DE102017111790B4 - Method and device for the detection of imperfections in fiber layers - Google Patents

Abstract

Method for recognizing defects (5, 6) in a multi-directional fiber fabric (4, 140) which is formed from fiber material of a fiber composite material for the production of a fiber composite component, the multi-directional fiber fabric (4, 140) having at least two fiber layers (141, 142, 143 ), in which the direction of electrically conductive reinforcing fibers differ from one another at an angle α, characterized in that a first fiber layer (1) is electrically contacted with a first electrode and at least one second electrode spaced apart from the first electrode, so that between the contacted first and second electrodes (111, 112, 113, 114) a measuring section (12, 130) is formed in the multi-directional fiber fabric (4, 140) in such a way that the between the first and second electrodes (111, 112, 113, 114) formed measuring section (12, 130) at an angle α to the electrically conductive reinforcing fibers of the first fiber layer and para llel runs to an assumed direction of the electrically conductive reinforcing fibers of a second fiber layer, an electrical resistance of the measuring section (12, 130) in the multi-directional fiber fabric (4, 140) by means of the first and second electrodes (111, 112, 113 , 114) is measured and a flaw (5, 6) in the second fiber layer is detected by an evaluation unit (150) as a function of the measured electrical resistance when the measured electrical resistance exceeds a predetermined threshold value.

Description

The invention relates to a method and a corresponding device for detecting flaws in a multi-directional fiber structure which is formed from fiber material of a fiber composite material for the production of a fiber composite component, the multi-directional fiber structure having at least two fiber layers in which the direction of electrically conductive reinforcing fibers is each other differ from each other at an angle.

Components made of a fiber composite material, so-called fiber composite components, have become indispensable in the aerospace industry. But the use of such materials is also becoming more and more popular in the automotive sector. In particular, critical structural elements are made from fiber-reinforced plastics due to their high weight-specific strength and rigidity with minimal weight. Due to the anisotropic properties of the fiber composite materials resulting from the fiber orientation of the reinforcing fibers, components can be precisely adapted to local loads and thus enable optimal material utilization in terms of lightweight construction.

Fiber composite materials generally have two essential components, namely on the one hand the fiber material with the reinforcing fibers and on the other hand the matrix material. During the manufacturing process, the matrix material infused into the fiber material is cured under pressure and temperature, so that the matrix material and the fiber material form an integral unit and the reinforcing fibers present in the fiber material are fixed in their predetermined order.

Since the load-bearing properties of fiber composite components made from such fiber composite materials are usually caused by the reinforcing fibers present in the fiber material, such fiber composite components have reducing load-bearing properties in directions outside the fiber plane as well as in directions outside the direction of the reinforcing fibers must be compensated for in some other way depending on the application. For this purpose, fiber fabrics are often used or manufactured, which are usually formed from several layers of fiber material, the individual fiber layers being arranged in such a way that the direction of the reinforcing fibers of one fiber layer differs from the direction of the reinforcing fibers of other fiber layers. This ensures that the fiber composite components not only have a unidirectional load-bearing property, but also have bi- or multidirectional load-bearing properties, which is due to the different directions of the load-bearing reinforcing fibers of the respective fiber layers.

In practice, such multidirectional or multi-directional fiber fabrics are often constructed in such a way that one fiber layer has a 0 ° orientation (so-called nominal fiber direction), while in particular the other fiber layers adjacent to this fiber layer are +/- 45 ° fiber orientation to this nominal fiber direction or +/- 90 ° fiber direction to this nominal fiber direction (nominally based on the reinforcing or main fibers).

The downstream quality control is an important element in the entire manufacturing process, especially when it comes to the automated fiber lay-up for the production of multi-directional fiber fabrics, since errors in the fiber lay-up, such as gaps between two fiber ribbons or deviations from the fiber orientation, can lead to undesired material properties of the later component, so that this component may not be able to continue to be used. Especially in the production of large, flat components, such as wing shells, the scrap of such a component due to incorrect fiber placement is one of the cost drivers, so it is desirable to either identify such scrap components very early on or to avoid them in principle.

Discarded fiber materials can be subjected to a visual inspection. However, if several layers of fiber material have been deposited, the underlying fiber layers cannot usually be checked by visual inspection, which means that this type of quality assurance is subject to physical limits.

From the EP 1 987 945 A1 a semifinished product for the production of components from fiber-reinforced composite materials is known, with electrically conductive fibers being connected in an inner fiber layer to form a sensor network. The electrically conductive fibers are then contacted with an electrical measuring device for resistance measurement.

