FR3065669A1 - METHOD FOR MAKING A SOUL OF STRUCTURAL MATERIAL SANDWICH AND AME - Google Patents

Abstract

A core of sandwich structural material in a compact state comprises a sheet sandwich comprising at least two superposed sheets. The core is adapted to be placed in an expanded state in which the sheet sandwich is stretched in the sheet thickness direction to form a honeycomb structure. Each sheet of the sheet sandwich has spatially periodic corrugations. A spatial period of the undulations is strictly less than a spatial period of the adhesive strips disposed on the sheets. A remainder of the Euclidean division of the spatial period of the adhesive tapes by the spatial period of the undulations is strictly greater than zero.

Description

065 669

53640 ® FRENCH REPUBLIC

NATIONAL INSTITUTE OF INDUSTRIAL PROPERTY © Publication number:

(to be used only for reproduction orders)

©) National registration number

COURBEVOIE © Int Cl ⁸ : B 32 B 3/28 (2017.01), B 32 B 3/12, 7/14, 15/00, 23/00, 29/08, B 31 D 3/02

A1 PATENT APPLICATION

©) Date of filing: 26.04.17. © Applicant (s): SAS ENGINEERING COMPOSITE 3D ©) Priority: Simplified joint stock company - FR. @ Inventor (s): BROWN FREDERIC. ©) Date of public availability of the request: 02.11.18 Bulletin 18/44. ©) List of documents cited in the report preliminary research: Refer to end of present booklet (© References to other national documents ® Holder (s): SAS ENGINEERING COMPOSITE 3D related: Joint stock company. ©) Extension request (s): ® Agent (s): CABINET PLASSERAUD.

(b4) METHOD FOR PRODUCING A SOUL OF SANDWICH AND SOUL STRUCTURAL MATERIAL.

FR 3 065 669 - A1 (oj) A core of sandwich structural material in a compact state comprises a sandwich of sheets comprising at least two superposed sheets. The core is adapted to be placed in an expanded state in which the sheet sandwich is stretched in the direction of sheet thickness to form a honeycomb structure. Each leaf of the leaf sandwich has spatially periodic undulations. A spatial period of the undulations is strictly less than a spatial period of the adhesive strips arranged on the sheets. A remainder of the Euclidean division of the spatial period of the adhesive tapes by the spatial period of the undulations is strictly greater than zero.

i

PROCESS FOR PRODUCING A CORE OF STRUCTURAL MATERIAL

SANDWICH AND SOUL

The present relates to the methods for producing webs of sandwich structural material, and to the webs of structural sandwich material obtained by such processes.

The sandwich structural materials are generally composed of two external skins secured to the opposite faces of a core. Said core is made in such a way that it has a strong structural resistance to compression and flexion while retaining a minimum weight. These structural materials have many applications, for example in the field of aeronautics or the automobile.

Among these materials, the best known are those comprising a honeycomb core. These cores are made up of shaped sheets then fixed together at precise points to constitute a network of cells of hexagonal profile, sometimes deformed, which extend perpendicularly to said external skins.

TECHNOLOGICAL BACKGROUND

Document US Pat. No. 5,431,980 discloses webs of structural materials which can be used to create walls which are at the same time rigid, light and curved.

To do this, the document provides in particular a core of structural material which comprises honeycomb-shaped cells, which cells have sides with particular shapes, of the type with wavy shapes, semicircle designs etc.

The cores are made from the other's corrugated strips, and connected superimposed one on one punctually to each other by fixing zones. The wavy bands having a pattern repeated over their entire length, and the pattern includes a flat area alternating with a wavy area. The flat areas of each wavy strip are alternately fixed either to a flat area of an upper wavy strip or to a flat area of a lower wavy strip. Furthermore, the core of material is deployable between a compact state and a deployed state by expansion of the superimposed corrugated strips in a direction perpendicular to the direction of said superimposed corrugated strips.

Said core can be produced in a wide variety of constituent materials, for example metals such as aluminum.

Alternatively, such a core can be produced from non-metallic materials such as cellulose.

ABSTRACT

The purpose of this is to provide a core of sandwich structural material having in particular improved mechanical characteristics, reduced density and / or reduced cost.

According to one aspect, a core of structural sandwich material in a compact state comprising a sandwich of sheets comprising at least two superimposed sheets, said sheets each extending substantially along an extension plane and being superimposed along a thickness direction substantially perpendicular in the plane of extension, the core being able to be placed in an expanded state in which the sandwich of sheets is stretched in the direction of thickness of sheets to form a honeycomb structure, the core being such that two sheets overlapping the sandwich of sheets adhering to each other by a plurality of adhesive strips interposed between the two sheets and adhering to each of said two superimposed sheets, said adhesive strips being oriented in a first direction of the extension plane and being juxtaposed periodically on the sheets in a second direction of the extension plane perpendicular to the first direction, said adhesive strips ives having a spatial period P2 in the second direction, the core being characterized in that: each sheet of the sandwich of leaves has undulations in the thickness direction, the undulations being spatially periodic in the second direction, in that the spatial period of the undulations is strictly less than the spatial period of the adhesive strips, and in that a remainder of the Euclidean division of the spatial period of the adhesive strips by the spatial period of the undulations is strictly greater than zero.

