Abstract:
Ultrasonic testing techniques may involve the measurement of ultrasonic waves from the tested part. These waves may reflect from surfaces of various layers within the part. Further, these waves may reflect from faults, defects, voids, fractures, and others. As such, the measured ultrasonic wave is a complex mix of these reflections. One method for detecting flaws, defects, and others may be to express the signal in terms of a set of basis functions. These functions may be summed to produce the measured signal. Further, basis functions may be chosen such that a select set of the basis functions characterize the fault and/or defect. In one exemplary embodiment, the coefficients associated with the basis function may be non-zero when a defect is present. As such, a defect may be detected quickly and automatically.

Description:
BACKGROUND OF THE INVENTION 
     The present invention generally relates to a system and method for interpreting sonic data. In particular, the present invention relates to a system and method for detecting flaws and/or defects in parts through analysis of ultrasonic data. The present invention relates generally to the nondestructive evaluation of materials, and more particularly to laser ultrasound inspection of engineering materials with ultrasonic bulk, surface, and Lamb waves. 
     DESCRIPTION OF PRIOR ART 
     Measurement of ultrasound is commonly performed to characterize materials. This includes measuring and detecting structures, and can be implemented to find defects or flaws within the parts or contained in the materials making up the parts. 
     Within many industries, inspection of engineering materials has extreme importance in assuring continued performance of structures. In other systems, parts or components need to be evaluated for defects or flaws. Many times these parts may be highly sensitive pieces made in complex engineered fashion and made up of complex materials. 
     Generated sonic waves propagate through an article. Defects in the part may reflect the waves or change other physical parameters associated with the wave. These sonic waves may be detected, and stored for later analysis. 
     These waveforms may be converted into a visual image to aid in diagnosing problems. Many times, in a typical system, and arrival of the sonic energy may be used to determine visually where a defect is, and possibly what type of defect is present. 
     However, this typical analysis of the collected waves usually only indicates a presence of a problem, and may not completely diagnose or locate a particular defect in the part or underlying material. Thus, while the conventional analysis may indicate the presence of a defect or flaw, it may not adequately describe the type and/or physical location of the defect or flaw. 
     This problem is exacerbated when dealing with composite parts. The interlocking or coupled relationship of various layers of materials, or type of construction gives rise to multiple complex echoes. Thus, in these systems, the echo waveform may not be easily used for visualization or interpretation. 
     As such, many typical sonic detection systems suffer from deficiencies in providing accurate indications of defects. Many other problems and disadvantages of the prior art will become apparent to one skilled in the art after comparing such prior art with the present invention as described herein. 
     SUMMARY OF THE INVENTION 
     Various aspects of the invention may be found in a method for detecting more and more defects in manufactured object. The invention converts complex measured ultrasonic waveforms into basis functions indicative of any defects within that part. First, a series of reference waveforms corresponding to the ideal part and or to flaws of various types at various places in depths within the part are generated. These reference waveforms form a series of basis functions that may be helpful in describing any observed waveform. Since a measured waveform may be represented in terms of an inner sum of these basis functions and the amplitudes of each basis function that correspond to a presence of that particular type of defect, the presence of the basis function corresponding to a particular type of defect indicates that in the particular type of defect is present. 
     In typical measurement systems, a series of waveforms may be generated from the part. Even in a simple layered structure, a complex series of echoes is generated in an ideal part. Additionally, the presence of any defects will alter the waveform within the part. However, due to the complex nature of the sonic characteristics of the part, defect location by echo timing is problematic. 
     However, in the present system, the waveforms for particular defects at particular location(s) may be stored as waveforms, and these may be added in combination with the ideal waveform to produce a reference waveform. The combination of a reference ideal waveform for the part, and the basis functions for defects are compared against the received waveform for the part. The presence of any of the basis functions for a corresponding defect thus indicates the location and type of defect present in the part. 
