CLAIMS

1. Ablative composite material comprising a matrix and a reinforcement, characterized in that:

the matrix is ​​a phenolic resin or an epoxy resin and

the reinforcement is formed of short carbon fibers with a length of between 0.5 mm and 20 mm, and a diameter of between 6 μm and 20 μm and whose porosity is less than 15%.

2. Ablative composite material according to claim 1, in which the matrix is ​​a phenolic resin, and comprising a maximum of 60% by mass of short carbon fibers relative to the total mass of said material.

3. Ablative composite material according to claim 2, in which the phenolic resin is chosen from novolak or resol resins.

4. Ablative composite material according to claim 1, in which the matrix is ​​an epoxy resin, and comprising a maximum of 60% by mass of short carbon fibers relative to the total mass of said material, said short carbon fibers having a lower porosity at 15%.

5. Ablative composite material according to claim 4, in which the epoxy resin is chosen from flame-retardant epoxy resins.

6. Ablative composite material according to claim 4 or 5, further comprising carbon powder, preferably in a mass content of between 5% and 20% relative to the total mass of said material.

7. Process for preparing the ablative composite material according to any one of claims 1 to 6, comprising mixing the matrix and the reinforcement.

8. Part of ablative composite material according to any one of claims 1 to 6.

9. A method of thermally protecting the surface of a fuel-propelled ammunition launcher, comprising applying a part according to claim 8 to said surface.

10. Ammunition launcher propelled by a fuel comprising at least one piece of ablative composite material according to claim 8.

NEW ABLATIVE COMPOSITE MATERIAL

The subject of the present invention is a new ablative composite material, as well as its method of preparation. It also relates to a part of said ablative composite material, the process for preparing said part, and the use of said material for the thermal protection of the surface of a fuel-propelled ammunition launcher.

During the implementation of weapons on the surface buildings, the departure of ammunition generates a very severe aerothermal aggression which requires the protection of the firing range zones by specific materials. Whether on the deck of ships or in more complex systems, the performance of thermal protection materials is essential to ensure the safety of the crew and the ship and to allow maximum availability of the combat system.

An ablative material draws its performance from its ability to absorb the thermal and aerodynamic flow during the departure of ammunition thanks to suitable thermal and mechanical characteristics. In the context of thermal protection development work, it is essential to identify the properties of the material which will favor the dissipation of energy during the ablation phenomenon. The more energy a material dissipates as it degrades, the more efficient it will be. In addition, the material must be a good insulator.

Ablation is a complex and strongly coupled phenomenon involving chemical, thermal and mechanical mechanisms. Ablation heat can be defined as the energy absorbed per mass of material consumed during ablation. The higher it is, the more energy it takes to degrade the material, or in other words, the less material it takes to protect a surface. It makes sense to seek to maximize it. The heat of ablation is directly related to the specific heat, the enthalpies of reaction and the emissivity of the material.

These solutions can be separated into two large families of very different materials, organic matrix composites and ceramic composites. Ultra-high temperature ceramic materials are mainly made up of borides, nitrides, carbides and oxides of metals such as hafnium, zirconium, tantalum or titanium. These elements have particularly high melting temperatures, above 2500°C. These are state-of-the-art technologies whose high cost is hardly compatible with implementation on large surfaces.

To date, there are several types of materials used as thermal protection or whose ablative resistance has been tested, as well as some materials developed by manufacturers. Mention may be made of materials based on thermosetting resins, in particular phenolic resin, materials based on elastomers as well as materials based on ceramics or materials of the carbon-carbon type.

Apart from the case of ceramic composites, it is possible to define the composite material with three main parameters: the resin, the reinforcement and the architecture of the reinforcement. Despite the number of combinations offered by these components, not all fiber-matrix combinations perform as well as each other. The question of the cohesion of the material is as essential as the individual quality of each element constituting the composite.

