JP2008122178A - Method of inspecting stacked state of laminate - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of detecting a laminating angle and laminating position of a laminate to manufacture CFRP at high quality and low cost using a periodic arrangement of auxiliary threads, constituting reinforced fiber sheets, without requiring such a process as arranging a marker in laminating or cutting a laminate. <P>SOLUTION: This is an inspection method for stacked state of a laminate laminated with a plurality of UD reinforced fiber sheets, involving carbon fiber and glass fiber which are periodically arranged therein. From the CT data of the laminate, a plurality of CT images in parallel to the laminating face are obtained, and each CT image is two-dimensional discrete-Fourier-transformed, thereafter for the power spectra obtained based on this, a horizontal frequency u and a vertical frequency v among the points taking a maximum value except the origin are obtained, so that by calculating tan<SP>-1</SP>(v/u)+π/2, the laminating angle θ of the UD reinforced fiber sheet is detected. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a detection method for nondestructively detecting a laminated form of a laminated body for improving quality of FRP manufactured based on the laminated body.

  In the field of manufacturing FRP, development has been carried out to improve the performance as a structural material by modifying the reinforcing fibers or matrix resin constituting the FRP. In addition to the constituent materials themselves, developments have been made to improve performance and reduce manufacturing costs by improving the stage of combining the materials.

  In particular, FRP used for aircraft structural materials, etc. uses a UD-reinforced fiber sheet without crimps that is woven so that the fiber orientation direction is one direction in order to maximize the mechanical properties, and this is used at a predetermined angle. To produce a reinforcing fiber substrate (laminated body) that achieves the designed strength. The UD reinforcing fiber sheet is generally woven with auxiliary yarns such as glass fibers, and these auxiliary yarns are usually arranged periodically.

  Recently, an RTM molding method has attracted attention as a method for producing high-quality FRP at a low cost. In the RTM molding, unlike the case of producing CFRP using a prepreg, a matrix fiber is impregnated later into a reinforcing fiber base material that has been laminated and shaped in advance using a pressure difference between the inside and outside of the mold.

  In order for FRP to exhibit sufficient strength as designed, it is necessary to laminate reinforcing fiber sheets at the exact lamination angle and at the lamination position as designed. However, these laminates may be manufactured by mistake because the setting of the lamination direction and the lamination position of the reinforcing fiber sheets is performed by an artificial work. For this reason, a laminated body or the like that is a primary structural material for an aircraft is cut out of a sample and inspected for a laminated state.

  As a means for inspecting such a laminated state, an inspection method described in Patent Document 1 is known. In the laminated state inspection method described in Patent Document 1, a marker metal wire is inserted into a reinforcing fiber sheet, and the metal wire is laminated so that the insertion positions of the metal wires are different from each other. By doing in this way, the presence of a metal wire from the outside of the laminated body is detected with an infrared camera by a magnetic or electromagnetic method, and the laminated state is detected.

Moreover, the inspection method of patent document 2 is known as a means to test | inspect another lamination state. In the fiberboard described in Patent Document 2, the frequency distribution in the fiber orientation direction is obtained by polar coordinate analysis of the two-dimensional power spectrum derived by the two-dimensional Fourier transform of the digital image signal of the cut surface cut perpendicular to the plate surface. It is measured based on the frequency distribution in the obtained fiber orientation direction. By doing in this way, the fiber orientation of the cross section which cuts a fiber board is detected, Comprising: By making a laminated body into a fiber board, it can divert to the test | inspection of a lamination | stacking state.
JP 2000-62838 A JP-A-9-158100

  An object of the present invention is to use a periodic arrangement of auxiliary yarns constituting the reinforcing fiber sheet without obtaining a process of arranging a marker at the time of lamination or cutting the laminated body, and a lamination angle of the laminated body, It is an object of the present invention to provide a method for detecting a stacking position and to provide a method for realizing high-quality and low-cost CFRP production.

  In order to solve the above-described problems, the present invention has the following configuration.

(1) A method for inspecting a laminate state of a laminate comprising a plurality of UD reinforcing fiber sheets, each of which includes carbon fibers and glass fibers, which are periodically arranged, wherein the laminate is obtained from CT data of the laminate. A plurality of CT images parallel to the surface are obtained, each CT image is subjected to a two-dimensional discrete Fourier transform, and the power spectrum obtained based on this CT image is set to the maximum value among the points that take local maximum values other than the origin. The laminated body is characterized by detecting the lamination angle θ of the UD reinforcing fiber sheet by obtaining the horizontal frequency u and the vertical frequency v of the points to be taken and calculating tan ⁻¹ (v / u) + π / 2. Lamination state inspection method.

  (2) A plurality of UD reinforcing fiber sheets laminated adjacent to each other from a horizontal frequency u ′ and a vertical frequency v ′ at which local maximum values differ from the maximum values for an arbitrary CT image parallel to the laminated surface. The method for inspecting the lamination state of the laminate according to (1), wherein the lamination angle θ ′ of the mixed CT image and / or the undulation of the UD reinforcing fiber is detected.

