Method and apparatus for defect detection in composite structures

Methods and apparatus for non-destructive testing of a composite structure utilizing sonic or ultrasonic waves. In response to a wideband chirp wave sonic excitation signal transmitted from a probe to the composite structure, a probe signal received is correlated with a library of predetermined probe signals and a graphical representation of defects detected is generated. The graphical representation provides detailed information on defect type, defect location and defect shape. Also contemplated is a probe for non-destructive testing of a composite structure comprising three or more transducers wherein each transducer is separately configurable as a transmitter or as a receiver; and a controller coupled to each of transducer for providing signals thereto and receiving signals therefrom, wherein the signals provided thereto include signals for configuring each transducer as either a transmitter or a receiver, and signals for providing an excitation signal from each transducer which is configured as a transmitter.

PRIORITY CLAIM TO RELATED APPLICATIONS

This application is a US National Stage application under 35 U.S.C. §371 of PCT/SG2011/000196, filed May 27, 2011, and published as WO 2012/091676 A1 on Jul. 5, 2012, which claims priority to Singapore Application No. 201009706-1, filed Dec. 29, 2010, and claims priority to Singapore Application No. 201009708-7, filed Dec. 29, 2010, which applications and publication are incorporated by reference as if reproduced herein and made a part hereof in their entirety, and the benefit of priority of each of which is claimed herein.

FIELD OF THE INVENTION

The present invention generally relates to non-destructive testing methods and apparatus, and more particularly relates to a method and apparatus for non-destructive testing from a single surface of a composite structure by utilizing sonic or ultrasonic waves.

BACKGROUND OF THE DISCLOSURE

Composite materials are increasingly being used for the inner and outer skins of commercial aircrafts. In order to meet the commercial aeronautics industry demands for airworthiness and flight safety, these new composite material structure require the development of new inspection technologies. Conventional inspection techniques include a so called “coin tap” testing method where the inspection conductor taps the suspected areas lightly with a hard and blunt tool to obtain indications of the underlying structure from the sound of the tap. Other testing methods include thermographic testing, non-linear spectroscopy, X-radiography, eddy current measurements and ultrasonic waves. Among these inspection methods, the ultrasonic wave method is the most commonly used testing method for non-destructive inspection of aircrafts. However, ultrasonic wave testing methods are not suitable for composite structures where non-isotropic properties of the composite structure materials cause high attenuation due to absorption and scattering.

Recent advances in sonic techniques such as pitch-catch method and resonance methods are able to obtain high sensitive responses from aircraft composite structures employing an excitation frequency lower than 100 kHz. In the pitch-catch method, a Lamb wave for composite structure inspection is generated and received by two respective piezoelectric probes located at a distance from each other on the surface of the composite. The behaviour of the Lamb wave in terms of wave mode, frequency, velocity, and level of attenuation is highly dependent on the material of the composite structure, the thickness of the laminate layers, and the material properties of the structure. Repeatable responses for complex composite structures are possible if the excitation signal is properly selected.

With respect to probe arrays for use with the pitch-catch method, various geometries have been proposed for the arrangement of transducers and the some prior art systems disclose multiple transducers in one probe device in which not all of the transducers are switched on or involved in nondestructive testing at the same time.

Commercially available Lamb wave-based testing apparati, however, are typically limited to two-dimensional location of defects and are conventionally not able to detect the presence of some types of defects, e.g., depth of delamination in carbon fiber composites. Further, when the presence of defects are detected, the such apparati do not provide a user-friendly way of identifying the various types of defects and do not enable an operator to differentiate between defects at different depths and defects of different types.

Thus, what is needed is a method and apparatus for Lamb wave-based non-destructive testing of composite structures which distinguishes between a variety of defects types not previously distinguishable and which provides a more user-friendly presentation of test results. Furthermore, other desirable features and characteristics will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and this background of the disclosure.

SUMMARY OF THE INVENTION

According to the Detailed Description, method for non-destructive testing of a composite structure is provided. The method includes providing a wideband chirp wave sonic signal to the composite structure for a predetermined time, a predetermined amplitude and a predetermined frequency as an excitation signal, and correlating a probed signal received from the composite structure with a library of predetermined probed signals. The method also includes outputting a graphical representation of defects detected, wherein the graphical representation of the defects detected conveys defect location information.

