U.S. patent application number 14/441192 was filed with the patent office on 2015-10-15 for method of applying an intermediate material making it possible to ensure the cohesion thereof, method of forming a stack intended for the manufacture of composite components and intermediate material.
The applicant listed for this patent is HEXCEL REINFORCEMENTS. Invention is credited to Jean-Marc Beraud, Jacques Ducarre.
Application Number | 20150290883 14/441192 |
Document ID | / |
Family ID | 47505177 |
Filed Date | 2015-10-15 |
United States Patent
Application |
20150290883 |
Kind Code |
A1 |
Beraud; Jean-Marc ; et
al. |
October 15, 2015 |
METHOD OF APPLYING AN INTERMEDIATE MATERIAL MAKING IT POSSIBLE TO
ENSURE THE COHESION THEREOF, METHOD OF FORMING A STACK INTENDED FOR
THE MANUFACTURE OF COMPOSITE COMPONENTS AND INTERMEDIATE
MATERIAL
Abstract
The present invention relates to a method for continuously
applying on a deposition surface of an intermediate material
composed of a unidirectional layer of reinforcing fibers associated
on at least one of its faces to a layer of thermoplastic and/or
thermosetting material that does not represent more than 10% of the
total weight of the intermediate material.
Inventors: |
Beraud; Jean-Marc; (Rives,
FR) ; Ducarre; Jacques; (Corbelin, FR) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
HEXCEL REINFORCEMENTS |
Dagneux |
|
FR |
|
|
Family ID: |
47505177 |
Appl. No.: |
14/441192 |
Filed: |
November 18, 2013 |
PCT Filed: |
November 18, 2013 |
PCT NO: |
PCT/FR2013/052760 |
371 Date: |
May 7, 2015 |
Current U.S.
Class: |
428/172 ;
156/164 |
Current CPC
Class: |
B32B 2262/106 20130101;
B29C 70/545 20130101; B32B 2307/516 20130101; B32B 3/30 20130101;
B32B 2260/046 20130101; B29K 2307/04 20130101; B32B 3/266 20130101;
B32B 2307/54 20130101; B29C 70/086 20130101; B29C 70/382 20130101;
B32B 7/08 20130101; B32B 2305/08 20130101; B29C 70/38 20130101;
B29K 2105/0881 20130101; B32B 2307/718 20130101; B32B 2260/023
20130101; B32B 5/022 20130101; B29C 70/20 20130101; B29C 70/56
20130101; B32B 5/26 20130101; B32B 2262/02 20130101; B29C 70/543
20130101; B29C 70/443 20130101; B29C 70/386 20130101 |
International
Class: |
B29C 70/38 20060101
B29C070/38; B29C 70/56 20060101 B29C070/56; B32B 5/26 20060101
B32B005/26; B32B 3/30 20060101 B32B003/30; B32B 5/02 20060101
B32B005/02 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 19, 2012 |
FR |
1260966 |
Claims
1- A method for continuously applying on a deposition surface of an
intermediate material composed of a unidirectional layer of
reinforcing fibers associated on at least one of its faces to a
layer of thermoplastic and/or thermosetting material, the layer(s)
of thermoplastic and/or thermosetting material forming the
intermediate material not representing more than 10% of the total
weight of the intermediate material, wherein said method comprises
the steps of: providing an intermediate material that has undergone
an operation applying spot transverse forces, performed in such a
way as to traverse the total thickness of the intermediate material
and accompanied by heating, leading to the at least partial melting
of the thermoplastic material or the partial or complete
polymerization of the thermosetting material, at the spot
application of transverse forces, and leading to the penetration of
the thermoplastic and/or thermosetting material and creating
bonding bridges in the thickness of the unidirectional layer of
reinforcing fibers, preferably extending from one main face to the
other of the unidirectional layer of reinforcing fibers,
continuously applying said intermediate material along a given
movement trajectory, with simultaneous application on the
intermediate material of a tension and a pressure, in such a way as
to apply the intermediate material on the deposition surface, the
deposition being performed by applying one face of the intermediate
material in the process of being laid up to a layer of
thermoplastic and/or thermosetting material on the deposition
surface and/or by applying the intermediate material in the process
of being laid up on the deposition surface carrying a thermoplastic
and/or thermosetting material, and by activating the thermoplastic
and/or thermosetting material that will exist at the interface
between the intermediate material and the deposition surface, in
such a way as to ensure the bond between the laid-up intermediate
material and the deposition surface.
2- The application method according to claim 1, wherein the
intermediate material is continuously applied, along a given
movement trajectory, under the action of a tension and a pressure
in such a way as to apply on the deposition surface a face of the
intermediate material in the process of being laid up corresponding
to a layer of thermoplastic and/or thermosetting material and to
activate, said layer of thermoplastic and/or thermosetting material
during its deposition, in such a way as to ensure the bond between
the laid-up intermediate material and the deposition surface.
3- The method for forming a stack by successive applications of
intermediate materials composed of a unidirectional layer of
reinforcing fibers associated on at least one of its faces to a
layer of thermoplastic and/or thermosetting, material, wherein the
intermediate materials are continuously applied according to the
method of claim 1.
4- The method for forming a stack according to claim 3, wherein the
stack includes several unidirectional layers of reinforcing fibers,
with at least two unidirectional layers of reinforcing fibers
extending in different directions.
5- The method according to claim 1 wherein, with the exception of
the areas bordering the spot application of transverse forces, over
at least 50% of its thickness, the layer of unidirectional fibers
is not impregnated with thermoplastic and/or thermosetting
material.
6-9. (canceled)
10- The method according to claim 1 wherein the movement trajectory
extends parallel to the direction of the unidirectional fibers.
11- The method according to claim 1 wherein the activation is
carried out by heating and is followed by cooling.
12- (canceled)
13- The method according to claim 1 wherein the operation of
applying spot transverse forces is performed in a direction
transverse to the surface of the intermediate material.
14- (canceled)
15- The method according to claim 1 wherein the operation of
applying spot transverse forces leaves perforations in the
traversed layers.
16- (canceled)
17- The method according to claim 1 wherein the transverse forces
are applied at application spots arranged in lines running parallel
to one another.
18- The method according to claim 1 wherein the intermediate
material is composed of a layer of carbon fibers, associated on
each of its faces to a layer of thermoplastic and/or thermosetting
material.
19- The method according to claim 1 wherein the unidirectional
layer of reinforcing fibers of the intermediate material is a
unidirectional sheet of carbon fibers.
20-21. (canceled)
22- The method according to claim 1 wherein the layer(s) of
thermoplastic and/or thermosetting material forming the
intermediate material is (are) non-woven materials made of
thermoplastic fibers.
23. The method according to claim 22, wherein the non-woven
materials forming the intermediate Material has (have) a basis
weight in the range from 0.2 to 20 g/m.sup.2.
