JP4631515B2 - Non-destructive inspection method for FRP structures - Google Patents

Description

  The present invention relates to a non-destructive inspection method for an FRP structure that is a fiber composite reinforced material, and more specifically, a non-destructive inspection of an FRP structure that enables quantitative and non-personal understanding of FRP defects. Regarding the method.

  In recent years, fiber reinforced composite plastics (FRP) are promising not only for small ships but also for structures such as ships in the future. For this reason, a technique for molding a large structure with FRP has been developed. There are several methods for this, but for example, using the VaRTM (Vacuum Assisted Resin Transfer Molding), relatively large sandwich panels can be molded, and by combining these, It can be a body. The sandwich panel is a structure in which a metal core material such as an aluminum honeycomb material, a non-metal core material such as an aramid paper honeycomb, or a foam material such as polyurethane foam is sandwiched between skins made of FRP as a core material. .

  As described above, the FRP originally has a laminated structure. For this reason, in the molding process, delamination may occur in the panel or resin impregnation may occur. This is called a defect. From now on, FRP molding technology for large-scale structures is expected to progress, but in the development of large-scale molding technology using FRP, it is essential to ascertain defects in quality assurance. In addition, several techniques are disclosed for the general nondestructive inspection methods, such as a thin plate (for example, patent documents 1-4). In particular, as an inspection method for examining defects in FRP, there is a technique called SIDER (Structural Irregularity and Damage Evaluation Routine) developed by the US Navy Research Institute (for example, Non-Patent Documents 1 and 2).

JP 2002-333436 A JP 2002-340869 A Japanese Patent Laid-Open No. 2003-014708 JP 2003-149214 A Colin P. Rat Cliff et al., “Field Testing and Long Term Monitoring”, 1st Annual CIBrE Bridge Workshop (1st Annual CIBrE Bridge and Bridge Bridge Evaluation) Workshop Annual Report (Bridge Evaluation Workshop), March 1st (March 1st), 2002, University of Delaware (Delaware State University, USA) C. P. Rat Cliffe, R.P. M.M. Crane (J. Crane), J.M. W. JW Gillespie, Damage detection in large composite structures using a broadband method, SAMPE Journal, Vol. 46, SAMPE Journal, Vol. 1, Journal of Advanced Materials Technology (Volume 46, Issue 1), January, 2004, USA

  However, the above-described general nondestructive inspection method is costly and troublesome and is not quantitative. For example, defects can be analyzed by UT (ultrasonic inspection) and X-ray analysis, but at the present time, there are large limitations on cost as well as performance limitations. Coin tapping is effective as an inspection method, but it is a method that only a craftsman can do, lacks quantitativeness, and results in a personal skill. Although the above-mentioned SIDER is effective for defect inspection of FRP, it is unknown how far it is effective for application to a general FRP structure, and further technical improvement is required.

  Therefore, the present invention has been made in view of the above, and a non-destructive inspection method for an FRP structure that can improve the SIDER and make it possible to grasp the defects of the FRP more clearly for a general FRP structure. The purpose is to provide.

  In order to achieve the above-described object, a non-destructive inspection method for an FRP structure according to the present invention uses an impulse hammer to vibrate inspection points provided at regular intervals on an FRP structure to be inspected, and obtains an acceleration. When acquiring the acceleration from the excitation force and the excitation force from the excitation force acquisition means, acquiring the frequency response function at each point, and using the frequency response function at a constant frequency as a function of the position of the inspection point In addition, in the non-destructive inspection method for FRP structures in which the presence or absence of defects is evaluated to a degree that deviates from the low-order polynomial approximation curve, the frequency response function is a frequency response function in the vicinity of the resonance mode.

  The nondestructive inspection method for an FRP structure according to the next invention is such that the frequency response function is obtained from acceleration or displacement in the nondestructive inspection method.

  As described above, according to the non-destructive inspection method for an FRP structure according to the present invention, it is possible to more clearly grasp the defect of the FRP with respect to a general FRP structure by improving SIDER.

  Hereinafter, the present invention will be described in detail with reference to the drawings. Note that the present invention is not limited to the embodiments. In addition, constituent elements in the following embodiments include those that can be easily assumed by those skilled in the art or those that are substantially the same.

