METHOD FOR WARNING OF THE RISK OF BREAKAGE OR DEFORMATION OF A COMPOSITE PART AND MANUFACTURED PART

Abstract

The invention relates to a method for warning of risk of rupture or deformation of a part (1) made of a composite material when it is subjected to a force, said part comprising a fibre-reinforced thermoplastic or thermohardenable matrix. Said method consists in: arranging said fibres in a lattice structure (2) produced by winding fibres to form bars (21) that join together or intersect at nodes (20); designing at least one bar (21) of said lattice and / or integrating, into the part, at least one additional bar (3) with a determined location and tensile strength; associating, with the at least one bar, inside the part, a sensor means (4) designed to detect the rupture thereof; and associating, with the sensor means (4), a means (5) for emitting, outside the part, a signal relating to the rupture.

Description

[0001] Method for warning of a risk of breakage or deformation of a composite material part, and part obtained

[0002] The present invention relates to the field of structural parts made of composite material, comprising a thermoplastic or thermosetting matrix reinforced with fibers, such as fittings for example.

[0003] Its purpose is a method for warning of a risk of breakage or deformation of such a structural part depending on its use, as well as a part made of composite material comprising a system for warning of a risk of breakage or deformation.

[0004] It should be noted that by fibre we mean all the forms in which reinforcing fibres can be presented, and in particular, but not limited to, strands, ribbons or cords of reinforcing fibres.

[0005] Composite parts used as structural components present the disadvantage of a risk of failure that cannot be prevented because they deform very little before breaking. This necessitates significant oversizing of these parts so that they only break after an ultimate stress, well above the maximum operating stresses. Furthermore, since they can occasionally be damaged without any visible signs, they are also oversized to withstand operating, ultimate, and fatigue loads, even after damage.

[0006] However, in terms of weight and cost, it would be preferable to make the damage to these composite parts more legible, by being able to detect a risk of breakage preventively.

[0007] We also know, from documents US 2007 / 037462, FR 2 865 539, FR 2 980 574, DE 10 2007 032351, WO 2007 / 003883, WO 2009 / 044191, or even JP 3 344805, EP 2 500 706 and EP 2 112 374, of objects which incorporate elements with a calibrated fragility associated with sensor means, with the disadvantages that they are not part of the structural elements, at best they connect structural elements, so that they can fail for reasons other than a stress on the resistance of the object, a shock for example.

[0008] The present invention therefore aims to propose a method for manufacturing a composite structural part, as well as the resulting composite structural part, which prevents the risk of breakage by integrating warning means of a risk into the elements that create resistance to stress.

[0009] According to the invention, the method for warning of a risk of breakage or deformation of a structural part made of composite material when subjected to stress, according to the invention, where said part is made of a fiber-reinforced thermoplastic or thermosetting matrix, is characterized in that it consists of:

[0010] - arrange said fibers into a lattice structure obtained by winding the fibers, impregnated or not with resin, onto studs or the like, so as to stretch the fibers between studs to form bars joining or crossing at nodes, where said bars are oriented so as to be subjected to tension or compression,

[0011] - to configure at least one bar of said truss and / or to integrate into said part at least one additional bar created from additional nodes and / or from one or more nodes of said truss, the location and breaking strength of which are determined in such a way that, on the one hand, its failure at its location is not detrimental to the integrity in use of said truss and therefore of said part, and on the other hand, that said breaking strength is calibrated to be of a value greater than that which allows to withstand an optimal stress in use of said part, while being less than that of maximum stress of said part,

[0012] - to associate with said at least one bar, internally to said part, a sensor means designed to detect its breakage, - to associate with said sensor means, a means for emitting, externally to said part, a signal relating to the breakage.

[0013] Thus, the present invention uses the properties of a lattice structure to create within it a secondary lattice, stretched between the nodes of the main lattice, and of which at least one of the bars is dedicated to measurement.

