JP5482119B2 - Fatigue damage evaluation method and apparatus - Google Patents

Description

  The present invention relates to a fatigue damage evaluation method and apparatus for evaluating a fatigue state of a site where a repeated load of a structure acts.

  In a structure such as an LNG tank, LNG is stored in the tank and consumed, so that the liquid level of the LNG in the tank rises and falls, and the tank, particularly at the junction (corner) between the tank side wall and the bottom plate. A large cyclic load acts.

  For this reason, cracks due to fatigue may occur at the corners, and it is necessary to inspect the fatigue damage state at the corners.

  Conventionally, in order to inspect crack damage, it was necessary to open the tank and inspect from the inside of the tank. In order to open the tank, a spare tank that temporarily transfers the LNG stored in the tank is necessary. Also, since a person enters the inside and inspects the entire circumference, a lot of time and labor are required, and the inspection cost is high. It was. Furthermore, in the conventional inspection method, the position of damage can be estimated, but the degree of damage cannot be estimated.

  Further, in some cases, it is difficult to inspect itself because a complicated structure cannot enter a part to be inspected or an inspection apparatus cannot be installed in a narrow space.

JP-A-10-26613 JP 2008-180558 A

  In view of such circumstances, the present invention eliminates the need for an operator to directly inspect a site to be inspected, and allows the detection of fatigue cracks while maintaining the current status without changing the current status of the structure, and fatigue. A fatigue damage evaluation method and apparatus capable of estimating the degree of cracks are provided.

  The present invention acquires an AE detection curve for an examination site over time, and generates fatigue cracks and crack progress based on the AE count number in a specific frequency band corresponding to the AE generated by the progress of internal cracks in the AE detection curve. The present invention relates to a fatigue damage evaluation method for judging a state.

  The present invention also relates to a fatigue damage evaluation method for judging the occurrence of fatigue cracks and the progress of cracks based on an increase in the number of AE counts in the specific frequency band over time.

  Further, the present invention obtains the AE detection curve in advance by using a test member that models the inspection site as reference data, and compares the AE count number in the specific frequency band of the inspection site with the reference data to determine fatigue cracks. The present invention relates to a fatigue damage evaluation method for judging the occurrence and crack propagation state.

  The present invention also relates to a fatigue damage evaluation method for obtaining a specific frequency band area of a specific frequency band portion of the AE detection curve and determining the occurrence of fatigue cracks and crack progress based on the specific frequency band area.

  In addition, the present invention obtains the area S0 of the AE detection curve and the specific frequency band area S and obtains the area ratio S / S0, and determines the occurrence of fatigue cracks and the crack propagation state based on the area ratio S / S0. This relates to a fatigue damage evaluation method.

  The present invention also relates to a fatigue damage evaluation method for obtaining a crack growth rate based on the area ratio from the relationship between the ratio of the AE detection curve area and the specific frequency band area (S / S0) and the crack growth rate. It is.

  The present invention further includes an AE sensor attached to a site to be inspected, and a fatigue crack progress determination unit to which an AE signal is input from the AE sensor. The fatigue crack progress determination unit is based on the AE signal. According to a fatigue damage evaluation apparatus for calculating a specific frequency band AE count in a specific frequency band corresponding to an internal crack progress of a signal and judging the occurrence of fatigue cracks and crack progress based on the specific frequency band AE count It is.

  In the present invention, the fatigue crack growth determination unit obtains a ratio between the total AE count obtained from the AE signal and the specific frequency band AE count (specific frequency band AE count / total AE count). The present invention relates to a fatigue damage evaluation apparatus that obtains a ratio and determines the occurrence of fatigue cracks and the progress of cracks based on the ratio.

  Furthermore, the present invention includes a plurality of AE sensors attached to the inspection target part, and the fatigue crack progress determining unit identifies a position of a crack generated based on a reception time difference of signals from the plurality of AE sensors. The present invention relates to a fatigue damage evaluation apparatus.