In particular embodiments, the core can also include one or more of the following arrangements:

• said remainder of the Euclidean division of the spatial period of the adhesive tapes by the spatial period of the corrugations is greater than one tenth of the spatial period of the corrugations, preferably greater than one fifth of the spatial period of the corrugations;

• the undulations extend substantially in the first direction;

The corrugations are arranged continuously on each sheet of the sandwich of sheets, in particular at the location of said adhesive strips;

• said adhesive strips have a strip width in the second direction greater than the spatial period of the corrugations, so that, in the second direction, each adhesive strip covers more than one corrugation of a sheet to which said adhesive strip adheres;

• the undulations have a general form of zigzags, in particular in which said zigzags have peak vertices with a predefined apex angle, in particular an angle greater than 10 degrees and less than 60 degrees;

• placed in the expanded state to form the honeycomb structure, said honeycomb structure comprises cells of generally substantially hexagonal shape, and each of the walls of said cells is corrugated by the undulations of the sheets of the sandwich of sheets;

• two walls of said honeycomb structure, belonging respectively to two adjacent cells and being oriented according to respective substantially identical orientation planes, have respective corrugations respectively out of phase with respect to each other; and • the sheet sandwich is a sandwich of metal sheets or cellulose.

According to one aspect, a method of producing a core of structural material comprising the steps of: providing at least two corrugated sheets in a sheet thickness direction, at least one of the two sheets having a plurality of adhesive strips oriented in a direction first direction of an extension plane of the sheets, the undulations having a spatial period of undulation in a second direction of the extension plane, the second direction being perpendicular to the first direction; and stacking said at least two sheets to obtain a sheet sandwich such as two overlapping sheets of the sheet sandwich adhered to each other by the plurality of adhesive strips, the plurality of adhesive strips being interposed between the two sheets and juxtaposed periodically in the second direction, said adhesive strips having a spatial period in the second direction, the spatial period of the undulations being strictly less than the spatial period of the adhesive strips, and a remainder of the Euclidean division of the spatial period of the adhesive strips by the spatial period of the ripples is strictly greater than zero.

In particular embodiments, the method can also include one or more of the following arrangements:

The step of providing said at least two sheets comprises the steps of:

o Place the plurality of adhesive strips on at least one continuous strip of material;

o Cut said continuous strip to form said at least two sheets; and o forming periodic undulations in said at least two sheets;

• periodic ripples are formed to extend in the first direction;

• said at least two sheets are metallic and the process steps are carried out sequentially in the following order:

o Place the plurality of adhesive strips on the continuous strip of material so that the first direction is substantially along a width direction of the continuous strip;

o Cut the continuous strip to form said at least two sheets so that two successively cut sheets in the continuous strip have a phase shift of the adhesive strips in the second direction relative to each other, in particular a shift of phase substantially equal to half of the spatial period of the adhesive strips; and o forming periodic ripples in said at least two sheets to provide said at least two sheets; and o stacking said at least two sheets to form the sheet sandwich).

• periodic ripples are formed to extend in the first direction;

• said at least two sheets are made at least partially of cellulose, and the step of providing said at least two sheets comprises the steps of:

o Form the corrugations on a first continuous strip of material from which a first of said at least two sheets is extracted, and form the corrugations on a second continuous strip of material, distinct from the first continuous strip, of which a second of said at least two sheets is extracted, the first direction being a direction substantially of a length of the continuous strip;

o Periodically place adhesive strips on the first continuous strip and adhesive strips on the second continuous strip, the adhesive strips of the first continuous strip being phase shifted in the second direction relative to those of the second strip, in particular a phase shift substantially equal to half of the space period of the adhesive strips; and o Cutting and stacking the first continuous strip and the second continuous strip so as to form the sheet sandwich comprising the first sheet and the second sheet.

BENEFITS

Having a remnant of the Euclidean division of the spatial period of the adhesive tapes by the spatial period of the undulations strictly greater than zero, allows a structural reinforcement of the honeycomb structure that the soul forms in its expanded state, thus presenting a better performance / density, both from the point of view of compression, shear (regardless of the direction) and energy absorption.

In the methods of the prior art, only certain whole values of the ratio between the spatial period of the adhesive tapes by the spatial period of the corrugations were accessible. The present invention aims in particular to vary said ratio continuously and not discretely as previously, which first of all makes it possible to modulate significantly the weight / mechanical strength ratio and consequently, as desired, to significantly increase the strength constant weight mechanical, or significantly reduce the weight at constant mechanical strength.

Furthermore, the manufacturing process is simplified by the absence of an entire multiplicity constraint between the spatial period of the adhesive tapes and the spatial period of the corrugations. The technical management of making the corrugation pitch coincide with the adhesive tape printing pitch is eliminated, which makes this technique compatible with different cell sizes and different thicknesses of sheets or strips, without having to manage any offset of the pattern due to variations. This technique therefore makes it possible to reduce the tools necessary for the production of a full range of honeycombs.

Finally, the complete non-multiplicity between the spatial period of the adhesive tapes and the spatial period of the undulations makes it possible to produce corrugated alveolate structures of small cell size, hitherto impossible to produce due to the difficulty of managing on a small scale the coincidence of the wave pattern with the print pattern of the adhesive tapes.