24-25. (canceled)
26- An intermediate material composed of a unidirectional layer of
reinforcing fibers associated on at least one of its faces to a
thermoplastic and/or thermosetting material, the layer(s) of
thermoplastic and/or thermosetting material forming the
intermediate material not representing more than 10% of the total
weight of the intermediate material wherein the intermediate
material has undergone an operation of applying spot transverse
forces, performed in such a way as to traverse the total thickness
of the intermediate material and being accompanied by heating
leading to the at least partial melting of the thermoplastic
material or a partial or complete polymerization of the
thermosetting material, at the application spots of transverse
forces, and leading to a penetration of the thermoplastic and/or
thermosetting material and creating bridges in the thickness of the
unidirectional layer of reinforcing fibers, preferably extending
from one main face to the other of the unidirectional layer of
reinforcing fibers, and in that the operation of applying spot
transverse forces is performed with a density of application points
of 40000 to 250000 per m.sup.2 and leads to an opening factor of 0
to 2%.
27- The intermediate material according to claim 26, wherein, with
the exception of the areas bordering the application spots of
transverse forces, over at least 50% of this thickness, the layer
of unidirectional fibers is not impregnated with thermoplastic
and/or thermosetting material.
28- The intermediate material according to claim 26 the
intermediate material is composed of a layer of carbon fibers
associated on each of its faces to a layer of thermoplastic and/or
thermosetting material.
29- The intermediate material according claim 26 wherein the
unidirectional layer of reinforcing fibers present in the
intermediate material is a unidirectional Sheet of carbon
fibers.
30-31. (canceled)
32- The intermediate material according to claim 26 wherein the
layer(s) of thermoplastic and/or thermosetting material forming the
intermediate material is (are) non-woven materials made of
thermoplastic fibers.
33- The intermediate material according to claim 32, wherein the
non-woven material(s) forming the intermediate material has (have)
a basis weight in the range from 0.2 to 20 g/m.sup.2.
34- (canceled)
35- A method for manufacturing a composite part comprising a step
of forming a stack using the method of claim 3 by successive
applications of intermediate materials, said intermediate materials
each being composed of a layer of reinforcing fibers associated on
at least one of its faces to a layer of thermoplastic and/or
thermosetting material or of a mixture of thermoplastic and
thermosetting materials, followed by a step of diffusion, by
infusion or injection, of a thermosetting resin, of a thermoplastic
resin or a mixture of such resins, inside the stack, followed by a
step of hardening of the desired part by a step of
polymerization/reticulation following a defined
pressure-temperature cycle, and a cooling step.
36-39. (canceled)
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to the technical field of
reinforcing materials, suitable for the forming of composite parts.
More precisely, it relates to methods and uses for improving the
resistance to delamination of materials during their
application.
[0003] 2. Description of Related Art
[0004] The fabrication of composite parts or articles, i.e.
comprising, firstly, one or more reinforcements or fibrous sheets
and, secondly, a matrix (which is, usually, mainly of thermosetting
type and can include one or more thermoplastics) can, for example,
be produced by a method called "direct" or "LCM" (Liquid Composite
Molding) method. A direct method is defined by the fact that one or
more fibrous reinforcements are employed in the "dry" state (i.e.
without the final matrix), the resin or matrix, being implemented
separately, for example by injection into the mold containing the
fibrous reinforcements (the "RTM" method, for Resin Transfer
Molding), by infusion through the thickness of the fibrous
reinforcements ("LRI" method or Liquid Resin Infusion method, or
"RFI" method or Resin Film Infusion method), or else by manual
coating/impregnation with roller or brush, on each of the
individual layers of fibrous reinforcement, applied successively to
the form.
[0005] For the RTM, LRI or RFI methods, it is generally necessary
to first of all manufacture a fibrous preform or stack of the shape
of the desired finished article, then impregnate this preform or
stack with a resin intended to form the matrix. The resin is
injected or infused by differential pressure at a given
temperature, then once the entire required quantity of resin is
contained in the preform, the whole is taken to a higher
temperature to perform the cycle of polymerization/reticulation and
thus lead to its hardening.
[0006] Composite parts used in the automotive, aeronautical or
naval industries are particularly subject to very strict
requirements, particularly in terms of mechanical properties. To
save fuel, the aeronautical industry has replaced many metallic
materials by composite materials, which are lighter.
[0007] The resin which is subsequently added, particularly by
injection or infusion, to the unidirectional reinforcing sheets
during the production of the part can be a thermosetting resin, for
example of epoxy type. To allow proper flow through a preform
composed of a stack of different layers of carbon fibers, this
resin is usually very fluid, for example with a viscosity in the
order of 50 to 200 mPas. at the infusion/injection temperature. The
major drawback of this type of resin is its fragility after
polymerization/reticulation, which causes the produced composite
parts to have poor impact resistance.
[0008] In order to solve this problem, it has been proposed in
documents of the prior art to combine the unidirectional layers of
carbon fibers with intermediate polymer layers, and in particular
with a non-woven material made of thermoplastic fibers. Such
solutions are notably described in the patent applications or
patents EP 1125728, U.S. Pat. No. 6,828,016, WO 00/58083, WO
2007/015706, WO 2006/121961 and U.S. Pat. No. 6,503,856. The
addition of this intermediate layer of polymer, such as a non-woven
material, makes it possible to improve the mechanical properties in
the Compression After Impact (CAI) test, a test commonly used to
characterize the impact resistance of structures.
[0009] The applicant has also proposed, in the earlier patent
applications WO 2010/046609 and WO 2010/061114, particular
intermediate materials consisting of a sheet of unidirectional
fibers, in particular made of carbon, coupled by adhesion of each
of its faces with non-woven thermoplastic fiber material (also
known as non-woven material), as well as the method for
manufacturing these materials.
[0010] When employing such intermediate materials, particularly in
the form of veiled tapes, the Applicant has observed that upon the
automated lay-up of a veiled tape, the latter is bonded to the
preceding ply by a combination of a pressure and heating action
followed by cooling, the latter being possibly achievable without
any particular calorie-extracting action, by using a "natural"
process. The tape is then bonded to the preceding ply by its lower
face, and this mechanical bond is shear stressed all the time the
tape is being laid-up. The stress is of an intensity proportional
to the (lay-up tension)/(bonded length). The laying-up tension
being generally considered to be constant, and the result is that
the shear stress is higher in the first centimeters of lay-up and
will decrease with the length of the laid-up tape. The shear stress
is distributed over the whole thickness of the tape and, if the
laying-up tension is too high, a delamination of the tape in its
central area, which is composed of dry reinforcing fibers, has been
observed in some cases by the applicant in the first centimeters of
lay-up. Indeed, the applicant has observed that in such materials
comprising a tape of unidirectional fibers associated on at least
one of its faces to a layer of thermoplastic and/or thermosetting
material, a preferential mechanical bond is established between the
filaments located on their main faces on the tape and the
thermoplastic and/or thermosetting material, whereas the central
area of the tape, which solely composed of filaments, is the area
with a lower shear strength.
[0011] This phenomenon can also be accentuated in the case of
materials associated on each of their main faces to a layer of
thermoplastic and/or thermosetting material, when a laying-up
member, of the small or large roller type depending on the width of
the material to be laid up, is used to lay up the material. In this
case, in the very first millimeters, or even centimeters, of
bonding of the material, the face in contact with the roller tends
to adhere to it, which can also promote the delamination of the
material when its other face is then bonded to the surface on which
it is laid and which can be a support or the preceding ply.
