EP3114262A1

EP3114262A1 - Reinforcing textile structure for composite materials

Info

Publication number: EP3114262A1
Application number: EP15714561.6A
Authority: EP
Inventors: Jean-Michel Gault; Julie FOUREL
Original assignee: Chomarat Textiles Industries SAS
Current assignee: Chomarat Textiles Industries SAS
Priority date: 2014-03-04
Filing date: 2015-03-04
Publication date: 2017-01-11
Anticipated expiration: 2035-03-04
Also published as: MA39491A; FR3018285B1; PL3114262T3; CN106460259A; US20170067191A1; WO2015132526A1; FR3018285A1; KR20160130259A; PT3114262T; ES2895103T3; EP3114262B1

Abstract

A reinforcing textile complex for composite materials, comprising a stack of textile layers with a view to their impregnation by a polymer resin, the including complex comprising: • an assembly of weft threads (2); • an assembly of warp threads (3, 4) associated in pairs, each pair comprising two threads of different type, at least one of which (3) is based on high toughness threads, the two threads of a given pair being woven with the weft threads in a "leno" weave.

Description

TEXTILE REINFORCING COMPLEX FOR MATERIALS

COMPOSITE

Technical area

The invention relates to the field of the textile industry, and more particularly to textiles used as reinforcement for composite materials. It is more specifically a complex formed by a stack of reinforcing layers for impregnation with a polymeric resin, and in particular thermosetting resin. It relates more specifically to a configuration of this type of complex allowing one of its layers to provide both a mechanical strengthening function, and drainage of the impregnating resin for closed molds.

Previous techniques

In general, the manufacture of composite materials from fibrous reinforcements can be achieved by infusion techniques, whereby the resin is introduced into a mold at particular points, and moves within or around the fibrous layers. towards suction points. The infusion process is based on three fundamental physical principles which are the pressure difference, the viscosity of the resin and the permeability. Indeed, the migration of the resin through the textile structure (impregnation) can not take place if the permeability is not sufficient and if the pressure in the mold is constant. The permeability of a reinforcement represents its ability to be traversed by a fluid, in this case the resin. At the microscopic scale, it is related to the microporosity of the locks (assembly of fibers). On the mesoscopic scale, it is linked to the spaces separating the constituent locks from the weaving of the reinforcement. At the macroscopic scale, it depends on the weaving of the reinforcement. Permeability is expressed in m ² .

Classical roving fabrics (twill, cloth, standard gauze, etc.) or Non Crimp Fabrics (NCF) used in the infusion process have a permeability of the order of 10 ^{~ 10} to 10 ^{~ n} m ² for the glass. This permeability is generally not sufficient to ensure the correct filling of the piece which is often large. In order to improve this permeability, two types of infusion can be used for monolithic structures. It is thus possible to carry out an infusion with external drainage. In this case, the resin flows with a draining fabric, highly permeable, placed above the stack of preformed fibers. The pressure differential between the arrival of resin, located at the level of the draining, and the vent, located on the base of the preform, causes the infusion of the resin first in the draining and then through the thickness of the dry preforms. The external draining is then removed from the room using a tear-off fabric. The major disadvantage of this method is the large number of waste (tearing tissue, external draining net) and the time of setting up consumables. The infusion process with internal drainage is also known. In order to limit the waste, the draining fabric is positioned inside the textile structure. It is a very porous layer allowing a good flow of the resin through the preform. In general, it is a Continuous Filament Mat or a synthetic net that will stay in the room. The major disadvantage of this type of product is the impact on the mechanical properties due to the increase of the resin content in the final laminate.

Thus, the Applicant has described in EP 0 395 548 a textile structure composed of a stack of two reinforcing layers, composed almost exclusively of high-tenacity yarns, for example made of glass, trapping between them an aerated layer formed by from relatively thin and wavy synthetic threads. This central layer, which forms the core of the stack is relatively openwork and allows the passage of the resin between the two layers of reinforcement, which are much less permeable to the resin.

This solution, if it has great advantages, nevertheless has the disadvantage of generating resin accumulation zones which have mechanical properties significantly lower than the outer layers, and especially as the fibrous material which constitutes the soul is not composed of high tenacity yarns.