BRIEF DESCRIPTION OF THE DRAWINGS

To be able to be carried out, the invention is set out in a sufficiently clear and complete manner in the following description which is, in addition, accompanied by drawings in which:

FIG. 1 is a schematic view of a portion of an example of a core of structural material, seen in perspective and substantially from above, when the core is in the expanded state,

FIG. 2 is a schematic plan elevation view of the core of FIG. 1,

Figure 3 is a schematic perspective view of the core of Figure 1, when the core is in a compact state, Figure 4 shows the steps of an example of a method of making a core of material structural sandwich such as the core of FIG. 1, FIG. 5 illustrates a detail of an adhesive deposition step of the method of FIG. 4, FIG. 6 illustrates a detail of a deformation step of the method of FIG. 4, and FIG. 7 shows the steps of another example of a method for producing a core of sandwich structural material such as the core of FIG.

1.

DETAILED DESCRIPTION

In the following description, the terms "lower", "upper", "high", "low" etc ... are used with reference to the drawings for greater ease of understanding. They should not be understood as being limitations on the scope of the invention.

Figures 1 and 2 illustrate a core 1 in expanded state as it would be during its use. FIG. 3 shows the core 1 in compact state, before its expansion. The compact state is that which the core 1 has before use, for example, during the transport of the core 1.

The core 1 extends substantially in directions of core extension X ', Y' and is intended to be between an upper surface la and a lower surface lb, also called skins, opposite in a thickness direction of core Z ', to constitute a sandwich structural material 3.

In the example illustrated in FIGS. 1 to 3, the core 1 comprises four sheets 2. The core 1 of structural material is however not limited to the presence of a particular quantity of sheets 2, and, according to the applications and specifications desired, the core 1 could include more or less sheets 2 without departing from the scope of the invention.

Sheets 2 can be made of different materials. For example, sheets 2 could be made of metallic material or cellulose. In the case of cellulose material, it could be that in order to obtain a core of structural sandwich material 1 of a given strength, the sheets 2 are impregnated with a hardened resin.

ίο

The core 1, in expanded state, reveals a honeycomb structure 4 comprising a plurality of cells 5 juxtaposed with each other to form a periodic network of arbitrary dimensions.

By “cell” is thus meant for example an elementary mesh of said periodic network.

By “honeycomb structure”, it is meant that the structure 4, although formed from sheets 2 originally planar, is a three-dimensional structure, the sheets 2 being assembled and shaped by expansion to form a structure of arbitrary dimensions, mainly composed of voids between the sheets 2, and nevertheless having high mechanical strength characteristics.

Each cell 5 has a plurality of faces 6. For example in the case of FIGS. 1 to 3, the cells 5 are hexagonal and have six faces 6.

The cells 5 can form, as illustrated in the example of FIGS. 1 and 2, a network of regular hexagonal cells. It could also be that the cells 5 form a network of cells other than hexagonal, for example trapezoidal, and / or that the cells are not regular.

By "cell" is thus meant a three-dimensional structure, a section of which has a closed shape on itself, in particular a hexagon, in the case of a cell of a network of the "honeycomb" type.

The periodic network formed by the juxtaposition of cells 5 can thus be a honeycomb type network.

In such a network with hexagonal cells, the cells 5 can be juxtaposed so that each face 6 of a cell 5 constitutes a face 6 of two adjacent cells.

The honeycomb structure 4 thus forms a compact and resistant network, advantageously a “honeycomb” network.

More specifically, as illustrated in FIG. 3, the honeycomb structure 4 comprises a sandwich of sheets 7 comprising at least a first sheet 8 and a second sheet 9. In the example of FIG. 3, the sandwich of sheets 7 comprises four sheets. It is however contemplated that the sandwich of sheets 7 could contain a variety of envisaged numbers.

The first and second respectively of substantially sheets according to the sheet applications along directions of extension X, Y. They are shaped according to a substantially

Z, sheet thickness direction perpendicular to the extension directions X, Y, so that the sheet sandwich 7 is stretched in the sheet thickness direction Z to form the honeycomb structure.

The directions of extension X, Y and of sheet thickness Z are not usually collinear with the directions of extension of core X ', Y' and of thickness of core Z 'respectively, but rotated by 90 ° , so that the extension directions X, Y are respectively collinear with a core extension directions X 'and the core thickness direction Z', while the sheet thickness direction Z is collinear with a direction of extension of the soul Y '.

The core of sandwich structural material 1 is in particular such that the first and second sheets 8, 9 comprise at least one portion with periodic protruding patterns, such as for example corrugations 11. In the example of FIGS. 1 to 3 , the sheets 8, 9 are entirely wavy. It could be that only a more or less large part, continuous or not, of the sheets 8, 9 is deformed into undulations.

The corrugations 11 can have several shapes. For example, the corrugations 11 can be more or less curved than those shown in the figures. According to the example of Figures 1 to 3, the undulations have a general zigzag shape. In particular, the zigzags can form peak vertices with a predefined angle A of vertex. In a particular example, the angle of the vertices of the zigzags is an angle greater than 10 degrees and less than 60 degrees.

The corrugations 11 are formed by deformation of the sheets 8, 9 in a sheet thickness direction Z. The shape given to the corrugations 11 can be one-dimensional. One-dimensional undulations are such that they have an elongation in a preferred direction. In the example of FIGS. 1 to 3, a first direction L1 of elongation of the corrugations 11 is parallel to a width La of the sheets 8, 9. This could be the case for a core 1 made of aluminum, for example. However, it is envisaged that the first direction L1 may not be parallel to the width La of the sheets 8, 9. For example, the first direction L1 could be parallel to a length Lo of the sheets 8, 9. This could be the case for a core 1 made of paper (ie cellulose). In another example, the first direction Ll could be at a non-zero angle with the length Lo and the width La of the sheets 8, 9. The undulations 11 could be two-dimensional, or at an angle with respect to the width La of the sheets 8, 9.