(3) A method for inspecting a laminate state of a laminate comprising a plurality of UD reinforcing fiber sheets, each of which includes carbon fibers and glass fibers, which are periodically arranged, wherein the laminate is obtained from CT data of the laminate. A plurality of CT images parallel to the surface are obtained, each CT image is subjected to a two-dimensional discrete Fourier transform, and the power spectrum obtained based on this CT image is set to the maximum value among the points that take local maximum values other than the origin. The horizontal frequency u and the vertical frequency v of the points to be taken are obtained, the total number of pixels M in the horizontal direction of the CT image and the total number of pixels N in the vertical direction are divided by u and v, respectively. Is multiplied by the length per unit pixel in the vertical direction to calculate the horizontal period length l _x and the vertical period length l _y ,

The method for inspecting the laminated state of the laminate according to (1), wherein the arrangement interval l of the glass fibers arranged in the UD reinforcing fiber sheet is detected by calculating

  (4) Multiplying the acquisition position of the CT image by the thickness per unit pixel of the CT image, and detecting as a lamination position of the UD reinforcing fiber sheet, any one of (1) to (3) A method for inspecting a lamination state of the laminate according to claim 1

(5) An arbitrary layer is used as a reference layer, and CT images having at least two parallel cross sections perpendicular to the laminated surface and perpendicular to the direction of the glass fiber of the reference layer are compared, and the distance l ₁ between the CT images is compared. The movement distance l _{2 of the} cross section of the glass fiber of the layer other than the reference layer moving between the CT images is obtained, and tan ⁻¹ (l ₂ / l ₁ ) is calculated. The angle η formed by the glass fiber of the layer with respect to the CT image is detected, the angle formed by the glass fiber of the layer other than the reference layer with respect to the direction of the glass fiber of the reference layer is detected, and the lamination angle of the UD reinforcing fiber sheet A method for inspecting a laminate state of a laminate, wherein

(6) The arbitrary layer is a reference layer, the CT images of at least two parallel sections perpendicular to the laminated surface and perpendicular to the glass fiber direction of the reference layer are compared, and the CT images move between the CT images. A laminating state of a laminated body characterized by detecting a movement width l _w of a glass fiber cross section of a layer different from an arbitrary layer, detecting a wave of the glass fiber, and detecting a wave of the UD reinforcing fiber sheet. Inspection method.

  (7) The laminated body obtained by collating the lamination state of the UD reinforcing fiber sheet obtained by the lamination state inspection method according to any one of (1) to (6) with lamination design information Quality inspection method.

  The carbon fiber in the present invention refers to a fiber having a carbon mass content of 90% or more obtained by heating carbonization treatment of raw material fibers such as organic fibers. Depending on the raw material fibers, polyacrylonitrile-based, rayon-based or pitch-based They are similar to the graphite crystal structure, have high performance, small thermal shrinkage during graphitization, and advantageous carbonization yield. Carbon fiber has a property of transmitting X-rays generally used for X-ray CT.

  Glass fiber is obtained by melt-drawing glass into a fiber. In the present invention, the glass fiber is mainly used as an auxiliary thread for a UD reinforcing fiber sheet using carbon fiber, and is typically assumed to be a long fiber having a diameter of about 100 μm. Glass fiber has the property of absorbing X-rays generally used for X-ray CT.

  The UD (unidirectional) reinforcing fiber sheet refers to a sheet used as a laminated member constituting the reinforcing fiber base material when manufacturing the reinforcing fiber base material before impregnation with the matrix resin in the production of CFRP. A reinforced fiber sheet called non-crimp, which does not crimp (bend) when carbon fiber is woven and laminated in one direction, and which can improve the mechanical properties of CFRP over a general crimp material. In the present invention, a sheet woven with carbon fibers as main fibers and glass fibers as auxiliary yarns (warp yarns) is assumed.

  The laminated state is a generic term for a laminated structure and a laminated form.

The laminated structure of the laminated body generally represents the type, laminated angle and lamination order of the reinforcing fiber sheets constituting the laminated body. In the present invention, the laminated angle in the case of using a UD (unidirectional) reinforcing fiber sheet It shall represent the stacking order. As a typical example of a specific laminated structure, there is a pseudo isotropic lamination in which the layers are laminated in the order of [−45 ° / 90 ° / 45 ° / 0 °] _s . Here, [X °] means that the angle formed with the reference line is X, and is usually described in a range of −90 ° <X ≦ 90 °. In the present invention, for the sake of simplicity, the angle is described in the range of 0 ° to 180 °, which is the same purpose. [X ° / Y °] means that the first sheet is laminated at X °, and then the second sheet is laminated at Y °. Furthermore, [X ° / Y °] _s represents a configuration in which the layers are stacked symmetrically (S represents “Symmetric”) as [X ° / Y ° / Y ° / X °].

  The laminated form of the laminated body means an angle deviation in the plane of each layer constituting the laminated body, a swell or inclination to the outside of the plane, and the like. The UD reinforcing fiber sheet constituting the laminated body should ideally be laminated as a set laminating direction and a plane parallel to the laminating surface, but in reality, the set laminating direction and angle are Since they are misaligned and are laminated as curved surfaces with undulations, even if they are laminated with the original laminated structure, mechanical strength as designed may not be realized. Therefore, it is necessary to inspect the laminated form.

  In the present invention, CT data refers to data obtained by obtaining a three-dimensional transmittance distribution in an object from projection (data formed through the inside of the object). In the case of the present invention, specifically, it refers to a set of data obtained by dividing a laminate into unit volume regions in three-dimensional coordinates and corresponding X-ray absorption rate data for each region. The finer the unit volume, the higher the spatial resolution can be realized. However, the resolution and the imaging range become a trade-off such that the imaging range becomes narrow due to limitations on the amount of data that can be handled by the computer and the calculation time.