From the DE 10 2011 115 406 A1 a method for connecting two fiber composite components is known, the adhesive connection to be checked with the aid of an electrical resistance measurement.

From the DE 10 2014 103 219 A1 a method for determining the fiber orientation is known in which, starting from a main electrode, the resistances to spaced electrodes are measured in a star shape.

Finally from the DE 10 2013 107 103 A1 a fiber laying head is known in which the semi-finished fiber product to be deposited is energized and thus tempered with the aid of an electrical contact device.

Against this background, the object of the present invention is to provide an improved device and an improved method with which defects in multi-directional fiber layers can be detected non-destructively, precisely those defects that are not visible and are embedded within the fiber structure in intermediate fiber layers .

The object is achieved according to the invention with the method according to claim 1 and the device according to claim 10.

According to claim 1, a method for recognizing defects in a multi-directional fiber structure is proposed, the multi-directional fiber structure being formed from fiber material of a fiber composite material for the production of a fiber composite component. The fiber structure has at least two fiber layers, each fiber layer having main or reinforcing fibers and the direction of the reinforcing fibers differs between the fiber layers. The direction of the reinforcing fibers of a fiber layer is mostly essentially parallel and oriented in the same direction. However, the fiber layers of the fiber structure are arranged one above the other so that one fiber layer has a first direction of the electrically conductive reinforcing fibers and the at least second other fiber layer has a second direction of the electrically conductive reinforcing fibers, the first direction differing from the second direction at a predetermined angle . Typical angles between these directions are 45 ° and 90 °.

Fiber materials with electrically conductive reinforcing fibers can in particular be carbon fiber reinforced composite materials.

According to the invention, a first fiber layer of the multi-directional fiber lay-up is now contacted by two electrodes spaced apart from one another, so that a measuring section is formed in the multi-directional fiber lay-up between the contacted first electrode and the contacted second electrode. The first fiber layer contacted by the two electrodes is generally one of a maximum of two outer fiber layers of the present multi-directional fiber structure. Of course, more than two electrodes can also be contacted with the first (outer) fiber layer at a distance, as a result of which more than one measurement section is formed in the multi-directional fiber structure. In the following, however, we will continue to speak of two electrodes, although the principle can be extended to more than two electrodes without any problems.

The two electrodes are contacted with the first fiber layer in such a way that the measuring section formed between the first and second electrode runs at an angle to the electrically conductive reinforcing fibers of the first fiber layer, the measuring section at the same time being parallel to an assumed direction of the electrically conductive reinforcing fibers second fiber layer is aligned, which is located below the first fiber layer and is usually covered by the first fiber layer and thus not visible.

The assumed direction of the reinforcing fibers of the second fiber layer generally results from the assumption that the second fiber layer was correctly aligned with regard to its fiber orientation. The assumed direction of the electrically conductive reinforcing fibers of the second fiber layer can thus also be regarded as the desired direction of the reinforcing fibers of the second fiber layer.

An electrical resistance measuring device is now used to measure an electrical resistance of the measuring section in the multidirectional fiber structure by means of the first and second electrodes, which contact the first fiber layer of the fiber structure, with the measured resistance then being used to measure a defect in the second fiber layer caused by the electrodes is not contacted, can be determined by an evaluation unit if the measured electrical resistance exceeds a predetermined threshold value.

It was recognized that the electrical resistance in such a multi-directional fiber structure is proportional to the defects in the inner or inner fiber layers, so that defects in internal fiber layers can be determined by a corresponding resistance measurement via electrodes contacted on the outer fiber layers.

This makes it possible for the first time to be able to determine imperfections in multi-directional fiber layers in a non-destructive manner, in which case a manual follow-up inspection can basically be dispensed with, since the method can in principle be automated by a corresponding device. So it is conceivable that the fiber lay-up is built up and a corresponding defect detection is run through only after the build-up of the fiber lay-up.

In an advantageous embodiment, a gap between the electrically conductive Reinforcing fibers of the second fiber layer recognized as flaws depending on the measured electrical resistance by the evaluation unit when the measured electrical resistance exceeds a predetermined threshold value for this flaw. Such a gap arises, for example, from the fact that, when the second fiber layer was deposited, the tolerances to adjacent fiber ribbons may not have been observed. Such defects also arise when the fiber material has production-related defects and, for example, the corresponding reinforcing fibers are missing at one point. A gap as a defect is characterized by a lack of reinforcing fibers.

