EP3642020A1

EP3642020A1 - Method and device for inspecting a joining surface

Info

Publication number: EP3642020A1
Application number: EP18724838.0A
Authority: EP
Inventors: Lennert HEILMANN
Original assignee: Deutsches Zentrum fuer Luft und Raumfahrt eV
Current assignee: Deutsches Zentrum fuer Luft und Raumfahrt eV
Priority date: 2017-06-19
Filing date: 2018-05-11
Publication date: 2020-04-29
Also published as: US11745437B2; JP2020524099A; US20200130289A1; DE102017113430A1; CN110944826B; WO2018233928A1; CN110944826A; JP7046988B2

Abstract

A method for inspecting a joining surface (14) of a substrate, wherein a component is to be adhered to the joining surface of the substrate by means of an adhesive material (27), wherein the method comprises the following steps: • - providing at least one planar test textile (20), which has a fiber material (21) and an adhesive primer (22), • - applying the planar test textile to at least one part of the joining surface of the substrate to which the component is to be adhered so that the adhesive primer of the planar test textile contacts the joining surface of the substrate, • - at least partially curing the adhesive primer of the planar test textile in order to integrally bond the planar test textile to the substrate by means of the adhesive primer, • - pulling off the planar test textile after at least partially curing the adhesive primer and inspecting the joining surface by means of a qualitative evaluation of the fracture pattern between the cured adhesive primer and the planar test textile and/or by means of a quantitative evaluation of the pull-off force determined when pulling off the planar test textile.

Description

Method and device for checking a joining surface

The invention relates to a method and a device for checking a joining surface of a substrate, wherein a component is to be glued to the joining surface of the substrate by means of an adhesive. The invention also relates to a method of bonding a substrate to such a device using the verification method. Due to their weight-specific strength and rigidity, fiber composite materials are an indispensable part of any component. Fiber composite materials consist mainly of two essential components, namely a fiber material and a matrix material. In the production of fiber composite components from a fiber composite material, the fiber material is usually brought into the corresponding later component form and then cured the matrix material infused into the fiber material. Curing takes place in the vast majority of cases by temperature and possibly pressurization. By curing, the load-bearing fibers of the fiber material are forced in their predetermined direction and form together with the hardened matrix material an integral unit for load transfer.

Unfortunately, fiber composite components have some disadvantages in the production compared to isotropic materials, since the component form of a fiber composite component is usually formed by appropriate molds, which represent a kind Negativab- pressure of the later component form. As a result, it is not unusual for complex fiber composite components made of different components, which are either made of fiber composite materials or composed of isotropic materials, to be glued together in order to be able to produce the complex geometry. The repair of fiber composite components can be done in local damage by gluing repair patches by first removed at the damaged site, the fiber material and matrix material of the fiber composite material and so the damaged area is prepared and then a repair patch is glued, which is glued into the resulting space and fill it up again.

Such bonding, in which at least one of the joining partners is a fiber composite component made of a fiber composite material, is not entirely uncritical with regard to certification and validation. For example, in the aviation and aerospace industry, high standards have to be set for such an adhesive bond in order to meet the safety requirements, especially with regard to safety-critical components. The particular challenge here is that a non-destructive testing of bonds or glued joints is only possible to a limited extent. At present there is no non-destructive testing method with which the bonding strength of bonds can be demonstrated.

Because of this and in the past occurred damages the certification authorities for the structural gluing in the aviation prescribe special regulations. Thus, according to EASA AMC 20-29 or FAA AC 20-107b, safety-relevant bonding is currently only permissible if a) a possible failure of the bond is limited to an uncritical size by design measures (typically by alternative load paths or redundancy in the design b) Each individual glued joint is loaded with the maximum design critical load to validate the strength of the joint, or

c) A reproducible and reliable non-destructive test method is used to ensure the strength of each bond. Another major disadvantage in the repair of fiber composite components by means of gluing is that the structure to be repaired was already in operation and may have come into contact with media which adversely affect the formation of adhesive forces during bonding. Therefore, glued repairs (without additional application of rivets) are currently not carried out, as long as a failure of the repair is critical for the safety of the aircraft. However, in order to carry out glued repairs in accordance with the approval authorities, intensive research is being carried out into possibilities for validating a repair.

US Pat. No. 7,736,452 B2 discloses a method for non-destructive testing of an adhesive bond in the repair of fiber composite components, in which case the adhesive bond is checked indirectly. The damaged area on the fiber composite component is repaired in a first step and a corresponding glued repair patch is used. Subsequently, in the vicinity of the repaired site, a test patch, which has the same properties and the same material as the repair patch, adhered and loaded after curing of the adhesive bond with a corresponding force. If the test patch withstands the applied force, the durability of the repaired point is assumed.

From US 2008/001 1075 A1 a method for quality control of a fiber composite component and a possible adhesive bond is known, in which case a metallic structure is adhered to the surface of the fiber composite component. The metallic structure has a predetermined breaking point. After curing of the adhesive bond, the metallic structure is now subjected to a force. If the predetermined breaking point breaks, the adhesive bond with the surface of the fiber composite component is effective. If the adhesive bond breaks instead of the predetermined breaking point, it was not faultless.

But not only in fiber composite components, there is the desire of a non-destructive inspection of the joining surface for the purpose of adhesion between a substrate and other components. Thus, surface coating is a widely used method for certain technical or aesthetic functions fulfill. Thus, for example, in civil aviation corresponding aluminum structures are used which are exposed to aggressive media and are therefore particularly at risk from corrosive attack. Therefore, these aluminum structures are subjected to an electrochemical treatment and then sealed with a surface coating. This primer layer serves on the one hand as corrosion protection and on the other hand as an adhesion-promoting layer for a subsequent bonding process.

At present, however, there is no method by which the joining surface of a substrate, whether made of a fiber composite material or of another material, can be checked directly for its effectiveness with respect to a splice. It is therefore an object of the present invention to provide an improved method with which the joining surface of a substrate, in particular a fiber composite component as a substrate to which a component is to be glued, checked directly for bonding and the effectiveness of such bonding can be ensured in advance.