  In the present invention, the CT image refers to an image in which the CT data is reconstructed with respect to a cross section of a laminate, and the distribution of X-ray absorption at each point of the cross section is imaged in a two-dimensional manner. . Since it is difficult to grasp the CT data on the three-dimensional coordinates as it is, usually, a certain direction is set and expressed by a CT image representing a cross section in that direction. In the present invention, the pixel value of a CT image refers to the brightness of a pixel that represents the intensity of the X-ray absorption rate on a three-dimensional coordinate corresponding to each pixel of the CT image. In general, it is often expressed by 256 gradations from 0 to 255. Also in the present invention, 256 gradations are adopted. Although the present invention uses a set of materials in which the CT image has a large difference in the amount of X-ray transmission / absorption between the carbon fiber and the glass fiber, and can be sufficiently implemented in 256 gradations, When the diameter of the fiber is thin, or when using another set of fibers having a small difference in transmission / absorption amount, it is assumed that the contrast in the CT image becomes weak. In such a case, 256 or more It is desirable to employ pixel values expressed in the gradations.

  In the two-dimensional discrete Fourier transform, the distribution of pixel values of the CT image is f (x, y), the total number of pixels in the x (horizontal) direction of the CT image is M, and the total number of pixels in the y direction is N. The conversion from the (x, y) coordinate system represented by the following expression to the (u, v) coordinate system, or F (u, v) itself converted from f (x, y) is referred to as It is represented by

  The horizontal frequency is a variable of the two-dimensional discrete Fourier transform represented by u in the above equation, and f (x, y) represents the periodicity in the x direction, and the vertical frequency is represented by v in the above equation. A variable of a two-dimensional discrete Fourier transform, which represents the periodicity of f (x, y) in the y direction.

The power spectrum is a value obtained by squaring the absolute value of a two-dimensional discrete Fourier transform.
The value of the power spectrum is

When f (x, y) is distributed in the x direction with a period of the number of M / u pixels and distributed in the y direction with a period of the number of N / v pixels, the coordinates (u, v) Take the maximum value. Due to the nature of the power spectrum, if the local maximum value is obtained at the coordinates (u, v), the local maximum value is also obtained at the coordinates (−u, −v), so that v> 0, u ≧ 0, and v = 0. I will think in a limited way. It is rare that the distribution of f (x, y) has only one period, and usually includes other periods, and the coordinate having the maximum value in the power spectrum is other than (u, v) (u ′, v ′). ) May also exist. In this case, as the amplitude of the period of the distribution of f (x, y) corresponding to (u, v) is larger,

Therefore, when the power spectrum has a plurality of maximum values, it is possible to determine what period distribution amplitude is strong in f (x, y) by comparing these maximum values. is there.

  The “lamination angle” in the present invention refers to an angle formed by the reference line at the time of lamination and the orientation direction of the UD reinforcing fiber sheet carbon fiber. In addition, when the laminate is viewed alone, it is assumed that the reference line at the time of lamination is unknown, but in such a case, in such a case, an arbitrary one layer is represented and the reinforcing fiber of the layer is represented. The direction may be regarded as a reference line and expressed as an angle with respect to the reference line. Usually, the glass fiber used as the auxiliary yarn always forms a certain angle with the carbon fiber. Therefore, by obtaining the orientation direction of the glass fiber, the orientation direction of the carbon fiber can be known, and the lamination angle can also be known. Moreover, since the UD (one direction) reinforcing fiber sheet is handled in the present invention, the lamination angle can be limited to 0 ° or more and less than 180 °. Therefore, in the present invention, when the calculation is less than 0 ° or 180 ° or more, a value obtained by multiplying the value by an integer multiple of 180 ° is added to convert the value to 0 ° or more and less than 180 °. That value is taken as the stacking angle. For convenience of calculation, the angle is often expressed in radians (for example, the above equation), but the stacking angle itself is described in “°”. As long as there is no confusion, it will be read as appropriate.

  “Parallel to the laminated surface” means parallel to a reference surface when the UD reinforcing fiber sheets are first laminated. In a normal laminating operation, the upper surface of the work desk used when performing the laminating operation serves as a reference plane, and thus means that it is parallel to the first layer during the laminating operation. In addition, when viewed from the laminate alone, it may be difficult to determine which surface is the reference surface, but in this case, in such a case, the planarity is more flat when left on a flat plate. The higher surface shall be regarded as the reference surface.

  The CT image in which a plurality of adjacent UD reinforcing fiber sheets laminated together means a CT image in which a plurality of adjacent UD reinforcing fiber sheets are imaged on one CT image. When the CT image is acquired, if the laminated surface and the UD reinforcing fiber sheet are completely parallel, one type of UD reinforcing fiber sheet should be captured in one CT image. Since the undulation is inclined with respect to the surface, a plurality of adjacent UD reinforcing fiber sheets are often imaged in one CT image. In the case of such a CT image, it is difficult to determine at which position and at which lamination angle the UD reinforcing fiber sheet is located, which has hindered the practical application of inspection technology using conventional CT images for laminated materials. It was.