  FIG. 1 is an explanatory diagram showing an apparatus configuration of a non-destructive inspection method for an FRP structure according to the present invention. The FRP sandwich panel 1 to be inspected (molded by the VaRTM method) is placed on the flexible urethane foam 2. In this embodiment, the FRP sandwich panel 1 is vibrated with an impulse hammer 4 as a vibration force acquisition means to obtain a vibration force, and the acceleration when the vibration is applied is measured with an acceleration pickup 3 as a acceleration acquisition means. To do.

  An FFT analyzer 7 is used for the measurement. The impulse hammer 4 and the acceleration pickup 3 are connected to the FFT analyzer 7 via a power source and amplifiers 5 and 6, respectively. The FFT analyzer 7 is connected to the personal computer 8 so that the data of the FFT analyzer 7 can be processed.

  FIG. 2 is an explanatory diagram showing measurement points set on the sandwich panel. As an example, a sandwich panel having a size of 1000 × 2000 (mm) was prepared. Then, a grid having a length of 200 (mm) and a width of 200 (mm) is drawn on one side, and basically, the intersection is measured by exciting with an impulse hammer. However, in order to determine whether or not the inspection method is effective, the FRP sandwich panel used here is preliminarily divided into a line A that is a defective line and a B line that is a line that does not have a defect. Shake the intersection of.

  Here, the contents of the nondestructive inspection method of the present invention will be outlined. FIG. 18 is an explanatory diagram showing a general SIDER inspection method. SIDER vibrates the inspection points a to m of the inspection object 11 with an impulse hammer, and conceptually superimposes the data diagram 12 of the frequency response function (FRF) 13 obtained from the acceleration at each point. And each frequency response function 13 in the fixed frequency 14 is caught as a position function of position am. FIG. 19 is an explanatory diagram showing this way of understanding. A function 15 in the figure is a function of positions a to m at a constant frequency.

  FIG. 20 is an explanatory diagram showing the concept of a damage index. The function 15 obtained as described above has a characteristic that can be approximated by a low-order polynomial curve, often a third-order polynomial curve, if there is no defect in the FRP structure to be inspected. Therefore, a cubic polynomial passing through the four points 17, 18, 19, and 20 on each side of the point 16 to be inspected is obtained. In the figure, the polynomial approximate curve is drawn with a dotted line. The degree of the actual frequency response function deviating from the curve (the difference between the two) is the damage index 22. If the damage index 22 is large, it can be considered that there is a defect in the inspection target part.

  FIG. 17 is a flowchart showing the steps of the nondestructive inspection method of the present invention. In this method, as in the case of SIDER, first, a lattice is drawn on the inspection object to mark an intersection (step S101). The marked point is hit / excited with an impulse hammer, and frequency response data is acquired by FFT (steps S102 and S103). Note that it is preferable to obtain an average of five times for acquisition of the frequency response by the impulse hammer and the FFT analyzer.

  In the present invention, not a simple frequency response function, but a vibration mode specific to the FRP structure to be inspected is determined and used for inspection (step S104). While simple frequency response functions tend to vary and high-frequency components are disadvantageous for creating damage indexes, low-order vibration mode shapes are less susceptible to adverse effects due to high-frequency components, and the characteristics of the structure appear more clearly. Cheap. Further, since the low-order vibration mode shape can be expressed even with a small number of data, it is advantageous for calculating a damage index by computer processing.

  Next, the frequency of each mode is determined (step S105). The mode shape is obtained from the imaginary term of the frequency response function of acceleration / excitation force (hereinafter referred to as A / F) (step S106). The reason for obtaining from the imaginary term is that, generally, the mode becomes clearer when looking at the phase delay, and when the real term becomes clearer than the imaginary term, the mode may be obtained from the real term. From here, there are two methods, one of which calculates the damage index for the mode shape obtained from the imaginary term (or the real term in some cases) of the frequency response function of A / F (step S107), This is a method for determining the presence or absence of a defect based on the size. This is optional, but it is convenient to visualize the actual defect position at a glance by visualizing the damage index in different colors according to the inspection location.

