Inspection method for composite structure or composite structural material

Abstract

To provide an inspection method for composite structures or composite structural materials for easily evaluating soundness of a composite structure or a composite structural material by non-destructively inspecting it.SOLUTION: An inspection method for composite structures or composite structural materials for easily evaluating soundness of a composite structure or a composite structural material by non-destructively inspecting it, the inspection method for composite structures or composite structural materials includes: externally vibrating a surface of the composite structure or the composite structural material as an inspection subject to acquire a feature quantity of a preset evaluation index; and then, evaluating soundness of the composite structure or the composite structural material based on a reference amount of the evaluation index obtained from the composite structure or the composite structural material known to be in a sound state.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a method for inspecting a composite structure or a composite structural material, and more particularly to a method for inspecting a composite structure or a composite structural material for non-destructively inspecting for the presence or absence of abnormalities in a composite structure formed by laminating a plurality of structural materials, a composite structural material formed by laminating a plurality of materials, or a composite structural material formed from a plurality of matrix materials. [Background technology]

[0002] For structures such as incinerators, ducts, and tanks, it is necessary to conduct non-destructive inspections on a regular or irregular basis to check for the occurrence of abnormalities, such as a deterioration in physical properties or the occurrence of cavities, in order to evaluate their soundness from the perspective of construction management and aging management.

[0003] These structures are generally formed by laminating a plurality of structural materials with different characteristics (composite structures) so as to meet the required characteristics.

[0004] For example, an incinerator is made of an inner fireproof material and an outer steel casing (can body) to withstand high temperatures during incineration and to prevent gases and ash from being emitted to the outside. In addition, ducts and tanks may be lined with liners to prevent corrosion of the main body.

[0005] Additionally, composite structures using metal / metal composites such as bimetals and clad materials, resin / resin composites, wood / wood composites, metal / concrete composites, metal / ceramic composites, metal / resin composites, ceramic / resin composites, etc. also exist in a wide range of fields.

[0006] When attempting to carry out the above-mentioned non-destructive inspection of soundness assessment for such composite structures, unlike structures made of a single material, it is necessary to inspect both the outer and inner surfaces, in addition to the condition of each layer (physical properties, structural soundness such as cracks and cavities) and the condition of the interfaces between each layer (adhesion, peeling, etc.), which is not an easy task.

[0007] For example, in the case of an incinerator, it is not easy to inspect it from the inside, and in particular, in the case of an incinerator that processes waste contaminated with radioactive materials, it is difficult to inspect it from the inside, considering the risk of radiation exposure to the inspector.

[0008] Therefore, currently, corrosion thinning of the outer casing (can body) is measured using an ultrasonic thickness gauge with a probe of approximately φ10 mm. However, since this method involves selecting a representative point and measuring the thickness directly below the probe, it requires a great deal of effort to measure the entire surface of a large area of ​​the outer casing (can body), and it cannot be said to be an efficient inspection method.

[0009] In addition, visual inspection using a fiberscope is used as a method of inspecting incinerators for waste contaminated with radioactive materials from the inside. However, although it is possible to confirm abnormalities such as cracks on the surface of the inner fireproofing material, it is not easy to grasp the progression of cracks inside the fireproofing material, and it is not possible to confirm the adhesion at the interface between the inner fireproofing material and the outer steel casing (can body), which promotes corrosion of the outer steel casing (can body).

[0010] Similarly, it is not easy to check from the outside the condition of the ducts lined with a liner, the tank body, or the condition of the interface between the body and the liner, so at present these are checked from the inside using a fiberscope.

[0011] On the other hand, although they are not composite structures, there are composite structural materials formed by laminating multiple materials such as a cable, a core wire, an insulating material, and a coating material, and composite structural materials formed from multiple matrix materials, such as FRP (Fiber Reinforced Plastics) formed with resin and fiber (glass fiber or carbon fiber) as the matrix material. There are also composite structures that use these composite structural materials.

[0012] Even in such composite structural materials, it is not easy to inspect the condition of each layer and the condition of the interfaces between each layer, or the condition of each matrix material and the condition of the interfaces between each matrix material.

[0013] Furthermore, assessing the integrity of composite structures using these composite materials is more difficult.

[0014] As such, it is not easy to non-destructively inspect the condition of each layer and the interface between layers in a composite structure or composite structural material, or the condition of each matrix and the interface between each matrix in a composite structural material, to evaluate their soundness, and further technological development is desired.

[0015] The present inventors have previously proposed techniques for evaluating the soundness of structures with embedded metal components such as anchors and PC structures (e.g., Patent Documents 1 to 4). However, these techniques are limited to evaluating the soundness of each component that ultimately constitutes a composite structure, and do not inspect the condition of each layer or the condition of the interfaces between layers. [Prior art documents] [Patent documents]

[0016] [Patent Document 1] JP 2015-45637 A [Patent Document 2] JP 2016-24069 A [Patent Document 3] JP 2017-219534 A [Patent Document 4] JP 2019-132658 A Summary of the Invention [Problem to be solved by the invention]

[0017] In view of the problems in the conventional technology described above, an object of the present invention is to provide an inspection method for a composite structure or composite structural material that non-destructively inspects the composite structure or composite structural material and easily evaluates its soundness. [Means for solving the problem]

[0018] As a result of extensive research, the present inventors have found that the above-mentioned problems can be solved by the following inventions, and have completed the present invention.

[0019] The invention described in claim 1 is A method for inspecting a composite structure or a composite structural material in a non-destructive manner to evaluate the soundness of the composite structure or the composite structural material, comprising the steps of: The surface of the composite structure or composite structural material to be inspected is externally vibrated to obtain feature quantities for a preset evaluation index, and then This is a method for inspecting a composite structure or composite structural material, characterized in that the soundness of the composite structure or composite structural material is evaluated based on a reference amount of the evaluation index obtained from a composite structure or composite structural material known to be in a sound state.