  The undulation of the UD reinforcing fiber sheet means that the UD reinforcing fiber sheet is inclined with respect to the laminating surface, and the position is changed in the vertical direction with respect to the laminating direction at a partial portion, and the waviness amount means the fluctuation range.

  The length per unit pixel of the CT image refers to the length in the actual laminate corresponding to the pixels constituting the CT image. As described above, since the imaging range of CT data has a trade-off relationship with the spatial resolution, the length per unit pixel of the CT image is also limited by the imaging range.

The horizontal cycle length represents one wavelength of the horizontal cycle of the pixel value of the CT image.
The vertical period length represents one wavelength of the period in the vertical direction of the pixel value of the CT image.

  The arrangement | positioning space | interval of glass fiber means the arrangement | positioning space | interval in the same layer of the glass fiber arrange | positioned as an auxiliary | assistant thread | yarn to a UD reinforcement fiber sheet.

  The thickness per unit pixel of the CT image refers to the thickness of the actual laminate corresponding to one CT image. As described above, the thickness per unit pixel of the CT image is also limited by the imaging range, as is the length per unit pixel of the CT image.

  Lamination design information refers to information regarding the number of laminated UD reinforcing fiber sheets constituting the laminate and the lamination angle when the UD reinforcing fiber sheets are laminated.

  According to the laminate state detection method and laminate inspection apparatus of the present invention, a laminate can be obtained nondestructively without a process of inserting a metal wire that is not necessary in the laminate or cutting the laminate. Lamination forms such as fiber orientation and lamination position can be detected. By introducing an inspection apparatus using this method, 100% inspection can be performed and mixing of defective products can be prevented.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 is a diagram showing a CT image acquired when performing the inspection method of the present invention.

In the present invention, X-rays are adopted as a radiation source used for CT, and the CT data 1 of the laminated body is data indicating the distribution of the X-ray absorption degree of each part of the laminated body in three dimensions, and has a total of four dimensions. It is data. From this CT data 1, a plurality of CT images 11 parallel to the lamination surface are acquired in the lamination direction 2. The UD reinforcing fiber sheet has a structure in which carbon fibers 111, which are main reinforcing fibers, are woven as warps of glass fibers 112 arranged periodically at regular intervals, and the carbon fibers 111 and the glass fibers 112 are unidirectional in the direction 2. Are aligned. Since the carbon fiber 111 relatively transmits X-rays and the glass fiber 112 relatively absorbs X-rays, mainly the glass fibers stand out and are displayed on the CT image. That, CT image 11, the glass fibers arranged at intervals of periodically l, has a period of length l _x in the horizontal direction, it has a period of length l _y in the vertical direction.

  FIG. 2 is a diagram illustrating an example of a laminated configuration of the UD reinforcing fiber sheet of the present invention.

  The laminate of the present invention is designed such that UD reinforcing fiber sheets in a plurality of directions are stacked at a certain angle. For example, the UD reinforcing fiber sheet 41 having a 45 ° direction with the horizontal direction set to 0 °. A UD reinforcing fiber sheet 42 having a 90 ° direction is laminated thereon, a UD reinforcing fiber sheet 43 having a 135 ° direction is laminated thereon, and a UD reinforcing fiber sheet 44 having a 0 ° direction thereon. And a UD reinforcing fiber sheet 41 having a 45 ° direction is laminated thereon. Usually, the lamination direction is reversed such that the lamination angle is 0 ° → 45 ° → 90 ° → 135 ° with the center in the lamination direction of the laminate as a target. However, in such a laminated body, the setting of the lamination direction and the lamination position of the reinforcing fiber sheets is performed by an artificial operation, and thus the lamination angle is not necessarily as designed.

  In the present invention, a two-dimensional discrete Fourier transform is performed on each of a plurality of CT images acquired as shown in FIG. 1, and a power spectrum obtained based on the two-dimensional discrete Fourier transform is used to determine an arbitrary position in the laminate as shown in FIG. 2. The lamination angle of the UD reinforcing fiber sheet is detected.

  A two-dimensional discrete Fourier transform is performed on each acquired CT image, and the obtained power spectrum is exemplified below.

  FIG. 3 is a diagram showing a CT image of a laminated surface forming an angle of 0 ° and its power spectrum.

  FIG. 4 is a diagram showing a CT image of a laminated surface forming an angle of 45 ° and its power spectrum.

  FIG. 5 is a diagram showing a CT image of a laminated surface forming an angle of 90 ° and its power spectrum.

  FIG. 6 is a diagram showing a CT image of a laminated surface forming an angle of 135 ° and its power spectrum.

  As shown in the above figures, the power spectrum reflects the direction of the original CT image. This will be described below.

  First, the distribution of pixel values of a CT image is expressed as f (x, y) where x is the horizontal direction and y is the vertical direction. At this time, the two-dimensional discrete Fourier transform F (u, v) of f (x, y) is expressed as the following equation.

  Here, M is the total number of pixels in the x (horizontal) direction of the CT image, and N is the total number of pixels in the y direction.

  u represents the periodicity of f (x, y) in the x direction, and is called the horizontal frequency. v represents the periodicity of f (x, y) in the y direction and is called the vertical frequency.