The very severe aggressions generated during the firings involve a strong erosion of the surface of the thermal protections used. It is therefore essential to offer material solutions whose behavior is controlled to guarantee the availability of equipment.

There is therefore a need for an ablative material to obtain satisfactory thermal insulation properties suitable in particular for ammunition launchers.

The object of the present invention is therefore to solve the problems of thermal insulation and of controlling degradation during a retained shot or a missile launch shot.

It also aims to provide an ablative material having suitable thermal protection properties, in particular for use in particular for the preparation of ammunition launchers.

Thus, the present invention relates to an ablative composite material comprising a matrix and a reinforcement, characterized in that:

the matrix is ​​a phenolic resin or an epoxy resin and

the reinforcement is formed of short carbon fibers with a length of between 0.5 mm and 20 mm, and a diameter of between 6 μm and 20 μm.

The material according to the invention is therefore formed of a matrix and of short carbon fibers as reinforcement.

Preferably, the length of the carbon fibers is less than 20 mm.

The carbon fibers used according to the invention can be obtained from pitch or PAN (polyacrylonitrile) precursors.

Advantageously, the short carbon fibers have a porosity of less than 15%, preferably less than or equal to 10%, more preferably less than or equal to 5%.

It is important that the material according to the invention can be adapted to be subjected to severe aerothermal stress. Also, it is desirable, even essential, to limit the porosity, in particular the pores of large size which substantially accelerate the erosion of the material and to ensure that the material is as homogeneous and isotropic as possible. Preferably, the cohesion and the density of the carbon (carbon fibers) are maximized and the susceptibility to tearing is limited.

According to one embodiment, the matrix of the material of the invention is a phenolic resin. Phenolic resins are essentially resins derived from formaldehyde and phenol.

Preferably, the phenolic resin is chosen from novolac resins (prepared by acid catalysis) or resole resins (prepared by base catalysis). Preferably, the matrix of the material according to the invention is a phenolic matrix of resole type.

According to one embodiment, the matrix of the material of the invention is a phenolic resin (phenolic matrix) and said material comprises a maximum rate of 60% by mass of short carbon fibers as defined above with respect to the mass total of said material, said short carbon fibers preferably having a porosity of less than 15%.

According to one embodiment, the material comprises at least 10% by mass of short carbon fibers as defined above relative to the total mass of said material.

Preferably, the matrix of the material of the invention is a phenolic resin and said material comprises from 25% to 40% by mass of short carbon fibers

as defined above relative to the total mass of said material, said short carbon fibers having a porosity of less than 5%.

The increase in the content of short carbon fibers makes it possible to increase the conductivity of the material without degrading its ablative properties, which makes it possible to limit the rise in temperature on the front face and to limit the loss of mass without compromising performance. insulation of the material.

A particularly preferred material according to the invention comprises a phenolic matrix reinforced with 25% by mass of short carbon fibers as defined above having a low porosity, in particular less than 5%. Preferably, the pore size of the carbon fibers is less than 1 mm. The functional characteristics of the material result from the compromise between the thermal conductivity of the material and its resistance to jet erosion.

According to one embodiment, the matrix of the material of the invention is an epoxy resin.

According to one embodiment, the ablative composite material according to the invention comprises a matrix which is an epoxy resin, and comprises a maximum rate of 60% by mass of short carbon fibers as defined above with respect to the total mass said material, said material having a porosity of less than 15%.

According to one embodiment, the material comprises at least 10% by mass of short carbon fibers as defined above relative to the total mass of said material.

According to one embodiment, the ablative composite material comprises, as matrix, an epoxy resin chosen from fireproof epoxy resins.

As preferred flame-retardant epoxy resins, mention may be made, for example, of epoxy resins rich in carbon, in particular with a carbonaceous residue at 1000° C. under nitrogen of between 20% and 80% by mass.