The object is achieved with the method for checking a joining surface according to claim 1, the method for bonding components according to claim 12 and a device according to claim 16 according to the invention.

According to claim 1, a method for checking a joining surface of a substrate is proposed, wherein one or more components are to be glued to the joining surface of the substrate by means of an adhesive material or adhesive.

The substrate may be a fiber composite component of a fiber composite material, wherein the fiber composite component may be made of a fiber composite material. Such a fiber composite material generically comprises a fiber material and a matrix material. In addition, such a fiber composite material contain other components or materials that are application-specific. The substrate may, however, also be another material, in particular isotropic material, such as, for example, a polymer material, metal material, organic materials and / or inorganic materials. As polymer materials, for example, duromers (epoxies, unsaturated polyesters, vinyl esters, phenolic resins), elastomers (rubber, polysulphides, silicones, polyurethanes), thermoplastics (Polyetherketonke- ton, polyamide, polyester, etc.) can be used. As metal materials or alloys are in particular steel, aluminum, titanium, magnesium, non-ferrous metals, etc. into consideration. In particular, bones, wood and teeth can be used as organic materials. As inorganic materials in particular glass, cement, ceramics, rocks are conceivable. In this case, the substrate may not be a fiber composite component made of a fiber composite material.

A component may consist of the same material as the substrate or have such a material. However, it is also conceivable that the component consists of another material, as mentioned above, or has such a material. One conceivable combination which is frequently encountered in civil aviation is a substrate made of a fiber composite material onto which a component made of a metal material is to be glued. However, the component may also be a material which inherently contains an adhesive material, such as, for example, surface coatings, sealants or lacquers. It is conceivable in particular that a prepreg (preimpregnated fiber material of a fiber composite material) is placed directly on the adhesive primer and cured, in which case the matrix material of the prepreg forms the property of an adhesive. In order to be able to check the joining surface directly and above all non-destructively, it is proposed according to the invention that initially at least one sheet-like test textile be provided which contains a fiber material and an adhesive primer. An adhesive primer is a material that is usually applied to the joining surface in preparation for an adhesive bond to be produced. After curing of an adhesive primer, the adhesive would be applied to the adhesive primer, so that the adhesive primer is a link between the joining surface of the component on the one hand and the adhesive on the other. An adhesive primer (also called a primer) serves to prepare the joining surface for subsequent bonding. In the context of the present invention, such an adhesive primer may also be those matrix materials that are part of a fiber composite material. In an advantageous embodiment, in which the substrate is formed from a fiber composite material, the adhesive primer may be the matrix material from which the fiber composite component is made or that matrix material which is part of the fiber composite material from which the repair patch is made. The adhesive primer may also be that material which is to form the later adhesive layer. The adhesive primer and the adhesive, which is to adhere the later component to the fiber composite component, can be the same material.

The sheet-like test textile further contains a fiber material, which is preferably made of textile or non-textile raw materials and which has preferably been processed from linear structures to a sheet-like structure. The fiber material of the sheet-like test textile can have a non-rigid state in the uncured state of the adhesive primer. These may be, in particular, fiber materials which are also used for the production of fiber composite components and thus are part of fiber composite materials. It is also conceivable, however, for the fiber material to be, for example, a metallic material, which in principle is not limp, but deforms under a tensile and / or compressive load.

The sheet-like test textile is generally provided in such a way that the fiber material of the sheet-like test fabric is already impregnated with the adhesive primer and is therefore immediately available for the subsequent steps. It is also conceivable, however, for the fiber material and adhesive primer to be provided separately and then joined together during the further process steps still to be discussed.

In the next step, the sheet-like test textile is now applied to at least a part of the joining surface of the substrate, so that the adhesive primer of the sheet-like test fabric contacts the joining surface of the substrate. The joining surface, in other words, is thus by the adhesive primer of the sheet-like test textile wetted or occupied. If the fiber material of the test textile already has the adhesive primer as a common unit, then the adhesive primer and the fiber material are applied to the substrate in one step. If both components are present separately, either the adhesive primer and then the fiber material of the test textile are applied first or the fiber material of the test textile is first applied and then the adhesive primer is applied to the fiber material. In the second case, the adhesive primer infused into the fiber material of the test fabric and then forms the boundary layer between fiber material and joining surface.

In the next step, after the sheet-like test fabric has been applied to the joining surface, the adhesive primer of the sheet-like test fabric is cured to cohesively connect the sheet-like test fabric to the substrate in the region of the joint surface by means of the adhesive primer. Depending on the primer used, the curing of the adhesive primer can thus take place, for example, at room temperature or at a corresponding temperature and if appropriate pressurization. Depending on the adhesive primer used, the primer is activated by the corresponding specific carrier, which activates the curing process and partially or completely hardens, ie consolidates, the adhesive primer. After the curing or polymerization of the adhesive primer, the sheet-like test textile was firmly bonded or glued to the substrate in the region of the joining surface by means of the adhesive primer. After the adhesive primer of the sheet-like test fabric has cured, the sheet-like test fabric is pulled off the joining surface, preferably such that a force is exerted on the test fabric substantially orthogonal to the joining surface and in the direction away from the joining surface. Then, the joining surface by a qualitative evaluation of the fracture pattern or by a quantitative assessment of the removal of the sheet-like

Test textile determined peel force are checked. The peel force can be removed over time and / or over the path or test path, whereby a Abziehkraftverlauf is formed over time and / or over the path. The review In this case, the fracture pattern means that either the joining surface of the component or the test textile or both is examined.

If there is insufficient or insufficient bonding of the adhesive primer on the joining surface of the substrate, the primer is separated from the substrate, whereby the poor pretreatment of the joining surface is detected. Correct surface pretreatment results in cohesive material separation within the primer, typically breaking up chemical chains in the adhesive primer, creating a clean surface with high surface energy. Due to the geometrical certainty of the textile, a uniform and defined surface topology is formed at the same time, which represents an optimal substrate for the subsequent bonding. Such a surface is guaranteed to be free from contamination, to prepare and pretreat the joining surface free of the "human factor" and to guarantee adhesion .The subsequent joining process with application of the adhesive to the primer therefore takes place under maximum process reliability, since the condition of the joining surface is known.

