plate P of material (obtained by numerical simulation).

As this appears in FIG. 2B, the zones of greatest stress are located here at the level of the lateral intercellular bridges.

The curve in Figure 3 shows two main trends: on the one hand, a quasi-linear initial slope and, on the other hand, a plateau where the stiffness is close to zero. Such a stiffness value makes it possible to deal with vibrations in an optimal manner and to isolate the components to be protected.

Although not represented in FIG. 3, a resumption of stiffness has been observed when the various cells 10 come into contact and come into abutment with each other.

In dynamics, simulations on infinite periodic structures make it possible to observe frequency zones where the waves are reflected and cannot propagate. The study of these zones called forbidden bands (or "bandgaps") has made it possible to show on the one hand the interest of inserting local resonators of maximum diameter (figure 4A), and on the other hand to highlight the the effect of the deformation on the frequencies of the forbidden bands (FIG. 4B).

FIG. 4A represents approximately the dimensions of the forbidden bands as a function of the radius of the resonator inserts 12 and of the frequencies f, for a compression rate of 20%.

Similarly, FIG. 4B represents the influence of compression deformation on these forbidden bands as a function of the frequencies f, for resonator inserts 12 with a radius of 2 mm.

The effects presented on the curves of figure 4B appear at high frequencies, but it is easy to go down in frequency, by optimizing the constituent materials and the dimensions of the cells 10.

According to a first embodiment, the auxetic metamaterial according to the invention is used to produce insulating parts by extrusion in two dimensions, that is to say in the form of a block or a plate having a constant section in the third direction (perpendicular to the plane of the figures). This variant which is illustrated, in particular, by FIGS. 2A and 2B, makes it possible to have resonators of significant mass and a different stiffness in this third direction, which can prove to be useful depending on the applications. In this case, the manufacturing method envisaged uses a mold printed in 3D to carry out the molding of the plate P with an elastomer material of the silicone type.

According to another embodiment, provision is made to produce an insulating part in auxetic metamaterial with a cross-section that varies according to the three dimensions (for a structure developed in 3D). In such a mode illustrated by FIG. 5, the cells 10 and the resonator inserts 12 (one of which is shown exploded) are then no longer cylinders, but spheres, which reduces their mass and therefore their potential effect but which makes it possible to have prohibited bands for the vibrations in all the directions.

For this other mode, the spherical cells then carry six connecting bridges 11 with the adjacent cells 10 and the manufacturing process will use either a lost negative mold or a suitable 3D print.

Claims (10)

Metamaterial for filtering vibratory waves, the structure of which comprises at least one auxetic modular element (1), characterized in that said auxetic modular element (1) comprises at least one cell (10) carrying elastically deformable peripheral bridges (11) and enclosing a rigid resonator insert (12). Metamaterial according to claim 1, characterized in that said auxetic modular element (1) comprises four cells (10a, 110b, 10c, 10d) interconnected by said bridges (11) so as to form a closed loop (1a). Metamaterial according to one of the preceding claims, characterized in that the walls of said cell (10) and of said bridges (11) are made in one piece and in the same elastomeric material and in that said rigid resonator insert (12 ) is made of metal. Metamaterial according to one of the preceding claims, characterized in that the thickness of the bridges (11) is at least equal to that of the wall of the cell (10). Metamaterial according to one of the preceding claims, characterized in that said bridges (11) extend perpendicular to each other at the periphery of the cell (10). Metamaterial according to one of the preceding claims, characterized in that said cell (10) has a substantially circular section, the interior volume of which is entirely occupied by the rigid resonator insert (12). Metamaterial according to the preceding claim, characterized in that said cell (10) is cylindrical and carries four bridges (11). Metamaterial according to claim 7, characterized in that said said bridges (11) extend radially and diametrically opposed in pairs. Metamaterial according to claim 6, characterized in that said cell (10) is spherical and carries six bridges (11). Metamaterial insulating part for filtering vibrations in motor vehicles, characterized in that it comprises a periodic series of auxetic modular elements (1) according to one of the preceding claims, connected to each other by said bridges (11 ).