[0020] The invention described in claim 2 is The composite structure is a multi-layer composite structure formed by stacking a plurality of structural materials, obtaining a feature quantity for a preset evaluation index from a vibration waveform obtained by externally vibrating a surface of the composite structure to be inspected, or from a frequency distribution obtained by converting the vibration waveform; The method for inspecting a composite structure or composite structural material as described in claim 1, characterized in that the soundness of the condition of each layer of the composite structure to be inspected and the condition of the interface between each layer are evaluated based on the obtained characteristic amount of the evaluation index and a reference amount of the evaluation index obtained from a composite structure known to be in a sound state.

[0021] The invention described in claim 3 is The composite structural material is a composite structural material formed by laminating a plurality of materials, Obtaining a feature quantity for a preset evaluation index from a vibration waveform obtained by externally vibrating a surface of the composite structural material to be inspected, or from a frequency distribution obtained by converting the vibration waveform; The method for inspecting a composite structure or composite structural material as described in claim 1, characterized in that the soundness of the condition of each layer of the composite structural material to be inspected and the condition of the interface between each layer are evaluated based on the obtained characteristic amount of the evaluation index and a reference amount of the evaluation index obtained from a composite structural material known to be in a sound state.

[0022] The invention described in claim 4 is The composite structural material is a composite structural material formed from a plurality of matrix materials, Obtaining a feature quantity for a preset evaluation index from a vibration waveform obtained by externally vibrating a surface of the composite structural material to be inspected, or from a frequency distribution obtained by converting the vibration waveform; The method for inspecting a composite structure or composite structural material as described in claim 1, characterized in that the condition of each matrix material of the composite structural material being inspected and the soundness of the interface between each matrix material are evaluated based on the obtained characteristic amount of the evaluation index and the reference amount of the evaluation index obtained from a composite structural material known to be in a sound state.

[0023] The invention described in claim 5 is 5. A method for inspecting a composite structure or a composite structural material according to claim 1, characterized in that the vibration is performed at one or more selected points on the surface of the composite structural material to be inspected.

[0024] The invention described in claim 6 is 5. The method for inspecting a composite structure or a composite structural material according to claim 1, wherein the striking is performed using a test hammer.

[0025] The invention described in claim 7 is The method for inspecting a composite structure or composite structural material according to any one of claims 2 to 4, characterized in that the vibration waveform is acquired using one of an AE sensor, an acceleration sensor, a displacement sensor, a microphone, and a laser displacement sensor.

[0026] The invention described in claim 8 is 5. The method for inspecting a composite structure or a composite structural material according to claim 2, wherein a feature obtained from a vibration waveform is used as the feature of the evaluation index.

[0027] The invention described in claim 9 is 5. The method for inspecting a composite structure or a composite structural material according to claim 2, wherein the frequency distribution is acquired by subjecting the vibration waveform to a fast Fourier transform.

[0028] The invention described in claim 10 is 5. The method for inspecting a composite structure or a composite structural material according to claim 2, wherein a feature amount obtained from the frequency distribution is used as the feature amount of the evaluation index.

[0029] The invention described in claim 11 is 5. An inspection method for a composite structure or composite structural material according to claim 2, characterized in that the evaluation of the soundness of the composite structure or composite structural material is performed based on the degree of deviation of a feature of the evaluation index obtained from the vibration waveform or the frequency distribution from a reference value of the evaluation index.

[0030] The invention described in claim 12 is The method for inspecting a composite structure or a composite structural material according to any one of claims 1 to 4, characterized in that, when evaluating the soundness, a reference amount of the evaluation index is set by a mock-up test or a simulation.

[0031] The invention described in claim 13 is 5. An inspection method for a composite structure or composite structural material as described in any one of claims 1 to 4, characterized in that when evaluating the soundness, the standard amount of the evaluation index is set based on either the state of the composite structure or composite structural material being inspected immediately after installation or maintenance, the state of a portion where deterioration is not expected to progress, or a relative comparison of the states.

[0032] The invention described in claim 14 is In the case where the evaluation of the soundness is an evaluation of the soundness against poor construction or deterioration, 5. The method for inspecting a composite structure or a composite structural material according to claim 1, wherein the reference amount of the evaluation index is set by a mock-up test or a simulation.

[0033] The invention described in claim 15 is In the case where the evaluation of the soundness is an evaluation of the soundness against poor construction or deterioration, The method for inspecting a composite structure or a composite structural material according to any one of claims 1 to 4, characterized in that the reference amount of the evaluation index is set based on the state of the composite structure or composite structural material to be inspected immediately after installation or maintenance.

[0034] The invention described in claim 16 is The method for inspecting a composite structure or composite structural material according to any one of claims 1 to 4, characterized in that the soundness of the composite structure or composite structural material to be inspected over its entire surface is evaluated by creating a contour diagram based on the characteristic quantities of the evaluation index over the entire surface of the composite structure or composite structural material to be inspected.

[0035] The invention described in claim 17 is as follows: The method for inspecting a composite structure or a composite structural material according to any one of claims 1 to 4, characterized in that, when evaluating the soundness of the composite structure or the composite structural material, a reference amount of the evaluation index is obtained from the results of AI learning.