The first and second sheets 8, 9 also adhere to each other by means of a plurality of adhesive strips 13. The adhesive strips 13 are interposed between the two sheets 8, 9. The adhesive strips 13 lie in a thickness direction Z between the first and the second sheet 8, 9.

By “strip” is meant a distribution of adhesive product between two superposed sheets, in a direction of elongation, continuously or intermittently, and having a predetermined width. The term "adhesive strip" does not exclusively include a line or line of adhesive or even a set of dots of adhesive extending in a direction of elongation.

In the example of FIGS. 1 and 3, the adhesive strips 13 are one-dimensional and extend (or are oriented) in the first direction L1, parallel to the width La of the sheets 8, 9, that is to say in a direction of elongation of the corrugations 11. It could however be that the adhesive strips 13 are not parallel to the width La of the sheets 8, 9. For example, the adhesive strips 13 could extend in a direction parallel to a length Lo of the sheets 8, 9. In another example, adhesive strips 13 could extend at a non-zero angle, preferably not perpendicular, with the length Lo and the width La of the sheets 8, 9.

In the example shown in FIGS. 1 to 3, the direction of elongation of the adhesive strips 13 is substantially parallel to a direction of elongation of the corrugations 11. It may however be that the adhesive strips 13 are at a non-zero angle ( but not equal to 90 degrees) with the corrugations 11. For example, when the corrugations 11 are arranged at an angle with respect to the sides of the sheets 8, 9, while the strips of adhesive 13 are parallel to one side of the sheets 8, 9. In another example, the corrugations 11 could be two-dimensional.

In the case of FIGS. 1 to 3, the adhesive strips 13 have a width D (FIG. 3). The width D is constant from one strip to another and between adhesive strips 13 of different sheets 2. Having adhesive strips 13 of the same width D inside the same sheet and between sheets of the sheet sandwich 7 makes it possible to produce a regular mesh of the honeycomb structure 4. It is however envisaged that the adhesive strips 13 may be non identical in width D inside a sandwich of sheets 7. As will be explained in more detail below, the width D can be chosen as a function of the undulations of the sheets 8, 9. The width D is chosen so that 'it contains several undulations 11.

The undulations 11 are periodic with a spatial period P1. By "period" is meant that the undulations 11 have a pattern which repeats at least in one direction. In the case illustrated in FIG. 3, the spatial period P1 of the undulations 11 is a distance, in the direction X peak to peak of the reproducible undulations 11. The direction X is a direction perpendicular to the direction of elongation of the corrugations 11. Thus for one-dimensional corrugations which have an elongation direction substantially parallel to a direction of elongation of the adhesive tapes 13, a direction for calculating the period of the corrugations 11 may be a direction perpendicular to the direction of elongation of the corrugations 11. The direction of calculation of the spatial period P1 of the corrugations 11 is also used to calculate a spatial period P2 of the adhesive strips 13, as described below. Whatever the direction chosen for the calculation of the periods, the same direction is chosen to determine the spatial period P1 of the corrugations 11 and the spatial period P2 of the adhesive strips 13.

For corrugations 11 at an angle to the adhesive strips 13, the spatial period Pl of the corrugations 11 can be determined with respect to a cut in the sheets 8, 9 along a plane perpendicular to a direction of elongation of the adhesive strips 13, which plane being understood along a width direction of the adhesive strips 13. Another way of calculating the spatial period P1 in the case of the corrugations 11 at an angle to the adhesive strips 13 would be to determine it in a direction perpendicular to the direction of elongation of the corrugations 11, and to use this direction to calculate the spatial period P2 of the adhesive strips 13.

The adhesive strips 13 are periodically placed on each of the sheets 8, 9. That is to say that they are spaced apart by a constant distance. The distance between two consecutive adhesive strips 13a, 13b (edge to edge) constitutes a spatial period P2 of the adhesive strips 13. Another way of measuring the period would be to calculate the distance between the centers of consecutive strips in a direction perpendicular to the direction strip elongation, that is to say in a second direction L2 perpendicular to the first direction LI.

The spatial period PI of the corrugations 11 and the spatial period P2 of the adhesive strips 13 are chosen such that the spatial period PI of the corrugations 11 is strictly less than the spatial period P2 of the adhesive strips 13. In addition, a remainder of the Euclidean division of the spatial period P2 of the adhesive strips 13 by the spatial period PI of the corrugations 11 is strictly greater than zero. In other words, for each sheet 8, 9 a spatial period P2 of the adhesive strips 13 is not an integer multiple of a spatial period PI of the corrugations 11.

Thus, for the example illustrated in FIG. 3, the adhesive strips 13 start in the second direction L2 at different locations (illustrated by points Ptl and Pt2 in FIG. 3) of the spatial period PI of the corrugations 11, and this for at least two adhesive strips 13 consecutive.