SUMMARY OF THE INVENTION
[0012] In this context, the objective of the invention is to remedy
the delamination problems that can be observed in some cases,
during the application of intermediate materials composed of a
layer of reinforcing fibers associated on at least one its faces to
a layer of thermoplastic or thermosetting material or a mixture of
thermoplastic and thermosetting materials, such as for example with
the veiled tapes described in the patent applications WO
2010/046609 and WO 2010/061114, which are implemented in the
production of stacks in particular. To do this, the present
invention proposes a new deposition method implementing a prior
step and making it possible to preserve the integrity of the
intermediate materials used during deposition (laying-up).
[0013] The present invention relates to a method for continuously
applying on a deposition surface of an intermediate material
composed of a unidirectional layer of reinforcing fibers associated
on at least one of its faces to a layer of thermoplastic and/or
thermosetting material, the layer(s) of thermoplastic and/or
thermosetting material forming the intermediate material not
representing more than 10% of the total weight of the intermediate
material, and preferably representing 0.5 to 10%, and more
preferably 2 to 6%, of the total weight of the intermediate
material, wherein: [0014] prior to its application, the
intermediate material has undergone an operation applying spot
transverse forces, performed in such a way as to traverse the total
thickness of the intermediate material and accompanied by heating,
leading to the at least partial melting of the thermoplastic
material or the partial or complete polymerization of the
thermosetting material, at the spot application of transverse
force, and leading to the penetration of the thermoplastic and/or
thermosetting material and creating bonding bridges in the
thickness of the unidirectional layer of reinforcing fibers,
preferably extending from one main face to the other of the
unidirectional layer of reinforcing fibers, [0015] the intermediate
material is continuously applied, along a given movement
trajectory, with simultaneous application on the intermediate
material of a tension and a pressure, in such a way as to apply it
on the deposition surface, the deposition being performed by
applying one face of the intermediate material in the process of
being laid up to a layer of thermoplastic and/or thermosetting
material on the deposition surface and/or by applying the
intermediate material in the process of being laid up on the
deposition surface carrying a thermoplastic and/or thermosetting
material, and by activating the thermoplastic and/or thermosetting
material that will exist at the interface between the intermediate
material and the deposition surface, in such a way as to ensure the
bond between the laid-up intermediate material and the deposition
surface.
[0016] In the context of the invention, before the deposition
operation the intermediate material undergoes an operation applying
spot transverse forces, in such a way as to increase cohesion in
the thickness of the intermediate material. The integrity of the
intermediate material is then better preserved during its
deposition, in spite of the shear stresses it undergoes.
[0017] The invention also relates to a method for forming a stack
by successive applications of intermediate materials composed of a
unidirectional layer of reinforcing fibers associated on at least
one its faces to a layer of thermoplastic and/or thermosetting
material, wherein the intermediate materials are applied according
to the continuous method of the invention. The produced stack
includes several unidirectional layers of reinforcing fibers, with
at least two unidirectional layers of reinforcing fibers extending
in different directions.
[0018] Another subject of the invention is the use, in a continuous
application method according to the invention, of an intermediate
material having previously undergone an operation applying spot
transverse forces, to preserve the cohesion of the material during
its deposition, and in particular in the first centimeters of
deposition.
[0019] Another subject of the invention is a method for fabricating
a composite part comprising a step of formation, according to the
method defined in the context of the invention, of a stack by
successive applications of intermediate materials, said
intermediate materials being each composed of a layer of
reinforcing fibers associated on at least one of its faces to a
layer of thermoplastic or thermosetting material, followed by a
step of diffusion, by infusion or injection, of a thermosetting
resin, of a thermoplastic resin or of a mixture of such resins,
inside the stack, followed by a step of consolidation of the
desired part followed by a step of polymerization/reticulation
according to a defined pressure-temperature cycle, and a cooling
step.
[0020] The present invention also relates to intermediate materials
composed of a unidirectional layer of reinforcing fibers associated
on at least one of its faces to a thermoplastic and/or
thermosetting material, the layer(s) of thermoplastic and/or
thermosetting material forming the intermediate material not
representing more than 10% of the total mass of the intermediate
material and preferably representing from 0.5 to 10%, and more
preferably from 2 to 6%, of the total mass of the intermediate
material, having undergone an operation applying spot transverse
forces, performed in such a way as to traverse the total thickness
of the intermediate material and being accompanied by heating
leading to the at least partial melting of the thermoplastic
material or the partial or complete polymerization of the
thermosetting material, at the application spots of transverse
forces, and leading to the penetration of the thermoplastic and/or
thermosetting material and creating bridges in the thickness of the
unidirectional layer of reinforcing fibers, preferably extending
from one main face of the unidirectional layer of reinforcing
fibers to the other. Advantageously, the operation applying spot
transverse forces is carried out with a density of application
points of 40000 to 250000 per m.sup.2, and preferably of 90000 to
110000 per m.sup.2 and the obtained intermediate material has an
opening factor of 0 to 2%, and preferably of 0 to 1% and more
preferably of 0%. In particular, such an intermediate material can
have an opening factor of 0 to 2% and preferably of 0%, and have
been obtained with a density of application points of 90000 to
110000 per m.sup.2.
[0021] The following description, with reference to the appended
figures, makes it possible to better understand the invention and
details various variant of implementations, indiscriminately
applicable to the methods and uses forming the subject of the
invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0022] FIGS. 1A and 1B are schematic views illustrating two modes
of application of intermediate materials that can be used in the
context of the invention.
[0023] FIG. 2 schematically represents the forces applied to an
intermediate material at the start of its deposition.
[0024] FIG. 3 is a schematic view illustrating another mode of
application of intermediate materials that can be used in the
context of the invention.
[0025] FIGS. 4A to 4C are schematic views illustrating the
successive application of intermediate materials appearing in tape
form.
[0026] FIG. 5 is a schematic view of a series of application points
where transverse forces, penetrations or perforations are
exerted.
[0027] FIG. 6A is an overall photograph of a perforated
intermediate material that can be used in the context of the
invention.
[0028] FIG. 6B is a photograph corresponding to a microscopic view,
giving a detailed view of the effect of a perforation of the
material shown in FIG. 6A.
[0029] FIG. 6C is a photograph of another perforated intermediate
material that can be used in the context of the invention, having
different features (OF).
[0030] FIG. 6D is a photograph corresponding to a microscopic view,
giving a detailed view of the effect of a perforation of the
material shown in FIG. 6C.
[0031] FIG. 6E shows a microscope image of a cut in the thickness
of a stratified material produced from the intermediate material
shown in FIG. 6C with infusion of RTM 6 resin (from Hexcel
Corporation.RTM.) at 60% fiber volume ratio.
[0032] FIG. 7 schematically represents a device for applying spot
transverse forces.
[0033] FIG. 8 studies the resistance to delamination of an
intermediate material used in the context of the invention, as a
function of the tension applied to said intermediate material
during a perforation operation.
[0034] FIG. 9 studies the resistance to delamination obtained as a
function of the density of microperforations applied to the
intermediate material, in different cases of grammage of the
unidirectional sheets of carbon fibers.
[0035] FIG. 10 shows the resistance to delamination results
obtained for various intermediate materials as a function of the
veil and of the grammage of the unidirectional sheet of carbon
fiber used.
[0036] FIG. 11 shows the resistance to delamination results
obtained as a function of the basis weight of the veil.