[0014] According to an additional feature of the method according to the invention, the resistance of at least one additional bar is calibrated by reducing its cross-section relative to that of the other bars, or by using a less resistant material than that used for the other bars, or by creating on said bar a shape accident capable of causing an over-stress, or by under-sizing an additional node.

[0015] According to another additional feature of the method according to the invention, second means for detecting the breakage of one of said elements are incorporated into the lattice structure, associated with elements of said structure.

[0016] Under significant stress, in addition to the secondary lattice structure dedicated to detection, the primary lattice structure may also be damaged without this being detectable or visible in the behavior of the composite part or the object containing said part. Therefore, the secondary sensors are designed to provide an alert to enable rapid decision-making.

[0017] The present invention also relates to a structural part made of composite material comprising a warning system for a risk of breakage or deformation when subjected to stress, said composite part being made of a thermoplastic or thermosetting matrix reinforced with fibers, which is characterized in that said fibers are arranged in a lattice structure obtained by winding the fibers, impregnated or not with resin, onto studs or the like, so as to route the fibers between said studs to form bars joining or crossing at nodes, said bars being oriented so as to be subjected to tensile or compressive stress, said composite part further comprising at least one bar created from additional nodes and / or one or more nodes of said lattice, the location and breaking strength of which are predetermined,in such a way that, on the one hand, its breaking strength is calibrated to be lower than that required for the said part and higher than that required to withstand optimal stress during use of the said part, and on the other hand, that its breaking does not compromise the integrity of the said part during operation; in that said, at least one bar, is associated with a sensor means designed to detect its breaking; and in that said sensor means is associated with a means for emitting a signal relating to the breaking.

[0018] The breakage of at least one bar dedicated to measurement thus constitutes the first observable damage to the part, which retains its integrity in nominal operation.

[0019] When the part is under stress, the observed breakage of the measuring bar indicates an overload exceeding the nominal load. Exceeding this alert threshold may trigger a warning or maintenance action.

[0020] The sensor medium can take various forms, including, but not limited to:

[0021] - an electrical conductor, or an optical fiber, placed in the bar dedicated to measurement, which breaks simultaneously with this bar,

[0022] - a strain gauge by elongation of the bar, consisting for example of a coil or a conductor, the variation in length of said conductor during deformation directly impacting the resistance of the conductor,

[0023] - or any other system that allows for the measurement of deformation or stress.

[0024] It should be noted that the inclusion in the resin of the lattice can allow the sensor to be placed close to the bar dedicated to the measurement, because the resin constituting the matrix has a negligible rigidity compared to that of the composite material constituting the lattice, the local deformation near the bar dedicated to the measurement will be similar in the resin to that of the bar.

[0025] The means of emitting a signal can be achieved in various ways, including, but not limited to:

[0026] - via a wired connection to the sensor, passing through the matrix,

[0027] - via a wireless connection, through communication electronics directly embedded in the matrix, or printed on the matrix,

[0028] - by means of optical transmission, using a transparent matrix,

[0029] - or by using as a sensor an RFID antenna that can be interrogated remotely by an active source capable of detecting its breakage or deformation.

[0030] The present invention also relates to a variant of the method for warning of a risk of breakage or deformation of a structural part made of composite material when subjected to stress, said part being made of a thermoplastic or thermosetting matrix reinforced with fibers, the method being characterized in that it consists of:

[0031] - arrange said fibers into a lattice structure obtained by winding the fibers, impregnated or not with resin, onto studs or the like, so as to stretch the fibers between said studs to form bars joining at nodes, said bars being oriented so as to be subjected to tension or compression,

[0032] - design at least a part of said part through at least one bar of said truss and / or at least one additional bar created from additional nodes and / or one or more nodes of said truss, the location and breaking strength of which are determined such that, on the one hand, at its location, when the part is subjected to a force reaching or exceeding the nominal force, it is subjected to a force causing its failure, and that its failure is not detrimental to the integrity in use of said truss and therefore of said part, on the other hand, that said breaking strength is calibrated to be of a value greater than that enabling it to withstand optimal stress in use of said part, while being less than that of the maximum stress of said part, and in that said part of said part consists of an externally identifiable portion,and which is designed to withstand deformation upon the rupture of said at least one bar.