According to a preferred embodiment, when the matrix is ​​an epoxy resin, the material of the invention further comprises carbon powder, preferably in a mass content of between 5% and 20% relative to the total mass of said material.

As carbon powder, mention may in particular be made of carbon powder whose particle size is less than 1 mm.

The present invention also relates to a process for preparing the ablative composite material as defined above, comprising mixing the matrix and the reinforcement as defined above.

The present invention also relates to a process for preparing a part of ablative composite material as defined above. This process essentially consists of performing compression molding (mold/mandrel). The preparation process and the associated parameters make it possible to control the final quality and the characteristics of the material obtained.

According to one embodiment, the method of the invention comprises a step of mixing the matrix and the reinforcement, and a step of molding said mixture by compression.

Thus, the present invention also relates to a process for preparing a part of ablative composite material as defined above, comprising a phenolic resin as matrix.

The present invention therefore also relates to a process for preparing a part of ablative composite material as defined above, in which the matrix is ​​a phenolic resin, and comprising from 10% to 60% by mass of short carbon fibers per relative to the total mass of said material.

Said method consists of several steps allowing the implementation of the invention. The manufacturing cycle includes putting the mixture under pressure and temperature according to several different cycles (temperature/pressure pairs) making it possible to obtain the characteristics required for the material.

The implementation cycle is adapted to the nature of the phenolic resin used. The essential parameter for the implementation is therefore the coupling between the pressure and the temperature. Implementation by compression is essential to obtain a material that meets the desired performance. A homogeneous mixture and a perfect distribution of the fibers in the mixture guarantee first-class performance.

The present invention also relates to a process for preparing a part of ablative composite material as defined above, comprising an epoxy resin as matrix.

The present invention therefore also relates to a method for preparing a part of ablative composite material as defined above, in which the matrix is ​​an epoxy resin, and comprising between 10% and 60% by mass of short carbon fibers per relative to the total mass of said material. Said method consists of several steps allowing the implementation of the invention. The manufacturing cycle includes putting the mixture under pressure and temperature according to several different cycles (temperature/pressure couples) making it possible to obtain the characteristics required for the material.

The implementation cycle is adapted to the nature of the epoxy resin used. The essential parameter for the implementation is therefore the coupling between the pressure and the temperature. Implementation by compression is imperative to obtain a material that meets the desired performance. A homogeneous mixture and a perfect distribution of the fibers in the mixture guarantee first-class performance.

The present invention also relates to a piece of ablative composite material, said material being as defined above. Preferably, the present invention relates to a piece of ablative composite material obtained by the aforementioned method.

The present invention also relates to a process for thermal protection of the surface of a fuel-propelled ammunition launcher, comprising the application of a part as defined above to said surface.

Preferably, the thermal protection method of the invention is intended to protect the firing environment against departures of ammunition, in particular those propelled by solid fuel.

Among the equipment allowing the launching of ammunition propelled by a fuel, mention may be made, for example, of vertical, tilting or inclined missile launchers.

The present invention therefore also relates to ammunition launchers propelled by a fuel, comprising at least one piece of ablative composite material as defined above.

EXAMPLES

Example 1: Preparation of a piece of ablative material comprising a phenolic resin

A piece of material comprising a phenolic resin according to the invention is prepared according to the method described in table 1 below.

Table 1

Example 2: Preparation of a piece of ablative material comprising an epoxy resin

A piece of material comprising an epoxy resin according to the invention is prepared according to the method described in Table 2 below.

Table 2

Example 3: Ablative properties of materials

Inventions based on phenolic and epoxy resins show a homogeneous distribution of carbon fibers without preferential orientation.

The main thermo-physical characteristics are reported in the table below.

Table 3

During degradation, the material must degrade in a safe and linear manner. This means that the erosion should be gradual and controlled with good cratering linearity as the exposure time increases. During degradation, the coal resulting from the degradation must remain confined to the upper part of the plate and the thermal allocation must not cause any deep degradation of the thermal protection.