In addition, an apparatus for non-destructive testing of a composite structure is provided. The apparatus includes a transmitter, a receiver, a user interface, a storage device and a controller, which includes the function of excitation signal amplification. The transmitter provides a wideband chirp wave sonic signal to the composite structure for a predetermined time, a predetermined amplitude and a predetermined frequency as an excitation signal. The receiver receives a probed signal from the composite structure in response to the excitation signal. The user interface presents a graphical representation of defects detected and the storage device stores a library of predetermined probed signals. The controller is coupled to the receiver, the storage device and the user interface for correlating the probed signal received with the library of predetermined probed signals and providing signals to the user interface for outputting a graphical representation of defects detected conveying defect location information.

Further, probe for non-destructive testing of a composite structure is provided. The probe includes three or more transducers and a controller. The three or more transducers are each separately configurable as a transmitter or as a receiver. The controller is coupled to each of the three or more transducers and provides signals to each of the transducers and receiving signals from each of them. The signals provided by the controller include signals for configuring the transducers as either a transmitter or a receiver and signals for providing an excitation signal having a predetermined time, a predetermined amplitude and a predetermined frequency from each of the three or more transducers which is configured as a transmitter.

DETAILED DESCRIPTION

Referring toFIG. 1, a front planar view100depicts a probe102operating as an apparatus for non-destructive testing of a composite structure104. The probe102utilizes a conventional pitch-catch method wherein a Lamb wave is generated by the probe102while the probe102is in contact with the composite structure104. A transmit piezoelectric device106of the probe102transmits the Lamb wave as an excitation signal into the composite structure104and a receive piezoelectric device108located at a predetermined distance from the transmit piezoelectric device106along the surface of the composite structure104receives Lamb wave reflections as a probed signal from the composite structure104.

Those skilled in the art will understand that the behaviour of the Lamb wave in terms of wave mode, frequency, velocity, and level of attenuation highly depends on the material structures, thickness of the laminates and material properties of the composite structure104. The repeatable, verifiable response to complex composite structures can be obtained if the excitation signal is probably selected. For example, the left side (a) ofFIG. 1depicts the probe102passing over a portion of the composite structure104having no defects. The right side (b) ofFIG. 1depicts the probe102passing over a portion of the composite structure104having a disbond defect110.

To determine the nature of the response, a reference composite structure200with known defects is tested.FIG. 2, comprisingFIGS. 2A and 2B, depicts a typical reference composite structure200for equipment calibration.FIG. 2Ais a left, top front perspective view202of the reference composite structure200andFIG. 2Bis a front cross-sectional view204of the reference composite structure200. In the cross-sectional view204, an outer surface206of the reference composite structure200is made of a laminate material such as fiberglass or carbon fabric and covers the honeycombed inner structure. The reference composite structure200includes a number of predefined defects such as a machined core defect208, a pillow insert defect210, and a potted core defect212(which correspond respectively to the defects of disbonds, delaminations, and crushed core portions) for probing to develop a library of predetermined probed signals for comparison to actual defects.

Referring toFIG. 3, a flow diagram300depicts an overview of a conventional non-destructive composite structure testing method using the probe102(FIG. 1). At step302, the system, which includes a tool to measure the signals from the probe102, is initially set up by passing the probe102across the outer surface206of the reference composite structure200to generate a set of predetermined probed signals corresponding to the predefined defects208,210,212in the reference composite structure200. The reference composite structure200includes engineered defect having types similar to those in the actual composite structures (e.g., aircraft structures) to be inspected. Also, the probe102and its operational mode (i.e., the excitation signal generation mode) should be selected in response to the shape and material of the actual composite structures. For example, a probe102which uses pitch-catch techniques may be more suitable for a first composite structure while a probe which uses resonance or mechanical impedance analysis (MIA) techniques may be more suitable for a second composite structure. Among the conventional inspection techniques, pitch-catch is the most commonly used as it is capable of detecting most defect types in the composite structures, including honeycomb composite structures. Conventional systems using the pitch-catch technique, however, may need several excitation signal transmissions before a defect is detected. This is typically determined during step302.

Once the predetermined probed signals and the protocol for generating them are determined from step302, the composite structure can be inspected304using the determined protocol and signals, and identified defect areas can be marked306.

