System and Method for Damage Diagnosis

Abstract

The object of the invention is to provide a damage diagnostic system that uses a damage detection system that obtains propagation intensity distribution data, which is expanded in the two dimensions frequency and propagation time, by converting the output value from an oscillation detection sensor that was obtained when oscillation is performed by an oscillator, and for one mode or two or more modes that are selected from the fundamental mode and higher mode of Lamb waves, obtains certain characteristic values from the data, for example three indices, which are the slope of the mode dispersion of the A1 mode (rate of change of the propagation time with respect to the frequency), the amount of decrease in the propagation time of the A1 mode, and the amount of increase in the propagation time of the S0 and S1 modes, and outputs the measurement results. The measurement results are displayed on a display device.

1 . A system for damage diagnosis for diagnosing a damage that occurred on or within an object, the system comprising:
 an oscillator for applying a broadband ultrasonic oscillation to the object to generate a broadband Lamb wave within the object;   an oscillation detection sensor for detecting the broadband Lamb wave from the object, the detected broadband Lamb wave including at least one mode of Lamb wave; and   a processing unit, being connected to the oscillator and the oscillation detection sensor, for   (1) obtaining time-frequency transformation data by performing a time-frequency transformation to the broadband Lamb wave detected by the oscillation detection sensor, wherein the time-frequency transformation data indicates a propagation time of the at least one mode of Lamb wave, and the propagation time is the time for Lamb wave to propagate from the oscillator through the oscillation detection sensor, and   (2) identifying, based on the propagation time of the at least one mode of Lamb wave in the time-frequency transformation data, whether or not the damage has occurred on or within the object, and/or identifying the size or length of the damage that occurred on or within the object.   
     
     
         2 . The system for damage diagnosis according to  claim 1 , wherein
 the processing unit, in the identifying process (2), based on whether or not the propagation time of the at least one mode of Lamb wave matches a reference value, identifies whether or not the damage has occurred on or within the object, and/or identifies the size or length of the damage that occurred on or within the object.   
     
     
         3 . The system for damage diagnosis according to  claim 1 , wherein
 the broadband Lamb wave includes two or more modes of Lamb waves; and   the processing unit, in the identifying process (2), based on whether or not the propagation time of at least one mode of Lamb wave of the two or more modes of Lamb waves matches a reference value, identifies whether or not damage has occurred in the object, and/or identifies the size or length of the damage that occurred on or within the object.   
     
     
         4 . The system for damage diagnosis according to  claim 3 , wherein
 the identifying process (2) comprises a selection step for selecting the at least one mode Lamb wave from the two or more modes of Lamb waves to be compared with the reference value.   
     
     
         5 . The system for damage diagnosis according to  claim 1 , wherein
 the time-frequency transformation data obtained by the processing unit is a two-dimensional propagation intensity distribution data in which frequency is one of the two dimension and propagation time is the other.   
     
     
         6 . The system for damage diagnosis according to  claim 1 , wherein
 the at least one mode Lamb wave includes a plurality of waves having mutually different frequencies; and   the propagation time of the at least one mode of Lamb wave is a propagation time of a maximum intensity portion of at least one of the plurality of waves.   
     
     
         7 . The system for damage diagnosis according to  claim 1 , wherein said at least one mode is A1 mode. 
     
     
         8 . The system for damage diagnosis according to  claim 1 , wherein said at least one mode is S0 mode and S1 mode. 
     
     
         9 . The system for damage diagnosis according to  claim 1 , wherein said at least one mode is A1 mode, S0 mode, and S0 mode. 
     
     
         10 . The system for damage diagnosis according to  claim 1 , wherein
 the at least one mode Lamb wave includes a plurality of waves having mutually different frequencies; and   the processing unit, in the identifying process (2), calculates propagation times of two of the plurality of waves, calculates a change ratio of the propagation times by means of dividing a difference of the two propagation times by a difference of the frequencies of the two waves, and based on whether or not the change ratio matches a reference value, identifies whether or not the damage has occurred on or within the object, and/or identifies the size or length of the damage that occurred on or within the object.   
     
