NDT test method for specimen

Abstract

The present invention relates to a method for non-destructive testing of a test object by means of acoustic waves, the method comprising the steps of (S2) receiving raw data indicative of acoustic waves propagated through the test object (4) from an inspection device (5) in a measurement position in mechanical contact with the test object (4), (S3) offering an option to process the raw data by at least a first and a second processing algorithm, and (S4) processing the raw data by at least one of the first and second processing algorithms. The first processing algorithm comprises deriving information about the test object (4) from multiple reflections of the acoustic waves. The second processing algorithm comprises deriving information about the test object (4) from the travel time of a single reflection of the acoustic waves. Furthermore, the present invention relates to a system for carrying out the method, including an inspection device. The inspection device comprises a housing (1), a contact element (2) protruding from the housing (1) and including a cavity (25), and an acoustic wave sensor (3, 51) mounted in the cavity (25).

Description

[Technical Field]

[0001] The present invention relates to a method, an inspection system, and an inspection device for non-destructively inspecting a test object using acoustic waves. [Background technology]

[0002] In the field of non-destructive testing (NDT), acoustic waves are commonly used to examine man-made structures such as slabs, pavements, walls, decks, piles, and shafts made of concrete, wood, metal, etc. Depending on their shape, structures can be classified into plate-like structures such as slabs, pavements, walls, and decks, and pile-like structures such as piles and shafts. Information obtained about the structure includes the thickness of the (plate-like) structure, the length of the (pile-like) structure, and the general internal characteristics of the structure (such as defects).

[0003] The principle of inspecting structures using acoustic waves can be applied to both plate-like structures and pile-like structures, but the equipment used to measure acoustic waves and the methods used to process the measured data have traditionally differed between the two categories of structures.

[0004] Impact echo (IE) is an NDT technique that uses impact-generated stress (acoustic) waves that propagate through plate-like structures and are reflected by internal defects and external surfaces. Impact echo can be used to assess the thickness of thin concrete structures such as slabs, pavements, walls, and decks, and to identify defects such as cracks, spalling, voids, honeycombing, and spalling. A steel ball impactor is typically used to generate the acoustic waves. The diameter of the ball is usually selected based on the expected thickness of the structure. IE is based on measuring multiple wave reflections over a short period of time. As a result, IE probes must be capable of measuring high frequencies, e.g., above 10 kHz, and especially up to approximately 30 kHz. The measured acoustic waves are then analyzed in the frequency domain to determine the integrity of the structure.

[0005] Pile integrity testing (PIT), also known as low-strain dynamic testing or low-strain integrity testing, is a nondestructive testing method used to assess the integrity of piles and shafts. This method is primarily applied in civil engineering to assess the integrity of concrete piles, such as those used in timber shafts and deep foundations, but is not limited to this. Similar to impact echo, this method relies on impact-generated stress (acoustic) waves. The acoustic waves are typically generated using a hammer at the top of the pile, located next to the probe. The acquired signal represents the propagation time, or travel time, from the initial impact to the waves reflected from the bottom of the pile or from any defects in the pile. In PIT, the waves travel a longer distance than in IE, so generally only a small fraction of the reflected waves are captured. As a result, PIT probes typically perform at low frequencies, such as 100 Hz to 10 kHz. The integrity of the structure is then determined by analyzing the time-domain waveforms.

[0006] Because the two fields, IE and PIT, are separate and have different requirements, the probes and processing algorithms used in one field are not suitable for the other, and vice versa. This means that an inspector who wants to inspect both plate-like and pile-like structures must prepare two types of equipment, i.e., probes and processing algorithms, which is impractical and costly. Summary of the Invention

[0007] The problem that the present invention aims to solve is therefore to provide an improved method and apparatus for non-destructive testing of test bodies by means of acoustic waves, and in particular to extend the range of application of such a method and apparatus, in particular to apply it to different types and shapes of test bodies.

[0008] The differences in the types and shapes of the test specimens can be defined as follows:

[0009] Specifically, "plate-like" means that the two lateral dimensions of the specimen are significantly greater than the depth dimension of the specimen, e.g., at least two or three times greater. Plate-like specimens are, for example, slabs, pavements, walls, decks, etc. They are typically made of concrete, reinforced concrete, or rock.

[0010] In particular, "pile-like" means that the depth dimension of the specimen is significantly greater than the two lateral dimensions of the specimen, for example, two or three times greater. Pile-like specimens are, for example, piles or shafts. These are usually made of concrete, metal, especially iron or steel, or wood.