Referring next toFIG. 4is a flow diagram400depicts the inspection portion304of the non-destructive composite structure testing method. Conventional pitch-catch inspection systems will have the capabilities of excitation generation, response acquisition, and processing, as well as information management for facilitating the inspection operation. The flow diagram400depicts the order of these, operations. Initially, an excitation signal is generated and provided402to the composite structure404(e.g., the composite structure104(FIG. 1)). The excitation signal provided at step402is an excitation signal appropriate to typical defects found in the particular type of composite structure404. A probed signal, which is a response of the composite structure to the excitation signal provided at step402, is received406and passes through a signal conditioning process408to be placed in a format where the defect features can be extracted before being presented (i.e., displayed) in a visual or graphical representation410. The results may then be saved412for future reference.

Since the introduction of the pitch-catch technique for non-destructive testing of composite structures in the 1980s, several products have become available in the market. These products include the BondaScope product manufactured by NDT Systems, Inc. of Huntington Beach, Calif., USA, shown inFIG. 5(including a handheld probe500and a computing device502for processing and presenting the defect inspection information). A trace of an exemplary excitation signal is depicted in a graph504inFIG. 5. These products also include the BondMaster product manufactured by Olympus Corporation of Tokyo, Japan, shown inFIG. 6(including a handheld probe600and a computing device602for processing and presenting the defect inspection information). A trace of an exemplary excitation signal is depicted in a graph604inFIG. 6. The probes500,600are embedded with two piezoelectric elements for transmitting and receiving signal. The Lamb wave is introduced into the composite structure104by a piezoelectric element through a probe tip506,606. The wave can be excited through impulse mode, radio frequency mode, or swept mode to produce an appropriate excitation signal for defect detection. As the frequency is highly dependant on the composite structure and the type and size of the defects, a swept mode excitation through multiple frequencies of lower than 50 kHz is often used as a first try to detect any unknown defects. The probes500,600are linked to the computing devices502,602for providing received probed signals to the devices502,602for data acquisition and data processing of received probed signals.

Referring toFIG. 7A, a graph700of the received probe signal of a trace702presented in the complex plane presents a circular closed or spiral-like trace702within a square box704when no defect is detected in the composite structure portion being tested. During the inspection operation, an operator will first obtain the response of the conventional device within a non-defect area. The operator will then set the square box704on a display to enclose the response curve. Thereafter, during inspection, as long as the response curve remains inside the square box704, an operator can determine that the conventional inspection apparatus does not detect a defect. When, however, a curve708goes outside the square box704, such as in the graph710of the received probe signal inFIG. 7B, the curve708indicates the pitch-catch probe500,600has detected a defect (i.e., the curve708going outside the square box704depicting detection of a defect in the composite structure portion being tested). Thus, an experienced technician is required to interpret the displayed responses to the inspection for determining defect presence, location and size.

Accordingly, it can be seen that conventional non-destructive testing apparati have the following general technical and operational shortcomings, which are highly unfavourable to the maintenance, repair and overhaul (MRO) operations for the aircrafts: they are difficult to use, they are unable to indicate the type of defects, they are unable to identify the depth of the defects in the composite laminates in a single inspection, and they are unable, to scan portions of the composite structure to precisely locate a defect's size and/or geometry.

The success of detecting defects in composite structures depends on the excitation modes and the selection of response processing methods. The material conditions, in terms of properties, structures, size, and defect types will influence the response. Proper excitation has to be selected to get the maximum sensitivity to the defect type. Without knowing where and what types of defect, the inspection operation is tedious, time consuming and difficult.

While conventional non-destructive testing systems aim to be able to detect defects of different types, depth and size, presently existing systems typically are unable to distinguish the types of the defects and the depths of the defects. Such information is important during an inspection as some extent of the severity of the defects can be determined from the defect type and defect depth information. In addition, such information helps decide the type and/or nature of maintenance or repair actions, if any such actions are needed. Also, without accurate defect depth information, defects, such as delaminations in carbon fibre skins, can easily be mixed up or confused with other defects due to the size of the defect, leading to inefficient and/or ineffective repair processes.