In the case of a faultless joining surface conforming to the quality, the adhesive primer adheres uniformly and as a rule over the entire surface of the substrate and indicates a correct bonding of the primer to the substrate. The breakage during removal of the sheet-like textile takes place cohesively in the primer, so that the interface with the substrate withstands the applied load. In this case, it can be assumed that the joining surface corresponds to the qualitative requirement for the bond.

However, if the fracture pattern has areas in which the primer on the joining surface is no longer present in parts, then the primer does not adhere to the entire surface of the joint surface, which may either be due to inadequate adhesion of the primer to the joint surface or because of the Subjacent substrate showed even more damage that were torn when tearing the test fabric with. In both cases, the quality of the joining surface was insufficient for subsequent bonding, which was shown by the fracture pattern. of the both on the joining surface as well as on the withdrawn Prüftextil with the naked eye can be seen. There is no need for interpretation or mental activity in the evaluation of the fracture pattern, since even the simple determination of uniformity of the fracture pattern is sufficient to assume a high-quality joining surface. In the case of a non-uniform fracture pattern, which in particular has damage in the fracture surface, it is to be assumed that the bonding surface is insufficient or not perfect for subsequent bonding.

Alternatively or additionally, the evaluation of the joining surface can also be performed quantitatively by determining the peel force during the removal of the sheet-like test fabric. If this peel force (for example, in relation to force / displacement) is substantially uniform and / or within a desired range and / or above a defined threshold value, then a flawless and permissible joining surface and at the same time flawless mechanical properties can be assumed. However, if the peel-off force has irregularities that show up in significant force peaks, and / or if the peel force is wholly or partially below the defined peel force, an insufficient quality of the joint surface is to be assumed (deflections of less than 30% or less than 20%). the average value is considered regular, depending on the adhesive primer). These usually localized force peaks in a peel force curve are those areas in which the adhesive primer was not cohesively broken within the primer, but where the adhesive primer did not adhere to the joining surface or where parts of the substrate of the joining surface were torn. The maximum peel force that can occur is defined by the textile texture and the cohesive breaking strength of the adhesive primer in the desired state. If errors occur, then the peel force at the appropriate location is always less than the maximum peel force that will occur with a purely cohesive-refracting adhesive primer. In these areas, the peel force falls below a predetermined threshold (eg below the maximum peel force minus tolerance), which is immediately recognizable and suggests an insufficient joining surface. If the peel force is below the threshold value over the entire test path, a defect of the adhesive primer must be assumed. It is thus possible, based on a qualitative evaluation of the fracture pattern and / or a quantitative evaluation of the peel force to ensure the underlying joining surface in terms of their property to ensure secure bonding, without the device must actually be glued or corresponding temporary test specimens must be arranged near the joining surface. Rather, the joining surface can be checked directly, wherein at a positive review of the joining surface is achieved simultaneously that the joining surface now represents an optimal surface and provides a corresponding surface energy for subsequent bonding. As a result, the quality of the subsequent bonding can also be influenced in a defined manner by this process and the quality of this bond can be guaranteed.

In addition, an indirect process control can be carried out, which is representative of the entire bond. Thus, for example, a test textile can be arranged as a test specimen, for example, on an additional adhesive primer next to the repair site, which is then removed at a later time after use.

In addition, it becomes possible with the present invention to produce a reproducible and well-defined primer layer (layer thickness, topology) regardless of the amount of applied adhesive primer, since excess primer material is removed together with the test fabric. Furthermore, the method according to the invention allows the adhesive primer in film and / or film form to be applied to the substrate, so that restrictions such as particle size or viscosity of the adhesive primer play only a minor role. In addition, the bonding of the adhesive primer to the substrate can be mechanically checked over the entire surface in the course of the activation process. In addition, the present invention allows a virtually unlimited storage of the substrate before further processing, since the application of the adhesive primer and the activation are temporally decoupled. Activation takes place by removing the test fabric.

Depending on the adhesive primer, different curing mechanisms may come into play. For example, chemical reactions such as polyreactions (polyaddition, polycondensation, chain polymerization), physical reactions (Solidification, evaporation, sol-gel process) or the adhesion by pressurization conceivable. In general, the curing under defined conditions such as temperature or pressure / vacuum or under adhesive-specific conditions (eg UV radiation) take place. Furthermore, hardening of the adhesive primer will result in firm adhesion to the substrate. In principle, the fiber material of the test textile may be embedded in the adhesive primer, so that below and above the fiber material is the adhesive primer.

However, it is also conceivable that the fiber material rests on the adhesive primer, so that there is no adhesive priming above the fiber material of the test textile.

The joining surface created after peeling off the test fabric may be characterized by raised areas and depressions. The recesses represent the fiber prints, while the raised areas represent the open areas of the fiber material of the test fabric. This provides, inter alia, an advantage for the subsequent application of an adhesive film, as this allows the area under the adhesive film to be vented by means of vacuum. Thus, no air pockets under the adhesive, which can otherwise lead to pores in the adhesive seam. This problem often occurs when adhesive films are applied to smooth surfaces. Trapped air bubbles can not be removed by applying a vacuum, since the evacuation path of the air bubbles is blocked by adhering adhesive. However, the adhesive film does not close the channels that produce the fiber material of the test fabric, since the film initially rests on the raised areas.

At the same time, the elevations can serve as spacers. When joining components, adherence to a defined adhesive layer thickness is very important. This is usually realized by spacers in the adhesive or on the component. These ensure that the components can only be approximated to a defined degree. However, these spacers are usually a weak point in the bond because they cause a stress concentration under mechanical stress. The raised areas, which can be formed by the fiber material impressions, can serve as spacers, since the adhesive is removed from the cavities. gene of fiber prints can not be completely squeezed out. However, they are not foreign bodies but part of the adhesive primer remaining on the substrate and thus do not generate any stress concentrations. In an advantageous embodiment, the fibrous material of the surface-shaped test textile is an open-pore fibrous material or an open fabric in which parallel fibers of the fibrous material do not contact each other directly. As a result, the adhesive primer is embedded in the resulting interstices of the fiber material, whereby a cohesive break in the primer between the individual fibers of the fiber material can be effected. By choosing the textile architecture (eg pore size), the fracture pattern and thus the surface finish can be influenced in an application-specific manner.