An alternative solution dedicated to infusion has been proposed by the Applicant in the document FR 2870861. This solution is, derived from the previous one, consists in using as a core a polyester knit.

Another solution has also been proposed by the Applicant in EP 0 672 776. In this solution, the fibrous webs are composed of unidirectional structures comprising son of high strength and high tenacity. Each of these plies is deformed so that the weft yarns have an inclination that is not perpendicular to the warp direction. Several of these plies are associated, combining different inclinations of the reinforcing son.

This assembly is performed without insertion of core layers facilitating creep. It is the inclination of the different threads of the superposed sheets, which allows the creep of the resin. This solution, if it has the advantage of not including fibrous materials other than those of the reinforcing layers, however has the disadvantage of a relatively low permeability to the resin in the warp direction.

It is therefore conceivable that it is therefore necessary to achieve a compromise between the mechanical performance of the composites obtained and the flow rate of the resin.

Presentation of the invention

The invention therefore proposes to provide a solution which has both good longitudinal permeability to the resin for easy impregnation during infusion process, combined with high mechanical performance for the composite obtained.

For this purpose, the invention relates to a reinforcing textile structure for composite materials, intended to form an intermediate layer to be integrated into a textile complex formed of a stack of textile layers for impregnation with a polymeric resin.

This intermediate layer is characterized in that it comprises:

A set of weft threads;

And a set of associated warp yarns in pairs, each pair comprising two yarns of different type, at least one of which is based on high tenacity yarns, the two yarns of the same pair being woven with yarns of weft according to a gauze armor. In other words, the invention consists in producing an intermediate layer which has good mechanical properties, because it is made from high-tenacity yarns, and which has good resin permeability in the warp direction and / or frame. This layer thus acts as a "structural internal draining", thus combining the advantages in terms of permeability of a synthetic internal draining and the mechanical characteristics close to a standard reinforcement.

Indeed, the configuration of the gauze pitch with two son of different nature makes some of these son, namely high-tenacity son, have a limited or no filling, and define between them channels in which the resin can easily move.

These channels are all the better defined as some of the warp son, namely the high tenacity son, are all on the same side of the sheet of weft son. Only the warp son of the second type ensure the maintenance of the main son between them.

The low clogging of the high-tenacity warp yarns is all the more important as the tension difference between the two types of warp yarns is important. It is also to a lesser extent a function of the difference of title between these two types of son. This makes it possible to work with voltage differences on the two types of warp yarns, so that the yarn of lower title supports the largest embossing.

In practice, it is possible to modulate the reinforcing properties of the draining layer by using as weft yarns which are also of high tenacity, thus imparting bidirectional reinforcement in the warp and weft directions as well.

However, in some applications, it may be useful to use only high tenacity wires in the warp direction.

As regards the warp yarns, the yarns of the second type, that is to say those of the lowest type, may be of different natures, namely either synthetic organic yarns, or even high-tenacity yarns similar to the main threads. In the latter case, the entire characteristic layer can thus be made based on high-tenacity yarns, which may be advantageous for certain properties of compatibility, or heat resistance, although the yarn of the second type does not does not participate in the mechanical strength of the product. By the construction of this layer, it is possible to very finely adjust the mechanical properties of reinforcement in the warp and weft direction, by selecting the weights of the weft and warp threads accordingly. In the case where the areal weight of the weft son is substantially equal to that of the warp son, the reinforcement is substantially balanced. This makes it possible to create channels not only in the warp direction, but also in the weft direction, thus with a large permeability in both directions. However, in the case where the permeability needs to be high in only one direction, namely the warp direction, lower-order weft threads can be used.

The influence of the binding yarns, that is to say the warp yarns of the second type, can be all the more reduced if the mass density of the warp yarns of the first type is greater by more than eight or at least three or four times that of the warp threads of the second type.

The creep capacity of the resin can be modulated according to the width of the channels defined between the main threads. Thus, in a first case, it can be expected that these channels between son are of the order of magnitude of the width of a wire. Thus, the pitch between the warp (and weft) can be between two and three times the width of one of these son.

It is also possible to provide channels of greater width, providing a pitch between the son which is greater for example to four times the width of a wire.