[0037] The invention uses the continuous application of an
intermediate material, along a given movement trajectory, with
simultaneous application on the intermediate material of a tension
and a pressure in such a way as to apply it on the deposition
surface, the laying-up being carried out by applying one face of
the intermediate material in the process of being laid up
corresponding to a layer of thermoplastic and/or thermosetting
material on the deposition surface and/or by applying the
intermediate material in the process of being laid up on the
deposition surface carrying a thermoplastic and/or thermosetting
material, and by activating, at the deposition area, the interface
between the intermediate material and the deposition surface, in
such a way as to ensure the bond between the laid-up intermediate
material and the deposition surface.
DETAILED DESCRIPTION OF THE INVENTION
[0038] FIG. 1A illustrates the application of an intermediate
material 1 composed of a layer of unidirectional fibers 2
associated to a single one of its faces named 1.sub.1 to a layer of
thermoplastic and/or thermosetting material 3. The intermediate
material is applied so that its face 1.sub.2, which corresponds to
the layer of unidirectional fibers 2, is applied against the
deposition surface 4. In this case, the deposition surface 4 is
itself composed of a layer of thermoplastic and/or thermosetting
material 5 which is activated and which ensures the bond with the
intermediate material. The activation is ensured by appropriate
means that are not represented, as the intermediate material is
laid up.
[0039] Usually, the intermediate material is continuously applied,
along a given movement trajectory, with simultaneous application on
the intermediate material of a tension and a pressure in such a way
as to apply on the deposition surface a face of the intermediate
material in the process of being laid up corresponding to a layer
of thermoplastic and/or thermosetting material and by activating
said layer of thermoplastic and/or thermosetting material during
deposition, in such a way as to ensure the bond between the laid-up
intermediate material and the deposition surface. One such
possibility where the intermediate material is applied in such a
way as to apply the layer of thermoplastic and/or thermosetting
material 3 against the deposition surface 4 is shown in FIG.
1B.
[0040] Whatever the scenario, the activation is done at or near the
deposition area, in such a way as to render sticky the layer of
thermoplastic and/or thermosetting material ensuring the bonding,
before the contact between the intermediate material and the
deposition surface is achieved.
[0041] Conventionally, in the context of the invention, the
formation of composite parts involves the production of a stack or
preform of intermediate materials. Each intermediate material
comprises a layer of reinforcing fibers associated on at least one
of its faces to a layer of thermoplastic or thermosetting material
or of a mixture of thermoplastic or thermosetting materials. In
order to form the desired stack, each intermediate material is
applied on a surface which can be, either a support element in the
case of the application of the first layer of intermediate
material(s) required to produce the stack, or a previously applied
intermediate material. The application of each intermediate
material is preferably performed in such a way that at least one
layer of thermoplastic or thermosetting material or a mixture of
thermoplastic and thermosetting materials is applied on the
deposition surface and is activated during its deposition, in such
a way as to ensure the bond with the surface on which the
intermediate material is applied. Such a deposition facilitates the
application of the first ply, which can be applied on any type of
gluing surface compatible with the chosen polymer material. In
addition, at least one layer of thermoplastic or thermosetting
material or a mixture of thermoplastic and thermosetting materials
thus exists at the interface of two intermediate materials applied
one on top of the other and ensures their mutual bond.
[0042] In the context of the invention, the application of an
intermediate material is performed continuously, with application
of a pressure on the latter in such a way as to apply it on the
deposition surface. The force resulting from this pressure can, for
example, be of 0.3 to 8 N per cm of width of the intermediate
material. To ensure an adequate application, the intermediate
material is stretched during its deposition. To do this, it is
stretched parallel to the direction of the unidirectional fibers.
In particular, a tension of 2 to 50 g per cm of width of the
intermediate material can, in particular, be applied to the
intermediate material. The result is that in the first centimeters
of deposition, the intermediate material 1 undergoes a shear stress
due to the fact that it is stretched in one direction due to its
bonding to the deposition surface 4 and in the opposite direction
due to the tension applied to the latter, as schematically
represented in FIG. 2.
[0043] Advantageously, the laying-up member is a rotating device of
large roller, roller or small roller type, according to the width
of the intermediate material applied. This laying-up member is
coupled to a device for moving and feeding the material during its
deposition. The deposition of the intermediate material can thus be
performed in an automated manner using a control device.
[0044] FIG. 3 illustrates another embodiment wherein the movement
of the intermediate material 1 is ensured as it is laid up by
exerting a pressure, preferably substantially perpendicular to the
deposition surface 4 to which it is applied. The laying-up member
is composed of a roller 6 which exerts a pressure on the material
1, in such a way as to apply it to the deposition surface 4. In the
example illustrated in FIG. 3, the intermediate material is
composed of a unidirectional sheet 10 associated on each of its
faces to a layer of thermoplastic and/or thermosetting material 20
and 30. The handling of such symmetrical intermediate materials is
easier, given that in all cases two layers of thermoplastic and/or
thermosetting material exist at the interface, and the material can
be applied to either one of its faces. The layer of thermoplastic
and/or thermosetting material located at the interface of the
intermediate material in the process of being laid up and the
surface on which it is applied is activated as the deposition is
carried out, by any appropriate means, for example by a heating
device, particularly an infrared light, a hot gas duct or a laser
represented by the reference number 7 in FIG. 3, oriented toward
the deposition area of the intermediate material. It has in
particular been demonstrated that the use of a laser diode of 500 W
and of a wavelength between 965 nm and 980 nm offered the
possibility of laying up the intermediate material at speeds of 1
m/second over 50 mm in width. A higher power makes it possible to
further increase this speed or to lay up a greater width. The
activation makes it possible to soften the polymer layer to be
activated by effecting an at least partial melting in the case of a
thermoplastic material and the start of polymerization in the case
of a thermosetting material.
[0045] After cooling, which can occur naturally, without additional
extraction of heat, the bonding of the material to the deposition
surface is thus ensured. The depositing trajectory of the
intermediate material can be straight or curved. The unidirectional
fibers follow the depositing trajectory.
[0046] FIGS. 4A to 4C illustrate an embodiment wherein different
strips 100 of intermediate materials are laid up one in front of
the other along parallel deposition trajectories, in such a way as
to form layers 200.sub.1 to 200.sub.n. As illustrated in FIG. 4A,
the device 300 for activating the thermoplastic and/or
thermosetting material forms a single component with the laying-up
member 400 so that they can move together. The laying-up member 400
is moved for the depositing of the various strips 100 which are cut
at the end of the trajectory using a cutting member (not
represented). When a layer is entirely applied, the orientation of
the laying-up member is modified, as illustrated in FIG. 4B, in the
case of the first layer 200.sub.1, in such a way as to lay up the
different strips of successive intermediate materials that must
form the following layer along a different deposition trajectory
from the preceding layer. FIG. 4C represents the depositing of the
second layer 200.sub.2. The strips 100 of intermediate materials
forming one and the same layer are laid up adjacently, without
inter-strip spacing, and with a gluing over 100% of their surface
area. It is thus possible to produce a said multi-axial material.
The depositing method illustrated in FIGS. 4A to 4C is particularly
suitable for the application of intermediate materials of a width
between 3 and 300 mm and with small width variation, typically
having a standard deviation on the width of less than 0.25 mm.