Thus, the pore size in particular affects the peel force and the resolution of the method with respect to the fracture pattern. Ultimately, the porosity of the textile also determines which fraction of the fracture surface is cohesively fractured and which fraction has an imprint of the fibers or of the material of the textile. The appropriate choice of porosity ultimately determines the percentage of free space of the fabric.

In an advantageous embodiment, the fracture pattern between the cured adhesive primer and the sheet-like test textile is recorded by means of a camera, wherein a uniform or non-uniform fracture pattern can then be determined automatically by means of an image evaluation unit from the recorded image data. In this case, either the joining surface or the area-shaped test textile are torn off after tearing off or both together with the aid of the camera in order to obtain an image of the breakage pattern after tearing off the flat test fabric. The image evaluation unit can then be used to determine whether the fracture pattern is uniform, ie whether the adhesive primer has been cohesively cracked cleanly and without defects, or if the fracture pattern is uneven and contains corresponding imperfections where the adhesive primer does not adhere properly to the joint surface. With an appropriately equipped image evaluation unit, it is also possible to determine whether the adhesive primer adheres to the entire surface of the substrate over the entire surface. Thus, it is conceivable that with a defect-free joining surface, a first part of the entire adhesive primer adheres to the joining surface of the substrate over the entire surface, ie without gaps or imperfections, while a second part of the entire adhesive primer remains on the test textile. With the aid of the image evaluation unit, it can then be determined whether the adhesive primer adheres or remains over the entire surface of the joining surface of the substrate and / or the test textile, it then being possible to conclude on a defect-free joining surface.

For this purpose, it is particularly advantageous, for example, if, depending on the color of the substrate or the color of the joining surface of the substrate, a color is selected for the adhesive primer in order to achieve the greatest possible contrast between the color of the joining surface of the substrate and the color of the adhesive. to obtain primer. The highest possible contrast makes it easier to identify and identify defects within the fracture pattern.

In addition, the color can also be chosen such that it has been selected as a function of the color of the test textile or of the fiber material of the sheet-like test textile in order to be able to better recognize irregularities or defects in the rupture pattern on the sheet-like test textile.

In addition, it is also advantageous if the peel force is determined during the removal of the sheet-like test fabric by means of a force sensor, wherein a uniform or non-uniform force profile can be determined by means of a force evaluation unit from the determined peel force. This also makes it possible to automate the process of analyzing or evaluating the fracture pattern. Alternatively or additionally, it can be determined with the aid of the force evaluation unit from the determined peel force whether the peel force runs completely or partially below a threshold value, which suggests a faulty joining surface as a quantitative evaluation. The image evaluation unit and the force evaluation unit can thereby run in the form of software modules on a digital computing unit, wherein the computing unit is then signal-technically connected to the camera or the force sensor. In a further advantageous embodiment, the sheet-like Prüftextil is additionally conditioned after curing of the adhesive primer, so as to burden the adhesive primer addition by external influences. For this purpose, the test textile is exposed to a predetermined test temperature over a predetermined period of time and / or is communicated with a medium over a predetermined period of time, with the test fabric being removed only after conditioning. The medium can diffuse through the thin film in a short time in the boundary layer, so that critical scenarios for the connection can be generated and tested with. This makes it possible to draw conclusions about the stress on the bond during real operation, so that a further examination can be realized as merely a mere check of the joining surface. In particular, the (exposed) adhesive primer of the test textile is brought into contact with the medium and conditioned.

When the test fabric is peeled off, the test fabric leaves an imprint in the surface of the broken adhesive primer. As a result, on the one hand the surface is increased, which is advantageous for a later gluing process. On the other hand, this provides a mechanical anchoring (positive connection) between adhesive primer and adhesive, which is also advantageous in terms of strength. Thus, for example, it is conceivable and advantageous if a test textile is provided whose fiber material is designed such that the impression of the fibers of the fiber material remaining in the adhesive primer has undercuts after removal.

In a further advantageous embodiment, a test textile is provided whose fiber material has an equidistant grid, whereby the impression remaining on the surface of the primer has a defined grid. This facilitates the optical evaluation and quantification of any errors, since a kind of measuring grid is imprinted in the surface. In a further embodiment, it is conceivable that the entire surface of the adhesive base is completely cohesively broken. In this case, the adhesive forces between the fiber material of the test textile and primer must be greater than the forces that are necessary for a cohesive refraction of the primer. In such a case, the test textile leaves a completely cohesively broken surface. For example, the fiber material of the test textile can be pretreated mechanically, physically and / or chemically in order to roughen it (to set a surface state which is advantageous for the formation of adhesion forces) and thus to increase the adhesion forces of the primer to the fiber material. Examples of a mechanical pre-treatment would be: blasting, grinding, for a physical pretreatment: plasma treatment, corona treatment, flaming. Examples of a chemical pretreatment would be: etching, fluorination, coating, treatment with acids or alkalis or other substances which change the surface. The roughening of the fiber material additionally increases the free surface of the primer, which allows an even better adhesion of the adhesive film.

In a further advantageous embodiment, the fibers of the fiber material can also be provided with a special coating which serves as a bonding agent. This coating can remain on the surface of the primer in the area of the fiber prints after the test textile has been removed and can perform functional tasks in the subsequent bonding or, for example, improve the adhesion to the adhesive or, for example, act as a crack stopper for the subsequent adhesive layer. According to the present invention, the adhesive base can first be completely cured before the sheet-like Prüftextil is removed. As a result, the test textile can remain on the joining surface of the substrate until further processing of the substrate and thus protect the joining surface from contamination. It is also conceivable that the adhesive primer is only partially cured before the test fabric is removed. This can improve the likelihood of a cleanly cohesively broken surface after stripping and residual reactivity of the adhesive primer can result in better bonding to the subsequently applied adhesive. The cohesive breakage of the adhesive primer produces a reactive surface with high surface energy, which adhere better to later adhered components. Spacers may be used to achieve a defined layer thickness of the remaining adhesive primer. In the simplest form, the fibers of the fiber material or the fiber material itself represent the spacers.