  The power spectrum is obtained by squaring the absolute value of a two-dimensional discrete Fourier transform of a CT image. In other words, the value of the power spectrum is

When f (x, y) is distributed with a period of M / u pixels in the x direction and with a period of N / v pixels in the y direction, coordinates (u, v) It has the property of taking a local maximum. Due to the nature of the power spectrum, if the local maximum value is obtained at the coordinates (u, v), the local maximum value is also obtained at the coordinates (−u, −v), so that v> 0, u ≧ 0, and v = 0. I will think in a limited way.

  There are few cases where the distribution of f (x, y) has only one period, usually including other periods, and the coordinates having the maximum value in the power spectrum are (u ′, v ′) other than (u, v). ) May also exist. In this case, as the amplitude of the period of the distribution of f (x, y) corresponding to (u, v) is larger,

Therefore, when the power spectrum has a plurality of maximum values, it is possible to determine what period distribution amplitude is strong in f (x, y) by comparing these maximum values. is there.

As described above, the power spectrum reflects the period of distribution of pixel values of the original CT image. The period of the CT image is composed of glass fibers periodically arranged on the UD reinforcing fiber sheet at regular intervals, and has a period in a direction perpendicular to the orientation direction of the glass fibers. The orientation direction of the glass fiber is the lamination direction of the UD reinforcing fiber sheet. Therefore, the distribution direction of the power spectrum and the lamination direction of the UD reinforcing fiber sheet reflected in the CT image form an angle of 90 °,
When the distribution of the power spectrum is in the direction of 90 ° as shown in FIG. 3, if the stacking direction of the UD reinforcing fiber sheet shown in the CT image is 0 ° (180 °), the power spectrum as shown in FIG. 3 is oriented in the direction of 135 °, the direction of the power spectrum distribution is 0 ° as shown in FIG. 3 when the lamination direction of the UD reinforcing fiber sheet in the CT image is 45 ° (225 °). When the direction of the UD reinforcing fiber sheet shown in the CT image is 90 °, the power spectrum distribution is shown in the CT image when the distribution of the power spectrum is 45 ° as shown in FIG. It can be detected that the lamination direction of the UD reinforcing fiber sheet is 135 °.

  In general, to calculate the direction of a sparsely distributed power spectrum, local coordinate analysis or centroid calculation is required, and the detection procedure becomes complicated. In the present invention, it is possible to detect a simple stacking angle by pinpointing a point having a maximum value among points having a maximum value in the power spectrum.

  FIG. 7 is a diagram showing a process of detecting the stacking angle of the UD reinforcing fiber sheet and / or the arrangement interval of the glass fibers arranged in the UD reinforcing fiber sheet from the coordinates of the point having the maximum value in the power spectrum.

As in the previous technique, the power spectrum is distributed in the original CT image f (x, y) with a period of the number of M / u pixels in the x direction and with a period of the number of N / v pixels in the direction. Sometimes, it has a property of taking a local maximum value at coordinates (u, v). Since the original CT image reflects the UD reinforcing fiber sheet in which the glass fibers are periodically arranged at regular intervals and laminated at a constant angle, the original CT image has a period of almost a constant number of pixels. Therefore, the power spectrum has a clear maximum value at coordinates corresponding to the fixed number of pixels. However, since the power spectrum generally has a large maximum value even at the origin, the origin is considered. Therefore, a point having a maximum value appearing in the power spectrum is extracted, an angle φ formed by a vector connecting the point and the origin and the horizontal direction is set, and a coordinate having the maximum value is (u, v), and tan ^−1. It is obtained by calculating (v / u), and the lamination angle θ of the UD reinforcing fiber sheet can be obtained by calculating φ + π / 2.

  FIG. 8 is a diagram showing a CT image in which laminated surfaces having angles of 0 ° and 135 ° are mixed and its power spectrum.

  The CT image has not only a periodicity in one direction as shown in FIGS. 3 to 6 but also a mixture of periods in two or more directions as shown in FIG. This is due to the fact that adjacent sheets of the laminated UD reinforcing fiber sheets are simultaneously captured in one CT image. In this case, it is not easy to visually determine the stacking angle of the UD reinforcing fiber sheet that appears in the CT image, but even in such a case, the stacking angle of the UD reinforcing fiber sheet that appears in the CT image is the strongest. A method of extracting and detecting a lamination angle of a representative representative UD reinforcing fiber sheet will be described below.

  FIG. 9 is a diagram illustrating a process of detecting a stacking angle of a mixed stacked surface from a power spectrum of a CT image in which stacked surfaces in different directions are combined.

In addition to (u, v), the coordinate having the maximum value in the power spectrum also has (u ′, v ′). At this time, if the maximum value of the power spectrum at (u ′, v ′) is larger than the value at (u, v), the period corresponding to (u ′, v ′) is also present in the original CT image. It shows that it is remarkable. For (u ′, v ′), the angle φ ′ formed by the vector connecting the point and the origin and the horizontal direction is obtained by calculating tan ⁻¹ (v ′ / u ′), and the laminated surface in the desired direction is appealed. Also in the CT image, the lamination angle θ ′ of the UD reinforcing fiber sheet can be obtained by calculating φ ′ + π / 2.

  Also, by detecting the stacking angle of adjacent layers and taking the correspondence of whether the mixed angle is the same stacking angle as the layer stacked above or the same stacking angle as the layer stacked below, With respect to the cross-section from which the CT image is acquired, it is possible to detect a stacked form of which part of the corresponding UD reinforcing fiber sheet is undulating up and down.