[0011] Both the plate-shaped and pile-shaped specimens can have any shape in the horizontal plane, i.e., in the two horizontally extending planes. In particular, the shape in the horizontal plane can be circular, rectangular, or square. Furthermore, the shape in the horizontal plane, i.e., the cross section in the horizontal plane, can vary along the depth direction.

[0012] In both the plate-shaped test specimen and the pile-shaped test specimen, the measurement position, particularly the impact position for generating the acoustic waves, is located on the measurement side of the test specimen, particularly substantially coinciding with the horizontal plane.

[0013] Test Method According to a first aspect of the present invention, this problem is solved by a method for non-destructively testing a specimen with acoustic waves. The method includes receiving raw signals indicative of acoustic waves propagated through the specimen from an inspection device at a measurement location in mechanical contact with the specimen. To generate the acoustic waves, the method may include generating acoustic waves at an impact location on the specimen, particularly by impacting the specimen with an impactor such as a hand-held hammer or steel ball. Such impacts generate acoustic waves over a wide range of frequencies.

[0014] As acoustic waves propagate through a test specimen, they are attenuated, reflected, and scattered. These effects can be frequency-dependent, i.e., they can affect different frequency components of the acoustic wave differently. Reflected acoustic waves are typically processed to obtain information about the specimen, such as its thickness and length, or material properties such as defects and sound velocity. These reflections may be reflected from one or more discontinuities within the specimen, such as flaws, layers, or specimen boundaries. These are therefore referred to as single and multiple reflections, respectively. Depending on the material, dimensions, and shape of the specimen, the dominant frequency components of the reflected waves range from 100 Hz to 30 kHz. For a typical plate-shaped specimen, the dominant frequency components of the reflected waves are between 5 and 30 kHz. For a typical pile-shaped specimen, the dominant frequency components are between 100 Hz and 6 kHz, due to the greater attenuation of higher frequencies due to the longer travel path.

[0015] The method further comprises: providing an option to process the raw data with at least first and second processing algorithms; processing the raw data with at least one of a first and a second processing algorithm; the first processing algorithm includes deriving information about the test object from multiple reflections of the acoustic wave; The second processing algorithm involves deriving information about the test piece from the travel time of a single reflection of the acoustic wave.

[0016] The first processing algorithm may be suitable for obtaining information about a plate-shaped specimen, and in particular may be an algorithm used in impact echo testing, such as a conventional IE algorithm.

[0017] The second processing algorithm is suitable for obtaining information about pile-like specimens. In particular, the second processing algorithm may be an algorithm used in pile integrity testing, such as a conventional PIT algorithm. The two types of algorithms are described in detail in the next chapter.

[0018] The raw data received from the inspection device according to the method is preferably processed by a first and / or second processing algorithm. This means that the same inspection device can be used to acquire data for both plate-shaped and pile-shaped specimens. The requirement, as mentioned above, is that the device be sensitive to acoustic waves in the relevant frequency range. Examples of devices capable of acquiring suitable raw data are listed below:

[0019] In one embodiment, the method is implemented on a computer and provides a user with options for processing the raw data, e.g., via a GUI. The user may then be prompted to select either a first or second processing algorithm for processing the raw data. Alternatively, the method may include automatically selecting the first or second processing algorithm based on characteristics of the raw data, e.g., frequency range, dominant frequency content, or travel time of reflected waves in the data. In another embodiment, the method may include processing the raw data with both the first and second processing algorithms. This may include, for example, displaying the data processed by both algorithms to the user, e.g., in the frequency and time domains, e.g., via a GUI.

[0020] Plate-shaped specimen The first processing algorithm may be an algorithm, such as an IE algorithm, adapted to process raw data acquired on a plate-shaped specimen. Thus, the first processing algorithm may include determining a frequency spectrum of the raw data, particularly by applying a Fourier transform to the raw data. Furthermore, the first processing algorithm may include using frequency components of the raw data having frequencies of at least 15 kHz, particularly at least 20 kHz. This is due to the plate-like shape of the specimen, where the depth dimension of the reflected waves propagating laterally through the specimen is on the order of 1 cm or 10 cm to 1 m.

[0021] In one embodiment, the first processing algorithm includes detecting a dominant frequency component in the frequency spectrum. In particular, the dominant frequency component can be defined as the maximum frequency component, i.e., the Fourier component with the largest amplitude within a defined frequency range, e.g., between 5 and 30 kHz. Alternatively, the dominant frequency component can be determined by determining the maximum value of the envelope mean or windowed mean of the frequency spectrum, e.g., within a defined frequency range.