In a further advantageous embodiment, a deviation from the assumed direction of the electrically conductive reinforcing fibers (target direction) of the second fiber layer is recognized as defects depending on the measured electrical resistance by the evaluation unit when the measured electrical resistance exceeds a predetermined threshold value for this incorrect position .

The greater the deviation from the assumed direction of the electrically conductive reinforcing fibers of the second fiber layer, the greater the electrical resistance that can be determined with the help of the resistance measuring device, so that in addition to the fact that such a deviation is detected, it can also be determined how great it is is the deviation from the desired direction of the electrically conductive reinforcing fibers of the second fiber layer.

In a further advantageous embodiment, this layer is contacted at a distance with a first electrode configured as a roller or cylinder and a second electrode configured as a roller or roller, the electrodes configured as a roller or cylinder being moved or displaced over the first fiber layer so differently To set measurement positions at which the electrical resistance of the measurement section in the multi-directional fiber structure is measured. For example, with two electrodes designed as rollers or cylinders, an entire component can be measured, which, for example, was built up in the form of a multi-directional fiber structure from several fiber layers on a molding tool.

It is particularly advantageous if the electrodes designed as rollers or cylinders are moved over the first fiber layer during the resistance measurement, so that the corresponding resistance measurement is carried out continuously during the movement of the electrodes designed as rollers or cylinders.

In a further advantageous embodiment, the multi-directional fiber structure has at least three fiber layers, so that at least one further third fiber layer is provided which, together with the first fiber layer, encloses the second fiber layer. This means that the second fiber layer is enclosed between the two fiber layers (first fiber layer and third fiber layer) and adjoins the first fiber layer with a first side and the third fiber layer with a second side.

The third fiber layer also has electrically conductive reinforcing fibers which have a direction that is different from the direction of the reinforcing fibers of the second fiber layer, the electrically conductive reinforcing fibers between the second fiber layer and the third fiber layer differing from one another at an angle.

According to the invention, the third fiber layer, just like the first fiber layer, is contacted with at least two electrodes, so that the third fiber layer is contacted with at least a third electrode and a fourth electrode, so that between the third electrode and the fourth electrode, which contact the third fiber layer , a measuring section in which the fiber fabric is formed. The third and fourth electrodes are contacted with the third fiber layer in such a way that the measuring section runs at an angle to the direction of the reinforcing fibers of the third fiber layer and also parallel to an assumed direction of the electrically conductive reinforcing fibers of the second fiber layer, so that preferably the first and second electrode formed measuring path to the measuring path formed by the third and fourth electrode is essentially identical (within contact tolerances).

With the help of the electrical resistance measuring device, the electrical resistance in the measuring section formed by the third and fourth fiber layer can now be determined, with a fault in the second fiber layer being detected by the evaluation unit as a function of the measured electrical resistance. It is conceivable that the electrical resistance of the measuring section formed by the first and second electrodes is measured first, while the resistance of the measuring section formed by the third and fourth electrodes is then measured, with a defect then being determined by the evaluation unit as a function of the measured value Resistance of the first measuring section (first and second electrode) and the electrical resistance of the second measuring section (third and fourth electrode) is detected. This can increase the accuracy of the error detection and, in particular, deviations from the assumed direction (target Direction) of the reinforcing fibers can be recognized finer and with higher resolution.

In a further advantageous embodiment of this, the electrical resistance of the measuring section formed by the first and second as well as third and fourth electrodes is determined by a four-wire measurement by the electrical resistance meter, whereby very fine differences in the electrical resistances can be detected.

Here, too, it is conceivable that the third and fourth electrodes are designed as a roll or roller and thus contact the third fiber layer, so that, similar to the exemplary embodiment, with regard to the first and second electrode as a roll or cylinder, the third and fourth electrode also opposite the third fiber layer or the fiber scrim as a whole is displaceable or movable in order to set different measuring positions at which the electrical resistance of the measuring section in the multi-directional fiber scrim is to be measured.