     In this way, a defect in an interface is represented by the amplitude corresponding to that sort of defect, rather than as a series of complex echoes. This technique may be applied in a variety of situations. This includes simple parts where multiple echoes are generated from a single flaw, for example, a reverberation against either a front or back wall, or for separation and identification of flaws near the front or rear surfaces of the part. 
     The various comparison waveforms or representations of such waveforms may be generated in several ways. For example, the basis functions may be derived through a computational model, or they may be derived through experimental measurements of reference parts. In the case of basis functions referring to defects, the reference parts were contained a known defect. Thus the type and parameters of the waveforms generated by the specific defect may be groomed from such experimental measurement. 
     Other aspects of the invention include describing the defective structures by using the amplitudes of these basis functions to draw images. When the presence of the basis function indicating a specific flaw or defect type is determined, an image of the part or location may be generated. A simple graph such as a graph of amplitude versus location may indicate the specific point where a flaw is located. Other imaging schemes may include B-scans and C-scans where both B and C are capitalized. In these B-scans or C-scans, the parameter viewed would be the amplitude of various basis functions. Thus, the presence of an amplitude for a basis function at a particular location in a B-scan or C-scan would indicate the presence of the particular type of defect associated with the basis function at the point on the object. 
     In another aspect of the invention, the detection of flaws or defects is improved even in the presence of noise. Further descriptions of how this method aids in the detection of such defects or flaws in the presence of noise is described in detail later in this application. 
     Other aspects, advantages and novel features of the present invention will become apparent from the detailed description of the invention when considered in conjunction with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic block diagram of a system that diagnoses, locates, and classifies defects in parts using sonic waves, according to the invention. 
     FIG. 2 is block diagram of an exemplary defect detection system of FIG.  1 . 
     FIGS. 3-6 are time domain wave diagrams detailing how the system of FIG. 1 might work. 
     FIGS. 7,  8 , and  9  are plots of basis function amplitudes as a function of position where the cases of FIGS. 4,  5 , and  6 , are illustrated respectively. 
     FIG. 10 is a time domain representation of a set of waveforms from a target measurement. 
     FIG. 11 is a B-scan image corresponding to the noiseless waveforms of FIG. 10, indicating the presence of multiple defects in its construction and/or make up. 
     FIG. 12 a  shows the location of simulated defects in a part as indicated in FIG.  11 . FIG. 12 b  depicts plots of basis function amplitudes versus position for the waveforms depicted in FIG.  10 . 
     FIG. 13 is a time domain representation of the waveforms of FIG. 10, but having noise present. 
     FIG. 14 is a corresponding B-scan of the waveform of FIG.  13 . 
     FIG. 15 a  shows the location of simulated defects in a part as indicated in FIG.  14 . FIG. 15 b  depicts plots of basis function amplitudes versus position for the waveforms depicted in FIG.  13 . 
    
    
     DETAILED DESCRIPTION 
     FIG. 1 is a schematic block diagram of a system that diagnoses, locates, and classifies defects in parts using sonic waves, according to the invention. A sonic testing system  100  contains a sonic wave generator. The sonic wave is generated in a number of ways, including by a laser that directs coherent electromagnetic radiation to a tested part  102 , a piezoelectric transducer attached to the part, or an electromagnetic transducer (EMAT) Typically this sonic energy is ultrasound energy. 
     The sonic energy propagates through the part  102 , and is detected in a sonic energy collection device  104 . The sonic energy may also be detected in a number of ways, including laser interferometer techniques, piezoelectric transducers attached to the part, and EMAT systems. Or a gas buffer measurement technique in which the sonic energy passes to a gaseous medium, and pressure in this medium is measured through such techniques as a laser. 
     In some cases, a defect creates reflections in the medium making up the part. Or, the defect may change velocity parameters, attenuation parameters, or other characteristics of the sonic energy. In any case, the sonic energies are transformed in some manner by a defect. The defect may then be identified and/or located through the detection of anomalous sonic signals. 
     The collected sonic energies are converted to an electric signal and stored in some format. In this example, the energy collection device is tethered to a computer. The energy collection device and/or the computer can convert the collected signals to an appropriate format, and store them for later analysis. 