[0033] Thus, according to this variant, a composite part with a lattice structure is created, designed to withstand stresses. This part includes a section, also subjected to said stresses, whose lattice structure has a lower breaking strength than the rest of the lattice, but greater than the desired strength of the composite part and less than its maximum breaking strength. Furthermore, this section of the composite part is identifiable, and failure of its structure results in an externally visible change, such as deformation.

[0034] The deformation of the part including at least one bar dedicated to measurement thus constitutes the first noticeable damage to the part, which retains its integrity in nominal operation.

[0035] It is therefore possible to detect, before a risk of breakage of the composite part, that it has been subjected to a force greater than the nominal force.

[0036] When the part is under stress, the observed breakage of the measuring bar indicates an overload exceeding its nominal load. Reaching this warning threshold may trigger preventive or maintenance action.

[0037] The present invention also relates to a structural part made of composite material comprising a means of warning of a risk of breakage or deformation when subjected to stress, said composite material part being made of a thermoplastic or thermosetting matrix reinforced with fibers, which is characterized in that said fibers are arranged in a lattice structure obtained by winding fibers, impregnated or not with resin, onto studs or the like, so as to tension the fibers between said studs to form bars joining at nodes, said bars being oriented so as to be subjected to tension or compression,

[0038] in that said part comprises at least one portion which incorporates at least one bar of said truss and / or at least one additional bar created from additional nodes and / or one or more nodes of said truss, said measuring bar, the location and breaking strength of which are determined such that, on the one hand, at its location, when the part is subjected to a force reaching or exceeding the nominal force, it is subjected to a force causing its rupture, and that its rupture is not detrimental to the integrity in use of said truss and therefore of said part, on the other hand, said breaking strength is calibrated to be of a value greater than that enabling it to withstand optimal stress in use of said part, while being less than that of maximum stress of said part,

[0039] and, in that said part consists of an externally identifiable portion, and which is designed to undergo deformation upon the rupture of said at least one bar.

[0040] The least resistance to breakage of the bar dedicated to measurement can be obtained in various ways such as, but not limited to, a reduced section compared to those of the other bars of the truss, a zone of weakening, giving this bar an initial shape to reduce its resistance to buckling by passing the winding over a particular point of passage for example, integrating into this bar an intermediate coil whose resistance is limited so that it breaks beyond a certain force exerted on the bar.

[0041] According to a particular embodiment, the measuring bar comprises tensioned fibers and less tensioned fibers, the latter being able to allow an increased movement of the part after rupture of said tensioned fibers.

[0042] According to a particular embodiment of the composite material part according to the invention, the part of said part intended for identifying the break comprises a primary lattice structure made from a reinforcing fiber having a high modulus and a low elongation at break, said primary structure being associated with a secondary structure, concurrent or not with said primary structure and made from reinforcing fibers having a lower modulus, a higher elongation at break and / or a higher breaking stress than the fibers of said primary structure.

[0043] Failure of the primary structure under a stress defined by the component's design results in a transfer of the stress path to the secondary structure. This change in stress path manifests as a modification of the overall stiffness, detectable elongation, and / or visible cracks, allowing for the detection of damage to the component.

[0044] Advantageously, the secondary structure will be able to support a final load before failure greater than the primary structure, so as to ensure the proper functioning of the part despite the damage sustained.

[0045] Thus for example, in a lattice structure made from HM (high modulus) carbon fibers, the so-called measuring bar(s) are doubled with (HR) (high strength) carbon fibers, so as to obtain a decrease in stiffness after the rupture of the HM fibers, the final maximum force being higher than the first rupture force, by using HR fibers having a higher elongation at break and allowable values ​​than HM fibers.