This makes it possible to contact a fiber fabric formed from at least three fiber layers on its respective outer layers (first fiber layer and third fiber layer), so that a common one through the first and second electrodes on the first fiber layer and through the third and fourth electrodes on the third fiber layer Measurement section is formed in the fiber structure, so that the electrical resistance in the common measurement section can be measured with the help of the resistance meter. This is particularly advantageous if the electrodes designed as rollers or rollers are stationary and the fiber fabric formed from several layers is passed or transported through the roller or roller arrangement, which is used, for example, when conveying multi-directional fiber layers for fiber storage. As a result, the electrical resistance in the common measuring section can be continuously determined and corresponding defects in the inner fiber layer can be detected.

The invention is moreover also achieved according to the invention with the device according to claim 10, the device for recognizing defects being designed in a multi-directional fiber structure. For this purpose, the device has at least two electrodes which are spaced apart from one another and which are provided and designed so that multi-directional fiber fabrics formed from several fiber layers make contact on a common side (first fiber layer). The device furthermore has an electrical resistance measuring device which is designed to determine the electrical resistance in the measuring section formed by the contacted first and second electrodes within the fiber structure, with an evaluation unit being provided which then based on the measured electrical resistance a Can detect the defect. A flaw is detected with the aid of the evaluation unit when the measured electrical resistance exceeds a predetermined and adjustable threshold value.

Advantageous configurations of the device can be found in the corresponding subclaims.

• 1 - schematische Darstellung des Messprinzips zur Erkennung von Lücken;
• 2 - schematische Darstellung des Messprinzips zum Erkennen von Faserfehlausrichtungen;
• 3 - schematische Darstellung der erfindungsgemäßen Messvorrichtung;
• 4 - schematische Darstellung einer als Elektrode ausgebildeten Walze.

The invention is explained in greater detail using the attached figures. Show it:

• 1 - Schematic representation of the measuring principle for the detection of gaps;
• 2 - Schematic representation of the measuring principle for detecting fiber misalignments;
• 3 - Schematic representation of the measuring device according to the invention;
• 4th - Schematic representation of a roller designed as an electrode.

1 shows schematically the measuring principle of the present invention for detecting flaws within fiber layers. In the embodiment of 1 is a first fiber layer 1 , a second fiber layer 2 and a third layer of fiber 3 shown that together the fiber scrim 4th form. The second fiber layer is arranged between the first fiber layer and the third fiber layer and is thus through the two outer fiber layers 1 and 3 locked in.

In 1 are the reinforcing fibers of the individual fiber layers 1 to 3 shown, the direction of the reinforcing fibers of the first fiber layer 1 have an angle of + 45 °, while the reinforcing fibers of the third fiber layer 3 have an angle of -45 °. Together, the reinforcing fibers form the first fiber layer 1 and the reinforcing fibers of the third fiber layer 3 an angle of 90 °. The degrees are defined in relation to the nominal fiber direction, which is through the reinforcement fibers of the second fiber layer 2 is formed and is 0 °. The reinforcing fibers of the second fiber layer 2 thus have an angle with respect to the nominal fiber direction of 0 °, so that between the reinforcing fibers of the second fiber layer 2 and the reinforcing fibers of the first fiber layer 1 an angle of + 45 ° is spanned, while between the reinforcing fibers of the second fiber layer 2 and the reinforcing fibers of the third fiber layer 3 an angle of -45 ° is defined.

As in the embodiment of 1 can be seen are in the area 5 the second fiber layer 2 no reinforcement fibers, so the second fiber layer 2 in the area 5 has a defect, namely a gap or a gap. In further consideration, this will now be detected with the aid of the following invention.

According to the invention, the outer fiber layer is now applied 1 a first electrode 10 and a second electrode 11 contacted so that between the first electrode 10 and the second electrode 11 a measuring section 12 within the fiber structure 4th is formed, within which the electrical resistance in a first measurement R ₁ is determined. The first electrode 10 and the second electrode 11 are at the first electrical resistance measurement R ₁ so on the first fiber layer 1 arranged that they lie in an area in which the second fiber layer 2 has appropriate reinforcement fibers. When measuring the resistance, a current would flow through the first fiber layer 1 through and then along the reinforcing fibers, which are electrically conductive, the second fiber layer to the second electrode 11 so that a very low electrical resistance can be expected here. Only the contact resistance between the electrode and the first fiber layer 1 and the transition resistances from the first fiber layer to the second fiber layer have a significant influence on the measured electrical resistance.