The fact that the spatial period P2 of the adhesive tapes 13 is not an integer multiple of a spatial period PI of the corrugations 11 overcomes the constraint, during the manufacturing process, that the adhesive tapes 13 are applied to Identical places in the spatial period PI of the corrugations 11. Thus, the corrugation given to the sheet 2 is no longer related to a desired size of the cell 5, which makes it possible to simplify the manufacturing process. Furthermore, the freedom from the multiplicity between the period PI of the corrugations 11 and the period P2 of the adhesive strips 13 makes it possible to be able to form cores 1 with an increased number of possibilities for cell size 5 and corrugations 11.

According to one example, the remainder of the Euclidean division of the spatial period P2 of the adhesive strips 13 by the spatial period PI of the undulations 11 is greater than one tenth of the spatial period PI of the undulations 11. According to another example, the rest of the Euclidean division of the spatial period P2 of the adhesive strips 13 by the spatial period PI of the undulations 11 is greater than one fifth of the spatial period PI of the undulations 11.

It is envisaged that for certain materials, a resin could be placed and crosslinked over a portion or the whole of the honeycomb structure 4. In this way, the resin forms a plurality of menisci making it possible to stiffen the overflowing patterns and thus increase the tensile and compressive strength of the core of sandwich structural material 1, in particular in the directions of core extension X 'and Y'.

Two examples of methods for producing such a core of sandwich structural material 1 will now be described with particular reference to FIGS. 4 to 7.

Figure 4 in relation to Figures 5 and 6 illustrates steps of such a method 99 applicable particularly to metallic materials, and giving a material as illustrated in Figures 1 and 3. Figure 7 illustrates steps of such process 999, particularly applicable to materials containing cellulose.

As shown in FIG. 4, the method 99 for producing a core of sandwich structural material 1 firstly comprises a first step 100 of supplying a strip of material 15. The material for this method 99 is preferably metallic .

More specifically, the strip of material 15 may extend substantially in directions of extension X, Y comprising a direction of longitudinal extension X and a direction of transverse extension Y. The strip of material 15 is initially substantially smooth, c that is to say that it does not have the corrugations 11. However, it could be that the strip of material 15 is prestressed. According to an example of prestressing, the strip of material 15 is printed in its thickness with rounded patterns of small amplitude compared to those subsequently printed.

The strip of material 15 may have a defined width, for example substantially equal to the thickness E (illustrated in FIG. 1) desired for the core 1, in the direction of transverse extension Y, for example between a few centimeters and a few meters. The strip of material 15 can moreover have a significantly greater length in the direction of longitudinal extension X, for example from a few meters to several hundred meters. The strip of material 15 can thus be wound on itself around the transverse extension direction Y, so as to form a roll 20 of strip which is unwound as the core of structural material is produced. sandwich 1.

In a second step 200 of method 99, the plurality of adhesive strips 13 are placed on the strip of material 15.

The adhesive strips 13 can for example extend substantially in the direction of transverse extension Y, that is to say perpendicular to a direction of unwinding of the strip 15.

Preferably, a plurality of adhesive strips 13 arranged periodically, in particular periodically in the direction of longitudinal extension X, are placed on the strip of material 15. To this end, the strip of material 15 can be pressed between two rollers. adhesive deposit 21a, 21b.

As illustrated in FIG. 5, the contact surface of one or of the two adhesive deposition rollers 21a, 21b may in particular comprise one or more adhesive 22 allowing a supply of adhesive to arrivals

The material location 15 (undulations of the contact surfaces of the adhesive deposition rollers 21a, 21b with the strip of material 15.

The adhesive strips 13 are placed on the strip before a deformation of the strip 15 step described below.

The adhesive is chosen so as to be in an inactive state (that is to say non-sticky) in order to prevent an adhesive deposit on the shaping rollers 18, 19, described below. The adhesive can be activated later, when several sheets 2 are assembled to form the sheet sandwich 7.

In a third step 300 of cutting the strip 15, the strip of material 15 is cut to form a plurality of sheets 2. The first sheet 8 and the second sheet 9 are formed in particular. To this end, as illustrated in the figure 6, the strip can be cut in the direction of transverse extension Y, to form sheets 2 that are substantially rectangular.

More specifically, the strip of material 15 is cut to a predetermined length so that the strips of adhesive 13 are out of phase (or phase shift φ) between two consecutive sheets. That is to say, cutting at a place other than halfway through the period of the bands, between two bands.

By “phase shifted” is meant that on two consecutive sheets 2 taken from the strip 15 when these are superimposed, the adhesive strips 13 are offset from one sheet to the other in the direction of sheet thickness Z. adhesive strips 13 are out of phase between two consecutive sheets, when superimposed, the adhesive strips 13 do not line up in the direction of sheet thickness.

The phase shift φ can be between two consecutive sheets and be repeated in groups of two sheets, or between three or more consecutive sheets.

The phase shift φ can be chosen such that it is one half of the spatial period P2 (φ = Ρ2 / 2) of the adhesive strips 13.

Thus, when the core 1 is manufactured, the adjacent cells 5 and being oriented according to respective substantially identical orientation planes will have respective undulations 11 respectively out of phase with respect to each other. The cells 5 of the core 1 will have different undulations with respect to each other, at least between adjacent cells. Thus, even if the adhesive strips 13 are arranged periodically so as to create cells of equal sizes, their shape will be different from one cell to another.