Finally, conventional non-destructive testing systems include a handheld unit that typically does not perform in the same manner as a XY-stage scanner. Without the ability to accurately locate a position, geometry and/or boundary of a defect prohibits the recording of inspection results that are traceable for future reference, thus preventing assuring that no spot in the targeted inspection area is missing, that no area will be inspected twice, and, more importantly, preventing improved inspection visualisation and user friendliness of the inspection tools.

A present embodiment of the invention as described below overcomes these drawbacks of the prior art and presents a method and apparatus for detecting and identifying common defects in composite structures. The method includes the excitation signal design, feature extraction technique, defect identification and defect type visualization. The method and apparatus consist of a signal processing unit, ADC/DAC capabilities and a display. The apparatus works with a pitch-catch probe embedded with piezoelectric elements for guided Lamb wave generation and sensing. Referring toFIGS. 8and9, a first flow diagram800depicts an overview of the non-destructive composite structure testing method in accordance with the present embodiment and a second flow diagram900depicts a procedure for generating802a library of predetermined probed signals for a reference composite structure200of the non-destructive composite structure testing method in accordance with the present embodiment.

The method of identifying the defects in accordance with the present embodiment and depicted inFIG. 8is by way of direct comparison of processed features. Responses of targeted, predefined defects is acquired at step802, wherein a library of predetermined probed signals is acquired, processed and saved in a data base. During inspection804, one or more probe tips transmit excitation signals to the composite structure being inspected and probed signals are received at the surface of the composite structure. The probed signals are correlated with (i.e.; compared with)806the library of predetermined probed signals and defect type information, defect location information and/or defect size information is determined and displayed808.

Therefore, during building802the reference data base and carrying out the actual inspection804, the method and apparatus of the present invention includes an excitation signal production mode, a feature extraction mode, a feature identification mode and a defect visualization mode.

Referring back toFIG. 9, the flow diagram900for generating the library of predetermined probed signals initializes902a counter n to one and provides904an excitation signal from one or more transmitter probe tip(s). One or more receiver probe tip(s) are examined to see if they have acquired data (i.e., received probed signals)906. The probed signals are then processed908through fast Fourier transformation (FFT) and/or phase shifting to derive910a reference n. The counter n is incremented by one912and processing determines914whether all of the references have been captured. If all references have been captured914, an n size database is stored916as the library of predetermined probed signals. If, on the other hand, all references have not been captured914, processing returns to provide904another excitation signal by transmission from a probe tip.

Both the library reference database building step802and the inspection step804involve an excitation signal production mode (e.g., step904). In the excitation signal production mode in accordance with the present embodiment, a signal swept mode is utilized because it can capture a wide range of material conditions, including defect types and depth. The present embodiment differs from conventional signal swept modes in that the excitation signal is a linear chirp wave in which the frequency increases or decreases uniformly with time over a wide frequency band. Referring toFIG. 10, which includesFIGS. 10A, 10B and 10C, signaling diagrams of the wideband chirp excitation sweep signal of the non-destructive composite structure testing method800in accordance with the present embodiment is shown.FIG. 10Adepicts a graph1000of the excitation sweep signals1002in accordance with the present embodiment wherein the sweep is over a twenty kilohertz (20 kHz) frequency range and increases from twenty kilohertz (20 kHz) to 40 kilohertz (40 kHz) within a predetermined time of three milliseconds (3 ms) in the time domain.FIG. 10Bdepicts a graph1010in the time domain which traces the excitation sweep signals1012in accordance with the present embodiment where the sweep is also over a twenty kilohertz (20 kHz) frequency range but the sweep decreases frequencies from 40 kilohertz (40 kHz) to twenty kilohertz (20 kHz) within a similar predetermined time of three milliseconds (3 ms).FIG. 10Cdepicts a graph1022of the excitation sweep signals in the frequency domain in accordance with the present embodiment where the sweep either increases or decreases in the range from twenty kilohertz (20 kHz) to 40 kilohertz (40 kHz) within a predetermined time of three milliseconds (3 ms).

The total predetermined time of the excitation signal is less than ten milliseconds (10 ms) and is preferably approximately three milliseconds (3 ms). The peak-to-peak amplitude of the excitation signal is a value in the range from one volt to one hundred volts and selection of the voltage is determined in response to the thickness of the laminates206(FIG. 2) of the composite structure as the signal needs to pass through the laminates206to detect any defects underneath.