     In an exemplary embodiment of the invention, the stored signal is compared to a reference waveform corresponding to an ideal part. Additionally, basis waveforms for various kinds of defects are also stored. The basis waveforms correspond to the waveforms generated by particular flaws, and can include such parameters as a particular flaw at a particular depth. 
     The measured waveform is then represented in terms of the ideal waveform and or the basis waveforms. The measured waveform may be thought of as a linear sum of the ideal part reference waveform and any basis waveforms for a particular defect at a particular location. 
     In algebraic terms, a measured waveform Y(t) may be signified as: 
     
       
           Y ( t )= X   1   bf   1 ( t )+ X   2   bf   2 ( t )+ X   3   bf   3 ( t )+ . . .  X   m   bf   m ( t ).  (Eqn 1) 
       
     
     where the m X i  are the amplitudes of the m bf i  that are basis functions as described previously. Thus, in the present invention, the measured wave may be compared against linear combinations of the ideal wave and any basis functions. 
     In the measurement system, a defect detection system  106  detects defects in the part  102 . This is accomplished by comparing the received waveform with the ideal waveform and such basis functions. The defect detection system may operate in real time, or it may operate on previously stored data. In any case, the defect detection system  106  compares the observed wave with a combination of basis functions describing the response of the part and the response associated with any defects. 
     For discretely time sampled waveform data, the matrix notation of the discrete time sampled measured wave function y may be delineated as:          (           y   o             ⋮             y   n           )     =       (           bf   00         …         bf     m                 o               ⋮       ⋰       ⋮             bf     o                 m           ⋯         bf     m                 n             )          (           x   o             ⋮             x   m           )                              
     In this sense, the vector Y is the time sampled waveform data, the matrix  BF  is a matrix of appropriate basis functions, and the coefficient vector X contains the amplitudes associated with the basis functions described in the matrix  BF . Thus, when a defect of a particular type is present, the appropriate coefficient will be non-zero. 
     A monitor  135 , or other visualization method, is available to view the data. In one embodiment, the amplitude of a coefficient is mapped to a color scheme at the appropriate location. Thus, a color-generated map may be generated indicating the location of where the coefficient is higher and lower, allowing an observer to decide where a particular defect is in the part or materials making up the part. 
     It should be noted that the implementation of the wave comparison is easily implemented in a digital computer. In this manner, the basis functions may be added easily as they are determined. 
     The basis functions may be determined in a variety of ways. They may be derived by empirically testing parts and deriving the defect functions based on the results. Or, the basis functions may be determined though computer modeling techniques. 
     In an exemplary embodiment, the characteristic amplitudes of the various basis functions may be directly derived form the observed data itself. From Eqn. 1, the equation for the real time digitally sampled response of the part, we can show that: 
     
       
         (   bf     t     bf )   −1     bf     t     y   =(   bf     t     bf   )  −1     bf     t     bf       x = x     
       
     
     where bf is the basis function matrix, the superscript t denotes the transpose of the matrix, the superscript −1 denotes the inverse of the matrix, y is the observed results, and x is the vector of amplitudes for the basis functions making up the signal. Thus, the entire range of amplitudes for the basis functions can be determined for a defect space. A non-zero amplitude indicates that a particular type of defect is present. 
     The amplitude vector may also be a function of position. Thus, the same state space analysis may be employed not just for the presence of some specific defect, but may occur for determining the specific location of it as well. In this case, if the amplitude is viewed on a scale of position, the specific point where the defect occurs may be viewed, as the amplitude will rise to a non-zero value on a localized basis. 
     The amplitude vector may be plotted using B-scans or C-scans of the part or object. Where particular amplitude goes from zero to non-zero, this indicates the presence of a particular defect or flaw in the measured object at that point. Thus, the inherent properties of the object and the specific defects are used to identify and/or locate with particularity these problems. Thus, the object may be graphically reproduced in several dimensions with the amplitude characteristics of the defects. 