In a fourth step 400 of deformation or corrugation, at least a portion of each sheet 8, 9 is deformed in the direction of thickness of sheet Z, substantially perpendicular to the directions of extension X, Y. A portion is thus obtained or a whole wavy sheet 8, 9.

As shown in FIG. 6, it is possible, for this purpose, to compress the sheet 8, 9 between two shaping rollers 18, 19 whose contact surfaces with the sheet 8, 9 have a plurality of etched patterns 18a, 19a . The etched patterns 18a, 19a are for example zigzags in order to form the undulations 11 in the form of zigzags.

The deformed portion of the sheet 8, 9 obtained thus has a plurality of protruding patterns, in the form of undulations, each protruding pattern extending substantially outside the extension plane XY formed by the directions of extension X, Y .

According to one example, the overhanging patterns are one-dimensional patterns in the direction of transverse extension Y. The overhanging patterns are for example undulations having a general zigzag shape in a section along an XZ plane perpendicular to the direction of extension transverse Y.

Alternatively, the overhanging patterns can be two-dimensional patterns extending in the directions of longitudinal extension X and transverse Y.

As can be seen in Figure 4, all of the contact surfaces of the shaping rollers 18, 19 with the sheets 2 can be covered with etched patterns 18a, 19a, so that the strip 15, once pressed between the rollers 18 and 19, is corrugated over its entire longitudinal extension, without any residual smooth part. In the example of the figures, the corrugated portion thus constitutes the entire sheet 2.

In this embodiment, a honeycomb structure 4 can be obtained, the whole of each sheet 2 of which is corrugated.

Alternatively, the contact surfaces of the shaping rollers 18, 19 with the sheets 8, 9 may have smooth parts between engraved patterns 18a, 19a, so that the sheets 2, once pressed between the rollers 18 and 19 , have residual smooth parts.

In a fifth step 500 of superposition of the sheets, also illustrated in FIG. 4, the sheets 2 are superimposed on each other in the direction of sheet thickness Z to obtain the sandwich of sheets 7. Thus, in particular the sheet first and second sheet 8, 9 to each other.

More specifically, the first and second sheets 8, 9 can respectively comprise a plurality of adhesive strips 13 extending respectively in the direction of transverse extension Y. It is then possible to superimpose the first sheet 8 on the second sheet 9, and the phase shift φ induced in the cutting step will cause alternation, in the direction of longitudinal extension X, of the respective adhesive strips 13 of the first and second sheets 8, 9. During the superposition of the sheets 2, the overflowing patterns 14 cooperate between them since the same wavy pattern was applied to each of the sheets 8, 9.

Steps 100, 200, 300, 400 and 500 are preferably carried out sequentially in this order.

A sixth step 600 of pressing the sheet sandwich (not shown) comprises pressing the sheet sandwich 7 in the direction of sheet thickness Z. For this purpose, the sheet sandwich 7 can be placed flat in a press capable of compress the sandwich of sheets 7 in the direction of sheet thickness Z. This sixth step 600 of method 99 thus makes it possible to adhere the sheets 2 adjacent to each other at the location of the adhesive strips 13 so that the sandwich of sheets 7 form a unique and united structure.

During this step 600, it is also possible to heat the sandwich of sheets 7 in particular to activate the adhesive strips 13.

In an advantageous embodiment of step 600, the surfaces of the press in contact with the sheet sandwich 7 can have engraved patterns similar to the corrugations 11 of the sheets 2 of the sheet sandwich 7. In this way, step press allows optimal adhesion of the sheets 2 between them.

During a seventh step 700 of stretching the sandwich, the sheet sandwich 7 obtained after the pressing step 600 is stretched along the sheet thickness direction Z to form the honeycomb structure 4 illustrated in the figure. 1.

To this end, it is for example possible to fix two drawing supports, respectively on an upper end 7a and a lower end 7b of the sandwich of sheets 7 opposite in the direction of sheet thickness Z. The two drawing supports are then moved and spaced apart from each other, in the direction of sheet thickness Z, so as to space the top 7a and bottom 7b ends of the sheet sandwich 7 apart to stretch said sandwich 7 and form a honeycomb structure 4.

The honeycomb structure 4 thus obtained comprises the plurality of cells 5, each cell 5 comprising the plurality of faces 6, and in particular several double faces, each double face being constituted by two sheets 2 glued together by an adhesive strip 13. The plurality of faces 6 also includes one or more single faces constituted by a single sheet 2.

Depending on the arrangement of the adhesive strips 13, it is then possible to obtain different configurations for the honeycomb structure 4.

Thus, in the embodiment illustrated in FIG. 1, in which the adhesive strips 13 binding adjacent sheets 2 are alternated in the direction of longitudinal extension X, the stretching step 700 makes it possible to obtain a honeycomb structure 4 of the “honeycomb” type, with cells, formed by the network of cells 5, of substantially hexagonal shape. Each cell 5 comprises in this embodiment five faces 6, including four single faces linked together in pairs by a double face.

The cells of the network formed by cells 5 thus have a prism shape comprising a base located in a plane perpendicular XZ to the direction of transverse extension Y, and extending in said direction of transverse extension Y. The cells of the network formed by cells 5 have in particular a hexagonal prism shape in the example of FIGS. 1 and 2.

Depending on the stretching distance, said hexagonal prism can be regular or else be stretched or compressed according to the direction of sheet thickness Z.