When the original CT image f (x, y) is distributed in the x direction with a period of M / u pixels and in the y direction with a period of N / v pixels, coordinates (u, v) Therefore, the number of pixels M / u and N / v of the period distributed in the x and y directions can be obtained from the power spectrum, and the actual length per unit pixel can be obtained from this. By multiplying, it is possible to calculate the horizontal period length l _x and the vertical period length l _y that the glass fibers arranged in the UD reinforcing fiber sheet described in FIG. 1 have in the x and y directions,

By calculating, it is possible to obtain the arrangement interval l of the glass fibers arranged in the UD reinforcing fiber sheet.

  By the method described above, the stacking angle, waviness, waviness amount, and glass fiber arrangement interval of the UD reinforcing fiber sheet can be obtained from the CT image parallel to the laminated surface. The CT image in which these stacked structures and stacked forms are detected is calculated by multiplying the number of CT images acquired until the CT image is acquired by the thickness corresponding to each CT image, thereby calculating the stacked body. The position of the UD reinforcing fiber sheet can be matched with the actual position of the UD reinforcing fiber sheet, and the position of the UD reinforcing fiber sheet is laminated at what position in the stacking direction of the laminate, and how much it is undulated. Can be inspected.

1 to 9 have shown the detection method of the laminated structure of the laminated body using CT images parallel to the laminated surface. Fig. 10 compares the CT images of at least two cross-sections with any one layer as a reference layer, perpendicular to the lamination plane and orthogonal to the glass fiber direction 50 of the reference layer, and detects the lamination angle of the reinforcing fibers It is a figure showing the process to do. The upper diagram is a diagram of the laminated surface as viewed from above, and the lower diagram is a diagram of the surface from which the CT image is acquired as viewed from the front. When the CT image 61 is acquired and then the CT image 62 is acquired, the cross section 51 of the glass fiber 5 appears to move to the fifth cross section 52 in the direction of the arrow 72. At this time, when the distance between the CT image 61 and the CT image 62 is l ₁ and the distance between the cross section 51 and the cross section 52 is l ₂ , the angle η formed with respect to the glass fiber direction of the reference layer is tan ^−1. It can be calculated as (l ₂ / l ₁ ). Therefore, it can be detected that the stacking angle is shifted by η from the stacking angle of the reference layer.

FIG. 11 shows a process of detecting the swell of reinforcing fibers by comparing CT images of cross sections that are perpendicular to the laminated surface and perpendicular to the direction of the glass fibers 50 of the reference layer and are parallel to each other and at least two distances apart. FIG. The upper figure is a view of the laminated surface from above, the lower left figure is the front view of the surface from which the CT image was acquired, and the lower right figure is perpendicular to the laminated surface as with the CT image. Although it is, it is the figure seen from the direction which can grasp | ascertain what kind of form the glass fiber is extending in the longitudinal direction. The cross-sections 51, 52, 53, 54 of the glass fiber 5 when the CT images 61, 62, 63, 64 of the cross-sections orthogonal to the glass fiber 50 and parallel to each other and at least two distances are acquired are in the laminating direction. It appears to move up and down by a range l _{w in} a direction perpendicular to This range l _w corresponds to the undulation of the glass fiber 5 shown in the lower right figure, and this can be detected.

  Table 1 is a table showing an example of design information of the stacking angle and stacking position of the stack.

  By the above-mentioned method, the lamination angle of the UD reinforcing fiber sheet of each layer of the laminate is obtained. It is inspected against the stacking position to determine how far the determined stacking angle is from the pre-designed stacking angle. The illumination may be done by a human or sequentially on a computer.

[Example 1]
A 60 mm × 60 mm UD reinforcing fiber sheet (Toray Industries, Inc. CZ8431DP, T800 unidirectional fabric) is 24 ply based on the design information in Table 1 to produce a 60 mm × 60 mm × about 6 mm laminate, The laminate was imaged with a resolution of 60 μm using a line CT apparatus. The main parts of this X-ray CT apparatus are an X-ray source (L7901 manufactured by Hamamatsu Photonics Co., Ltd., a focal size of 7 μm), an X-ray detector (E5764SD-P1K manufactured by Toshiba Corporation), and a CT data reconstruction system (BIR, Inc. ACTIS + 3).

  CT data was acquired as 120 CT images continuous in the stacking direction. One CT image has a number of pixels of 1024 × 1024 and is expressed in 256 gradations.

  For each of the CT images obtained as described above, a power spectrum is obtained using numerical processing software matlab (The Math Works, Inc., 6.5.1.199709 (R13) Service Pack 1). The results shown in FIGS. 3 to 6 and FIG. 8 were obtained. Next, for the power spectrum obtained in this way, the horizontal frequency u and the vertical frequency v at the point where the maximum value is taken out of the maximum values excluding the origin are obtained. Table 2 shows the obtained horizontal frequency u and vertical frequency v. u and v represent the period of the horizontal and vertical pixel values in the original image by the number of pixels (pixel).

By calculating tan ⁻¹ (v / u) from the horizontal frequency u and the vertical frequency v thus obtained, the lamination angle θ of the UD reinforcing fiber sheet was detected. Table 2 shows the detected lamination angle θ of the UD reinforcing fiber sheet.