It looks different when the first electrode 10 and the second electrode 11 in the area of the defect 5 is shifted so that the measuring section 12 now within the range 5 runs where the second fiber layer 2 currently has no reinforcement fibers. In such a second measurement R ₂ one would then measure an electrical resistance that is significantly greater than the first resistance measurement R ₁ as one through the electrodes 10 and 11 The current flow caused for the electrical resistance measurement is not exactly along the measuring section 12 runs and optionally either over the first fiber layer 1 or in areas of the second fiber layer 2 evades where the corresponding reinforcing fibers are available.

Therefore, based on a resistance measurement, as shown schematically in FIG 1 shown, it can be recognized whether eb is within the fiber structure 2 that is in the fiber structure 4th is located, there is a flaw in the form of missing reinforcing fibers, because flaws are within the second fiber layer, provided the measurement section 12 corresponding to the nominally assumed fiber orientation of the reinforcing fibers of the second fiber layer 2 is always proportional to these imperfections.

2 shows schematically the second measuring principle, in which a deviation from the assumed fiber orientation of the reinforcing fibers of the second fiber layer 2 as a defect 6th is detected. Again, the first electrode is used 10 and the second electrode 11 on the first fiber layer 1 of the fiber structure 4th contacted, whereby the measurement section formed thereby 12 has an orientation that corresponds to the assumed orientation (desired direction) of the reinforcing fibers of the second fiber layer 2 corresponds. In fact, the target direction is changing 13th from the actual direction 14th (Actual direction) at an angle α from that as a defect 6th should be detected.

When measuring resistance R ₃ it can now be determined that the measured electrical resistance of the measuring section 12 is higher than under ideal, standardized conditions, so that here a deviation can be concluded as a defect.

In contrast to the defect 5 , in which reinforcing fibers are missing, it can be determined that the measured electrical resistance is higher than the ideal, standardized resistance, but is still significantly lower than in the case of missing reinforcing fibers. As a result, the following can be determined: $${\text{R.}}_1<{\text{R.}}_3<{\text{R.}}_2$$

As a result, the two different types of errors 5 and 6th based on a threshold value from the measured electrical resistances, so that it can not only be recognized whether there is a defect, but also of what type.

3 shows schematically an embodiment of a device for detecting errors according to the measuring principle of FIG 1 and 2 , the device 100 Rollers 101 , 102 , 103 and 104 has, on the circumference electrodes 111 , 112 , 113 , 114 are arranged. The reels 101 to 104 as well as the electrodes arranged thereon 111 to 114 are signaling with an electrical resistance meter 120 connected, which is the electrical resistance in the through the electrodes 111 to 114 formed measuring section 130 determined. The measuring section 130 is located within the fiber structure 140 made of three fiber layers 141 , 142 and 143 is formed. The fiber layers 141 and 143 are the outer fiber layers, which are contacted with the respective electrode, while the fiber layer 142 from the two outer fiber layers 141 , 143 is enclosed and lies within.

The device also has an evaluation unit 150 which is then based on the measured electrical resistance in the measuring section 130 a defect is detected or not.

According to the device 100 the 3 can the fiber fabric 140 be conveyed in the direction indicated by the arrow, the resistance in the changing measuring section being continuously increased during the conveying of the fiber material 130 measured and corresponding defects can be continuously detected.

The electrodes 111 to 114 are on the outer side of the respective roller 101 to 104 arranged that they are offset in the axial direction, whereby a measurement over the entire width of the fiber structure 140 becomes possible.

Such a roller is for example in 4th shown. The roller 101 has different electrodes 111a to 111h, the position of each individual electrode differing radially or with respect to the circumference. For example, the electrode 111a is offset radially with respect to the electrode 111b arranged next to it, so that the electrode 111a contacts the respective fiber layer, while the electrode 111b does not contact the fiber layer. A corresponding measurement can then be carried out in the fiber structure at the axial position of the electrode 111a. The roller turns 101 further, the next electrode 111b contacts the fiber structure, while the electrode 111a then no longer contacts the corresponding fiber layer, whereby a corresponding measurement can then be carried out at the axial position of the electrode 111b.

Thus, by turning the roller 101 continuously measure the entire width of the fiber structure. The individual electrodes 111a to 111h are mutually insulated accordingly, so that the measurement is not influenced by other electrodes.

It has been shown in principle that with an approx. 6 cm long measuring section and a layer structure consisting of three fiber layers, the outer layers are oriented +/- 45 ° and the inner layer has normalized 0 ° and runs in the direction of measurement, an electrical resistance without Defect of approx. 1 ohm can be measured. However, if the fiber structure has a gap in the intervening fiber layer, so that reinforcing fibers are missing here, the resistance increases to approx. 120 ohms. If there is a deviation from the standardized fiber orientation, a resistance between 120 ohms and 1 ohm is measured. If there is a deviation of approx. 5 °, the resistance increases to approx. 20 ohms even in areas in which reinforcement fibers are present.