[0036] The invention described in claim 18 is The method for inspecting a composite structure or composite structural material according to claim 17, characterized in that the AI ​​learning is any one of machine learning, deep learning, supervised learning, and unsupervised learning. Effect of the Invention

[0037] According to the present invention, it is possible to provide a method for inspecting a composite structure or composite structural material, which allows for non-destructive inspection of the composite structure or composite structural material and for easily evaluating its soundness. [Brief description of the drawings]

[0038] [Figure 1] FIG. 11 is a diagram showing an example of a vibration waveform acquired by striking. [Diagram 2] FIG. 13 is a diagram illustrating vibration duration. [Diagram 3] FIG. 13 is a diagram showing an example of a frequency distribution converted from a vibration waveform. [Figure 4] FIG. 2 is a diagram showing an example of the relationship between the time domain and the frequency domain by wavelet transform of a vibration waveform. [Diagram 5]FIG. 1A is a diagram for explaining how vibrations caused by striking are diffused and attenuated in the steel casing (can body) and the fireproof material in the first embodiment when there is no corrosion on the steel casing (can body) and the fireproof material is in a sound condition, (b) is a diagram showing a frequency analysis obtained by striking, and (c) is a diagram showing a vibration waveform obtained by striking. [Figure 6] FIG. 1A is a diagram for explaining how vibrations caused by striking are diffused and attenuated in the steel casing (can body) and the fireproof material in a state in which there is slight corrosion in the steel casing (can body) and cracks in the fireproof material in the first embodiment; FIG. 1B is a diagram showing a frequency analysis obtained by striking; and FIG. 1C is a diagram showing the vibration waveform obtained by striking. [Figure 7] FIG. 1 shows, in the first embodiment, a state in which the steel casing (can body) is significantly corroded and cracks have developed in the fireproof material, (a) a diagram explaining how vibrations caused by striking are diffused and attenuated in the steel casing (can body) and the fireproof material, (b) a diagram showing a frequency analysis obtained by striking, and (c) a diagram showing a vibration waveform obtained by striking. [Figure 8] FIG. 11 is a schematic perspective view showing the configuration of a peeling simulation specimen produced using a composite material of metal (steel) and resin (FRP) in the second embodiment. [Figure 9] This is a frequency distribution obtained by striking a sound specimen similar to the peeling simulated specimen shown in Fig. 8. [Figure 10] This is the frequency distribution obtained by striking the peeling simulation specimen shown in Figure 8. [Figure 11] This is a frequency distribution obtained by vibrating a healthy part of a duct lined with a resin in the third embodiment. [Figure 12] This shows a frequency distribution obtained by vibrating a portion of a duct lined with a resin material, where separation had occurred, in the third embodiment. [Figure 13] In the fourth embodiment, this is a frequency distribution obtained by vibrating a location where peeling is definitely occurring (peeled portion 1) and the opposite surface where no peeling has occurred (sound portion 1). [Figure 14]In the fourth embodiment, this is a frequency distribution obtained by vibrating a portion (peeled portion 2) which may show signs of peeling and its opposite surface (sound portion 2) where no peeling has occurred. [Figure 15] FIG. 13 is a schematic perspective view showing an inspection method for an FRP plate material in the fifth embodiment. [Figure 16] FIG. 16 is a diagram showing the relationship between the fatigue count and the evaluated peak frequency obtained in the FRP plate material shown in FIG. [Figure 17] FIG. 23 is a schematic plan view illustrating a location where a strike is performed in the sixth embodiment. [Figure 18] FIG. 23 is a contour diagram showing the measurement results in which vibration duration is used as an evaluation index in the sixth embodiment. [Figure 19] FIG. 23 is a contour diagram showing a measurement result in which the natural frequency is used as an evaluation index in the sixth embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0039] [1] Basic concept of the present invention 1. Overview of the Invention The present invention is an inspection method for a composite structure or composite structural material that non-destructively inspects the composite structure or composite structural material to evaluate its soundness, in which the surface of the composite structure or composite structural material to be inspected is externally vibrated to obtain characteristic quantities for predetermined evaluation indexes, and then the soundness of the composite structure or composite structural material is evaluated based on the reference quantities of the evaluation indexes obtained from a composite structure or composite structural material that is known to be in a sound state.

[0040] That is, when the object to be inspected is a composite structure consisting of multiple layers formed by stacking multiple structural materials, feature quantities for a predetermined evaluation index are obtained from a vibration waveform obtained by externally vibrating the surface of the composite structure to be inspected, or from a frequency distribution obtained by converting the vibration waveform, and the condition of each layer of the composite structure to be inspected and the condition of the interfaces between each layer are evaluated based on the feature quantities of the evaluation index obtained and reference quantities of the evaluation index obtained from a composite structure known to be in a healthy state.

[0041] When the object to be inspected is a composite structural material formed by stacking multiple materials such as a cable, feature quantities for a predetermined evaluation index are obtained from a vibration waveform obtained by externally vibrating the surface of the composite structural material to be inspected, or from a frequency distribution obtained by converting the vibration waveform, and the soundness of the condition of each layer of the composite structural material to be inspected and the condition of the interfaces between each layer are evaluated based on the feature quantities of the evaluation index obtained and reference quantities of the evaluation index obtained from a composite structural material known to be in a sound state.

[0042] In addition, when the inspection object is a composite structural material formed from multiple matrix materials such as FRP, feature quantities for a predetermined evaluation index are obtained from a vibration waveform obtained by externally vibrating the surface of the composite structural material to be inspected, or from a frequency distribution obtained by converting the vibration waveform, and the state of each matrix material of the composite structural material to be inspected and the soundness of the interface between each matrix material are evaluated based on the feature quantities of the evaluation index obtained and the reference quantities of the evaluation index obtained from a composite structural material known to be in a sound state.

[0043] By adopting such an inspection method for a composite structure or composite structural material, the condition of each layer of the composite structure or composite structural material and the condition of the interfaces between each layer, or the condition of each matrix in the composite structural material and the condition of the interfaces between each matrix, can be non-destructively inspected, and its soundness can be easily evaluated.

[0044] 2. Mechanism of the method for inspecting a composite structure or composite structural material according to the present invention The mechanism of the inspection method for a composite structure or composite structural material according to the present invention can be considered as follows: In the present invention, the mechanism of a composite structural material formed by laminating a plurality of materials such as the above-mentioned cable, and the mechanism of a composite structural material formed from a plurality of matrix materials such as FRP can be considered to be substantially the same as the mechanism of a composite structure consisting of multiple layers formed by laminating a plurality of structural materials, so that the following description will basically be given along with a composite structure consisting of multiple layers formed by laminating a plurality of structural materials.

[0045] (1) Evaluation based on vibration waveform By externally vibrating the surface of the composite structure to be inspected, a vibration waveform of the composite structure to be inspected can be obtained.