  According to the present invention, an AE detection curve for an examination site is acquired over time, and the occurrence of fatigue cracks based on the AE count number in a specific frequency band corresponding to the AE generated by the progress of internal cracks in the AE detection curve, Since the crack propagation state is determined, the current state of the structure is maintained and no manual inspection is required, so that the inspection period and inspection cost can be greatly reduced.

  According to the present invention, an AE sensor attached to a site to be inspected and a fatigue crack growth determination unit to which an AE signal is input from the AE sensor, the fatigue crack growth determination unit is based on the AE signal. Since a specific frequency band AE count in a specific frequency band corresponding to the progress of an internal crack in the AE signal is calculated and the occurrence of fatigue cracks and crack progress are determined based on the specific frequency band AE count, The inspection period and inspection cost can be greatly reduced since the inspection is maintained and no manual inspection is required.

(A) is an AE detection graph when an aluminum alloy is subjected to a fatigue test at room temperature, and (B) is an AE detection graph when an aluminum alloy is subjected to a fatigue test at low temperature. (A) is an AE detection graph when a 9% Ni steel is subjected to a fatigue test at room temperature, and (B) is an AE detection graph when a 9% Ni steel is subjected to a fatigue test at low temperature. . It is a schematic block diagram which shows an example of the fatigue damage evaluation apparatus which concerns on this invention. It is a graph which shows the relationship between AE and a threshold value, and the relationship with AE count number. It is explanatory drawing about AE generation | occurrence | production. It is a figure which shows the relationship between AE detection curve area ratio and fatigue crack growth rate. It is a figure which shows an example of the safety design curve relevant to fatigue crack growth rate and (DELTA) K.

  Embodiments of the present invention will be described below with reference to the drawings.

  There is elastic wave (Acoustic Emission) (hereinafter referred to as AE) generated by releasing strain energy when the material is deformed or broken. AE is fatigue crack growth, oxide film breakage, FRP fiber breakage, etc. Occurs.

  The present invention enables detection of fatigue cracks from the outside of the tank and estimation of the degree of fatigue cracks by detecting AE waves.

  First, the principle of the present invention will be described.

  The present inventor conducted a fatigue test of the member, detected AE by the AE sensor, and examined the detection result. As a result of the progress of fatigue damage, the number of AE counts at a specific frequency portion (greater than a predetermined threshold in the AE detection signal) We have found that the count of things increases. It is considered that when the crack growth rate increases, the released energy increases, AE having a larger amplitude value is generated, and AE having a high frequency component is frequently generated. In other words, an increase in the AE count at a specific frequency is considered to be related to the occurrence of fatigue cracks and the progress of fatigue cracks.

  Therefore, the present inventor proposes a method and an apparatus for detecting a fatigue crack, estimating the degree of fatigue crack, and estimating the progress state of the fatigue crack based on an increase in the AE count in the specific frequency portion over time. .

  Hereinafter, AE detection results when a fatigue test is performed on iron alloys and aluminum alloys, which are representative materials, are shown.

  FIG. 1A is a three-dimensional AE detection graph showing an AE detection curve representing an AE count number corresponding to a frequency with time when a fatigue test of a test member at a room temperature of an aluminum alloy is performed. In the figure, the X-axis is the AE frequency, the Y-axis is the number of repetitions of the repeated load (time: the number of repetitions increases from the front to the back, that is, the time elapses), and the Z-axis is the AE count number. The number of repetitions was 0 to 90000 times. FIG. 1A shows an AE detection curve until just before the test member breaks.

  As can be seen from this AE detection graph, the number of repetitions A (0 to 10,000), number of repetitions B (50000 to 60000), number of repetitions C (70000 to 80000), and number of repetitions D (80000 to 90000) are shifted. There is a frequency band in which a change with time is seen in the curve showing the AE count number. That is, in the frequency band of 160 kHz to 180 kHz, the AE count number increases with time. In particular, in the frequency band of 160 kHz to 170 kHz, a significant increase in the AE count can be confirmed. It can also be seen that the test member broke when the number of repetitions was D or more.