This seventh step 700 of the process 99, can also comprise, depending on the material, firing of the honeycomb structure 4 or of resin deposition. For this, the resin is placed (for example by dipping) at least on the corrugated portion of cell 5 of the honeycomb structure 4, then, during a crosslinking step, the resin is crosslinked to obtain a resinated honeycomb structure.

With reference now to FIG. 7, another example of method 999 for producing a core 1 of structural material will be described. Process 999 is particularly suitable for cores 1 made at least in part of cellulose, such as for example paper or cardboard. The process is preferably carried out in the order below:

A first step 1100 of process 999 consists in providing a strip of material 115. The material 115 for this process 999 is preferably made at least in part of cellulose.

More specifically, the strip of material 115 may extend substantially in directions of extension X, Y comprising a direction of longitudinal extension X and a direction of transverse extension Y. The strip of material 115 is substantially smooth, it that is, it has no ripples. However, it could be that the strip of material 115 is prestressed.

The strip of material 115 may have a defined width, for example substantially equal to a desired length for the core 1, in the direction of transverse extension Y, for example between a few centimeters and a few meters. The strip of material 15 can also have a much smaller width in the direction of longitudinal extension X, for example between a few centimeters and a few meters, to form a thickness of the core 1. The strip of material 115 can thus be wound on itself around the transverse extension direction Y, so as to form a roll 120 of tape unwound as the core of sandwich structural material 1 is manufactured.

In a second deformation or ripple step 1200, at least a portion of the strip of material 115 is deformed in the direction of sheet thickness Z, substantially perpendicular to the directions of extension X, Y. The ripple can be carried out by passing the strip 115 between two shaping rollers 118, 119, similar to the rollers 18, 19 described above, whose contact surfaces with the strip have a plurality of etched patterns, for example zigzags, in order to form the undulations 111. The patterns printed on a strip of cellulose material, such as strip 115, may be different from those printed on a strip of metallic material, such as strip 15. The patterns in bidirectional gold overhang, as described rollers 118, 119 may be entirely or only partially covered with patterns 118a, 118b as described above to provide a strip

115 fully wavy or only partially wavy. Step 1200 can be done such that the corrugations extend along a length of the strip 115, as illustrated in FIG. 7.

can be on top. Likewise

In a third step 1300 of the method 999, the plurality of adhesive strips 113 are placed on the strip of material 115.

The adhesive strips 113 can for example extend substantially in the direction X, that is to say parallel to a direction of unwinding of the strip 115. The adhesive strips 113 can be, for example, lines of adhesive poured onto the strip 115 continuously by one or more clarinets 121. The process 999 can have at least two production lines in parallel with the strip 115 and an identical strip 115 ', and the clarinet (s) 121, 121' of a line are shifted in direction Y relative to the other production line. So when the strips of material 115, 115 'of each production line are glued to each other, there is a phase shift φ of the adhesive strips 113, 113' in the transverse direction Y. It could be that there has more than two production lines in parallel.

In a fourth step 1400 of process 999, the two strips 115, 115 ′ impregnated with adhesive strips 113, 113 ′ of each production line are stacked, making the edges coincide, so as to glue the strips of material 115, 115 ′ between them and form an assembly 116. As described above, the adhesive strips 113, 113 'are then out of phase between two stacked strips 115, 115'.

In a fifth step 1500, the assembly 116 is cut, for example, by a cutter, and are stacked in groups of two together so as to form the sandwich of sheets 7.

Any of the methods 99, 999 for producing a structural sandwich material above can also comprise a tenth step of adding the skins 1a, 1b, comprising adding a top surface and / or a lower surface on the core 1, so in particular to close the openings of the cells 5 of the honeycomb structure.

The upper surface and the lower surface thus constitute the skins 1a, 1b external to the core 1 making it possible to protect the openings of the cells 5 and therefore to constitute a resistant structural sandwich material.

Claims (15)