[0046] An example of the acquired vibration waveform is shown in Figure 1. In Figure 1, the vertical axis represents amplitude (mV) and the horizontal axis represents the elapsed time (sec) from the start of vibration, and it can be seen that the vibration attenuates over time.

[0047] At this time, if an abnormality (such as a crack, cavity, or peeling) occurs in the state of each layer or in the state of the interface between layers in the composite structure, the damping time changes as will be described in the "Specific embodiment" below, and since this change in damping time is related to the degree of occurrence of the abnormality, the occurrence status of the abnormality can be known by measuring the time that the vibration continues (vibration duration). In other words, the vibration duration can be used as a feature of the evaluation index.

[0048] Specifically, as shown in Figure 2, the time required for the amplitude to decrease to X% (e.g., 10%) of the maximum value is defined as the vibration duration, and the vibration duration is used as the feature of the evaluation index. By comparing it with a preset standard vibration duration (diagnosis standard), the degree of abnormality that has occurred in the target composite structure can be known.

[0049] In the above, the vibration duration is used as a feature of the evaluation index. However, other features obtained from the vibration waveform, such as the maximum amplitude width, the S / N ratio, the number of peaks exceeding a preset threshold, the average amplitude, the standard deviation of the amplitude, and the amplitude distribution, are also related to the degree of occurrence of the abnormality, similar to the vibration duration, and therefore may be used as a feature of the evaluation index and a diagnostic criterion.

[0050] In the present invention, it is preferable to use a test hammer that is generally used for tapping inspection, is light in weight, and is easy to carry, but there is no particular limitation as long as it is a hammer that can apply vibration to the target and obtain a vibration waveform, such as a plastic hammer, a rubber hammer, a wooden hammer, an iron hammer other than a test hammer, or a tapping rod with a steel ball attached to the tip. Instead of tapping, a specific frequency may be input as an elastic wave using a piezoelectric element, a laser, or the like.

[0051] In addition, when acquiring the vibration waveform, it is preferable to use an AE (Acoustic Emission) sensor from the viewpoint of acquiring the generated vibration with high accuracy, but an acceleration sensor, a displacement sensor, a microphone, or a laser displacement sensor may also be used.

[0052] (2) Evaluation based on frequency distribution A frequency distribution can be obtained by performing a fast Fourier transform on the vibration waveform acquired by striking.

[0053] An example of a frequency distribution converted from a vibration waveform is shown in Figure 3. In Figure 3, the vertical axis is the vibration intensity (Magnitude: au [arbitrary unit]), the horizontal axis is the frequency (Frequency: Hz), and the maximum peak frequency is defined as the natural frequency.

[0054] In this case, if an abnormality (such as a crack, cavity, or peeling) occurs in the state of each layer or in the state of the interface between layers in the composite structure, the natural frequency changes as described in the "specific embodiment" below, and since this change is related to the degree of occurrence of the abnormality, the occurrence state of the abnormality can be known by measuring the natural frequency and comparing it with a preset standard natural frequency (diagnosis standard). In other words, the natural frequency can be used as a feature of the evaluation index.

[0055] In addition, other features obtained from the frequency distribution, such as the area, center of gravity, S / N ratio, natural vibration peak, number of natural vibration peaks, natural vibration peak in a pre-set frequency range, and number of natural vibration peaks in a pre-set frequency range, are also related to the degree of occurrence of the abnormality, similar to the natural vibration frequency, and therefore may be used as features of the evaluation index and diagnostic criteria.

[0056] In addition, a feature quantity shown in the relationship between the time domain and the frequency domain, which can be obtained by the wavelet transformation or the short time Fourier transformation (STFT) of the vibration waveform, is also related to the degree of occurrence of an abnormality, similar to the natural frequency, and may be used as a feature quantity of an evaluation index and a diagnostic criterion. FIG. 4 shows an example of a feature quantity shown in the relationship between the time domain and the frequency domain by the wavelet transformation. In FIG. 4, the horizontal axis indicates the elapsed time (sec) from the time of vibration application, and the vertical axis indicates the frequency (Hz), and the change in amplitude (au) in the time domain and the frequency domain is shown.

[0057] (3) Establishment of diagnostic criteria In the present invention, the diagnostic criteria are set in advance, taking into consideration the material and shape constituting the composite structure to be inspected.

[0058] That is, in order to inspect and evaluate the occurrence of anomalies in a composite structure, a selection is made among the above-mentioned evaluation indexes prior to the inspection, and a diagnostic criterion corresponding to the selected evaluation index is then set.

[0059] The diagnostic criteria can be set, for example, by any of the methods (i) to (v) described below. (i) Using a mock-up specimen fabricated in the same manner as the composite structure to be inspected, the evaluation indexes are measured, and the values ​​are set as diagnostic criteria. (ii) A composite structure to be inspected is created by simulation, an evaluation index is obtained, and the value is set as a diagnostic criterion. (iii) When a facility is newly installed or immediately after maintenance, the evaluation indexes are measured and the measured values ​​are set as diagnostic criteria. (iv) In the composite structure to be inspected, the evaluation index is measured at a portion where it is reasonably assumed that no abnormality such as deterioration has occurred, and the measured value is set as the diagnostic criterion. (v) In the composite structure to be inspected, the evaluation index is measured at multiple locations, and the values ​​are compared relative to each other to set diagnostic criteria.

[0060] The above (i) to (iii) are applicable to diagnostic criteria for soundness evaluation, as well as diagnostic criteria for various construction defects and various deteriorations, and (iv) and (v) are applicable as diagnostic criteria for soundness evaluation.

[0061] In the present invention, based on the above-mentioned evaluation indexes, the relative changes and aging changes of representative points or the entire surface of the composite structure being inspected are measured as characteristic quantities of the evaluation indexes, and analyzed based on the diagnostic criteria, thereby making it possible to evaluate abnormalities (e.g., cracks, cavities, peeling, etc.) in the condition of each layer and the condition of the interfaces between each layer.