  FIG. 1B is a three-dimensional graph showing the detection result of AE when a fatigue test is performed on a test member at a low temperature (about −160 ° C.) of an aluminum alloy.

  As this AE detection graph shows, an increase in the AE count over time is observed in a specific frequency band of 190 kHz to 230 kHz even at a low temperature. The number of repetitions A (0 to 10000), the number of repetitions B (50000 to 60000), the number of repetitions C (100,000 to 110000), and the number of repetitions D (130,000 to 137000).

  FIG. 2 (A) is a three-dimensional graph showing the detection result of AE when a fatigue test is performed on a test member of 9% Ni steel at room temperature, and the number of repetitions is 2000 to 60000 times.

  As can be seen from this AE detection graph, the number of repetitions A (2000 to 12000), number of repetitions B (32000 to 42000), number of repetitions C (42000 to 52000), and number of repetitions D (57000 to 60000) are shifted. In the frequency band of 160 kHz to 220 kHz, the AE count number increases with time. In particular, in the frequency band of 180 kHz to 200 kHz, a significant increase in the AE count number can be confirmed. It can also be seen that the test member broke when the number of repetitions was D or more.

  FIG. 2B is a three-dimensional graph showing the detection result of AE when a fatigue test is performed on a test member at a low temperature (about −160 ° C.) of 9% Ni steel.

  As shown in this AE detection graph, 9% Ni steel shows an increase in the AE count over time in a specific frequency band of 170 kHz to 250 kHz even at a low temperature. The number of repetitions A (0 to 10,000), the number of repetitions B (20,000 to 30,000), the number of repetitions C (40000 to 50,000), and the number of repetitions D (60000 to 70000).

  When the fatigue test is performed as described above, the AE count in a specific frequency band is generated in accordance with the occurrence of fatigue cracks and the development of fatigue cracks in the test member regardless of the difference in materials and the difference in environmental temperature. An increase in the number over time can be confirmed.

  Therefore, when a fatigue test is performed in advance using a test member that models a site where a repeated load of a structure acts, an AE detection curve is obtained for each predetermined number of repetitions when the number of repetitions is increased, and an AE detection graph And the AE detection graph is acquired as reference data.

  In the actual inspection, an AE sensor is provided in the inspection target part of the structure or in the vicinity of the inspection target part, and the AE count number of a specific frequency is monitored within the AE count number detected by the AE sensor and compared with the reference data. Thus, it is possible to detect the fatigue crack and estimate the degree of fatigue crack and the progress of the fatigue crack.

  In FIG. 3, an outline of the fatigue damage evaluation apparatus 1 according to the present invention will be described.

  In FIG. 3, 2 is an inspection target part of the structure, 3 is an AE sensor attached to the surface of the inspection target part 2, 5 is a control calculation unit, and 6 is a storage unit connected to the control calculation unit 5. , 7 is an operation input unit connected to the control calculation unit 5, and 8 is an output unit connected to the control calculation unit 5.

  The signal from the AE sensor 3 is subjected to necessary signal processing such as amplification and A / D conversion in the signal processing unit 4. For example, FIG. 4 shows an AE signal detected by the AE sensor 3, which is a threshold value 9 among the AE signals, and the signal processing unit 4 is a signal exceeding the threshold value 9 (hereinafter referred to as an AE count signal 11). Is output to the control calculation unit 5.

  The control calculation unit 5 counts the signal exceeding the threshold 9 in association with the frequency of the signal and records it in the storage unit 6. The signal processing unit 4 may only amplify the AE signal, and the control calculation unit 5 may detect the signal exceeding the threshold value 9.