In practice, the size of the channels between the warp threads of higher strength can advantageously be between 0.5 and 3 mm for good permeability in the warp direction. Indeed, below 0.5 mm the gap is not sufficient to let the resin and above 3 mm, there is a phenomenon of reinforcements nesting during the evacuation. It can thus be seen that textile structures placed on either side of the draining fabric can plug the channels with the application of vacuum and drop the permeability of the product. This intermediate layer may be associated with one or more additional layers to increase creep capacity. Preferably, these additional layers are made from high-tenacity yarns and identical to that of the reinforcing layers of the complex. It may for example be a veil, or a mat of glass fibers, which by its volume facilitates the passage of the resin during molding, and improves the draining effect of the characteristic intermediate layer, without adding of synthetic material. The use of a glass mat also improves the isotropy of the complex, by attenuating the anisotropy induced by the directions of the reinforcing son of the structural draining layer. It is possible to add an additional layer on one of the faces of the intermediate layer, or two additional layers, one on each side of the intermediate layer, with identical or different compositions from one additional layer to another. Of course, this additional layer may itself be composed of a stack of elementary layers if necessary. Such an intermediate layer has properties of high permeability at least in one direction, combined with high mechanical properties. It can therefore be associated by laminating with as many layers of reinforcement as necessary. In stacks of a large number of reinforcement layers, it can replace a reinforcing layer by gaining the draining effect while maintaining a good level of mechanical performance. This complexing can take place conventionally by sewing, gluing or needling, possibly in assembly with one or more surface sails.

Brief description of the figures

The manner of carrying out the invention, as well as the advantages which result therefrom, will emerge from the description of the embodiments which follow, in support of the appended figures in which:

Figure 1 is a top view of a textile structure forming the draining intermediate layer of a complex according to the invention.

Figures 2 and 3 are views in section respectively according to the plans ΙΙ-ΙΓ and III-

ΙΙΓ of Figure 1.

FIG. 4 is a sectional view of a complex according to the invention, including the intermediate layer of FIG. Way of realizing the invention

In general, the draining and structuring intermediate layer as illustrated in FIG. 1 comprises weft yarns 2 and warp yarns 3, 4. The weft yarns 2 are arranged in parallel, and have virtually zero packing. The warp threads 3, 4 are associated in pairs.

The weaving is performed using a weave no gauze between the two warp threads 4 and 3 on the one hand, and the weft thread 2 on the other hand. The two warp threads 3,4 intersect around the weft.

Due to the voltage difference between the two types of warp yarns, and their title deviation, a configuration is obtained in which the warp threads 3 of the first type rest on the weft yarn sheet 2. Each yarn chain 4 of the second type therefore passes under a weft thread 2 and on the warp thread 3, alternately on one side and the other side of the main warp thread 3 to which it is associated.

Thus, as illustrated in FIG. 2, the main warp threads 3 are all arranged on the same side of the sheet of weft threads 2, and the warp threads 4 of the second type, that is to say, of the title weaker, pass from one side to another of the structure, with a large embourgage.

Of course, the proportions of the various son illustrated in the figures are given only as an example, and the various son may differ in the reality of this representation.

It is also possible to modulate the number of son per unit length, in the warp direction and the weft direction to adjust the mechanical properties of the future reinforcement and the creep capacity of the resin. Various examples of practical realization have thus been realized.

Example 1

• weft yarn 2: 1,200 tex glass yarn, with a basis weight of 468 g / m ² ;

• warp 3 of the first type: 1,200 tex glass yarn, with a mass per unit area of 438 g / m ² ;

• warp 4 of the second type: polyester thread of 28 tex, with a weight per unit area of 16 g / m ² ;

• not between weft threads, 1 mm

• not between warp threads: repetitive pattern with two 4 mm separated threads and then 4 separate threads from 0.5 to 0.7 mm. Example 2

Weft frame 2: glass fiber 600 tex, with a basis weight of 240 g / m ² ;

First type 3 warp: 600tex glass fiber with a basis weight of 240 g / m ² ;

Second type 4 warp: 28 tex polyester yarn with a basis weight of 20 g / m ² ;

• not between weft threads: 1, 5 mm (approximately)

• not between warp ends: 1, 5 mm (approx.) Example 3

Frame 2: glass fiber 600 tex, with a basis weight of 276 g / m ² ;

First type 3: glass fiber of 1200 tex with a weight per unit area of 280 g / m ² ;

Second type 4: 28 tex polyester yarn with a weight per unit area of 8 g / m ²

In this example, the woven glass wires 2 are finer, but are arranged with a smaller pitch, so as to form a spacing of the order of one millimeter, corresponding to the width of a weft yarn.

