Stock material or miscellaneous articles – Structurally defined web or sheet – Honeycomb-like
Reexamination Certificate
1998-08-13
2001-07-31
Lorin, Francis J. (Department: 1775)
Stock material or miscellaneous articles
Structurally defined web or sheet
Honeycomb-like
Reexamination Certificate
active
06268038
ABSTRACT:
CROSS REFERENCE TO RELATED APPLICATION
This application corresponds to French application 97 10490 of Aug. 13, 1997, the disclosure of which is incorporated herein by reference.
FIELD OF THE INVENTION
The present invention relates to an acoustically resistive layer particularly for use in the production of walls of nacelles of aircraft motoreactors, as well as the process for production of this layer, but also to an acoustically absorbent panel provided with at least one such layer.
BACKGROUND OF THE INVENTION
It is known that aircraft motoreactors generate substantial acoustic emissions against which steps must be taken with greatest effectiveness and as to which many improvements have been provided.
As in all technological advances, the greatest gains are quickly obtained with the current means that are well known, but to improve further the struggle against acoustic emissions, it is necessary to work very pointedly on combinations of materials, as in the present invention, the results obtained being significantly improved.
There will be selected in the description that follows, the example of walls of nacelles of aircraft motoreactors, because the explanations can be immediately comprehensible, but nevertheless the uses are very numerous in aeronautics, as well as in other fields such as gas turbines, heat engines or blowers and more generally all machines which generate substantial noise which should be damped under difficult conditions of temperature, pressure and/or mechanical resistance.
To damp noise, particularly through the walls, resonators of the Helmholtz type are used which permit attenuating in a reactive manner certain radial acoustic components under certain conditions of dimensioning of the material. Such a resonator comprises a hollow structure of the honeycomb type disposed between two resistive layers.
The honeycomb structure provides a cavity which permits attenuating by trapping certain noisy frequencies in a reactive manner.
The acoustically resistive layer has, in addition to its role of partitioning the hollow structure, a dissipating role, which is to say that it permits transforming acoustic energy into heat.
The present invention relates more particularly to the production of an acoustically resistive layer which permits obtaining physical attenuation by transformation of the acoustic energy into heat, particularly incident waves.
There are already known embodiments of such resistive layers made by combining a honeycomb structure and a total rear reflector.
A first example consists in using as the resistive layer perforated metal or composite sheet, which permits obtaining a single layer, high structural resistance and good control of the proportion of open surfaces.
On the other hand, this type of layer has high acoustical non-linearity, high dependence on tangential flow and low resistance to erosion in the case of a composite layer.
A second example is the combination of perforated metal sheet with metallic cloth or composite. In this case, there is achieved control of the porosity of the constituents and the possible adjustment of the proportion as well as the high structural resistance with supplemental advantages of moderated acoustic non-linearity and moderated dependence on flow.
By contrast, the layer is doubled, which requires a delicate assembly process, which is long and costly, with risks of acoustic inhomogeneity if this assembly has disparities, as well as the risk of corrosion. It should also be noted that the choice of the materials can be imposed by the requirements of assembly.
A third example of the prior art consists in combining a grill and a metallic cloth or composite.
In this case, the structural resistance is high and the phenomena of acoustic non-linearity and dependence on flow are moderated.
On the other hand, surface acoustic homogeneity is lacking, with risk of aerodynamic relief. Repeatability is difficult to obtain and the adjustment of the open proportion of the surface of the grill is delicate because there is a dispersion during fabrication and above all because of the unavailability of grills with adjustable surface area.
There can also be cited a fourth example which consists in using a metallic or synthetic cloth without structural reinforcement.
In this embodiment, there is a monolithic layer, low non-linearity, low dependence on tangential flow and good control of the proportion of porosity.
On the other hand, the structural resistance is unfortunately low, more particularly with cloths which have good properties of acoustic damping.
SUMMARY OF THE INVENTION
The object of the present invention is to provide an acoustically resistive layer with a proportion of open surface which is easily and precisely adjustable, which meets acoustic objectives, which meets structural requirements to resist underpressure during flight, that resists the weight of humans in certain portions as well as aerodynamic and inertial forces of the entry of air into the motor housing, for example in the particular case of an aircraft motor reactor nacelle. In such an application, this material must also permit resisting the “fan blade off” phenomenon, which is to say the phenomenon of losing a blade.
The resistive acoustic layer according to the invention must also resist erosion arising from the penetration of sand into the air flow, to electrical phenomena such as lightning striking or against corrosion.
This resistive layer must also permit an adjustment of the properties, not only mechanical but acoustical, by the combination of two materials whose assembly poses no problems.
The present invention also has for its object the process of production of this resistive layer as well as an acoustic panel made with this resistive layer.
The present invention also relates to a process of production of an acoustically absorptive panel provided with a resistive layer according to the invention, as well as the obtained panel.
To this end, the resistive acoustic layer according to the invention comprises at least one layer of acoustically shock absorbing cloth and a reinforcing material, characterized in that this reinforcing material comprises filaments, with adjustable proportion of open surface, secured to said acoustically damping cloth.
These filaments are disposed unidirectionally, bidirectionally or even multidirectionally.
The invention also has for its object a process of production of a resistive acoustic layer which consists in disposing the acoustically absorbing cloth on a mold shaped to the profile of the layer to be obtained and disposing on this acoustically absorbing cloth filaments impregnated with a binder by filament winding and withdrawing the layer thus obtained from the mold. In this case, the binder will have an adhesive capacity permitting it to remain secured to the acoustic cloth during handling, before final hardening of the panel, without a supplemental operation.
According to a modification, the process consists in disposing the acoustically damping material on a mold shaped to the profile of the layer to be obtained, and disposing on this acoustically damping material filaments impregnated with a binder with the application by deposition and application with pressure and withdrawing the layer thus obtained from the mold. In this case, the binder will have an adhesive capacity permitting it to remain secured to the acoustic cloth during handling, before final hardening of the panel, without a supplemental operation.
The invention also relates to panels thus obtained which comprise at least one external resistive layer secured to one of the surfaces of a honeycomb core whose other surface comprises a total reflector or several honeycomb core structures superposed with the interposition between these cores of a septum of the acoustically resistive layer type.
The invention also relates to a process for production of an acoustic panel comprising an acoustically resistive layer which comprises the following steps in this order or in the reverse order:
emplacement of a mold shaped to the profile of the panel to be obt
Andre Robert
Batard Hervé
Porte Alain
Aerospatiale - Societe Nationale Industrielle
Lorin Francis J.
Young & Thompson
LandOfFree
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