[0062] In this case, the shaking work can be performed at many locations in a short period of time, and analysis and evaluation can be performed objectively based on the characteristics of the evaluation index and the diagnostic criteria. Therefore, even the entire concrete construction surface over a large area can be evaluated efficiently and in a short period of time without being influenced by the skill or subjectivity of the inspector.

[0063] [2] Specific embodiments Based on the above-mentioned "basic concept of the present invention," specific embodiments of various composite structures or composite structural materials will be described below.

[0064] 1. First embodiment In this embodiment, the soundness evaluation of an incinerator composed of an inner refractory material and an outer steel casing (can body) is performed as follows: (1) There is no corrosion on the steel casing (can body) and the refractory material is in good condition. (2) The steel casing (can body) has slight corrosion and the fireproofing material has cracks. (3) The steel casing (can body) is significantly corroded and cracks have developed in the fireproofing material. The applicability of the above-mentioned [basic concept of the present invention] will be specifically explained in three cases. Note that, here, the peak shape and natural frequency are adopted as the evaluation index based on the frequency distribution, and the vibration duration is adopted as the evaluation index based on the vibration waveform.

[0065] (1) There is no corrosion on the steel casing (can body) and the refractory material is in good condition. FIG. 5 shows (a) a diagram explaining how vibrations caused by striking are diffused and attenuated in the steel casing (can body 1) and the fireproof material 2 when there is no corrosion in the steel casing (can body) and the fireproof material 2 is in good condition, (b) a diagram showing a frequency analysis obtained from the striking, and (c) a diagram showing the vibration waveform obtained from the striking.

[0066] As shown in Figure 5(a), when there is no corrosion on the steel casing (can body) and the fireproofing is in good condition, i.e., when the interface between the steel casing (can body) and the fireproofing is in close contact and corrosive gas does not reach the steel casing (can body), the vibration caused by the striking is diffused and attenuated in the steel casing (can body) and the fireproofing. Therefore, as shown in Figure 5(b), a broad peak appears in the frequency distribution (natural frequency: 7331 Hz). And, since the vibration transmitted to the fireproofing is attenuated instantly, the vibration duration is short (1.89 ms) as shown in Figure 5(c).

[0067] (2) The steel casing (can body) has slight corrosion and the fireproofing material has cracks. FIG. 6 shows (a) a diagram explaining how vibrations caused by striking are diffused and attenuated in the steel casing (can body) and the fireproof material when there is slight corrosion in the steel casing (can body) and cracks in the fireproof material, (b) a diagram showing a frequency analysis obtained from the striking, and (c) a diagram showing the vibration waveform obtained from the striking.

[0068] As shown in Fig. 6(a), when there is slight corrosion in the steel casing (can body) and cracks in the fireproofing, i.e., when the interface between the steel casing (can body) and the fireproofing is peeled off and corrosive gas reaches the steel casing (can body) through the cracks in the fireproofing, the vibration caused by the striking resonates in the steel casing (can body). As a result, as shown in Fig. 6(b), a sharp natural vibration peak of the steel casing (can body) appears in the frequency distribution (natural frequency: 7873 Hz). As shown in Fig. 6(c), the vibration duration is longer than in case (1) (5.35 ms) due to the vibration caused by the striking resonating in the steel casing (can body).

[0069] In addition, if corrosion products adhere to the interface between the steel casing (can body) and the fireproof material after corrosion has occurred, the vibration duration may be shortened. Therefore, a different evaluation index is adopted in accordance with the actual corrosion form in addition to the evaluation index based on the vibration waveform.

[0070] (3) The steel casing (can body) is significantly corroded and cracks have developed in the fireproofing material. FIG. 7 shows (a) a diagram explaining how vibrations caused by striking are diffused and attenuated in the steel casing (can body) and the fireproofing material when there is significant corrosion in the steel casing (can body) and cracks have developed in the fireproofing material, (b) a diagram showing a frequency analysis obtained from the striking, and (c) a diagram showing the vibration waveform obtained from the striking.

[0071] As shown in Fig. 7(a), when the steel casing (can body) has slight corrosion and the fireproofing has cracks, that is, when the interface between the steel casing (can body) and the fireproofing has peeled off and the corrosion of the can body has progressed due to corrosive gas, the thickness of the steel casing (can body) decreases and flexural vibration of the steel casing (can body) occurs. As a result, the natural frequency calculated by (Formula 1) decreases, and a sharp natural frequency peak appears on the low frequency side as shown in Fig. 7(b) (natural frequency: 3131 Hz).

[0072]

number

[0073] In the above formula (1), f is the natural frequency (Hz), E is Young's modulus (Pa), and ρ is density (kg / m 3 ), a and b are the planar dimensions of the defect (m), h is the thickness of the plate (can body) (m), ν is Poisson's ratio, and m and n are the orders of the vibration mode.

[0074] Then, due to the occurrence of flexural vibration of the can body, the vibration duration becomes longer (20.89 ms) than in cases (i) and (ii), as shown in Figure 7(c).

[0075] In addition, if corrosion products adhere to the interface between the steel casing (can body) and the fireproof material after corrosion has occurred, the vibration duration may be shortened. Therefore, a different evaluation index is adopted in accordance with the actual corrosion form in addition to the evaluation index based on the vibration waveform.

[0076] Comparing (b) and (c) of Figures 5 to 7, they are clearly different from each other, and it can be seen that by applying the above-mentioned [basic concept of the present invention], it is possible to reliably diagnose and evaluate the occurrence of abnormalities in an incinerator composed of an inner refractory material and an outer steel casing (can body).

[0077] 2. Second embodiment In this embodiment, it will be specifically explained that the above-mentioned [basic concept of the present invention] can be applied to the diagnosis and evaluation of peeling (interface peeling) that occurs at the interface between metal (steel) and resin (FRP) due to poor construction, aging, etc., in the soundness evaluation of a composite material of metal (steel) and resin (FRP). Here, the natural vibration peak is adopted as the evaluation index based on the frequency distribution.