Further, M / u is calculated from the horizontal frequency u acquired as described above, and this is multiplied by a length of 60 μm per unit pixel in the horizontal direction to calculate l _x , and N / v is calculated from the vertical frequency v. calculating a l _y by multiplying the length 60μm per unit pixel in the direction. Furthermore, using l _x and l _y calculated in this way

Was calculated and the glass fiber arrangement interval l was detected. Table 2 shows the calculated l _x , l _y and l.

  Next, using the fact that the thickness of the actual laminate per CT image is 60 μm, CT image # 1 in Table 2 is set to 0, and 0.06 mm is added in order, and each CT image corresponds. The position in the laminate was detected. Table 2 also shows this.

From the results in Table 2, it can be seen in what lamination angle and order the UD reinforcing fiber sheets are laminated. That is, paying attention to the lamination angle of the UD reinforcing fiber sheet, the layer (thickness 0.30 mm) from 0 mm to 0.24 mm from the uppermost surface layer corresponding to CT images # 1 to # 5 is 45 °. It can be seen that the 1 ply UD reinforcing fiber sheets are laminated at the lamination angle of. Next, a layer (thickness 0.30 mm) of 0.30 mm to 0.60 mm from the uppermost surface layer in the laminated body corresponding to CT images # 6 to # 10 is a 2 ply UD reinforcing fiber at a lamination angle of 90 °. It can be seen that the sheets are stacked. Table 3 shows the results of analyzing the stacking angle and the stacking position by the same method as described above up to the 19th ply. By comparing Table 3 with Table 1, it can be seen that the stacking angle of 1 to 19 ply is as designed or how many times it deviates.
Specifically, it can be seen from Table 3 that the 11 ply UD reinforcing fiber sheet is deviated from the 6.3 ° design value.

[Example 2]
Similar to the first embodiment, as shown in FIG. 8, it seems that the laminated surfaces having at least two angles are mixed. This power spectrum distribution also appears to be in at least two directions. Therefore, it is difficult to detect the direction of the UD reinforcing fiber sheet that appears in the original image.

At this time, the coordinates having the maximum value in the power spectrum were (0, 6) and (4, 4). The power spectrum values of these coordinates were 2.8638 and 2.2104, respectively. Therefore, the maximum value of the power spectrum at the coordinates (0, 6) is larger, and it can be said that the maximum value is taken out of the maximum values, so that it is determined that the current image has periodicity in the direction corresponding to this. It turns out to be appropriate. That is, it can be seen that it is appropriate to calculate tan ⁻¹ (6/0) + π / 2 and detect the stacking angle of the UD reinforcing fiber sheet in the original image as 0 °.
On the other hand, the mixed angle other than 0 ° can be detected as 135 ° by calculating tan ⁻¹ (4/4) + π / 2. The CT image of FIG. 8 corresponds to CT image # 32 in Table 1, and when viewing the stacking angles of the upper and lower layers, # 31 is 135.0 ° and # 33 is 0.0 °. It can be determined that the layer is a laminated surface where layers of 135 ° and 0 ° overlap.
[Example 3]
From CT data obtained by the same method as in Example 1, the CT image of two parallel sections (two CTs), with the lowest layer as the reference layer, perpendicular to the laminated surface and perpendicular to the direction of the glass fibers of the reference layer. The distance between images was 5.04 mm).

In the acquired CT image, the position of the cross section of the glass fiber of the reference layer was not changed even if the cross section for acquiring the parallel CT image was changed. Compared to this, the glass fiber of the layer adjacent to the lowermost layer moved 4.80 mm position in the CT image when the position for acquiring the parallel CT image changed by 5.04 mm. From this, by calculating tan ⁻¹ (4.80 _/ 5.04), the angle formed by the glass fiber of the layer adjacent to the lowermost layer with respect to the direction of the glass fiber of the reference layer is 43.6 °. I asked for it.

Each laminated surface was confirmed to have no waviness with a resolution of CT data of 60 μm or more.
It was confirmed that there was no swell