Example 4

Frame 2: glass fiber 600 tex with a basis weight of 276 g / m ² ;

• first type 3 warp yarn: 600 tex glass yarn with a weight per unit area of 240 g / m ^2;

· Weft yarn of the second type 4: polyester yarn 28 tex with a mass per unit area of

18g / m ² .

• not between weft threads: 1 mm

• not between warp threads: 1.5 mm

The properties of these various examples were measured with respect to a reference complex, constructed according to the teachings of patent FR 2870861, comprising two reference reinforcing layers consisting of a glass fabric of 500 g / m ² , and a core Draining reference consisting of a warp knit based on a polyester fiber of 110 dtex, an overall weight of 110 g / m ² . The performance of these four examples can be summarized in the following table:

Permeability is a physical characteristic that represents the ease with which a material allows the transfer of fluid through a connected network. Darcy's Law makes it possible to connect a flow rate to a pressure gradient applied to the fluid by virtue of a characteristic parameter of the medium traversed, namely the permeability k.

The law of Darcy is expressed by: k = ^ x ^ x η

with:

- the permeability (in m ² ),

- the flow through the test specimen (in m ³ / s),

- the section of the test piece (in m ² ),

- η the dynamic viscosity of the fluid (in Pa.s)

- ΔΡ the pressure loss measured between the ends of the specimen (in Pa)

- and AL, the length of the test piece

The permeability can be measured along 3 axes. The permeability indicated in the table above corresponds to the permeability measured in the plane of the reinforcement, in the warp direction.

The draining properties of this characteristic layer can be expressed in complexes used to make composite parts. Such complexes include a plurality of backing layers chosen for their mechanical properties. Thus, as illustrated schematically in FIG. 4, the draining layer 1 can be integrated within a stack of several reinforcing layers 11-16 made by weaving warp 20 and weft 21 yarns, and whose number and orientations are determined according to the overall mechanical properties sought for the final composite part.

It follows from the foregoing that the reinforcing structure according to the invention makes it possible to combine both structural reinforcement properties with good permeability thus making it possible to obtain a draining structural reinforcement.

Claims

1 / textile reinforcing complex for composite materials, comprising a stack of textile layers for impregnation with a polymeric resin, characterized in that it comprises an intermediate layer (1) comprising:

A set of weft threads (2);

A pair of warp yarns (3, 4) associated in pairs, each pair comprising two yarns of different type, at least one of which is based on high tenacity yarns, the two yarns of the same pair being woven with the weft yarns in a "no gauze" weave;

so that said intermediate layer (1) provides a draining role within the complex. Complex according to claim 1, characterized in that the weft threads (2) of the intermediate layer (1) are based on high tenacity yarns.

3 / complex according to claim 1, characterized in that the warp son (3) of a first type have a higher type than the warp son (4) of the second type.

4 / complex according to claim 1, characterized in that the warp son (4) of the second type are based on synthetic organic son. 5 / complex according to claim 1, characterized in that the warp son (4) of the second type are based on son high tenacity.

6 / complex according to claim 1, characterized in that the basis weight of the weft son (2) of the intermediate layer is substantially equal to the mass per unit area of the warp son.

7 / complex according to claim 1, characterized in that the density of the warp son (3) of the first type is more than three more than four times higher than that of the warp son (4) of the second type.

8 / complex according to claim 1, characterized in that the pitch between the weft son and / or warp is between two and three times the width of a weft yarn. Complex according to claim 1, characterized in that the pitch between the weft and / or warp threads is greater than four times the width of a weft thread.

10 / complex according to claim 1, characterized in that it comprises at least one layer formed by a mat of fibers, in contact with the intermediate layer.

1 1 / Complex according to claim 10, characterized in that the layer formed by the fiber mat is of a material identical to that of the reinforcing layers.