[0047] In the context of the invention, the intermediate material
is prepared, prior to its continuous application during which the
latter undergoes a certain pressure and a certain tension giving
rise to the application of shear stresses, in such a way as to
guarantee a better cohesion of the intermediate material in spite
of the shear forces exerted on the latter during the lay-up
operation. This preparation consists in performing on the
intermediate material an operation applying spot transverse forces,
in such a way as to traverse the total thickness of the
intermediate material. This pointwise application of spot
transverse forces is accompanied by heating, leading to the at
least partial melting of the thermoplastic material or the partial
or complete polymerization of the thermosetting material, at the
application spots of transverse forces, and creates bonding bridges
in the thickness of the unidirectional layer of reinforcing fibers.
Preferably, these bonding bridges are established between the two
main faces of the unidirectional layer of reinforcing fibers.
[0048] The invention is adapted to the application of intermediate
materials wherein, over at least a part of the thickness of the
unidirectional layer, the unidirectional reinforcing fibers are
dry, i.e. not impregnated with thermoplastic and/or thermosetting
material, and therefore more sensitive to delamination. The
thermoplastic and/or thermosetting layer(s) associated with the
unidirectional sheet can however have slightly penetrated into the
latter upon attachment, generally carried out by thermocompression,
but the central part, in the case of a material including two
layers of thermoplastic and/or thermosetting material, or the part
opposite the layer of thermoplastic and/or thermosetting material
in the case of a material including only one layer of thermoplastic
and/or thermosetting material, which generally corresponds to at
least 50% of the thickness of the layer of unidirectional fibers,
remains unimpregnated and is therefore classed as dry. The
penetration operation consists in traversing the total thickness of
the intermediate material, while heating the thermoplastic or
thermosetting material in such a way that the latter is softened
and can be drawn into the layer of unidirectional fibers, at the
application spots of transverse forces. Once cooled, the
thermoplastic and/or thermosetting material creates bonding bridges
in the thickness of the layer of unidirectional fibers, which
reinforces its cohesion. After such an operation, with the
exception of the areas bordering the application spots of
transverse forces, over at least 50% of its thickness, the layer of
unidirectional fibers is dry, i.e. unimpregnated with thermoplastic
and/or thermosetting material.
[0049] In the context of the invention, the operation applying spot
transverse forces corresponds to an operation of penetration at
different application or penetration points. In the remainder of
the description, the terms "operation of spot application of
transverse forces" or "operation of penetration at different
penetration points" will be used indiscriminately to describe such
a step consisting in traversing an intermediate material, at least
over a part of its thickness. The operation of applying spot
transverse forces is preferably performed using the penetration of
a needle or a series of needles, which makes it possible to
properly control the orientation of the transverse forces. The
operation of applying spot transverse forces performed on the
intermediate material must be accompanied by heating, leading to
the at least partial melting of the thermoplastic material and/or
the softening of the thermosetting material at the application
spots of transverse forces. To do this, for example, a penetrating
member, itself heated, will be used. However, such an operation
could easily be performed using a hot gas jet. Although this is not
preferred, heating the layer of thermoplastic and/or thermosetting
material prior to the penetration operation could also be
envisioned.
[0050] Advantageously, the operation applying spot transverse
forces is performed by applying a tensile force to the intermediate
material. First of all, a sufficient tension, particularly of 15 to
3000 g per cm of width will be applied to the intermediate
material, usually as it is fed through, during the penetration
operation, in such a way as to allow the introduction of the chosen
penetrating means or member. Advantageously, the tensile force on
the intermediate material will be selected in such a way as to lead
to the at least partial retightening of the unidirectional fibers
after the operation of applying spot transverse forces. In
particular, an effort will be made to obtain the lowest opening
factor possible, to avoid damaging the mechanical properties of the
part subsequently obtained from such an application of intermediate
material. To obtain the lowest opening factor possible, the
penetration operation will be implemented by applying to the
intermediate material a tension such that the opening created by
the penetrating member or means can close up again after the
withdrawal of the latter. In particular, a tension of 300 to 2000 g
per cm of width will be applied to the intermediate material to
obtain such a retightening.
[0051] Of course, the member or the means used for the penetration
operation is withdrawn either after having traversed the
intermediate material in question by making a sole outward journey
or a return. This withdrawal will therefore preferably be made
before cooling of the thermoplastic and/or thermosetting material,
in order to allow the retightening of the fibers. The time to cool
the thermoplastic and/or thermosetting material to its setting
point will therefore be greater than the time required for the
fibers to retighten, or even to completely realign, under the high
tension that is applied to them.
[0052] The result or goal of this penetration operation is to
minimize the risks of delamination, which could occur during the
deposition of the intermediate material, in accordance with the
deposition step previously described, and particularly during the
first centimeters of deposition when it undergoes the main shear
forces.
[0053] Preferably, the penetration operation is performed in a
direction transverse to the surface of the intermediate material
that is traversed.
[0054] It has been observed that a penetration point density of
40000 to 250000 per m.sup.2, and preferably of 90000 to 110000 per
m.sup.2, would make it possible to obtain particularly satisfactory
results in terms of resistance to delamination. The penetration
operation can leave or not leave perforations in the intermediate
material that has been traversed. The openings created by the
penetration operation will usually have a circular or more or less
elongated cross section in the form of an eye or a slot, in the
plane of the intermediate material that has been traversed. The
resulting perforations are, for example, of a larger size, measured
parallel to the surface that has been traversed, reaching up to 10
mm and of a width of up to 300 .mu.m.
[0055] Advantageously, the operation of applying spot transverse
forces leads to an opening factor greater than or equal to 0 and
less than or equal to 5% and preferably of 0 to 2% and more
preferably of 0 to 1%, in such a way as to have as little impact as
possible on the mechanical properties of the composite parts
subsequently obtained. The opening factor can be defined as the
ratio of the surface area unoccupied by the material to the total
observed surface area, the observation of which can be achieved
from the top of the material with lighting from underneath the
latter. It can, for example, be measured using the method described
in the patent application WO 2011/086266. The opening factor can be
zero and correspond to a material with greatly improved
delamination.
[0056] Heating will be performed at the penetrating means or around
the latter, in such a way as to allow the softening of the
thermoplastic and/or thermosetting material initially present only
at the surface of the intermediate material, and its penetration
into the unidirectional fiber layers. A heating resistor can, for
example, be directly integrated into the penetration means, of
needle type. The melting of the thermoplastic material, or the
partial or complete polymerization in the case of a thermosetting
material, thus takes place around the penetrating means, which,
after cooling, leads to the creation of bonding bridges between the
fibers of the unidirectional layer. Preferably, the heating means
is directly integrated into the penetrating means, so that the
penetrating means is itself heated.
[0057] During the penetration, the intermediate material will be
able to abut a surface that can then be heated locally around the
penetrating means, in order to effect localized heating around the
latter or else, on the contrary, be totally isolated, in such a way
as to avoid a softening of the layer of thermoplastic or
thermosetting materials, or of a mixture of the two, with which it
will be in contact. FIG. 7 shows a heating/penetration device 600
equipped with an assembly of needles 700 aligned in accordance with
the selected penetration lines and spacing increments.
[0058] The penetration points are, preferably, arranged in such a
way as to form, for example a network of parallel lines, and will
therefore be advantageously arranged in two series S1 and S2 of
lines, so that: [0059] In each series S1 and S2, the lines are
parallel to each other, [0060] The lines of a series S1 are
perpendicular to the direction A of the unidirectional fibers of
the sheet, [0061] The lines of the two series S1 and S2 are secant
and together form an angle .alpha. different from 90.degree., and
particularly in the order of 50 to 85.degree. which is of around
60.degree. in the example illustrated in FIG. 5.