[0022] Preferably, the method further comprises receiving raw data from a plurality of different measurement positions from the inspection device and collecting a data set containing the dominant frequency components for each measurement position. Such a data set can be visualized, in particular by displaying it as a heat map. This means that the raw data from the inspection device is acquired at different measurement positions on the measurement side of the specimen, e.g., at intervals of 1 to 50 cm from each other. Typically, the impact position is shifted together with the measurement position. Typically, the impact position is in the vicinity of the measurement position, e.g., at a distance of 1 to 50 cm, in particular 10 to 20 cm, from the measurement position.

[0023] To obtain information about the specimen from the raw data, the method can further include detecting dominant frequency components that deviate from other dominant frequency components in the dataset. "Deviating" can be defined, inter alia, as deviating from the average value, e.g., the mean or median, of the dominant frequency components by more than a certain threshold, e.g., a standard deviation or a certain percentile, e.g., the 10% or 90% percentile. In particular, deviating dominant frequency components may be due to defects, e.g., cracks, spalls, voids, honeycombs, and delaminations, located at the corresponding measurement locations. Such detection of deviating dominant frequency components can also be performed manually by a user, for example, by evaluating data visualized as a heat map over the measurement locations, as described above.

[0024] Alternatively, the first processing algorithm may include detecting the thickness of the test object based on the dominant frequency component, which is particularly useful when the test object has a plate-like shape in which the acoustic waves propagate transversely to the plate-like shape.

[0025] Pile-shaped test specimen The second processing algorithm may be an algorithm adapted to process raw data acquired on a pile-like specimen, such as a PIT algorithm. Accordingly, the second processing algorithm may include evaluating the raw data in the time domain. Furthermore, the second processing algorithm may include using frequency content of the raw data up to 10 kHz, particularly between 100 Hz and 10 kHz. This is typically the frequency range of a single reflection of an acoustic wave in a pile-like structure, with the acoustic wave propagating along the longitudinal direction of the pile-like structure. In particular, the depth dimension of such pile-like structures, which is typically parallel to the longitudinal direction, is on the order of 1 to 50 m.

[0026] The second processing algorithm may include determining the length of the specimen based on the travel time of a single reflection of the acoustic wave. The specimen is assumed to have a pile-like shape with the acoustic wave propagating along its length. In this case, the single reflection may occur on the bottom surface of the specimen opposite the measurement side or on a defect within the specimen.

[0027] A requirement for determining the length or thickness of a specimen from travel time or frequency measurements is that the speed of sound within the specimen be known. Therefore, the speed of sound can be input as a standard value for the material of the specimen. Alternatively, the method may include estimating the speed of sound from measurements of travel time over a known distance, for example, along the measurement side between the impactor and the measurement location, or from measurements of travel time from the impact location through a known length of specimen and back to the measurement location.

[0028] Acoustic wave generation As mentioned above, the method includes generating acoustic waves at the impact location of the test piece, in particular by impacting the test piece with an impactor. The acoustic waves can be generated, for example, by striking the test piece manually, in particular with an impact hammer. Such an impact hammer may have a size of 10 cm to 30 cm and a weight of, in particular, 300 g to 3 kg.

[0029] Alternatively, generating acoustic waves may include activating an automated impactor to strike the test piece. Such an impactor may include a spring-loaded test weight. If the impact location is located a known distance from the measurement location, for example, by attaching the impactor to an inspection device, thereby defining a known distance between the impact location and the measurement location, the method may further include determining the speed of sound within the test piece based on the known distance. If directly arriving waves are evaluated, i.e., surface waves propagating along the measurement surface are evaluated, a correction factor must be applied to match the speed of the surface waves with the speed of sound within the test piece.

[0030] In one embodiment, particularly when acquiring data for pile-like structures, the method further comprises repeatedly generating acoustic waves at the impact locations to thereby generate a plurality of raw signals, particularly a plurality of raw signals for each measurement location. The plurality of raw signals may then be averaged, particularly for each measurement location, before determining the travel time. This improves the signal-to-noise ratio of the data and allows for a more accurate determination of the arrival time, and therefore the travel time, of the reflected waves.

[0031] Inspection System A second aspect of the present invention is an inspection device including an acoustic wave sensor (one embodiment of such an inspection device is described in detail below); The present invention relates to an inspection system including means adapted to perform the steps of the above-described method (such means may include processing means such as a CPU or FPGA). Furthermore, the means may be a personal computer, laptop or tablet computer capable of communicating with the inspection device. Preferably, the means includes a display configured to display a graphical representation of the raw data and / or processed data to a user.

[0032] In particular, the system may comprise a first processing means adapted to execute a first processing algorithm and a second processing means adapted to execute a second processing algorithm.