     
         11 . The system for damage diagnosis according to  claim 10 , wherein said at least one mode is A1 mode. 
     
     
         12 . The system for damage diagnosis according to  claim 4 , wherein
 the system comprises two oscillators, with one oscillator being attached to one surface in the thickness direction of the object, and the other oscillator being attached to the other surface in the thickness direction of the object; and   the processing unit executes an oscillation control process to control the oscillators, and executes the oscillation control process and the selection step under any of the conditions (a) to (c) below, where   condition (a) is such that the processing unit, in the oscillation control process, controls the two oscillators so that a symmetrical mode Lamb wave is generated in the object, and selects the symmetric mode Lamb wave in the selection process;   condition (b) is such that the processing unit, in the oscillation control process, controls the two oscillators so that an asymmetric mode Lamb wave is generated in the object, and selects the asymmetric mode Lamb wave in the selection process; and   condition (c) is such that the processing unit executes the processes under conditions (a) and the processes under condition (b) at different times.   
     
     
         13 . The system for damage diagnosis according to  claim 4 , wherein
 this system comprises two oscillation detection sensors, with one oscillation detection sensor being attached to one surface in the thickness direction of the object, and the other oscillation detection sensor being attached to the other surface in the thickness direction of the object; and   the processing unit executes the processes (1) and (2) under any one of the conditions (a) to (c) below; where   condition (a) is such that the processing unit, in the obtaining process (1), creates data in which an asymmetric mode is canceled out and a symmetric mode is emphasized by adding the broadband Lamb waves detected by the two oscillation detection sensors, and then the processing unit obtains time-frequency transformation data by performing the time-frequency transformation to the created data, and in the identifying process (2), selects a symmetric mode Lamb wave;   condition (b) is such that the processing unit, in the obtaining process (1), creates data in which the symmetric mode is canceled out and the asymmetric mode is emphasized by subtracting the broadband Lamb waves detected by the two oscillation detection sensors, and then the processing unit obtains time-frequency transformation data by performing the time-frequency transformation to the created data, and in the identifying process (2), selects an asymmetric mode Lamb wave; and   condition (c) is such that the processing unit executes the processes under conditions (a) and the processes under condition (b).   
     
     
         14 . The system for damage diagnosis according to  claim 1 , wherein
 the time-frequency transformation is any one of the wavelet transformation, short-time Fourier transformation, chirplet transformation, Wigner transformation, and Stockwell transformation, or a combination of any two or more of said transformations.   
     
     
         15 . The system for damage diagnosis according to  claim 1 , wherein
 the oscillator is attached to the object.   
     
     
         16 . The system for damage diagnosis according to  claim 1 , wherein
 the oscillation detection sensor is attached to the object.   
     
     
         17 . A method for damage diagnosis for diagnosing damage that occurred on or within an object, the method using
 an oscillator for applying a broadband ultrasonic oscillation to the object to generate a broadband Lamb wave within the object,   an oscillation detection sensor for detecting the broadband Lamb wave from the object, the detected broadband Lamb wave including at least one mode of Lamb wave, and   a processing unit being connected to the oscillator and the oscillation detection sensor, and   the method comprises the steps of:   (1) obtaining time-frequency transformation data by performing a time-frequency transformation to the broadband Lamb wave detected by the oscillation detection sensor, wherein the time-frequency transformation data indicates a propagation time of the at least one mode of Lamp wave, and the propagation time is the time for Lamb wave to propagate from the oscillator through the oscillation detection sensor; and   (2) identifying, based on the propagation time of the at least one mode of Lamb wave in the time-frequency transformation data, whether or not the damage has occurred on or within the object, and/or identifying the size or length of damage that occurred on or within the object.   
     
     
         18 . The method for damage diagnosis according to  claim 17 , wherein
 the time-frequency transformation is any one of the wavelet transformation, short-time Fourier transformation, chirplet transformation, Wigner transformation, and Stockwell transformation, or a combination of any two or more of said transformations.