[0062] Such a configuration is illustrated in FIG. 5. Given that at
the penetration points 500, the penetration of a member such as a
needle, can incur, not the formation of a hole, but rather a slot
as shown in FIGS. 6A and 6C, due to the fact that the
unidirectional fibers spread apart from one another at the
penetration point, the slots are thus offset with respect to one
another. This avoids the creation of an excessively large opening
due to the meeting of two slots that are too close together.
[0063] FIG. 6A shows an intermediate material composed of a
unidirectional sheet of 140 g/m.sup.2 of IMA 12K carbon fibers from
the Hexcel Corporation.RTM. with a 1R8D03 veil from Protechnic.RTM.
(Cernay, France) thermocompressed on either face. This intermediate
material has a width of 6.35 mm and an opening factor of 1.6%
(standard deviation 0.5%). It was produced by penetration with a
series of hot needles with a tension of 315 g/cm.
[0064] FIG. 6B shows a magnification of a perforated area of the
material shown in FIG. 6A.
[0065] FIG. 6C shows an intermediate material of 210 g/m.sup.2 of
IMA 12K fibers from Hexcel Corporation.RTM. with a 1R8D06 veil from
Protechnic.RTM. (Cernay, France) thermocompressed on either face,
of 6.35 mm in width having an opening factor of 0.5% (standard
deviation 0.3%). It was produced by penetration with a series of
hot needles with a tension of 315 g/cm.
[0066] FIG. 6D shows a magnification of a perforated area of the
material shown in FIG. 6C.
[0067] FIG. 6E shows a microscope image of a cut into the thickness
of a stratified material produced from the intermediate material
shown in FIG. 6C with infusion of RTM 6 resin (from Hexcel
Corporation.RTM.) at 60% fiber volume ratio. This microscope image
highlights the fact that the operation of penetration of the heated
needle through the intermediate material generates a movement of
the polymer on the surface of the intermediate material inside the
latter, thus increasing its resistance to delamination.
[0068] It appears that the basis weight of the reinforcing threads
and the veil have an effect on the opening factor obtained with one
and the same tension of the threads during perforation. The 210
g/m.sup.2 sheet has a smaller opening factor than the 140 g/m.sup.2
sheet, even though a veil of higher grammage was used. The
phenomenon of rearrangement of the filaments under tension occurs
more easily with a thicker material. The application WO 2010/046609
describes such intermediate materials having undergone a prior
penetration/perforation operation, composed of a unidirectional
sheet of carbon fibers, associated on each of its faces to a
non-woven material of thermoplastic fibers. The reader may refer to
this patent application for more details, given that it describes
in detail the intermediate materials that can be used in the
context of the invention. It should however be stressed that, in
this patent application, a penetration or perforation operation was
performed to improve the permeability of the stack during the
fabrication of the composite part. In the context of the invention,
such an operation is used to improve the cohesion of the
intermediate materials during their deposition, which employs
gradual deposit and a gradual bonding of the intermediate material
and forms bonding bridges between the unidirectional fibers. Such
an improvement is highlighted in the examples that follow.
[0069] In the context of the invention, whatever the variant of
implementation, the operation of applying spot transverse forces
will be performed by an appropriate penetrating means, preferably
automated, and in particular using a series of needles, pins or
otherwise. The needle diameter (in the regular part after the tip)
will in particular be of 0.8 to 2.4 mm. The application points will
usually be spaced apart by 5 to 2 mm.
[0070] The penetration operation is performed on the intermediate
materials which are then laid up, or even stacked to form a stack
required for the production of a composite part. It is not
necessary for the penetration points to then be superimposed during
the stacking of the intermediate materials. Preferably, the
produced stack is exclusively composed of intermediate materials
defined in the context of the invention, having undergone the
penetration operation.
[0071] According to a preferred embodiment in the context of the
invention, it is possible to produce the stack by superimposition
of intermediate materials composed of a reinforcing material based
on unidirectional carbon fibers, associated on at least one of its
faces to a layer of thermoplastic or thermosetting material or of a
mixture of the two. Such an intermediate material can be composed
of a unidirectional sheet of carbon fibers, associated on a single
one of its faces, or on each of its faces, to a layer of
thermoplastic or thermosetting material or of a mixture of the two.
Such intermediate materials have a proper cohesion, the layer(s) of
thermoplastic or thermosetting material or of a mixture of the two
having been previously associated with the reinforcing material,
preferably owing to the thermoplastic or thermosetting nature of
the layer by thermocompression.
[0072] The stack produced in the context of the invention can
comprise a large number of layers of intermediate materials, in
general at least four and in certain cases over 100, or even over
200. Each layer of intermediate material(s) can be composed either
of a single width of intermediate material, or of side-by-side
applications, produced jointly or not with the intermediate
materials. The stack will preferably be composed solely of the
intermediate materials defined in the context of the invention and
according to an advantageous embodiment, of intermediate materials
that are all identical.
[0073] The reinforcing fibers forming the intermediate materials
applied in the context of the invention and, therefore, used for
the creation of the stacks are, for example, fiberglass, carbon,
aramid, or ceramics, carbon fibers being particularly
preferred.
[0074] Conventionally, in this field, the term "unidirectional
sheet or layer of reinforcing fibers" is understood to mean a sheet
composed exclusively or quasi-exclusively of reinforcing fibers
applied along one and the same direction, in such a way as to
extend substantially parallel to one another. In particular,
according to a particular embodiment of the invention, the
unidirectional sheet does not include any weft yarn interlacing the
reinforcing fibers, or even any sewing that might have the goal of
giving cohesion to the unidirectional sheet before its association
to a layer of thermoplastic or thermosetting material or of a
mixture of the two. This makes it possible, in particular, to avoid
any undulations in the unidirectional sheet.
[0075] In the unidirectional sheet, the reinforcing yarns are
preferably not associated with a polymer binder and are therefore
designated as dry, i.e. they are neither impregnated, nor coated,
nor associated with any polymer binder before their association to
the layers of thermoplastic and/or thermosetting material. The
reinforcing fibers are, however, usually characterized by a
standard sizing concentration by weight that can represent at most
2% of their weight. This is particularly suitable for the
production of composite parts by resin diffusion, using direct
methods well known to those skilled in the art.
[0076] The constituting fibers of the unidirectional sheets are
preferably continuous. The unidirectional layer or sheet present in
the applied intermediate materials can be composed of one or more
yarns. A carbon yarn is composed of a set of filaments and
generally contains 1000 to 80000 filaments, advantageously 12000 to
24000 filaments. In a particularly preferred manner, in the context
of the invention, carbon yarns of 1 to 24K, for example of 3K, 5K,
12K or 24K, and preferably of 12K and 24K are used. For example,
the carbon yarns present within the unidirectional sheets have a
count of 60 to 3800 tex, and preferably 400 to 900 tex. The
unidirectional sheet can be produced with any type of carbon yarn,
for example High Resistance (HR) threads, the tensile modulus of
which is between 220 and 241 GPa and the stress rupture in tension
of which is between 3450 and 4830 MPa, Intermediate Modulus (IM)
yarns, the tensile modulus of which is between 290 and 297 GPa and
the tensile breaking stress of which is between 3450 and 6200 MPa
and High Modulus (HM) yarns, the tensile modulus of which is
between 345 and 448 GPa and the stress rupture in tension of which
is between 3450 and 5520 MPa (according to the "ASM Handbook", ISBN
0-87170-703-9, ASM International 2001).