[0078] FIG. 8 is a schematic oblique view showing the structure of a peeling simulation specimen made using a composite material of metal (steel) and resin (FRP). The peeling simulation specimen was made by causing peeling at part of the interface between the resin layer 3 (thickness: 10 mm) and the steel layer 4 (thickness: 10 mm) to provide an interfacial peeled portion.

[0079] Then, the surfaces of the specimens without interfacial peeling (sound specimens) and the simulated peeling specimens were vibrated to obtain vibration waveforms, which were then converted into frequency distributions. Note that the vibration position for the simulated peeling specimens was the upper position of the interfacial peeling (distance to the top surface of the peeling: 130 mm), and the vibration position for the sound specimens was the same.

[0080] FIG. 9 shows the frequency distribution obtained by striking a sound specimen, and FIG. 10 shows the frequency distribution obtained by striking a specimen simulating peeling.

[0081] 9 and 10, it can be seen that the same natural frequency peak is clearly shifted to the lower frequency side in the peeled simulated specimen compared to the sound specimen. This shift in natural frequency to the lower frequency side is considered to be caused by the reduction in thickness at the peeled portion, as in the "first embodiment."

[0082] These results show that by applying the above-mentioned [basic concept of the present invention] and confirming the shift of the natural frequency to the lower frequency side, it is possible to reliably diagnose and evaluate the occurrence of interfacial delamination in a composite material of metal (steel) and resin (FRP).

[0083] Furthermore, the above-mentioned shift in the natural frequency to lower frequencies can be observed throughout the entire test specimen, not just the upper part of the peeling. Therefore, evaluation based on the shift in the natural frequency to lower frequencies makes it possible to easily detect whether or not peeling has occurred, without being largely dependent on the measurement position.

[0084] Then, when attempting to identify and evaluate the location of peeling after detecting the occurrence of peeling, it is necessary to evaluate local vibrations. Therefore, it is preferable to perform the evaluation by combining the natural frequency on the high frequency side and the vibration propagation time, etc.

[0085] 3. Third embodiment In this embodiment, it is specifically explained that the above-mentioned [basic concept of the present invention] can be applied to the diagnosis and evaluation of liner peeling for the soundness evaluation of a metal duct lined with a liner. Note that here, the shape of the frequency distribution is adopted as the evaluation index, although it depends on the shape and material of the duct.

[0086] Metal ducts are often lined with a resin or other liner to prevent corrosion of the inside of the duct. In this case, if the liner peels off, corrosion of the duct can progress significantly and cause holes to form.

[0087] Therefore, it is necessary to diagnose and evaluate whether or not liner peeling has occurred. However, since entering the inside of a long and narrow duct to inspect it is laborious, it is preferable to diagnose and evaluate whether or not liner peeling has occurred by percussion testing from the outside of the duct.

[0088] FIG. 11 shows the frequency distribution obtained by vibrating the healthy part of a duct lined with a resin, and FIG. 12 shows the frequency distribution obtained by vibrating the part of a duct lined with a resin where peeling had occurred.

[0089] As shown in Figure 11, when the healthy part is vibrated, the vibration is absorbed by the liner, so the frequency distribution shows a broad shape. In contrast, when the part where peeling has occurred is vibrated, as shown in Figure 12, the vibration is not absorbed by the liner, so the frequency distribution shows a sharp shape.

[0090] These results show that by applying the above-mentioned [basic concept of the present invention] and checking the shape of the frequency distribution, it is possible to reliably diagnose and evaluate the occurrence of peeling in the plastic liner lining the duct.

[0091] It should be noted that this embodiment can be applied not only to ducts, but also to diagnosing and evaluating the occurrence of peeling in liners lining pipes, etc., and the occurrence of peeling at the interface between metal and composite materials such as FRP.

[0092] 4. Fourth embodiment In this embodiment, it will be specifically explained that the above-mentioned "basic concept of the present invention" can be applied to the diagnosis and evaluation of liner peeling for the soundness evaluation of a metal tank lined with a liner. Note that here, the peak position of the frequency distribution is adopted as the evaluation index, although it depends on the shape and material of the tank.

[0093] Metal tanks are often lined with resin or other materials to prevent corrosion of the inside of the tank. In this case, if the liner peels off, corrosion of the tank progresses significantly and may cause leakage from the tank.

[0094] Therefore, it is necessary to diagnose and evaluate whether or not liner peeling has occurred. However, since entering the inside of a closed tank to inspect it is laborious, it is preferable to diagnose and evaluate whether or not liner peeling has occurred by percussion sounding from the outside of the tank.

[0095] Specifically, a tank was created in which a surface of the resin liner where peeling is suspected (peeling portion) faces a surface where peeling is not occurring (sound portion), and the area where peeling is definitely occurring (peeling portion 1) and the opposite surface where peeling is not occurring (sound portion 1) were vibrated to obtain a frequency distribution for each. Also, the area where there is a possibility of peeling (peeling portion 2) and the opposite surface where peeling is not occurring (sound portion 2) were vibrated to obtain a frequency distribution for each.

[0096] Fig. 13 shows the frequency distribution obtained by vibrating a location where it is believed that peeling has definitely occurred (peeled portion 1) and its opposite surface where no peeling has occurred (sound portion 1), with the upper part being peeled portion 1 and the lower part being sound portion 1. Fig. 14 shows the frequency distribution obtained by vibrating a location where it is believed that there are signs of peeling occurring (peeled portion 2) and its opposite surface where no peeling has occurred (sound portion 2), with the upper part being peeled portion 2 and the lower part being sound portion 2.

[0097] In Figure 13, the peak measured at 2536 Hz in healthy section 1 is measured in the low frequency region at 801 Hz in peeled section 1. Similarly, in Figure 14, the peak measured at 1678 Hz in healthy section 2 is measured in the low frequency region at 1272 Hz in peeled section 2.