[0046] It should be noted that the lining can also be done with S-type glass fibers.

[0047] The advantages and characteristics of the processes and the composite material parts resulting therefrom according to the invention will become clearer from the following description, which relates to the attached drawing, which represents non-limiting embodiments thereof.

[0048] In the attached drawing:

[0049] - Figure 1 shows a schematic elevation view of a composite material part relating to the field of the invention. - Figure 2 shows the same composite material part equipped with a warning system for a risk of breakage or deformation according to the invention.

[0050] - Figure 3 represents the same part in composite material equipped with another warning system for a risk of breakage or deformation according to the invention.

[0051] - Figure 4 represents a schematic elevation view of a composite material part relating to the field of the invention, equipped with a means for warning of a risk of breakage or deformation according to the invention.

[0052] - Figure 5 represents the same part in composite material equipped with a variant of the means for warning of a risk of breakage or deformation according to the invention.

[0053] With reference to Figure 1, a composite part 1 can be seen, according to the invention. This composite part 1, used to illustrate the present invention without limitation, consists of a support arm, adapted to withstand mechanical stresses S during its use.

[0054] The composite part 1 comprises a thermoplastic or thermosetting matrix 10 reinforced with fibers which are arranged in a lattice structure 2 made up of the filament winding, according to a judiciously chosen path around spools or pulleys to form the nodes 20 of the lattice 2, while the straight parts extending between the nodes 20 constitute bars 21. The fibers may be pre-coated with a thermoplastic or thermosetting resin.

[0055] The preform consisting of the mesh 2 is then integrated into a matrix 10 to block the transverse deformations of the fibers, either by soaking in a bath of material constituting the matrix, at a temperature allowing to present a viscosity sufficient to cover the mesh of fibers 2, or by molding in a mold, the volume of filling of the part being injected in addition to the mesh 2 previously placed in the mold.

[0056] With reference to figure 2, it can be seen that, according to the invention, the lattice 2 comprises an additional bar 3, obtained by winding between a node 201 of the lattice 2 and an additional node 30, itself resulting from a winding with two nodes 202 and 203 of the lattice 2.

[0057] The additional bar 3 does not contribute to the nominal strength of the composite part 1, however it is subjected to tension or compression when the composite part 1 is stressed.

[0058] The additional bar 3 is configured to offer less resistance than the other bars 21, through, but not limited to, a smaller section, or the use of a less efficient material, or the presence, at any point, of a shape accident causing over-stress, or under-sizing of node 30, or a combination of several of these characteristics.

[0059] According to the invention, a sensor means 4 is associated with the additional bar 3, intended to be integrated into the matrix 10, and capable of measuring a deformation or a break in the additional bar 3. In the embodiment shown, the sensor means 4 is linked to signal emission means 5 arranged externally to the part 1, and connected to the sensor means 4 by a wired link 50.

[0060] The sensor means 4 can detect a deformation or breakage of the additional bar 3, and transmit this information to the signal emission means 5.

[0061] Referring now to figure 3, we can see a particular embodiment of the warning system according to the invention.

[0062] In this embodiment an additional bar 6 dedicated to the warning is made by winding a wire conductor 60 around two additional nodes 61 and 62, each of them coming from the creation of two additional bars, respectively 63 and 64, and 65 and 66, by windings with nodes of the lattice 2, respectively 204 and 205, and 206 and 207.

[0063] The additional bars 6, 63, 64, 65, and 66, along with the additional nodes 61 and 62, form a secondary lattice internal to lattice 2 between nodes 204, 205, 206, and 207, with bar 6 acting as a strain gauge subjected to stress. It will be understood that the variation in length of bar 6, and therefore of conductor 60, directly impacts the conductor's resistance.

[0064] Referring now to figure 4, we can see part 1 made of composite material according to the invention, which includes a vertical element 11 and a horizontal element 12.

[0065] According to this variant of the invention, the composite part 1 comprises a part 7, identifiable externally, comprising a bar 22 of the lattice 2, braced like a prop between a node 20 of the vertical element 11 and a node 20 of the horizontal element 12.