It is a figure which represents typically the CT image acquired when enforcing the inspection method of the present invention. It is a figure showing the laminated structure of the UD reinforcement fiber sheet of this invention. It is a figure showing the CT image of the laminated surface which makes an angle of 0 degrees, and its power spectrum. It is a figure showing the CT image of the laminated surface which makes an angle of 45 degrees, and its power spectrum. It is a figure showing the CT image of the laminated surface which makes an angle of 90 degrees, and its power spectrum. It is a figure showing the CT image of the laminated surface which makes an angle of 135 degrees, and its power spectrum. It is a figure showing the process of detecting a lamination angle from the coordinate of the point which takes the maximum value in a power spectrum. It is a figure showing CT image with which the lamination surface which makes an angle of 0 degrees and 135 degrees mixed, and its power spectrum. It is a figure showing the process of isolate | separating and detecting the lamination | stacking angle of the lamination | stacking laminated surface from the power spectrum of CT image with which the lamination | stacking surface of the different direction was mixed. It is a figure showing the process of using the arbitrary layer as a reference layer, comparing CT images of at least two or more cross sections perpendicular to the laminated surface and perpendicular to the glass fiber of the reference layer, and detecting the lamination angle of reinforcing fibers. FIG. 4 is a diagram illustrating a process of detecting waviness in the lamination direction of reinforcing fibers by comparing CT images of at least two or more cross sections perpendicular to the lamination surface and perpendicular to the glass fiber of the reference layer, using an arbitrary layer as a reference layer. is there.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Laminate 11 CT image 111 Carbon fiber 112 Glass fiber 2 Lamination direction 3 UD reinforcement fiber sheet lamination direction 4 UD reinforcement fiber sheet 41 UD reinforcement fiber sheet 42 laminated at an angle of 45 ° Laminated at an angle of 90 ° UD reinforced fiber sheet 43 UD reinforced fiber sheet 44 laminated at an angle of 135 ° UD reinforced fiber sheet 5 laminated at an angle of 0 ° 5 Glass fiber 50 Glass fiber 51 orthogonal to CT image Glass fiber reflected on CT image 61 Cross section 52 of glass 5 Cross section 53 of glass fiber 5 shown on CT image 62 Cross section 54 of glass fiber 5 shown on CT image 63 Cross section 6 of glass fiber 5 shown on CT image 64 6, 62, 63, 64 Lamination surface CT image orthogonal to the lamination angle θ ′ obtained from a CT image parallel to the laminated surface θ ′ obtained from a CT image parallel to another laminated surface Lamination angle φ of the UD reinforcing fiber sheet Angle φ ′ of the distribution of the power spectrum with the horizontal axis φ ′ Angle of the distribution of the power spectrum with the horizontal axis η Lamination angle of the UD reinforcing fiber sheet obtained from the CT image perpendicular to the lamination surface l _x Horizontal period length of glass fibers arranged in the UD reinforcing fiber sheet l _y Vertical period length of glass fibers arranged in the UD reinforcing fiber sheet l Period length l of glass fibers arranged in the UD reinforcing fiber sheet ₁ CT image 61 and the distance l ₂ distance l _w movement width on the cross section of the CT image of the glass fiber 5 between the section 51 and section 52 of the glass fibers between the CT image 62

Claims (7)

A method for inspecting a laminate state of a laminate comprising a plurality of UD reinforcing fiber sheets, each of which includes carbon fibers and glass fibers, which are periodically arranged, and is parallel to a laminate surface from CT data of the laminate A plurality of CT images are obtained, each of the CT images is subjected to a two-dimensional discrete Fourier transform, and the power spectrum obtained based on the CT images is obtained by taking the maximum value among the points having the maximum values other than the origin. By obtaining the horizontal frequency u and the vertical frequency v and calculating tan ⁻¹ (v / u) + π / 2, the lamination angle θ of the UD reinforcing fiber sheet is detected. Inspection method.   CT in which a plurality of UD reinforcing fiber sheets laminated adjacent to each other are mixed from the horizontal frequency u ′ and the vertical frequency v ′ at which local maximum values differ from the maximum values for an arbitrary CT image parallel to the laminated surface. The method for inspecting a lamination state of a laminate according to claim 1, wherein the lamination angle θ ′ of the image and / or the undulation of the UD reinforcing fiber is detected. A method for inspecting a laminate state of a laminate comprising a plurality of UD reinforcing fiber sheets, each of which includes carbon fibers and glass fibers, which are periodically arranged, and is parallel to a laminate surface from CT data of the laminate A plurality of CT images are obtained, each of the CT images is subjected to a two-dimensional discrete Fourier transform, and the power spectrum obtained based on the CT images is obtained by taking the maximum value among the points having the maximum values other than the origin. The horizontal frequency u and the vertical frequency v are obtained, the total number of pixels M in the horizontal direction of the CT image and the total number of pixels N in the vertical direction are divided by u and v, respectively, and the length per unit pixel in the horizontal direction, respectively. The horizontal period length l _x and the vertical period length l _y are calculated by multiplying the length per unit pixel in the vertical direction,
The method of inspecting the laminated state of the laminate according to claim 1, wherein the arrangement interval l of the glass fibers arranged in the UD reinforcing fiber sheet is detected by calculating   The multilayer body according to any one of claims 1 to 3, wherein the acquisition position of the CT image is multiplied by a thickness per unit pixel of the CT image and detected as a lamination position of the UD reinforcing fiber sheet. Method for checking the lamination state of An arbitrary layer is used as a reference layer, and CT images of at least two or more parallel cross sections perpendicular to the laminated surface and perpendicular to the direction of the glass fiber of the reference layer are compared, and a distance l ₁ between the CT images is compared. By obtaining the moving distance l _{2 of the} cross section of the glass fiber of the layer other than the reference layer moving between images and calculating tan ⁻¹ (l ₂ / l ₁ ), the layer other than the reference layer in the laminated surface is calculated. The angle η formed by the glass fiber with the CT image is detected, the angle formed by the glass fiber other than the reference layer with respect to the direction of the glass fiber in the reference layer is detected, and the lamination angle of the UD reinforcing fiber sheet is detected. A method for inspecting a laminate state of a laminate. Arbitrary layer is used as a reference layer, and CT images having at least two parallel cross sections perpendicular to the laminated surface and perpendicular to the direction of the glass fiber of the reference layer are compared, and the arbitrary layer moves between the CT images. A method for inspecting a laminated state of a laminate, comprising detecting a movement width l _w of a glass fiber cross section of a layer different from the above, detecting a wave of the glass fiber, and detecting a wave of the UD reinforcing fiber sheet.   A method for inspecting a quality of a laminate, wherein the laminate state of the UD reinforcing fiber sheet obtained by the method for inspecting a laminate state according to any one of claims 1 to 6 is collated with laminate design information.