List of reference symbols

1

first fiber layer (outer)

2

second fiber layer (inner)

3

third fiber layer (outer)

4, 140

Fiber scrim

5.6

Flaw

10

first electrode

11

second electrode

12, 130

Measuring section

13

Target direction

14th

Actual direction

100

contraption

101, 102, 103, 104

Rollers

111, 112, 113, 114

Electrodes

120

Ohmmeter

141, 142, 143

Fiber layers

150

Evaluation unit

111a to 111h

different electrodes

R ₁

first measurement

R ₂

second measurement

R ₃

Resistance measurement

α

angle

Claims (15)

Method for detecting defects (5, 6) in a multi-directional fiber fabric (4, 140) which is formed from fiber material of a fiber composite material for producing a fiber composite component, the multi-directional fiber fabric (4, 140) having at least two fiber layers (141, 142, 143 ), in which the direction of electrically conductive reinforcing fibers differ from one another at an angle α, characterized in that a first fiber layer (1) is electrically contacted with a first electrode and at least one second electrode spaced apart from the first electrode, so that between the contacted first and second electrodes (111, 112, 113, 114) a measuring section (12, 130) is formed in the multi-directional fiber fabric (4, 140) in such a way that the between the first and second electrodes (111, 112, 113, 114) formed measuring section (12, 130) under an angle α to the electrically conductive reinforcing fibers of the first fiber layer and parallel to an assumed direction of the electrically conductive reinforcing fibers of a second fiber layer, an electrical resistance of the measuring section (12, 130) in the multi-directional fiber fabric (4, 140) being determined by means of an electrical resistance meter is measured by means of the first and second electrodes (111, 112, 113, 114) and a defect (5, 6) in the second fiber layer is detected by an evaluation unit (150) as a function of the measured electrical resistance when the measured electrical resistance exceeds a predetermined threshold. Procedure according to Claim 1 , characterized in that a gap between the electrically conductive reinforcing fibers of the second fiber layer is recognized as a defect (5, 6) depending on the measured electrical resistance by the evaluation unit (150) when the measured electrical resistance exceeds a predetermined threshold value for this defect ( 5, 6). Procedure according to Claim 1 or 2 , characterized in that a deviation from the assumed direction of the electrically conductive reinforcing fibers of the second fiber layer is recognized as a defect (5, 6) depending on the measured electrical resistance by the evaluation unit (150) when the measured electrical resistance is a predetermined threshold value for this defect (5, 6) exceeds. Method according to one of the preceding claims, characterized in that the first fiber layer (1) is contacted with a first electrode configured as a roller or cylinder and a second electrode configured as a roller or cylinder, the electrodes (111, 112 , 113, 114) can be moved over the first fiber layer (1) in order to set different measurement positions at which the electrical resistance of the measurement path (12, 130) in the multi-directional fiber fabric (4, 140) is measured. Procedure according to Claim 4 , characterized in that the electrodes (111, 112, 113, 114) designed as a roller or cylinder are moved over the first fiber layer (1) during the resistance measurement (R ₃ ). Method according to one of the preceding claims, characterized in that the multi-directional fiber structure (4, 140) has a third fiber layer (3) which, together with the first fiber layer, encloses the second fiber layer (2) and in which the direction of the electrically conductive reinforcing fibers is opposite differ from the electrically conductive reinforcing fibers of the second fiber layer at an angle α from one another, the third fiber layer (3) being electrically contacted with a third electrode and at least one fourth electrode spaced apart from the third electrode, so that between the contacted third and fourth electrode a Measurement section (12, 130) is formed in the multi-directional fiber fabric (4, 140), the measurement section (12, 130) formed between the third and fourth electrodes (111, 112, 113, 114) at an angle α to the electrically conductive Reinforcing fibers of the third fiber layer and parallel to an assumed direction of the electr isch conductive reinforcing fibers of the second fiber layer, with an electrical resistance of the measuring section (12, 130) in the multi-directional fiber fabric (4, 140) being measured by means of the electrical resistance measuring device by means of the third and fourth electrodes (111, 112, 113, 114) and a flaw (5, 6) in the second fiber layer is detected by the evaluation unit (150) as a function of the measured electrical resistance when the measured electrical resistance exceeds a predetermined threshold value. Procedure according to Claim 6 , characterized in that the electrical resistance of the measuring section (12, 130) is determined by means of the first, second, third and fourth electrodes by a four-wire measurement by the electrical resistance measuring device. Procedure according to Claim 6 or 7th , characterized in that the first fiber layer (1) with first and second electrodes (111, 112, 113, 114) designed as a roll or cylinder and the third fiber layer (3) with as rolls or cylinders (101, 102, 103, 104 ) formed third and fourth electrodes (111, 112, 113, 114) are contacted, the electrodes (111, 112, 113, 114) formed as a roller or cylinder being moved over the respective fiber layer to different measurement positions at which the electrical Resistance of the measuring section (12, 130) in the multidirectional fiber fabric (4, 140) is measured. Procedure according to Claim 8 , characterized in that the first electrode (10) designed as a roll or cylinder contact the first fiber layer (1) and the third electrode designed as a roll or cylinder contact the third fiber layer (3) in such a way that the first electrode (10) of the third electrode is opposite, and / or that the second electrode (11) designed as a roll or cylinder contact the first fiber layer (1) and the fourth electrode designed as a roll or cylinder contact the third fiber layer (3) in such a way that the second electrode (11) of the fourth electrode is opposite. Device (100) for detecting imperfections (5, 6) in a multi-directional fiber fabric (4, 140), which is formed from fiber material of a fiber composite material for the production of a fiber composite component, wherein the multi-directional fiber fabric (4, 140) has at least two fiber layers (141, 142, 143), in which the direction of electrically conductive reinforcing fibers is from differ from one another at an angle α, characterized in that the device (100) has at least two spaced electrodes (111, 112, 113, 114) which are designed to contact the first fiber layer of the fiber structure (4, 140) so that between the first electrode and the second electrode, a measuring section (12, 130) is formed in the multi-directional fiber fabric (4, 140), an electrical resistance measuring device being provided for measuring an electrical resistance of the measuring section (12, 130) in the multi-directional fiber fabric (4, 140) is formed by means of the contacting first and second electrodes (111, 112, 113, 114), and wherein an electron cal evaluation unit (150) is provided, which is set up to detect a defect (5, 6) in the second fiber layer as a function of the measured resistance. Device (100) after Claim 10 , characterized in that the evaluation unit (150) is designed to detect a gap between the electrically conductive reinforcing fibers of the second fiber layer as a defect (5, 6) depending on the measured electrical resistance by the evaluation unit (150) and / or a deviation from the assumed direction of the electrically conductive reinforcing fibers of the second fiber layer to be recognized as a defect (5, 6) as a function of the measured electrical resistance by the evaluation unit (150). Device (100) after Claim 10 or 11 , characterized in that the multi-directional fiber fabric (4, 140) has a third fiber layer (3) which, together with the first fiber layer, encloses the second fiber layer (2) and in which the direction of the electrically conductive reinforcing fibers is opposite to the electrically conductive reinforcing fibers of the second fiber layer at an angle α from one another, the device (100) having a third and at least one fourth electrode which are designed to contact the third fiber layer of the fiber structure (4, 140) so that between the third electrode and the fourth electrode a measuring section (12, 130) is formed in the multi-directional fiber fabric (4, 140), the electrical resistance measuring device for measuring an electrical resistance of the measuring section (12, 130) in the multi-directional fiber fabric (4, 140) by means of the contacting third and fourth Electrodes (111, 112, 113, 114) formed and the electronic evaluation unit (150) for Detection of a defect (5, 6) in the second fiber layer is set up as a function of the measured resistance. Device (100) after Claim 12 , characterized in that the electrical resistance measuring device is designed for measuring the electrical resistance of the measuring section (12, 130) by means of the first, second, third and fourth electrodes by means of a four-wire measurement. Device (100) according to one of the Claims 10 to 13th , characterized in that one, several or all electrodes (111, 112, 113, 114) are designed as rollers or cylinders (101, 102, 103, 104) and are set up for moving on the respective contacted fiber layer in order to different measurement positions which the electrical resistance of the measuring section (12, 130) is measured in the multi-directional fiber fabric (4, 140). Device (100) according to one of the Claims 10 to 14th , characterized in that the device (100) for performing the method according to one of the Claims 1 to 9 is trained.

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