[0077] In the context of the invention, whatever the variant of
implementation of the method for forming a stack, the stack is
preferably composed of several intermediate materials each
comprising a layer of unidirectional reinforcing fibers, with at
least two layers of unidirectional reinforcing fibers extending in
different directions. All the layers of unidirectional reinforcing
fibers can have different directions, or only some of them can.
Otherwise, outside their differences in orientation, the layers of
unidirectional reinforcing fibers will preferably have identical
features. The favored orientations are usually those forming an
angle of 0.degree., +45.degree. or -45.degree. (also equivalent
to)+135.degree., and +90.degree. with the main axis of the part to
be produced. The 0.degree. corresponds to the axis of the machine
for producing the stack, i.e. the axis that corresponds to the
direction of feeding of the stack during its creation. The main
axis of the part, which is the largest axis of the part, is
generally merged with 0.degree.. It is, for example, possible to
produce quasi-isotropic, symmetrical or oriented stacks by choosing
the orientation of the plies. Examples of quasi-isotropic stacks
include the angles 45.degree./0.degree./135/.degree.90.degree., or
90.degree./135.degree./0.degree./45.degree.. Examples of
symmetrical stacks include 0.degree./90.degree./0.degree., or
45.degree./135.degree./45.degree.. In particular, stacks comprising
more than 4 unidirectional sheets, for example of 10 to 300
unidirectional sheets, can be produced. These sheets can be
oriented in 2, 3, 4, 5 or even more different directions.
[0078] Advantageously, the intermediate materials used include a
unidirectional sheet of carbon fibers having a grammage of 100 to
280 g/m.sup.2.
[0079] In the context of the invention, whatever the variant of
implementation, the layer(s) of thermoplastic and/or thermosetting
material present in the intermediate materials used is (are),
preferably, a non-woven material made of thermoplastic fibers.
Although these possibilities are not preferred, layers of
thermoplastic and/or thermosetting material or of a mixture of the
two or a fabric, porous film, mesh, knitted fabric or powder
deposition could be used. The term "layer of thermoplastic and/or
thermosetting material" means that said layer can be composed of a
single thermoplastic or thermosetting material, of a mixture of
thermoplastic materials, of a mixture of thermosetting materials or
of a mixture of thermoplastic and thermosetting materials.
[0080] The term "non-woven material", which can also be known as a
"veil", is also conventionally understood to refer to an assembly
of continuous or short fibers arranged randomly. These non-woven
materials or veils can for example be produced by dry methods
(drylaid), wet methods (wetlaid), melting methods (spunlaid), for
example by extrusion (spunbond), blown extrusion (meltblown), or by
spinning with solvent (electrospinning, flashspinning) well known
to those skilled in the art. In particular, the fibers forming the
non-woven material can have average diameters in the range from 0.5
to 70 .mu.m, and preferably from 0.5 to 20 .mu.m. Non-woven
materials can be composed of short fibers or, preferably, of
continuous fibers. In the case of a non-woven material of short
fibers, the fibers can have, for example, a length between 1 and
100 mm. Non-woven materials offer random and preferably isotropic
coverage.
[0081] Advantageously, each of the non-woven materials present in
the intermediate materials used has a basis weight in the range
from 0.2 to 20 g/m.sup.2. Preferably, each of the non-woven
materials present in the intermediate materials used has a
thickness of 0.5 to 50 microns, preferably of 3 to 35 microns. The
features of these non-woven materials can be determined using the
methods described in the application WO 2010/046609.
[0082] The layer(s) of thermoplastic or thermosetting material
present in the intermediate materials used, and particularly the
non-woven materials, is (are) preferably made of a thermoplastic
material chosen from among the polyamides, the copolyamides, the
ether or ester block polyamides, the polyphthalamides, the
polyesters, the copolyesters, the thermoplastic polyurethanes, the
polyacetals, the C2-C8 polyolefins, the polyethersulfones, the
polysulfones, the polyphenylene sulfones, the
polyetheretherKetones, the polyetherKetoneKetones, the phenylene
polysulphides, the polyetherimides, the thermoplastic polyimides,
the liquid crystal polymers, the phenoxys, the block copolymers
such as styrene-butadiene-methylmethacrylate copolymers, the
methylmethacrylate-acrylate of butyl-methylmethacrylate-copolymers
and mixtures thereof.
[0083] The other steps used for the manufacture of the composite
part are perfectly conventional for those skilled in the art. In
particular, the manufacture of the composite part implements, as
its final steps, a step of diffusion by infusion or injection of a
thermosetting resin, a thermoplastic resin or a mixture of such
resins, inside the stack, followed by a step of hardening of the
desired part with a step of polymerization/reticulation in a
defined pressure-temperature cycle, and a cooling step. According
to a particular embodiment, moreover suitable for all the variants
of implementations described in relation to the invention, the
steps of diffusion, hardening and cooling are implemented in an
open mold.
[0084] In particular, a resin diffused inside the stack will be a
thermoplastic resin as previously listed for the layer of
thermoplastic material forming the stack, or preferably a
thermosetting resin chosen from among the epoxides, the unsaturated
polyesters, the vinyl esters, the phenol resins, the polyimides,
the bismaleimides, the phenol-formaldehyde resins, the
urea-formaldehydes, the 1,3,5-triazine-2,4,5-triamines, the
benzoxazines, the cyanate esters, and mixtures thereof. Such a
resin can also comprise one or more setting agents well known to
those skilled in the art, to be used with the selected
thermosetting polymers.
[0085] In the case where the production of the composite part uses
the diffusion by infusion or injection of a thermosetting resin, a
thermoplastic resin or a mixture of such resins, inside the stack,
which is the major application envisioned in the context of the
invention, the produced stack, before the addition of this external
resin, does not contain more than 10% of thermoplastic or
thermosetting material. In particular, the layer(s) of
thermoplastic or thermosetting material or of a mixture of the two
represent 0.5 to 10% of the total weight of the stack, and
preferably 2 to 6% of the total weight of the stack, before the
addition of this external resin. Although the invention is
particularly suitable for the direct implementation of the method,
it is also applicable to indirect methods implementing materials of
prepreg type.
[0086] Preferably, in the context of the invention, the stack is
made in an automated manner.
[0087] The invention will preferably use an infusion inside the
stack, under reduced pressure, particularly under pressure below
atmospheric pressure, particularly of less than 1 bar and
preferably between 0.1 and 1 bar, of the thermoplastic or
thermosetting resin or a mixture of such resins for the production
of the composite part. The infusion will preferably be performed in
an open mold, for example by vacuum bag infusion.
[0088] The composite part is finally obtained after a thermal
processing step. In particular, the composite part is generally
obtained by a conventional cycle of hardening of the polymers in
question, by carrying out the thermal processing recommended by the
suppliers of these polymers, and known to those skilled in the art.