  Another method is a method of converting a displacement obtained by integrating acceleration into a displacement / excitation force (hereinafter referred to as X / F) (step S109), and calculating a damage index for the displacement (step S110). ). Since the displacement integrates the acceleration, this has the merit that the variation in high frequency is suppressed and the influence of the low-order mode becomes larger. Also for this, visualization by color coding is effective (step S111).

  The above is the outline of the present invention, which will be described in detail below with specific data. FIG. 3 is a frequency response function obtained from the imaginary term of A / F. The inspection points are a total of 21 points R01 to R21 on the B line in FIG. From this, you can see that the resonance modes overlap. From this, about 10 resonance modes are found, and the calculation frequency is also determined.

  Table 1 shows the determined mode numbers and calculated frequencies. As an example, 10 mode shapes extracted are as shown in FIGS. In these figures, the mode shape of the inspection object clearly appears. In general, the vicinity of the resonance mode means a bandwidth of about 2% to 10% with respect to the resonance frequency.

  FIG. 5 shows a frequency response function when the A / F of FIG. 3 is integrated and converted to X / F. Again, the mode and calculation frequency are determined. These are shown in FIGS. 6-1 to 6-3. Here, although the primary mode appears correctly, the displacement at the inspection points B17 to B21 in the calculation frequency range of 52 Hz to 1 kHz and 52 Hz to 350 Hz, that is, the displacement at the corresponding points in FIGS. 6-1 and 6-2 is obvious. It is excessive and disturbs the overall mode shape.

  FIGS. 7-1 and 7-2 show the phases of the frequency response functions of the inspection points B16, 18, 19 taken out. From this, it was found that the phase measurement at 150 Hz or less is inadequate. Since this point can be solved by preparing support conditions and measurement conditions, large values in B17 to B21 in FIG. 5 are not used for the evaluation of this embodiment.

  The above is the result of mode shape acquisition in the B line without defects in the FRP sandwich panel to be inspected. Next, the measurement results on the defective A line will be described. FIG. 8 is a function obtained from the imaginary term of the A / F frequency response function of the A line. Similar to the B line, the inspection points are A01 to A21 in the A line for a total of 21 points. From this, about ten resonance modes according to the present invention are found, and the calculation frequency is also determined.

  Table 2 shows the determined mode numbers and calculated frequencies. Ten mode shapes taken out as an example are as shown in FIGS. 9-1 to 9-10. As with the B line, the mode shape of the inspection object clearly appears.

  FIG. 10 shows a frequency response function when the A / F of FIG. 8 is integrated and converted to X / F. Again, the mode and calculation frequency are determined. These are shown in FIGS. 11-1 and 11-2. Here, the displacement at A20 is not smooth with the displacement at the surrounding positions. As shown in FIG. 12, the imaginary term of A / F and X / F should be a + or − peak, and the value of A20 in FIGS. Sex was considered.

  Therefore, when the frequency response function in the low frequency range is expanded as shown in FIG. 13, A20 and A21 do not start with 0 and do not end with 0. This is considered to be the cause of the displacement of A20, and this point can be eliminated by preparing support conditions and measurement conditions. Therefore, the value of A20 in FIGS. It was decided not to use it.

  FIGS. 14A and 14B are one of 100 Hz to 1 kHz mode shapes that can be found from the real terms of the frequency response functions in the A line and the B line, respectively. Thus, when the mode shape from the imaginary term of the frequency response function cannot be successfully acquired due to the relationship with the phase, the X / F of 100 Hz to 1 kHz with less influence of the phase and less influence of the high frequency. The mode shape may be acquired from the real term.

  FIGS. 15A and 15B are graphs showing damage indexes that can be found from low-order mode shapes in the A line and the B line, respectively. However, A20 and A21 are excluded as described above. Looking at this, the damage index is large at the portion of the defect (see FIG. 3) in A11 to A13 of the A line, and the defect can be discriminated. The B line itself is not on the defect, but there is a defect in the vicinity of B17 and B18 (see FIG. 3), which also appears well in the damage index of FIG. 15-2.

  FIGS. 16A and 16B are damage indexes that can be found from the real terms of the frequency response functions in the A line and the B line, respectively. The damage index is calculated from the sum of X / F of 100 Hz to 1 kHz with less influence of the phase and less influence on the high frequency side. From this, it can be seen that defective A07 to A12 are very large, and B17 and 18 are also large.