[0098] As described above, in the liner peeled parts (peeled parts 1 and 2), a strong vibration peak exists in the low frequency region below 1300 Hz that is not seen in the opposing positions (sound parts 1 and 2). Therefore, by applying the above-mentioned [basic concept of the present invention] and confirming the presence of a peak position in the low frequency region of the frequency distribution, it is possible to reliably diagnose and evaluate the occurrence of peeling in the plastic liner lining the duct.

[0099] And because peeled portion 1 shows a stronger vibration peak in the lower frequency range than peeled portion 2, when a vibration peak appears at about 1300 Hz or less, as in peeled portion 2, this can be used as a guide for a sign of peeling. When a vibration peak appears at about 1000 Hz or less, as in peeled portion 1, this can be used as a guide for the occurrence of peeling, and in this case, it is preferable to open the tank and visually check the inside to confirm the presence and condition of peeling.

[0100] Note that this embodiment can be applied not only to tanks, but also to diagnosing and evaluating the occurrence of peeling in liners lining pipes, etc., and the occurrence of peeling at the interface between metal and composite materials such as FRP.

[0101] 5. Fifth embodiment In this embodiment, it is specifically explained that the above-mentioned [basic concept of the present invention] can be applied to the soundness evaluation of a composite material (FRP) in which resin is reinforced with glass or carbon fiber. Note that, here, the evaluation peak frequency obtained from the frequency distribution is adopted as the evaluation index.

[0102] As mentioned above, ERP is a composite material in which resin is reinforced with glass or carbon fiber, and in recent years has been used in aircraft fuselages, automobile bodies, and various equipment parts, tanks, piping, etc.; however, it is not easy to non-destructively confirm from the surface the respective conditions of the resin and fiber (e.g., physical properties and structural integrity such as cracks and cavities), as well as the condition of the interface between the resin and fiber (e.g., adhesion, peeling, etc.).

[0103] This deterioration of FRP occurs due to load (e.g., static load, repeated fatigue load, thermal fatigue, etc.), ultraviolet rays, hydrolysis, etc., but in this embodiment, diagnosis and evaluation by vibration will be explained using the example of a case where an FRP plate material has suffered fatigue damage.

[0104] Specifically, as shown in FIG. 15, a uniaxial fatigue load of a predetermined magnitude is repeatedly applied in the longitudinal direction of the FRP plate material 5 for a predetermined time at predetermined time intervals, and a sensor is placed on the surface of the test object and vibrates it every predetermined number of times (fatigue count), a frequency distribution is created from the acquired vibration waveform, the peak frequency (evaluated peak frequency) is obtained, and the change in the evaluated peak frequency with the fatigue count is measured.

[0105] Fig. 16 is a diagram showing the relationship between the fatigue cycle and the evaluated peak frequency obtained by the above-mentioned measurement, where the horizontal axis is the fatigue cycle (N) and the vertical axis is the evaluated peak frequency (Hz). Fig. 16 shows that the evaluated peak frequency decreases as the fatigue cycle increases, and when it falls below 2500 Hz, the FRP plate breaks.

[0106] Furthermore, these results show that by measuring the evaluation peak frequency of the FRP plate material, the state of deterioration due to repeated fatigue can be diagnosed and evaluated, and therefore, by applying the above-mentioned [basic concept of the present invention] and setting the evaluation peak frequency corresponding to the stage before the FRP plate material breaks as the evaluation standard value, it is possible to reliably diagnose and evaluate the condition of the FRP.

[0107] 6. Sixth embodiment In this embodiment, it will be specifically explained that the above-mentioned "basic concept of the present invention" can be applied to the case where relative changes or aging changes over the entire surface of the test object are diagnosed and evaluated. In this embodiment, the vibration duration and natural frequency are adopted as the evaluation indexes.

[0108] Specifically, diagnosis and evaluation based on vibration was carried out on mortar-repaired joints in the inner wall of the tunnel that had been determined in advance to have a "float". Figure 17 shows the locations where vibration was carried out, showing the lining concrete part (1100mm x 1500mm) that sandwiched the mortar-repaired joints. Vibration was carried out on the parts of the lining concrete part indicated by circles on a 10cm grid, and the vibration duration and evaluation peak frequency at each position were obtained.

[0109] Figure 18 shows the measurement results using vibration duration as the evaluation index, and Figure 19 shows the measurement results using natural frequency as the evaluation index. In Figures 18 and 19, the lower left end of the lining concrete part is set as the origin, the vertical axis represents height position (mm) and the horizontal axis represents horizontal position (mm), and the measurement results of vibration duration (ms) are shown as contour diagrams in Figure 18, and the measurement results of evaluated peak frequency (Hz) are shown in Figure 19.

[0110] Figure 18 shows that the vibration duration in the center joint is longer than that in the surrounding lining concrete parts. And Figure 19 shows that the evaluated peak frequency in the center joint is significantly shorter than that in the surrounding lining concrete parts.

[0111] From these results, it can be seen that by applying the "basic concept" of the present invention, it is possible to diagnose and evaluate relative changes or aging changes over the entire surface of the object to be inspected.

[0112] The use of such a contour diagram allows easy visual judgment over the entire surface of the object to be inspected.

[0113] 7. Seventh embodiment In this embodiment, it is explained that AI (artificial intelligence) diagnosis can be applied to the above-mentioned [basic concept of the present invention] when performing a soundness evaluation of the composite structure or composite structural material to be inspected.

[0114] Specifically, AI is used to learn the results of diagnosis and evaluation based on the previous feature values ​​of the evaluation index and the reference values ​​of the evaluation index (AI learning). Then, the data obtained from the vibration waveform and frequency distribution obtained by vibrating the composite structure or composite material to be inspected (feature values ​​of the evaluation index) are used as input data, and the condition of the corresponding composite structure or composite material (presence or absence of abnormalities) is used as output data from the AI, making it possible to perform a soundness evaluation of the composite structure or composite material to be inspected (AI diagnosis). Then, by adding the results to the AI ​​as new data, the accuracy of the AI ​​diagnosis can be improved and performed more efficiently.