As stated above in regards toFIG. 10, the frequency sweep is over a wide frequency band and either decreases or increases across the frequency band. The reason for using a decreasing chirp wave frequency decreasing from fifty kilohertz (50 kHz) to ten kilohertz (10 kHz) (or in a narrower frequency band from forty kilohertz (40 kHz) to twenty kilohertz (20 kHz)) is for addressing the dispersal nature of the Lamb wave wherein high frequency waves travel faster than low frequency waves in certain mode. As such, increasing or decreasing the signal generates waves of different frequencies that will not interfere with each other. In addition, the linear and uniform frequencies permit all of the frequencies to be treated equally in term of intensity so that the response to any material conditions (e.g., defects) will be prominently detectable. In accordance with the present embodiment, the predetermined time of the excitation signal production is much shorter than conventional excitation times which advantageously minimize the dispersal effect of the Lamb wave and the trailing effects possibly caused by boundary reflections. Accordingly, the excitation signal in accordance with the present embodiment provides a wideband chirp wave generated over a period of a few milliseconds at high amplitude voltage (up to 100 V peak-to-peak).

The response of the excitation signal wave after it passes through the material is processed into the form that is stable and repeatable for the material condition. In accordance with the present embodiment, the response signal received by the receiving probe (i.e., the probed signal) is processed into a stable and repeatable form by computing the phase shift fast Fourier transformations of the response signal over a range of frequencies. The phase shift of such response signal can be expressed as

FFT( ) represents the Fast Fourier Transform of a real, one-dimensional time domain signal. In Equation [1], FFT(y)Tis the one-dimensional time domain signal of the transmitted or the excitation signal and FFT(x)Ris the Fast Fourier Transform of the received probed signal or response signal.

Referring toFIG. 11, a graph1100depicts a phase shift profile1102of the received probe signal as plotted against the excitation signal over a range of frequencies of the excitation signal in accordance with the present embodiment. The defect type or material condition is identified based on the distinct processed responses recorded during the reference data base building stage802,900. Using the excitation signal and the method for processing the received signal, distinct phase shift profiles can be distinguished for various material conditions and defects (such as defect type information and defect depth information, as well as intact, non-defect areas) in the reference composite structure, such as the reference composite structure200. A reference data base including a library of predetermined probed signals can be built (i.e., defined) during the reference data base building stage802,900. In this manner, defect responses (i.e., the probed signals) are collected, processed for the phased shift profile, and saved in the memory as the predetermined probed signals for the reference composite structure200for all types of defects contained therein.

Another method for processing response signals includes obtaining magnitudes of fast Fourier transformations (FFT) of the received probed signals. The magnitudes can be calculated as follows
Magnitude(x)=|FFT(x)R|=√{square root over ([Re[FFT(x)]]2+[Im[FFT(x)]]2)}  [2]
FIG. 12depicts a graph1200of a phase shift profile1202of magnitudes of fast Fourier transformations (FFT) of the received probe signal as plotted against the excitation signal over a range of frequencies of the excitation signal in accordance with the present embodiment.

FIG. 13Ais a graph1300of a phase shift profile of a predetermined received probed signal1302of a known defect as plotted against the excitation signal over a tolerance range of frequencies in accordance with the present embodiment for storage as a predetermined probed signal for storage in the reference data base.FIG. 13Bis a graph1350of a phase shift profile of a received probed signal1352as plotted against the excitation signal while detecting several defects, including the phase shift profile1302of the known defect depicted inFIG. 13Ain accordance with the present embodiment.

After the responses for all the defects are saved, a tolerance band is set for each of the phase shift profiles collected for the different material conditions (i.e., the predetermined probed signals indicative of different defects). The size of the tolerance band can be adjusted to suit the accuracy and sensitivity requirements for defect identification. The received probed signals collected during the inspection stage804(FIG. 8) are compared with the phase shift profile and/or the magnitude profile in real time during the actual inspection. A defect type can thus advantageously be determined based on the best match of the profile within the tolerance band set during the reference data base building stage802,900.