However, it is also conceivable that the test textile has additional spacers in order to achieve a predetermined layer thickness of the adhesive primer remaining on the substrate. Such spacers may be integrated into the fibrous material or may be part of the adhesive primer between substrate and fibrous material of the test fabric. Such spacers may be additional sheets, such as thin nonwoven mats, nets, and / or knickers), or a plurality of evenly distributed bodies, such as spheres of defined size. The spacers contained in the adhesive primer remain in the remaining on the substrate adhesive primer.

Incidentally, the object is also achieved with the method according to claim 12 for applying a material to a substrate, wherein first the joining surface is checked by means of the previously described method. If the check of the joint surface was positive, i. If there were no irregularities in the fracture pattern or no irregularities in the peel force could be discerned, the material is applied to the adhesive primer remaining after the removal of the sheet-like test fabric.

The material can be an adhesive, an adhesive with a component to be joined and / or a coating (such as, for example, paints).

In one embodiment, the substrate is a fiber composite component, which is produced from a fiber composite material comprising a fiber material and a matrix material.

The substrate may also be another material, in particular isotropic material, such as, for example, a polymer material, metal material, organic Materials and / or inorganic materials. As polymer materials, for example, duromers (epoxies, unsaturated polyesters, vinyl esters, phenolic resins), elastomers (rubber, polysulphides, silicones, polyurethanes), thermoplastics (Polyetherketonke- ton, polyamide, polyester, etc.) can be used. As metal materials, in particular steel, aluminum, titanium, magnesium, non-ferrous metals, etc. are considered. In particular, bones, wood and teeth can be used as organic materials. As inorganic materials in particular glass, cement, ceramic, rock or mixtures thereof are conceivable. In this case, the substrate may not be a fiber composite component made of a fiber composite material.

In a further advantageous embodiment, in particular in conjunction with a fiber composite component as a substrate, the material is an adhesive material, wherein a component is joined by means of the applied to the remaining after the removal of the sheet-like Prüftextils adhesive primer adhesive material. For this purpose, an adhesive can be applied to the remaining adhesive on the joining surface, which is then subsequently brought into contact with the component and then cured, so as to effect a solid adhesive connection. However, it is also conceivable that the adhesive and the component are applied and joined simultaneously, for example when the component is a prepreg in which matrix material has already been infused into a fiber material. The component may, however, also be a material which inherently contains an adhesive material, such as, for example, surface coatings, sealants, prepregs or lacquers. As with the method for checking the joining surface, the joining surface can be pretreated for bonding before checking the joining surface, for example by removing damaged material from the fiber composite component by milling or cutting. After the clean pretreatment of the damaged area to be repaired, the joining surface is then checked with the previously described method, and then the component is glued.

If the component to be joined is a repair patch, it is conceivable, for example, that in the fiber composite component in the area of the damaged, to be repaired If a Schäftung is introduced, based on the cross section of the Schäftung then a corresponding repair patch is made. The sheath is then also checked with the previously described method and, if the check of the joining surface was positive, the repair patch then glued into the Schaftung.

The object is also achieved with a device for checking a joining surface of a substrate, in particular a fiber composite component, according to claim 16, wherein the device has a camera and an image evaluation unit and / or a force sensor and a force evaluation and for performing the verification method as described above is trained. The camera and the image evaluation unit serve for the qualitative evaluation, while the force sensor and the force evaluation unit serve for the quantitative evaluation of the joining surface and of the priming material.

Based on the qualitative evaluation or the quantitative assessment of the joining surface can then be deduced whether the joining surface is sufficiently suitable for bonding or whether further preparatory measures must be carried out.

The invention will be explained in more detail by way of example with reference to the attached figures. Show it:

Schematic representation of the essential process steps for checking;

Schematic representation of a repair based on the review;

Exemplary embodiment of a check;

Schematic macroscopic representation of a fracture pattern.

FIGS. 1 a-1 c show a possible sequence of the verification method in a schematic representation. In the first step (a), first a substrate in the form of a fiber composite component 10 is provided which is constructed from a plurality of layers of fiber material 11. The fiber composite component 10, which is shown here in a cross-section, has a damage 12 which is to be repaired. This damage 12 extends over several fiber layers 1 1.

In the next step (b), the damaged area 12 of the fiber composite component 10 is removed, in which a shank 13 is introduced into the fiber composite component 10 over a large area.

This Schäftung 13 to remove the damaged area 12 can be introduced manually or mechanically, which is commonly referred to as surface preparation. Subsequently, the surface pretreatment, which can be done for example by means of grinding, blasting or milling. This process can also include cleaning or activation processes (eg by means of plasma). The result of the second step (b) is then a joining surface 14, which is to be introduced later in a repair patch. This joining surface 14 is prepared after step (b) to the extent that the step of bonding can begin. According to the invention, a check of the joining surface 14 is now carried out beforehand in order to ensure the effectiveness of the bond. For this purpose, in step (c) a sheet-like test textile 20 is placed on the joining surface 14 of the creation 13, wherein the sheet-like test fabric 20 has a fiber material 21 which is impregnated by an adhesive primer 22. In peripheral areas, the sheet-like Prüftextil can be turned over so as to generate a tab 23 for subsequent removal. In order to prevent the tab 23 from sticking to the test textile 20, a separating film 24 can be provided between the tab 23 and the test textile. It is also conceivable that by means of a release film, as is placed on the fiber composite component 10 in edge regions, a tab is generated, which prevents tethering.