  The storage unit 6 includes a data storage unit and a program storage unit, and the data storage unit stores the AE count signal 11 and previously acquired reference data, and the program storage unit stores the AE count signal 11. AE detection curve creation program for creating an AE detection curve based on this, AE detection graph creation program for creating an AE detection graph from the AE detection curve, a specific frequency or a specific frequency band from the AE count signal 11 or the AE detection graph A specific frequency band detection program to be detected, an AE area calculation program for calculating an area occupied by the AE detection curve from the AE detection curve, a crack determination program for determining a crack progress state from the area occupied by the AE detection curve and reference data, and the like Stored.

  The control calculation unit 5 operates the AE detection curve generation program, the AE detection graph generation program, the specific frequency band detection program, the AE area calculation program, and the crack determination program, and the obtained data is stored in the storage unit Record in 6.

  The control calculation unit 5, the AE detection curve generation program, the AE detection graph generation program, the specific frequency band detection program, the AE area calculation program, the crack determination program, and the like constitute the fatigue crack progress determination unit 12. .

  From the operation input unit 7, reference data acquired in advance is set and input, and data acquisition conditions from the AE sensor 3 are set. As the data acquisition condition, for example, when the number of repetitions is A (2000 to 12000), number of repetitions B (32000 to 42000), number of repetitions C (42000 to 52000), number of repetitions D (57000 to 60000). A signal is acquired, an AE signal is acquired at a predetermined time interval and a predetermined date and time interval, or a threshold value is set.

  As for the AE signal acquisition time, for example, when it is constantly oscillating like a bridge, the AE signal is acquired continuously or at a short time interval. The AE signal is acquired by combining them.

  The output unit 8 is a display, a printer, or a recording unit for recording on an external recording medium (FD, MO, memory card, etc.). The output unit 8 includes a created AE detection curve and the AE detection graph. , Fatigue crack growth judgment, etc. are displayed or output.

  The operation will be described below.

  As shown in FIG. 5, AE generated from a member to which a repeated load is applied includes an elastic wave generated by the progress of a crack, an elastic wave generated at the time of plastic deformation, and an elastic wave generated when a fracture surface comes into contact. Elastic waves generated when the oxide film peels and breaks are included. As described above, the elastic wave generated by crack propagation in AE has a higher frequency than other elastic waves, and the AE count increases with the progress of crack.

  The fatigue crack progress determination unit 12 detects a specific frequency band that increases with time in the high frequency portion from the AE detection curve at each repetition count, and compares it with reference data. The state of crack growth is determined (for example, FIG. 1A).

  As one method for determining the state of fatigue cracks and crack growth, an area occupied by a specific frequency band, that is, a specific frequency band area (S) is calculated and determined based on an increasing tendency of the frequency band area.

  As another method for judging the state of fatigue cracks and crack growth, the area occupied by the AE detection curve at each number of repetitions, that is, the ratio of the AE detection curve area (S0) to the specific frequency band area (S / S0) is used. Determined by the increasing tendency of the area ratio.

  Further, as shown in FIG. 6, there is a correlation between the area ratio (S / S0) and the fatigue crack growth rate, and the ratio of the area ratio (S / S0) and the fatigue crack growth rate for each temperature in advance for each material. Reference data is acquired, and the state of fatigue crack growth is determined by comparing the obtained area ratio (S / S0) with the reference data of the corresponding conditions. That is, by obtaining the area ratio (S / S0), the fatigue crack growth rate can be obtained or estimated.

  FIG. 6 shows the relationship between the area ratio (S / S0) of the aluminum alloy at a low temperature and the low temperature of 9% Ni steel and the fatigue crack growth rate.

  Also, the fatigue crack growth rate and ΔK, which is a target for safety design, have the well-known relationship shown in FIG. 7 and should be used as data when designing a structure by knowing the fatigue crack growth rate. You can also.