     FIG. 2 is block diagram of an exemplary defect detection system of FIG.  1 . The defect detection system  110  contains storage of ideal waveforms, storage of basis waveforms, storage of observed waveforms, and computational circuitry. This circuitry takes the ideal waveforms and basis waveforms, and compares them to the observed waveform in the computational circuitry. It should be noted that the components of the defect detection circuitry may exist all together in a stand-alone component, or may exist in whole or in part in the various components discussed in reference to FIG.  1 . 
     FIGS. 3-6 are time domain wave diagrams detailing how the system of FIG. 1 might work. In these figures, an observed waveform is compared to a linear combination of basis function  1 , basis function  2 , and/or an idealized waveform. 
     In FIG. 3, the linear combinations of the idealized waveform and the basis functions are performed. FIG. 4 shows the comparison of the linear combinations with an observed waveform. The observed waveform corresponds directly with the waveform indicative of the defect associated with the basis function  1 , and as such, a report may be generated that shows the presence of the defect associated with the basis function  1 . 
     FIG. 5 shows a situation where the observed waveform does not correlate with any combination of the idealized waveform and basis functions. This indicates the possible presence of a defect, but the defects associated with the basis functions  1  and  2  may be discounted. 
     FIG. 6 shows a situation that corresponds with the presence of both basis functions. This would tend to indicate that the defects associated with the basis functions  1  and  2  are both present. 
     FIGS. 7,  8 , and  9  are plots of the basis function amplitudes as a function of position for FIGS. 4,  5 , and  6 , respectively. FIG. 7 shows a non-zero value in the amplitude of basis function  1  at the point where the defect occurs. Thus, the defect associated with basis function  1  is present at that point. FIG. 8 shows no change in the amplitude of either of the basis functions. Thus, neither of the defects is present in the object at any measured point, although some other defect not described by the basis functions may very well exist. FIG. 9 shows a change in the amplitude of basis function  1  at the points where the defects occur. It also shows a change in the amplitude of basis function  2  at the point where the second defect occurs. Thus, both defects associated with basis functions  1  and  2  are present in the object at some of the measurement points. 
     The amplitude viewing may also localize defects much more efficiently when noise is present in the system. In this case, the analysis of a part may be made easier in the presence of noise. 
     FIG. 10 is a time domain representation of a set of waveforms from a target measurement. The waveforms indicate that the determination of a defect by reflection echo timing is problematic. Additionally, for multi-material layered objects, the echo interactions between the layers may make the problem even more difficult. 
     FIG. 11 is a B-scan image corresponding to the noiseless waveforms of FIG. 10, indicating the presence of multiple defects in its construction and/or make up. FIG. 12 a  shows the location of simulated defects in a part as indicated in FIG.  11 . FIG. 12 b  depicts plots of basis function amplitudes versus position for the waveforms depicted in FIG.  10 . 
     FIG. 13 is a time domain representation of the waveforms of FIG. 10, but having noise present. The amplitude of the noise is comparable to the signal amplitude. The ability to detect the reflection echoes is significantly reduced in this, and the signal to noise ratio (SNR) is low. 
     FIG. 14 is a corresponding B-scan of the waveforms of FIG.  13 . Note that the defects are harder to read the due to the added noise. 
     FIG. 15 a  shows the location of simulated defects in a part as indicated in FIG.  14 . FIG. 15 b  depicts plots of basis function amplitudes versus position for the waveforms depicted in FIG.  13 . Note that the amplitude information is extremely easy to read and to indicate the presence of defects, even in the presence of added noise. As such, the SNR for this case is much higher than that of the raw data. This tends to point out and to locate defects with greater precision. 
     The techniques may be extended to include frequency and phase domain descriptions of the waveforms. This is an alternative to the amplitude and time domain descriptions used in the previous description. 
     As such, a system and method for determining flaws in an object through the application of defect basis functions are described. In view of the above detailed description of the present invention and associated drawings, other modifications and variations will now become apparent to those skilled in the art. It should also be apparent that such other modifications and variations may be effected without departing from the spirit and scope of the present invention as set forth in the claims which follow.