After the test fabric 20 has been applied to the joining surface 14, the next subsequent step (d) consolidates the test fabric, i. hardened. For this purpose, the test textile 20 is subjected to heat and possibly pressure. Ultimately, the treatment of the applied sheet-like test fabric 20 depends on the manner in which the adhesive primer of the test fabric 20 hardens. If a matrix material which corresponds to the matrix material of the fiber composite component, or which corresponds to the adhesive of the subsequent bonding, is usually applied to the test textile with a corresponding temperature and pressure, as is the case, for example, in a vacuum construction customary for fiber composite technology increased temperature and pressure takes place.

In an optional step following this, the test textile can be conditioned for further testing by applying it to a desired test temperature and possibly to a medium. The medium can be, for example, water or other substances with which the fiber composite component regularly comes into contact. For example, the medium can diffuse into the boundary layer through a thin film in a short period of time. The subsequent check is done under the influence of media and temperature, so that critical scenarios for the connection can be created.

In the subsequent step (e), the test textile 20 is now removed from the joining surface 14 by means of the tab 23, which can be done manually or by machine. The entire test surface, ie the joining surface 14, can also be covered with a plurality of flat test textiles in a defined width, which are individually peeled off. As a result, a comparable peel force related to the textile width is measured. The take-off angle, the withdrawal speed and the withdrawal direction with regard to the fiber orientation can be defined depending on the requirements.

In an advantageous embodiment, the edges of these strips of test fabric are designed so that tearing of the strips is avoided. For this purpose, it is in particular conceivable that the strips are thermally sealed at the edge or, for example, have a selvage.

Normally, when the test fabric is peeled off, a cohesive break occurs in the adhesive primer, as a result of which parts of the adhesive primer remain on the joining surface 14 and a defined, clean surface preparatory to the subsequent bonding arises. If, after peeling off the test fabric 20, it has been found that the entire primer adheres evenly, completely and without defects to the joining surface 14, the adhesive primer has been cohesively refracted over the entire surface of the test fabric, which suggests that the interface with the fiber composite component 10 of FIG has withstood the applied load. In this case, the adhesive and the repair material can be applied directly to the primed joining surface 14.

However, if the fracture pattern has irregularities, damage or defects, then there was insufficiently prepared or pretreated joining surface 14 on which no secure bonding can be carried out. Such errors which can be detected on the fracture pattern can be seen in step (f). Here, the withdrawn test fabric is shown schematically, which contains both parts of the adhesive primer 22, which should actually adhere to the joining surface 14, as well as parts of the fiber composite component 10 in a first region 25, so that in the fracture image in the area 25 an irregularity or gives a flaw. In this area, the substrate of the joining surface 14 was not stable enough, so that adhesion of the adhesive primer 22 to the joining surface 14 resulted in greater adhesion than commonly found in the region 25 in the fiber composite component 10. The surface pretreatment was thus not sufficient in the region 25. In a further region 26, by contrast, the adhesive primer 22 did not sufficiently adhere to the joining surface 14, which likewise suggests inadequate surface pretreatment of the joining surface 14. Also in region 26, an irregularity or a defect, which is immediately recognizable to the naked eye, develops in the fracture pattern both in the fiber composite component and in the test textile.

This makes it possible to perform a qualitative assessment of the joining surface by determining whether the fracture pattern, for example at the joining surface 14, has flaws or irregularities manifested in the adherent adhesive primer not adhering to the joining surface 14 throughout , Alternatively or additionally, the peel force (F) can also be determined when the test fabric 20 is removed and then removed via the test path, as shown in step (g). The areas 25 and 26 correspond to the areas 25 and 26 in step (f), where the fracture pattern has corresponding defects. In these areas, the peel force drops abruptly, resulting in a lack of adhesion of the adhesive primer or the fiber composite material of the fiber composite component. Again, it can be assumed by deviations from a uniform peel force of corresponding defects. It is thus possible to check the joining surface not only directly with respect to its nature for the purpose of bonding, but at the same time to prepare the joining surface for the subsequent bonding process in a successful review that a defined adhesive surface is formed on which defines a corresponding adhesive Gluing can be guaranteed.

FIG. 2 shows the repair of the fiber composite component 10 shown in FIGS. 1a-1c. After the verification steps of Figures 1 a-1 c have been performed, a portion of the adhesive primer 22 remains on the joining surface 14 of the fiber composite component 10. On this adhesive primer, the corresponding adhesive 27 is then applied for repair, and then then the repair patch 28 in the Schäftung is introduced. The repair patch 28 may be, for example, also a fiber composite material. The adhesive layer 27 can be introduced simultaneously with the repair patch 28 in the form of a pre-preg. Optionally, an outlet of the test textile 20 and / or an outlet of the adhesive 27 with a test fabric can be arranged in a secondary test area 29. Over this the connection of the adhesive to the primer can be checked. In addition, this area can be used for a long-term test of the connection of the primer to the fiber composite component and the adhesive to the primer. For this purpose, the test fabric remains in the appropriate material (primer or adhesive) and will be deducted at a later date. In the meantime, the secondary test area can be painted over so that it has no influence visually and aerodynamically.

It is also conceivable that the binding of the adhesive 27 to the repair patch 28 is checked with the aid of the test textile. For this purpose, a release film is placed under the desired area, provided the adhesive with the Prüftextil and applied over the repair patch. After the repair patch has cured, the area is separated from the component by the release liner. Subsequently, the test fabric is subtracted from the separated area, whereby the interface of adhesive is loaded to the overlying repair layers and thus checked. Thus, all interfaces of the connection system, namely component primer, primer adhesive and adhesive repair patch can be tested. It is also conceivable that the connection of the adhesive 27 to the material of the repair patch 28 is checked with the aid of the test textile. In addition to the patch, an area is covered with release film, the adhesive is provided with the test textile and the material of the repair patch is applied over it. After the curing of the repair patch, the additional area is separated from the component by the release film. All test specimens in the secondary test area 29 can be tested either directly after the repair (or after any conditioning has taken place), or only at a later time to perform a long-term test. Before carrying out the long-term test, the test sections can also be conditioned. The test specimens in the secondary region 29 may be directly connected to the actual bond or separated therefrom by an interruption / gap. For process control during component production or bonding, accompanying samples can be manufactured with a control connection, which serves to validate the process and the correct adhesive connection to the components. For this purpose, a test connection is established in addition to the regular joining partners, as shown in Figure 3. In this test compound, a first test body 31 and a second test body 32 is used, wherein a first Prüftextil 33 and the second test body 32, a second Prüftextil 34 is arranged on the first test body 31. The first and the second test specimens are now joined together using their two test textiles, wherein a release film 35 is disposed between the two test textiles. In the next step, a regular gluing of both the actual component to be produced and the test connection 30 is carried out, so that the control gluing is carried out together with the actual component gluing in one process step.