[0066] The bar 22, known as the measuring bar, is positioned so as not to contribute to the strength of part 1 when the latter is subjected to stress, ensuring that in the event of breakage, the integrity of part 1 remains intact. It is configured to have a breaking strength greater than that required to withstand optimal stress during the use of part 1, but less than the maximum stress capacity of part 1.

[0067] Thus, the breakage of bar 22, leading to the deformation or breakage of part 7 of part 1, visible externally, makes it possible to detect that part 1 has been or is subjected to a force greater than the nominal one required.

[0068] With reference to Figure 5, we can see in a variant that part 7 of part 1 is traversed by a portion of the lattice 2, comprising a bar 23 extending between a node 20 of the vertical element 11 and a node 20 of the horizontal element 12 and having in a median portion, a winding on a coil 24, whose resistance to crushing, under the effect of a tension, is calibrated to break when part 1 is subjected to a force greater than the nominal force required.

Claims

DEMANDS 1) A method for warning of a risk of breakage or deformation of a structural part (1) made of composite material when subjected to stress, wherein said part is made of a fiber-reinforced thermoplastic or thermosetting matrix, characterized in that it consists of: - arrange said fibers into a lattice structure (2) obtained by winding the fibers, impregnated or not with resin, onto studs or the like, so as to stretch the fibers between studs to form bars (21) joining or crossing at nodes (20), where said bars (21) are oriented so as to be subjected to tension or compression, - configure at least one bar (21) of said truss and / or integrate into said part at least one additional bar (3) created from additional nodes (30) and / or from one or more nodes (201, 202, 203) of said truss (2), the location and breaking strength of which are determined so that, on the one hand, its failure at its location is not detrimental to the integrity in use of said truss (2) and therefore of said part, and on the other hand, said breaking strength is calibrated to be of a value greater than that which allows it to withstand optimal stress in use of said part, while being less than that of maximum stress of said part, - to associate with said at least one bar, internal to said part, a sensor means (4) designed capable of detecting its breakage, and - associate said sensor means (4), a means (5) of emitting, externally to said part, a signal relating to the break. 2) A method according to claim 1, characterized in that the resistance of at least one additional bar is calibrated by reducing its cross-section relative to that of the other bars, or by using a material that is less efficient than that used for the other bars, or by creating on said bar a shape anomaly capable of causing over-stress, or by undersizing an additional node. 3) Method according to claim 1 or claim 2, characterized in that second means for detecting the breakage of said elements are incorporated into the lattice structure, associated with elements of said structure. 4) A structural component made of composite material comprising a warning system for a risk of breakage or deformation when subjected to stress, said composite component being made of a thermoplastic or thermosetting matrix reinforced with fibers, characterized in that said fibers are arranged in a lattice structure obtained by winding the fibers, impregnated or not with resin, onto studs or the like, so as to route the fibers between said studs to form bars joining or crossing at nodes, said bars being oriented so as to be subjected to tensile or compressive stress, said composite component further comprising at least one bar created from additional nodes and / or one or more nodes of said lattice, the location and breaking strength of which are predetermined,in such a way that, on the one hand, its breaking strength is calibrated to be lower than that required for the said part and higher than that required to withstand optimal stress during use of the said part, and on the other hand, that its breaking does not compromise the integrity of the said part during operation; in that said, at least one bar, is associated with a sensor means designed to detect its breaking; and in that said sensor means is associated with a means for emitting a signal relating to the breaking. 5) A composite material part according to claim 4, characterized in that the sensor means is in the form of an electrical conductor, or an optical fiber, disposed in at least one additional bar, dedicated to measurement, designed to break simultaneously with said at least one bar. 6) A composite material part according to claim 4, characterized in that the sensor means is in the form of a strain gauge by elongation of the bar, the latter being made up of a coil or an electrical conductor, the variation of whose length during deformation impacts the resistance of said conductor. 