  In addition, since the propagation speed (sound speed) of AE is determined by the substance, the crack generation position can be specified using the propagation speed. That is, in order to specify a one-dimensional position, AE is detected by two AE sensors separated by a predetermined distance, a detection time difference is obtained, and a one-dimensional position can be specified by the detection time difference and the sound speed. Similarly, three AE sensors may be provided to specify a two-dimensional position, and four AE sensors may be provided to specify a three-dimensional position.

  Note that the present invention is not limited to structures subjected to repeated loads, and can be implemented even when detecting corrosion of materials. Further, the present invention can be applied to crude oil tank corrosion investigation, pressure vessel pressure test, pier monitoring, rotating machinery. It can be applied to various structures and fields such as abnormal monitoring of aircraft, investigation of aircraft in flight, material testing, etc.

  In addition, if the present invention is applied to the evaluation of fatigue damage of a tank, it is possible to detect the fatigue crack, estimate the degree of fatigue crack, and specify the position of the fatigue crack from the outside of the tank without opening the tank. Can be greatly reduced.

DESCRIPTION OF SYMBOLS 1 Fatigue damage evaluation apparatus 2 Inspection object part 3 AE sensor 4 Signal processing part 5 Control operation part 6 Storage part 7 Operation input part 8 Output part 9 Threshold value 11 AE count signal 12 Fatigue crack progress judgment part

Claims (8)

AE detection curves for the examination site are sequentially acquired over time, the acquired AE detection curves are sequentially compared, and a frequency band in which the AE count number of the AE detection curve increases with time is detected and detected. the frequency band to a specific frequency band, the generation of fatigue cracks on the basis of the AE count increasing tendency in the specific frequency band, the fatigue damage evaluation method characterized by determining the crack growth state. A fatigue test is performed in advance using a test member that models the test site, the AE detection curve is acquired in advance over time as reference data, a specific frequency band of the test site is detected from the reference data, and the test is performed. comparing the AE count and the reference data at a particular frequency band of sites, the generation of fatigue cracks by the increasing tendency of the AE count, fatigue damage evaluation method according to claim 1 for determining the crack growth state. The fatigue damage evaluation method according to claim 1, wherein a specific frequency band area of a specific frequency band portion of each AE detection curve is obtained, and the occurrence of fatigue cracks and the crack progress state are determined based on an increasing tendency of the specific frequency band area. Claiming the area S0 and the specific frequency band area S of each AE detection curve, obtaining the area ratio S / S0 , and determining the occurrence of fatigue cracks and the crack propagation state based on the increasing tendency of the area ratio S / S0 Item 3. The fatigue damage evaluation method according to Item 3 . The fatigue damage evaluation method according to claim 4 , wherein a crack growth rate is obtained based on the area ratio based on a relationship between a ratio (S / S0) between each AE detection curve area and the specific frequency band area and a crack growth rate. An AE sensor attached to a site to be inspected, and a fatigue crack progress determining unit to which an AE signal is input from the AE sensor, and the fatigue crack progress determining unit determines an AE detection curve for the test site over time Sequentially acquiring, sequentially comparing the acquired AE detection curves over time, detecting a frequency band in which the AE count number of the AE detection curve increases with time, setting the detected frequency band as a specific frequency band, A fatigue damage evaluation apparatus characterized by calculating a specific frequency band AE count in a frequency band and determining the occurrence of fatigue cracks and crack progress based on an increasing tendency of the specific frequency band AE count. The fatigue crack growth determination unit obtains a total AE count number obtained from an AE signal and the specific frequency band AE count number , obtains a ratio of (specific frequency band AE count number / total AE count number), and determines the ratio. The fatigue damage evaluation apparatus according to claim 6 , wherein the fatigue crack generation state and the crack propagation state are determined based on the fatigue crack generation state. The fatigue damage according to claim 7 , further comprising a plurality of AE sensors attached to the inspection target part, wherein the fatigue crack progress determining unit identifies a position of a crack generated based on a difference in reception time of signals from the plurality of AE sensors. Evaluation device.

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