  Therefore, it was found that the defect position to be inspected can be determined even by taking the damage index for the mode that can be found from the real term of the frequency response function. In addition, it was found that the method for obtaining the damage index by this method and the method for obtaining the damage index in the mode obtained from the imaginary term described above differ in the size and depth of the sensitive defect. Therefore, it is also effective to use both in combination.

  Thus, according to the non-destructive inspection method for an FRP structure according to the present invention, the degree of defects can be quantified by an index called a damage index that can be found from the vibration mode, and the location and degree can also be visualized. If the damage index is calculated from vibration modes, especially lower-order vibration modes, the vibration mode, which is the original data, is less susceptible to high frequency than the damage index is calculated from a simple frequency response function. Tends to be clearer.

  In addition, since the low-order vibration mode can be expressed with a small amount of data, the burden of the damage index calculation process can be reduced. When the inspection target is a large FRP structure, the number of inspection points becomes enormous, so the property that the burden of arithmetic processing is light is very effective. Moreover, since the instrument used for the inspection is small, such as an impulse hammer, an acceleration pickup, and FFT, it can be easily inspected on site. If this is used, it will be effective for defect inspection of FRP used for the superstructure of the large ship in the dock and the enclosure mast.

  As described above, the non-destructive inspection method for an FRP structure according to the present invention is useful for grasping a defect portion such as a peeling that occurs inside the FRP structure, and in particular, a defect of an FRP panel also used for a large ship. Suitable for grasping locations.