This step of hardening of the desired part is performed by
polymerization/reticulation according to a defined
pressure-temperature cycle, followed by cooling. In the case of
thermosetting resin, there is usually a step of gelation of the
resin before its hardening. The pressure applied during the
processing cycle is low in the case of reduced-pressure infusion
and higher in the case of injection into an RTM mold.
[0089] Advantageously, the composite part obtained has a fiber
volume ratio of 55 to 70%, particularly of 57 to 63%, which leads
to satisfactory properties for the field of aeronautics. The volume
fiber ratio (FVR) of a composite part is calculated from the
measurement of the thickness of a composite part, knowing the basis
weight of the unidirectional carbon sheet and the properties of the
carbon fiber, from the following equation:
FVR ( % ) = n plies .times. Basis Weight UD carbon .rho. carbon
fire .times. e board .times. 10 - 1 ( 1 ) ##EQU00001##
[0090] Were e.sub.board is the thickness of the plate in mm,
[0091] .rho..sub.carbon fiber is the density of the carbon fiber in
g/cm.sup.3,
[0092] the basis weight UD.sub.carbon is in g/m.sup.2.
[0093] The examples below illustrate the invention, but are in no
way limiting in nature.
[0094] Description of Initial Materials:
[0095] Copolyamide veil of a thickness of 118 .mu.m and of 6
g/m.sup.2, commercially available under the reference number 1R8D06
by Protechnic.RTM. (Cernay, France)
[0096] Copolyamide veil of a thickness of 59 .mu.m and of 3
g/m.sup.2, commercially available under the reference number 1R8D03
by Protechnic.RTM. (Cernay, France),
[0097] Unidirectional tape made with IMA 12K and 446 tex yarns from
Hexcel.RTM., so as to obtain a basis weight of 140, 210 or 280
g/m.sup.2.
[0098] Preparation of the Intermediate Materials
[0099] An intermediate material of a width of 6.35 mm corresponding
to a combination of polyamide veil/unidirectional carbon fiber
sheet/polyamide veil is produced and thermally bonded in accordance
with the method described in pages 27 to 30 of the application WO
2010/046609.
[0100] A device as illustrated in FIG. 7 is used to carry out a
penetration operation on the material, with an arrangement of the
penetration points as shown in FIG. 5. In all the tests performed,
the needles were heated to a temperature of 220.degree. C. The
needles used are made of treated steel with titanium carbonitride.
They have a tip of a length of 5.25 mm which has a diameter that
increases up to a diameter of 1.6 mm, to finish with a regular part
of constant diameter equal to 1.6 mm over a length of 14 mm.
[0101] Performance Tests
[0102] Test and Modeling Protocol
[0103] Specimens:
[0104] The specimens are made from a yarn of a length of 200 mm,
laminated to an adhesive tape of 50 mm on its two opposite faces.
The stress is exerted by a traction machine by way of the adhesive
tapes. A tractive force in a direction parallel to the length of
the specimen and of opposite direction is applied to each of the
faces of the specimen. The total stressed length is therefore
applicable to the whole sample, i.e. 200 mm.
[0105] The test is performed at constant speed until total
debonding of the specimen, and the value of the highest tensile
strength obtained is retrieved.
[0106] The following parameters were set for all the tests [0107]
Specimen length: 20 cm [0108] Glued length of the adhesive tapes: 5
cm [0109] Strain rate: 37.5 m/s
[0110] In each case, at least five specimens are tested.
[0111] 1. Study of the Effect of the Tension Applied to the
Intermediate Material During Microperforation
[0112] The effect of the tension applied to the intermediate
material during microperforation is studied on the median grammage
(210 g/m.sup.2). The result obtained can be extrapolated to the
whole range of grammages.
[0113] To vary the tension applied to the intermediate material,
the braking of the reels placed upstream of the microperforation
machine is increased.
[0114] The tension is controlled using a portable tensiometer of
DTBX 500-10 and 5000-20 type upstream of the microperforation
machine composed of a needle roller.
[0115] The results obtained are shown in FIG. 8 and demonstrate
that the tension applied to the intermediate material has no effect
on the resistance to delamination obtained. On the other hand, the
applied tension has an effect on the opening factor as the results
shown in TABLE1 demonstrate.
TABLE-US-00001 TABLE 1 OF (%) Tension (g/cm) 4 15 1 315 0 945
[0116] It is interesting to note that the tension has a linear
relationship with the opening factor in the case of a logarithmic
tension scale.
[0117] The tests shown in points 2 to 4 below were performed with a
tension 315 g/cm.
[0118] 2. Effect of the Perforation Density
[0119] To test the effect of the microperforation density, the
density was divided by two. The tests were performed for the two
grammages 210 and 280 g/m.sup.2 for one type of veil (1R8D06 of 6
g/m.sup.2).
[0120] The results obtained with the microperforation density
divided by two (MP/2 in FIG. 9) are compared to the performances
achieved without (Std in FIG. 9) and with microperforations (full
density MP in FIG. 9 which corresponds to 9.2 holes/cm.sup.2) for
equivalent grammage and veil type.
[0121] The results are shown in FIG. 9 and a clear rise in the
resistance to delamination is observed with an increase in the
perforation density.
[0122] It is therefore clearly apparent that the microperforations
improve the resistance to delamination and that this improvement
increases with the perforation density.
[0123] 3. Comparison of the Obtained Performance as a Function of
the Grammage of the Unidirectional Sheet and of the Veil.
[0124] The set of resistance to delamination results obtained as a
function of the grammage of the unidirectional material and of the
veil used are shown in FIG. 10.
[0125] It is apparent that whatever the case under examination, the
use of a perforated intermediate material (MP) compared to an
unperforated intermediate material (Std) makes it possible to
considerably improve the results and leads to better resistance to
delamination.
[0126] 4. Effect of the Percentage of Veil.
[0127] The proportion of veil is expressed in % by weight, with
respect to the weight of carbon fibers present in the intermediate
material.
[0128] The results obtained shown in FIG. 11 demonstrate that for
the same parameters of through stress, the resistance to
delamination grows with the increase in the percentage by weight of
veil.
[0129] 5. Effect of the Opening Factor Obtained after the
Penetration Operation on the Mechanical Properties of the
Stratified Materials.
[0130] It has been demonstrated that a stratified material produced
by injection of RTM6 epoxy resin (Hexcel Corporation.RTM.) into an
intermediate material in accordance with Paragraph 1 having
undergone a spot application of transverse forces combined with a
tension of 15 g/cm and leading to an opening factor of 4%
statistically gave a Compression value of 0.degree. according to
the EN2850B standard, around 7% lower than the same stratified
material produced from an intermediate material having undergone a
spot application of transverse forces combined with a tension of
945 g/cm and leading to an opening factor of 0%. The stratified
material produced from an intermediate material not having
undergone such transverse forces is still slightly better but is
not optimized in terms of delamination during automated lay-up. The
results are shown in TABLE 2.
TABLE-US-00002 TABLE 2 Compression 0.degree. - EN2850B (Mpa) IMA
12K - 1R8D06 2 faces - 194 Standard g/m.sup.2 - 300 mm/RTM6 Mean
deviation Intermediate material OF 0% non- 1665 100 microperforated
Intermediate material OF 0% 1612 102 produced at 945 cN/cm of
tension Intermediate material OF 4% 1514 93 produced at 15 cN/cm of
tension
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