[0115] The AI ​​learning used for AI diagnosis is not particularly limited, and any of the following may be adopted, such as machine learning, deep learning, supervised learning, and unsupervised learning.

[0116] Although the present invention has been described above based on the embodiment, the present invention is not limited to the above embodiment. Various modifications can be made to the above embodiment within the same and equivalent scope of the present invention. [Explanation of symbols]

[0117] 1 can body 2 Fireproof material 3 Resin layer 4 Metal (steel) layer 5 FRP board material

Claims

1. A method for inspecting a composite structure or a composite structural material in a non-destructive manner to evaluate the soundness of the composite structure or the composite structural material, comprising the steps of: The surface of the composite structure or composite structural material to be inspected is externally vibrated to obtain feature quantities for a preset evaluation index, and then A method for inspecting a composite structure or composite structural material, comprising: evaluating the soundness of the composite structure or composite structural material based on a reference amount of the evaluation index obtained from a composite structure or composite structural material known to be in a sound state.

2. The composite structure is a multi-layer composite structure formed by stacking a plurality of structural materials, obtaining a feature quantity for a preset evaluation index from a vibration waveform obtained by externally vibrating a surface of the composite structure to be inspected, or from a frequency distribution obtained by converting the vibration waveform; 2. A method for inspecting a composite structure or composite structural material as described in claim 1, characterized in that the soundness of the condition of each layer of the composite structure to be inspected and the condition of the interfaces between each layer are evaluated based on the obtained characteristic amount of the evaluation index and a reference amount of the evaluation index obtained from a composite structure known to be in a sound state.

3. The composite structural material is a composite structural material formed by laminating a plurality of materials, Obtaining a feature quantity for a preset evaluation index from a vibration waveform obtained by externally vibrating a surface of the composite structural material to be inspected, or from a frequency distribution obtained by converting the vibration waveform; The method for inspecting a composite structure or composite structural material described in claim 1, characterized in that the soundness of the condition of each layer of the composite structural material being inspected and the condition of the interface between each layer are evaluated based on the obtained characteristic amount of the evaluation index and the reference amount of the evaluation index obtained from a composite structural material known to be in a sound state.

4. The composite structural material is a composite structural material formed from a plurality of matrix materials, Obtaining a feature quantity for a preset evaluation index from a vibration waveform obtained by externally vibrating a surface of the composite structural material to be inspected, or from a frequency distribution obtained by converting the vibration waveform; The method for inspecting a composite structure or composite structural material as described in claim 1, characterized in that the condition of each matrix material of the composite structural material being inspected and the soundness of the interface between each matrix material are evaluated based on the obtained characteristic amount of the evaluation index and the reference amount of the evaluation index obtained from a composite structural material known to be in a sound state.

5. 5. A method for inspecting a composite structure or a composite structural material according to claim 1, wherein the striking is performed at one or more selected points on the surface of the composite structural material to be inspected.

6. 5. The method for inspecting a composite structure or a composite structural material according to claim 1, wherein the striking is performed by using a test hammer.

7. 5. A method for inspecting a composite structure or composite structural material according to claim 2, wherein the vibration waveform is acquired using one of an AE sensor, an acceleration sensor, a displacement sensor, a microphone, and a laser displacement sensor.

8. 5. The method for inspecting a composite structure or composite structural material according to claim 2, wherein a feature obtained from a vibration waveform is used as the feature of the evaluation index.

9. 5. The method for inspecting a composite structure or a composite structural material according to claim 2, wherein the frequency distribution is obtained by subjecting the vibration waveform to a fast Fourier transform.

10. 5. The method for inspecting a composite structure or a composite structural material according to claim 2, wherein a feature amount obtained from the frequency distribution is used as the feature amount of the evaluation index.

11. 5. An inspection method for a composite structure or composite structural material according to claim 2, characterized in that the evaluation of the soundness of the composite structure or composite structural material is performed based on the degree of deviation of a feature of the evaluation index obtained from the vibration waveform or the frequency distribution from a reference value of the evaluation index.

12. 5. An inspection method for a composite structure or composite structural material as described in any one of claims 1 to 4, characterized in that, when evaluating the soundness, the reference amount of the evaluation index is set by a mock-up test or a simulation.

13. An inspection method for a composite structure or composite structural material described in any one of claims 1 to 4, characterized in that when evaluating the soundness, the standard amount of the evaluation index is set based on either the state of the composite structure or composite structural material being inspected immediately after installation or maintenance, the state of a portion where deterioration is not expected to progress, or a relative comparison of the states.

14. In the case where the evaluation of the soundness is an evaluation of the soundness against poor construction or deterioration, 5. The method for inspecting a composite structure or composite structural material according to claim 1, wherein the reference amount of the evaluation index is set by a mock-up test or a simulation.

15. In the case where the evaluation of the soundness is an evaluation of the soundness against poor construction or deterioration, An inspection method for a composite structure or composite structural material described in any one of claims 1 to 4, characterized in that the reference amount of the evaluation index is set based on the state of the composite structure or composite structural material to be inspected immediately after installation or maintenance.

16. 5. A method for inspecting a composite structure or composite structural material as described in any one of claims 1 to 4, characterized in that the soundness of the composite structure or composite structural material to be inspected over the entire surface is evaluated by creating a contour diagram based on the characteristic quantities of the evaluation index over the entire surface of the composite structure or composite structural material to be inspected.

17. A method for inspecting a composite structure or composite structural material according to any one of claims 1 to 4, characterized in that, when evaluating the soundness of the composite structure or the composite structural material, a reference amount of the evaluation index is obtained from the results of AI learning.

18. The method for inspecting a composite structure or composite structural material according to claim 17, characterized in that the AI ​​learning is any one of machine learning, deep learning, supervised learning, and unsupervised learning.

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