7) A composite material part according to any one of claims 4 to 6, characterized in that the means for emitting a signal consists of a wire link passing through the matrix. 8) A composite material part according to any one of claims 4 to 6, characterized in that the means for emitting a signal consists of communication electronics embedded in the matrix. 9) A composite material part according to any one of claims 4 to 6, characterized in that the means for emitting a signal consists, while the matrix is ​​transparent, of an optical transmission means. 10) A composite material part according to any one of claims 4 to 6, characterized in that the detection and emission means is embedded or printed on the resin and consists of a remotely interrogable RF antenna. 11) A method for warning of a risk of breakage or deformation of a structural part (1) made of composite material when subjected to stress, said part being made of a fiber-reinforced thermoplastic or thermosetting matrix (10), characterized in that it consists of: - arrange said fibers into a lattice structure (2) obtained by winding the fibers, impregnated or not with resin, onto studs or the like (20), so as to stretch the fibers between said studs to form bars (21) joining at nodes, said bars (21) being oriented so as to be subjected to tension or compression, - design at least a part (7) of said piece through at least one bar of said truss and / or at least one additional bar (22; 23) created from additional nodes (24) and / or one or more nodes of said truss, the location and resistance to breakage of which are determined so that, on the one hand, at its location, when the part undergoes a force reaching or exceeding the nominal force, it undergoes a force causing its breakage, and that its breakage is not detrimental to the integrity in use of said truss and therefore of said part, on the other hand, said resistance to breakage is calibrated to be of a value greater than that enabling it to withstand an optimal stress in use of said part, while being less than that of maximum stress of said part, and in that said part (7) of said part (1) consists of an externally identifiable portion, and which is designed capable of undergoing deformation when said at least one bar breaks. 12) A structural part made of composite material comprising a means of warning of a risk of breakage or deformation when subjected to stress, said part made of composite material being made of a thermoplastic or thermosetting matrix (10) reinforced with fibers, characterized in that said fibers are arranged in a lattice structure (2) obtained by winding fibers, impregnated or not with resin, onto studs or the like (20), so as to tension the fibers between said studs (20) to form bars joining at nodes, said bars being oriented so as to be subjected to tension or compression, in that said part (1) comprises at least one portion (7) which incorporates at least one bar of said truss (2) and / or at least one additional bar (22; 23) created from additional nodes (24) and / or one or more nodes (20) of said truss, referred to as a measuring bar, the location and breaking strength of which are determined such that, on the one hand, at its location, when the part is subjected to a force reaching or exceeding the nominal force, it is subjected to a force causing its rupture, and that its rupture is not detrimental to the integrity in use of said truss and therefore of said part, on the other part, that said breaking strength be calibrated to be of a value greater than that which allows the part to withstand optimal stress in use, while being less than that of the maximum stress on said part, and, in that said part (7) consists of an externally identifiable portion, and which is designed to undergo deformation upon the rupture of said at least one bar. 13) Composite material part according to claim 12, characterized in that the measuring bar (22; 23) has a reduced section compared to those of the other bars (20) of the lattice structure (2). 14) Part made of composite material according to claim 12, characterized in that the measuring bar (22; 23) has a zone of embrittlement. 15) Part made of composite material according to claim 14, characterized in that the embrittlement zone consists of a winding on a coil (24) whose resistance is limited. 16) Part made of composite material according to claim 12, characterized in that the measuring bar (22; 23) comprises tensioned fibers and less tensioned fibers, the latter being able to allow an increased deflection of the part after rupture of said tensioned fibers. 17) A composite material part according to claim 12, characterized in that the part of said part intended for identifying the break comprises a primary lattice structure made from a reinforcing fiber having a high modulus and a low elongation at break, said primary structure being associated with a secondary structure, concurrent or not with said primary structure and made from reinforcing fibers having a lower modulus, a higher elongation at break and / or a higher breaking stress than the fibers of said primary structure.