1. core (1) of structural sandwich material in a compact state comprising a sandwich of sheets (7) comprising at least two sheets (8, 9) superimposed, said sheets each extending substantially along an extension plane (XY) and being superimposed in a thickness direction (Z) substantially perpendicular to the extension plane (XY), the core (1) being able to be placed in an expanded state in which the sheet sandwich (7) is stretched according to the thickness direction (Z) of sheets to form a honeycomb structure (4), the core (1) being such that two sheets (8, 9) superimposed on the sandwich of sheets (7) adhere to one another by a plurality of adhesive strips (13) interposed between the two sheets (8, 9) and adhering to each of said two superimposed sheets, said adhesive strips (13) being oriented in a first direction (Ll) of the extension plane ( XY) and being periodically juxtaposed on the sheets in a second direction (L2) of the plane of extension (XY) perpendicular to the first direction (L1), said adhesive strips (13) having a spatial period P2 in the second direction (L2), the core (1) being characterized in that: each sheet of the sheet sandwich (7) has undulations (11) in the thickness direction (Z), the undulations (11) being spatially periodic in the second direction (L2), in that the spatial period (PI) undulations (11) is strictly less than the spatial period (P2) of the adhesive strips (13), and in that a remainder of the Euclidean division of the spatial period (P2) of the adhesive strips (13) by the spatial period (Pl) of the undulations (11) is strictly greater than zero. 2. Core (1) of compact structural material according to claim 1, wherein said remainder of the Euclidean division of the spatial period (P2) of the adhesive strips (13) by the spatial period (Pl) of the corrugations (11) is greater to one tenth of the spatial period (Pl) of the undulations (11), preferably greater than one fifth of the spatial period (Pl) of the undulations (11). 3. Core (1) of compact structural material according to any one of claims 1 and 2, wherein the corrugations (11) extend substantially in the first direction (L1). 4. core (1) of compact structural material according to any one of claims 1 to 3, wherein the corrugations (11) are arranged continuously on each sheet of the sheet sandwich (7), in particular at the location said adhesive tapes (13). 5. Core (1) of compact structural material according to any one of claims 1 to 4, wherein said adhesive strips (13) have a strip width in the second direction (L2) greater than the spatial period (Pl) of corrugations (11), so that, in the second direction (L2), each adhesive strip (13) covers more than one corrugation (11) of a sheet (2) to which said adhesive strip (13) adheres. 6. Core (1) of compact structural material according to any one of claims 1 to 5, in which the corrugations (11) have a general form of zigzags, in particular in which said zigzags have peaks with an angle ( A) with a predefined vertex, in particular an angle (A) greater than 10 degrees and less than 60 degrees. 7. core (1) of structural material according to any one of claims 1 to 6, wherein, placed in the expanded state to form the honeycomb structure (4), said honeycomb structure (4) comprises cells (5) of generally hexagonal shape, and each of the walls of said cells (5) is corrugated by the corrugations (11) of the sheets (2) of the sheet sandwich (7). 8. core (1) of compact structural material according to claim 7, wherein two walls of said honeycomb structure (4), belonging respectively to two adjacent cells (5) and being oriented according to respective substantially identical orientation planes, have respective corrugations (11) respectively phase shifted relative to each other. 9. Core (1) of compact structural material according to any one of claims 1 to 8, in which the sandwich of sheets (7) is a sandwich of metallic sheets or of cellulose. 10. Method (99, 999) for producing a core of structural material comprising the steps of: Provide at least two sheets (8, 9) corrugated in a sheet thickness direction (Z), at least one of the two sheets (8, 9) having a plurality of adhesive strips (13) oriented in a first direction (Ll ) of an extension plane (XY) of the sheets (2), the undulations (11) having a spatial period (Pl) of undulation (11) in a second direction (L2) of the extension plane (XY) , the second direction (L2) being perpendicular to the first direction (L1); and Stacking said at least two sheets (8, 9) to obtain a sheet sandwich (7) such that two sheets (8, 9) superimposed on the sheet sandwich (7) adhere to each other by the plurality of strips adhesives (13), the plurality of adhesive strips (13) being interposed between the two sheets (8, 9) and juxtaposed periodically in the second direction (L2), said adhesive strips (13) having a spatial period (P2) in the second direction (L2), the spatial period (Pl) of the undulations (11) being strictly less than the spatial period (P2) of the adhesive strips (13), and a remainder of the Euclidean division of the spatial period (P2) of the strips adhesive (13) by the spatial period (Pl) of the corrugations (11) is strictly greater than zero. 11. The method of claim 10, wherein the step of providing said at least two sheets (8, 9) comprises the steps of: at. Placing the plurality of adhesive strips (13) on at least one continuous strip of material (15); b. Cut said continuous strip (15) to form said at least two sheets (8, 9); and vs. Form the periodic undulations (11) in said at least two sheets (8, 9). 12. The method of claim 11, wherein the periodic corrugations (11) are formed to extend in the first direction (L1). 13. The method of claim 10, wherein said at least two sheets (8, 9) are metallic and the steps of the method are carried out sequentially in the following order: at. Arrange the plurality of adhesive strips (13) on the continuous strip of material (15) so that the first direction (L1) is substantially in a direction width of the bandaged keep on going ( 15); b. Cut the strip continues (15) for form said at least of them leaves ( 8, 9) of such so that two leaves (8, 9) successively cut out in the band keep on going (15) present an offset of phase (φ) adhesive tapes (13) in the second direction (L2) relative to each other, in particular a phase shift (φ) substantially equal to half the spatial period (P2) of the adhesive tapes (13); and vs. Forming periodic corrugations (11) in said at least two sheets (8, 9) to provide said at least two sheets (8, 9); and d. Stack said at least two sheets (8, 9) to form the sheet sandwich (7). 14. The method of claim 13, wherein the periodic corrugations (11) are formed to extend in the first direction (L1). 15. The method of claim 10, wherein said at least two sheets are made at least partially of cellulose, and the step of providing said at least two sheets comprises the steps of: at. Form the corrugations (111) on a first continuous strip of material (115a) from which a first of said at least two sheets is extracted, and form the corrugations (111) on a second continuous strip of material (115b), distinct from the first strip continuous, from which a second of said at least two sheets is extracted, the first direction being a direction substantially of a length of the continuous strip; b. Periodically place adhesive strips (113) on the first continuous strip (115a) and adhesive strips on the second continuous strip (115b), the adhesive strips (113) of the first continuous strip (115a) being 5 phase shifted in the second direction (L2) with respect to those of the second strip (115b), in particular a phase shift (φ) substantially equal to half of the spatial period (P2) of the adhesive strips (13); and vs. Cut and stack the first continuous strip (115a) 10 and the second continuous strip (115b) so as to form the sandwich of sheets (7) comprising the first sheet (8) and the second sheet (9). 1/7 r> 2/7 4/7