FIG. 14depicts a block diagram1400of a non-destructive testing system in accordance with the present embodiment. The system includes a probe1402imbedded with a position transducer and a position sensor/encoder1404which cooperatively signal each other across an inspection area1406to generate information for processing by the computer1408for determination of defect size information, defect type information and defect location information from the excitation signals and the probed signals. A control box1410allows operator control of the method for inspection and defect identification of the system. The method comprises defining an inspection area before the actual inspection804. The position sensor/encoder1404is attached to the aircraft surface (i.e., the surface of the composite structure) and the inspection probe1402is imbedded with a position transducer so that the actual inspection area on the aircraft (i.e., position of the probe1402) is mapped onto the user interface (i.e., display screen)1412of the system to present a graphical or visual representation of defects detected.

Those skilled in the art will realize that the position sensor/encoder1404and the probe1402transducer allow the linear coordinates of the probe1402relative to a defined frame on the aircraft surface to be determined. Referring toFIG. 15, a graphical representation1500of defects1502,1504,1506detected are presented by the system ofFIG. 14in accordance with the present embodiment. As can be seen inFIG. 15, the area to be inspected can be gridded with a user-chosen number of uniform rows1508and columns1510to form a display panel1512comprised of a number of grid boxes1514. Each of the grid boxes1514is utilized to display the inspection result of the corresponding points on the actual aircraft surface. In the actual inspection operation, the user scans the inspection area1406with the probe1402and the processed results are displayed bit by bit in the grid boxes1514. The results of the inspections are illustrated with visual parameters such as shapes or colors corresponding to the defect types assigned during the reference data base building stage802,900to convey information such as defect location information, defect size information and/or the defect type information.

Thus it can be seen that the present embodiment is capable of identifying defect types and depths in composite structures and can generate a grid-based map of inspection areas with a handheld non-destructive testing apparatus. The present embodiment also advantageously allows the inspection scan results to be generated efficiently and saved for future use, thereby greatly enhancing the maintenance, repair and overhaul (MRO) operations for aircraft composite structures. Compared with conventional non-destructive testing for composite structures, methods and apparati in accordance with the present embodiment are able to detect and identify many defect types and clearly and effectively illustrate the inspection results on a display screen, including information on location, geometry and types of defects. While the results can be obtained by manually scanning the surface area, the method can be implemented on either a hand-held system for manual inspection or a X-Y stage for automated inspection.

Referring toFIG. 16, a diagram1600of a first geometry of transducers on a probe for use in the system1400in accordance with the present embodiment is shown. A probe for an in-service non-destructive test for the aerospace industries based upon the pitch-catch probe (which can be utilized in both isotropic materials, such as aluminum, as well as in anisotropic materials, such as carbon fiber or glass fiber composite) includes transducers1602in a two-dimensional transducer arrangement where the distance between each adjacent transducer is equal.FIG. 16shows the alignment of the transducers1602with scanning point/lines1604, wherein three transducers1602are depicted. Each of the transducers1602is separately configurable as a transmitter for transmitting excitation signals or as a receiver for receiving probed signals.

FIG. 17is a diagram1700of a second geometry of transducers1602,1702on a probe extending the arrangement depicted inFIG. 16in accordance with the present embodiment.FIG. 17shows the flexibility of the probe design in accordance with the present embodiment for future addition of transducers. It can be seen in the diagram1700that with each additional transducer1702, two scanning points1704can be obtained.

FIG. 18is a diagram1800of a third geometry of transducers1802on a probe for use in the system ofFIG. 14in accordance with an alternate embodiment and includes distances between the transducers1802and the distance between the scanning points1804. This third geometry depicted inFIG. 18includes four transducers1802located to form a rhombus shape.

Referring next toFIG. 19a front, right, top perspective view1900of a handheld probe for use in the system ofFIG. 14in accordance with the alternate embodiment includes a housing1902. The transducers1802can be seen projecting from the bottom of the probe and supporting legs1904help maintain the probe in a fairly even, upright position throughout an inspection scan and at an even distance from the surface of the composite structure being scanned. The supporting legs1904further ensure balance of the probe and prevent the transducers1804from being over-pressed while during the inspection scan.

FIG. 20depicts a bottom, left, front exploded perspective view2000of the handheld probe ofFIG. 19in accordance with the alternate embodiment. The view2000shows the modular design of the array probe housing to allow flexibility in replacing and modifying parts of the housing.