Subsequently, using the release film 35, the two joining partners 31 and 32 of the control compound 30 separated, then subsequently the Prüftextil 33, 34 of the two test specimens 31 and 32, as described above, by applying a peel force can be deducted. Subsequently, both test specimens can be checked by a qualitative and / or quantitative evaluation of their joining surface, the result of this test being representative of the joining process of the finished component joining.

In this case, it would be conceivable that the test connection 30 is not a control production, but the component connection to be produced, in a first step joining the two joining partners as in the test connection and then subsequently the test textile of both joining partners 31 and 32 is subtracted. If both fracture patterns of the peeled joining surface or the test fabric are without result, then in a next step, the two joining partners can be glued together using an adhesive layer. The test textile has the requirement, when tearing off a defined high force on the adhesive primer or To transfer the joining surface and leave a thin primer layer whose surface is clean and suitable for a subsequent gluing process. In order to manually tear off the test textile from the surface with little effort, the removal can be carried out in narrow strips of defined width as described above. The requirements placed on the test textile are achieved by using a fabric which has an open structure.

The architecture of the test fabric (type of binding, cross-sectional structure, thread design, monofilament / multifilament, thread thickness, free cross-sectional area, etc.) can be used to determine parameters such as the height of the test load or test voltage (is the voltage with which the respective interface is loaded). , The amount of peel force (the force needed to peel off the fabric), resolutions for any defects, area fraction of the cohesive fracture, layer thickness of the residual primer, and surface topology of the primer layer produced.

The test textile can in principle consist of all materials. Examples are plastics, natural materials or metals. The respective material is processed into a fabric, which may be a textile in the conventional sense, for example a woven or knitted fabric. But also fabrics such as expanded metal or grid or networks are conceivable.

The test textile may in principle be preimpregnated with primers or may be dry and soaked in situ during application by applying adhesive or primer to the test fabric.

Concerning. Figure 3, the following scenarios are conceivable. On the one hand, both test specimens can be uncured before the control bonding and cured with the test textile in this process. Furthermore, one of the test specimens may be uncured and the other consolidated before the control bonding. Finally, both test specimens can be cured.

Figure 4 shows schematically the process of tearing off an open fabric of monofilament yarns of round cross-section. When tearing off the Fasermate al 21 dissolves out of the adhesive primer 22, wherein the free surfaces between the individual fibers of the fiber material 21 break cohesively.

The exact topography of the generated surface is adjustable by the property of the test textile or by the shape of the fiber material. For example, an angular cross section of the fiber material with undercuts can be used to produce a relatively uniform thin primer layer.

The tearing off of the test fabric and the formation of a thin primer layer on the joining surface produces a particularly adhesive surface. The surface is thus very well prepared for the subsequent adhesive joining process.

For an automated process, an arithmetic unit 40 may be provided which is connected to a camera 41 and / or a force sensor 42, as shown schematically in greatly simplified form in FIG. The camera 41 takes on the fracture surface of the cohesively refrained primer, with the aid of an image analysis on the arithmetic unit 40 corresponding irregularities and non-full-surface adhesion of the primer 22 can be detected on the component. If the removal of the test textile is automated with a device, the force F can be detected with the aid of the sensor 42. By analyzing the force curve, the surface can then be checked as described above.

With the aid of the method according to the invention, it is also possible to test strongly curved surfaces. This is not possible with the vast majority of conventional approaches. In addition, the method according to the invention makes it possible to carry out the checking of the joining surface in a position-independent and / or position-independent manner. After checking for defects and determining a defect-free surface, the method according to the invention produces a clean, defined surface on which it can be glued directly afterwards. The surface quality, however, unlike conventional repair processes, is not human dependent. Moreover, the method according to the invention makes it possible to fix the condition of the pretreated joining surface. The adhesive application therefore does not have to take place immediately after completion of the surface pretreatment. Thus, a repair process can be made more flexible in terms of time. Finally, the invention also makes it possible to detect contaminations which become effective only during the bonding process at elevated temperature, for example by diffusion from the substrate material interior to the surface. This risk can not be detected by conventional surface analysis methods before gluing. The adhesive primer may be a reactive substance, for example, epoxy based, which has a similar property profile to the adhesive used for repair, but whose exact characteristics may be tailored to the particular task (in the simplest case: adhesive primer = adhesive). Among other things, this includes the execution of a very strong connection to the substrate, a good contamination tolerance as well as the ability to allow a particularly good connection to the adhesive in a subsequent step. The adhesive primer is color matched so that it is well visible from the substrate with the test fabric and can easily detect defects. The primer may be formulated so that its property changes during the later curing of the adhesive film and assumes the desired end property. This corresponds to an annealing step during the adhesive film curing at elevated temperature. So it is possible, for example, that the primer still has a residual reactivity after curing of the test fabric, so is not fully reacted, and thus crosslinked in the following bonding process with the adhesive and thus enters into particularly strong chemical bonds.

In particular, the textile is not provided with additional coatings, such as release agents, which could remain on the surface of the primer after the test as an adhesion-inhibiting residue. The textile is designed with respect to the filament or thread thickness and its binding or area distribution so that it leaves a regular surface and a defined thick layer of the primer after peeling. The tear-off textile can have predetermined breaking points at regular width intervals, by which it is segmented into strips. This allows the application in one piece and at the same time the individual segments can be deducted as strips of defined width, wherein the force is recorded with respect to a defined width.