It is explanatory drawing which shows the apparatus structure of the nondestructive inspection method of the FRP structure which concerns on this invention. It is explanatory drawing which shows the measurement point set on the sandwich panel. It is a figure which shows the frequency response function obtained from the imaginary term of A / F. It is the bar graph which shows the determined mode shape, a horizontal axis is an inspection point, and a vertical axis | shaft is a magnitude | size. It is the bar graph which shows the determined mode shape, a horizontal axis is an inspection point, and a vertical axis | shaft is a magnitude | size. It is the bar graph which shows the determined mode shape, a horizontal axis is an inspection point, and a vertical axis | shaft is a magnitude | size. It is the bar graph which shows the determined mode shape, a horizontal axis is an inspection point, and a vertical axis | shaft is a magnitude | size. It is the bar graph which shows the determined mode shape, a horizontal axis is an inspection point, and a vertical axis | shaft is a magnitude | size. It is the bar graph which shows the determined mode shape, a horizontal axis is an inspection point, and a vertical axis | shaft is a magnitude | size. It is the bar graph which shows the determined mode shape, a horizontal axis is an inspection point, and a vertical axis | shaft is a magnitude | size. It is the bar graph which shows the determined mode shape, a horizontal axis is an inspection point, and a vertical axis | shaft is a magnitude | size. It is the bar graph which shows the determined mode shape, a horizontal axis is an inspection point, and a vertical axis | shaft is a magnitude | size. It is the bar graph which shows the determined mode shape, a horizontal axis is an inspection point, and a vertical axis | shaft is a magnitude | size. It is a figure which shows the frequency response function when A / F of FIG. 3 is integrated and converted into X / F. It is a bar graph which shows the determined mode shape, a horizontal axis is a place and a vertical axis | shaft is a displacement. It is a bar graph which shows the determined mode shape, a horizontal axis is a place and a vertical axis | shaft is a displacement. It is a bar graph which shows the determined mode shape, a horizontal axis is a place and a vertical axis | shaft is a displacement. It is the graph which took out the frequency response function of test | inspection point B16,18,19, and showed the phase, A horizontal axis is a frequency and a vertical axis | shaft is a magnitude | size of the imaginary term of X / F. It is the graph which took out the frequency response function of inspection point B16,18,19, and showed the phase, a horizontal axis is a frequency and a vertical axis | shaft is a magnitude | size of the phase of A / F. It is a figure which shows the frequency response function obtained from the imaginary term of A / F of A line. It is the bar graph which shows the determined mode shape, a horizontal axis is an inspection point, and a vertical axis | shaft is a magnitude | size. It is the bar graph which shows the determined mode shape, a horizontal axis is an inspection point, and a vertical axis | shaft is a magnitude | size. It is the bar graph which shows the determined mode shape, a horizontal axis is an inspection point, and a vertical axis | shaft is a magnitude | size. It is the bar graph which shows the determined mode shape, a horizontal axis is an inspection point, and a vertical axis | shaft is a magnitude | size. It is the bar graph which shows the determined mode shape, a horizontal axis is an inspection point, and a vertical axis | shaft is a magnitude | size. It is the bar graph which shows the determined mode shape, a horizontal axis is an inspection point, and a vertical axis | shaft is a magnitude | size. It is the bar graph which shows the determined mode shape, a horizontal axis is an inspection point, and a vertical axis | shaft is a magnitude | size. It is the bar graph which shows the determined mode shape, a horizontal axis is an inspection point, and a vertical axis | shaft is a magnitude | size. It is the bar graph which shows the determined mode shape, a horizontal axis is an inspection point, and a vertical axis | shaft is a magnitude | size. It is the bar graph which shows the determined mode shape, a horizontal axis is an inspection point, and a vertical axis | shaft is a magnitude | size. It is a figure which shows the frequency response function when A / F of FIG. 8 is integrated and converted into X / F. It is a bar graph which shows the determined mode shape, a horizontal axis is a place and a vertical axis | shaft is a magnitude | size. It is a bar graph which shows the determined mode shape, a horizontal axis is a place and a vertical axis | shaft is a magnitude | size. It is a graph which shows the magnitude | size of the imaginary term of general A / F and X / F, a horizontal axis is a frequency and the vertical axis | shaft of an imaginary term is a magnitude | size. It is a graph which shows the magnitude | size of the A / F imaginary term in a low frequency range, a horizontal axis is a frequency and a vertical axis | shaft is a magnitude | size of an imaginary term. It is a graph which shows the mode shape of 100Hz-1kHz which can be found from the real term of the frequency response function in A line, a horizontal axis is a position and a vertical axis is a size of X / F. It is a graph which shows the mode shape of 100 Hz-1 kHz which can be found from the real number term of the frequency response function in B line, a horizontal axis is a position and a vertical axis | shaft is a magnitude | size of X / F. It is the graph which showed the damage index which can be found from the mode shape in A line, a horizontal axis is a place and a vertical axis | shaft is the magnitude | size of a damage index. It is the graph which showed the damage index which can be found from the mode shape in B line, a horizontal axis is a place and a vertical axis is a size of a damage index. It is the graph which showed the damage index which can be found from the mode shape obtained from the real term of the frequency response function in A line, a horizontal axis is a place, and a vertical axis is a size of a damage index. It is the graph which showed the damage index which can be found from the mode shape obtained from the real term of the frequency response function in B line, a horizontal axis is a place, and a vertical axis is a size of a damage index. It is a flowchart which shows the process of the nondestructive inspection method of this invention. It is explanatory drawing which shows the inspection method of a general SIDER. It is explanatory drawing which shows the concept which catches a frequency response function as a position function. It is explanatory drawing which shows the concept of a damage index.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Sandwich panel 2 Flexible urethane foam 3 Acceleration pick-up 4 Impulse hammer 5 Amplifier 6 Power supply 7 Analyzer 8 Personal computer 11 Test object 12 Data figure 13 Frequency response function 14 Frequency 15 Position function 22 Damage index

Claims (2)

The inspection points provided at regular intervals on the FRP structure to be inspected are vibrated with an impulse hammer, and the acceleration from the acceleration acquisition means and the excitation force from the excitation force acquisition means are acquired. get the frequency response function of the acceleration / exciting force at point, when the frequency response function of the acceleration / vibration force at a constant frequency as a function of the position of the inspection point, out of the low-order polynomial trendline In the non-destructive inspection method for FRP structures that evaluates the presence or absence of defects by the degree
A non-destructive inspection method for an FRP structure, wherein the frequency response function of the acceleration / excitation force is a frequency response function in the vicinity of a resonance mode. The non-destructive inspection method for an FRP structure according to claim 1, wherein the frequency response function of the acceleration / excitation force is obtained from acceleration or displacement.

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