FIG. 21includes a pair of transducer configuration diagrams2100,2110illustrating transmitter and receiver assignment of the transducers in an array2102of transducers during operation of the system ofFIG. 19in accordance with the four transducer alternate embodiment. In the first iteration2100, transducer (1) acts as a transmitter2104while transducers (2), (3), and (4) act as receivers2106. The next iteration2110, transducer (2) acts as a transmitter2104while transducers (3) and (4) remain as receivers2106. In this stage, transducer (1) actually behaves as a receiver; however the recorded signal can be ignored due to the similarity from the first iteration and so transducer (1) is treated as an inactive transducer2112.

The four transducer array probe is capable of inspecting multiple scan points/lines at one time thus reducing inspection time. Further it is capable of addressing fiber orientation in composite materials and more accurately determining the probability of a defect. The four transducer array reduces overlapping of scanned areas and, correspondingly, reduces missing spots or uninspected areas.

As can be seen fromFIGS. 16 to 18, the three or more transducers in the array probe are arranged systematically where the distances from one transducer to the adjacent ones are equal. Such arrangement ensures that the wave propagation distance between the transmitter and the receiver is the same, which allows flexibility of the transducers to be reconfigured as transmitters or receivers. It can also be seen that such arrangement allows future transducer addition to be incorporated without significant modification to the algorithm. For each additional transducer, two measurement points can be obtained with the proposed arrangement.

The array probe housing1902is designed to provide user comfort during operation and scanning. The round-shaped outer housing1902is designed to fit comfortably in an adult human hand. In addition, the housing1902is designed in modules to allow flexibility in design modifications as depicted inFIG. 20. Therefore, any changes to the transducer arrangement do not require the entire housing to be redesigned.

The proposed arrangement of the transducers, as well as the reconfigurability of each transducer as a transmitter or receiver, allows up to five (5) measurement points/lines to be obtained from each run. Referring to iteration2100, transducer one (1) is configured as a transmitter2104, while the others are configured as receivers2106. In the second iteration2110, transducer two (2) is configured as a transmitter2104while transducers three (3) and four (4) remain as receivers2106. In the second iteration2110, transducer one (1) acts as a receiver2106, but the received signal can be ignored

Compared with the conventional pitch-catch probes, a key unique feature of the transducer array probe in accordance with the present and alternate embodiments is the use of multiple transducers (i.e., three or more transducers), which are systematically arranged to achieve the optimal performance in terms of scan time and efficiency. As a result, multiple measurements can be obtained from a single excitation. The proposed transducer arrangement maintains the same distance from each transducer, which allows the flexibility to interchange the transmitting and receiving process. In addition, the placement of the transducers is such that the array probe is able to address the fiber orientation in composite materials. Another benefit of using the array probe is a higher degree of confidence in determining a defected area. In particular, measurement results can be aggregated and used to statistically determine the probability of a defect. Lastly, the use of the array probe in accordance with the present and/or alternate embodiments along with an automated process reduces the chances of uninspected spots, while maintaining reasonable scan time.

Thus, an probe for performing one-sided non-destructive testing for aircraft composite materials in accordance with the alternate embodiment ofFIGS. 18 to 21includes four (4) transducers, spaced twenty millimeters (20 mm) apart from one another and arranged to form two isosceles triangles; four (4) support legs; and a modular housing design to allow flexibility in future modifications. A probe in accordance with this alternate embodiment can achieve faster scanning as compared to traditional pitch-catch probe by, in addition to other benefits, reducing overlapping in scanned areas. Such probes can also achieve a high probability of defect detection due to the multiple scanning points, and achieve more accurate scan due to the reduction of missed areas. Further, such probes can address fiber orientations of the composite materials due to the angled placement of the transducers.

While probes designed in accordance with the present and/or alternate embodiments are well suited for aircraft maintenance, repair, and overhaul (MRO), they may also be used for inspections in other applications, such as welding and joint inspections.

Thus it can be seen that a method and apparatus for Lamb wave-based non-destructive testing of composite structures which distinguishes between a variety of defects types not previously distinguishable and which provides a more user-friendly presentation of test results has been disclosed which advantageously provides a more efficient, accurate and user-friendly inspection process for detecting defects in composite structures. While at least one exemplary embodiment has been presented in the foregoing detailed description of the invention, it should be appreciated that a vast number of variations exist, including a vast number of probe designs that are useful for such method and apparatus.