The test fabric with the fiber material and the adhesive primer is adjusted so that, when properly prepared and pre-treated, the bond between the substrate and the primer and the strength of the substrate are higher than the force required to cause the cohesive break in the adhesive primer cause. This means that when properly executed, the interface between the tear-off fabric and the primer will always be the weak point. In the case of relevant defects or contaminations in the substrate surface, these areas represent the weak point, ie their strength falls below that between the tear fabric and the primer, as evidenced by the change in the fracture pattern, since corresponding imperfections can then be identified.

LIST OF REFERENCE NUMBERS

10 - fiber composite component

1 1 - Fiber material layers

12 - damage

13 - Stem

14 - joining surface

20 - test textile

21 - Fiber material of the test textile

22 - adhesive primer

23 - tab

24 - release film

25 - first irregularity in the fracture image

26 - second irregularity in the fracture image

27 - adhesive

28 - repair patch

29 - secondary testing area

30 - test compound

31 - first specimen

32 - second specimen

33 - first test textile

34 - second test textile

35 - release film

Claims

claims

Method for verifying a joining surface of a substrate, wherein a component is to be glued onto the joining surface of the substrate by means of an adhesive material, characterized in that the method comprises the following steps:

Providing at least one sheet-like test textile comprising a fibrous material and an adhesive primer,

Applying the sheet-like test textile to at least a part of the joining surface of the substrate to which the component is to be glued, so that the adhesive primer of the flat test fabric contacts the joining surface of the substrate,

At least partially curing of the adhesive primer of the sheet-like test textile in order to join the sheet-like test textile to the substrate by means of the adhesive primer,

- Removing the sheet-like Prüftextils after the at least partial curing of the adhesive primer, and

- Check the joining surface by a qualitative assessment of the fracture pattern between the cured adhesive primer and the sheet-like Prüftextil and / or by a qualitative assessment of the determined during the removal of the sheet-like Prüftextils peel force.

2. The method according to claim 1, characterized in that the substrate is a fiber composite component, which is made of a fiber composite material comprising a fiber material and a matrix material.

3. The method according to claim 1, characterized in that the substrate is formed from a polymer material, metal material, a metal alloy, organic materials and / or inorganic materials.

Method according to one of the preceding claims, characterized in that it is determined for a qualitative assessment after removal of the sheet-like Prüftextils whether the adhesive primer adheres to the entire surface of the joining surface of the substrate, with a complete adhesion of the adhesive primer to a defect-free joint surface, otherwise on a faulty joining surface, is closed.

Method according to one of the preceding claims, characterized in that it is ascertained for a qualitative evaluation after the removal of the sheet-like test textile (20) whether the fracture pattern between the cured adhesive primer (22) and the flat test fabric (20) is uniform or irregular In the case of a uniform fracture pattern, an error-free joining surface (14) and, in the case of a non-uniform fracture pattern, an incorrect joining surface (14) are closed. 6. The method according to any one of the preceding claims, characterized in that it is determined for a quantitative assessment after subtracting the sheet-like Prüftextils (20), whether the peel off the sheet-like Prüftextils (20) determined peel force wholly or partially outside a predetermined target range and / or below a predetermined threshold value, wherein an error-free joining surface (14), otherwise a faulty joining surface (14), is concluded within the setpoint range and / or if the predetermined threshold value is not undershot. 7. The method according to any one of the preceding claims, characterized in that it is determined for a quantitative assessment, whether the removal force of the sheet-like Prüftextils (20) determined peel force a gleichmä- Has a continuous force curve, which is closed at a uniform force curve on an error-free joining surface (14) and a non-uniform force curve on a faulty joining surface (14).

Method according to one of the preceding claims, characterized in that a sheet-like Prüftextil is provided, the fiber material is an open-pored fabric.

Method according to one of the preceding claims, characterized in that the fracture image between the cured adhesive primer (22) and the sheet-like test fabric (20) is recorded by means of a camera, wherein a uniform or non-uniform fracture image is determined from the recorded image data by means of an image evaluation unit, and / or that the peel force is determined during the removal of the sheet-like test fabric (20) by means of a force sensor, wherein a uniform or uneven force profile is determined by means of a force evaluation unit from the determined peel force.

Method according to one of the preceding claims, characterized in that during and / or after curing of the adhesive primer (22) the sheet-like Prüftextil (20) is conditioned by the Prüftextil (20) applied for a predetermined period of time with a predetermined test temperature and / or by the sheet-like Prüftextil (20) over a predetermined period of time is associated with a medium, wherein after the conditioning, the test fabric (20) is subtracted.

Method according to one of the preceding claims, characterized in that the adhesive primer is fully cured before the sheet-like Prüftextil is removed, or that the adhesive primer is only partially cured.

12. The method according to any one of the preceding claims, characterized in that the test fabric is provided such that the Prüftextil on or a plurality of spacers arranged on the fiber material of the test fabric and / or contained in the adhesive primer.

Method for applying a material to a substrate, characterized in that the method comprises the following steps:

Checking the joining surface (14) of the substrate by means of the method according to one of the preceding claims,

and, if the verification of the joint surface was positive,

- Application of the material to the remaining after removal of the sheet-like test textile adhesive primer.

- Adding the component by means of an applied to the remaining after the removal of the sheet-like Prüftextils adhesive primer adhesive material (27).

14. The method according to claim 13, characterized in that the substrate is a fiber composite component, which is made of a fiber composite material comprising a fiber material and a matrix material. 15. The method according to claim 13 or 14, characterized in that the material is an adhesive material, wherein a component is joined by means of the applied to the remaining after the removal of the sheet-like Prüftextils adhesive primer adhesive material. 16. The method according to claim 15, characterized in that the adhesive primer (22) is only partially cured before the sheet-like Prüftextil is removed, wherein the adhesive (27) applied to the remaining, not yet fully cured adhesive primer (22) and the device then added by means of the applied adhesive (27).

17. Device for checking a joining surface of a substrate, wherein a component is to be glued to the joining surface by means of an adhesive material, wherein the device is a camera and an image evaluation unit and / or a force sensor and a force evaluation unit and is designed to carry out the method according to one of claims 1 to 12.