[0033] Furthermore, the inspection system may include an automated impactor as described above. The automated impactor is preferably in communication with a processing means, such as a tablet computer. In particular, the automated impactor is configured to send an activation signal to the processing means when the impactor impacts the specimen. This can be used as a start time for determining the travel time.

[0034] The above-described methods may also be implemented by a computer program, which may include instructions for causing an inspection system to perform the steps of the methods.

[0035] Inspection Equipment A third aspect of the invention relates to an inspection apparatus, in particular for the inspection system described above, meaning that all features described with respect to the system and method are also applicable to the inspection apparatus and vice versa.

[0036] The inspection device includes: a housing, for example made of plastic, in particular a protective enclosure, e.g., splash-proof and dust-proof, the housing having an ergonomic shape that allows the user to hold it easily and securely, and may for example be provided with a grip. - A contact element protruding from the housing and forming a cavity: In particular, the contact element is adapted to mechanically contact, e.g., be pressed against, the test object at the measurement location. The contact element preferably has a plate-like shape. In particular, the contact element preferably consists of a single plate of metal, more particularly stainless steel, which is preferably corrosion-resistant even when in contact with concrete. In one embodiment, the part of the contact element protruding from the housing has a conical, rounded, or flat shape. Each of these features contributes to a good mechanical coupling between the contact element and the test object for accurate, particularly sensitive, measurement of acoustic waves in the test object. In another embodiment, the contact element can completely cover the bottom surface of the device and thus "protrude" from the housing. Furthermore, especially in PIT measurements, applying an additional couplant, such as putty or gel, to the contact element or to the test object at the measurement location can further improve the coupling and increase sensitivity. - Cavity-mounted acoustic wave sensor: Preferably, the acoustic wave sensor is mounted, especially glued, to the wall of the cavity, especially to the wall extending along the impact direction of the contact element. This allows for a good coupling between the wave sensor and the contact element and thus the test piece, resulting in a particularly high sensitivity in a wide frequency range, for example, from 1 to 30 kHz, especially from 5 to 20 kHz. Furthermore, in this frequency range, spurious frequencies due to the natural vibrations of the sensor and the system of sensor and contact element can be avoided.

[0037] The acoustic wave sensor can be any sensor suitable for measuring vibrations in the above frequency range. Preferably, the acoustic wave sensor is a piezo or MEMS accelerometer, particularly a capacitive MEMS accelerometer. Such MEMS accelerometers are highly sensitive and cover the required frequency range. In particular, the raw data representing the acoustic waves measured by the acoustic wave sensor can cover a frequency range from zero to at least 15 kHz, particularly at least 20 kHz.

[0038] In one embodiment, the acoustic wave sensor is arranged on a flexible carrier or wire, in particular a flex print, to avoid transmission of vibrations from, for example, the housing via the carrier to the sensor. Furthermore, such a carrier avoids that the carrier's natural vibrations are present in the required frequency range. In this respect, it is also preferred that the flexible carrier extends along the impact direction of the contact element.

[0039] Furthermore, the contact element can be mechanically decoupled from the housing via a damping element between the contact element and the housing. In particular, the damping element can dampen the amplitude of vibrations of the housing by at least 50%, in particular by at least 90%, before reaching the contact element. In an embodiment, the damping element can comprise at least one O-ring, for example made of rubber. In a further embodiment, the damping element can comprise a damping adhesive.

[0040] Furthermore, the contact element can have a protrusion that is held in a corresponding notch in the housing. In particular, the protrusion extends from a circumferential side of the contact element. This facilitates a water- and dust-proof installation of the contact element in the housing while still being mechanically decoupled. In such an embodiment, the protrusion can be held in the notch by a damping element, in particular by at least one or two O-rings.

[0041] In one embodiment, the diameter of the contact element is 10-50 mm, particularly 20-30 mm. The height of the contact element may be 5-15 mm. Such contact elements do not have natural vibrations in the relevant frequency range that would otherwise lead to spurious frequencies in the raw data.

[0042] The protrusions of the contact elements preferably protrude from the housing by at least 2 mm, so that when the inspection device is pressed against the test piece to ensure a good connection, only the contact elements, and not the housing, come into contact with the test piece.

[0043] The cavity preferably has a slot-like shape, particularly adapted to the shape of the acoustic wave sensor on the carrier. In particular, the cavity may have a width of 5 mm or less, particularly 3 mm or less, and a length of at least 10 mm. Furthermore, the cavity may have a depth between 5 mm and 10 mm and / or rounded edges. To easily fix the sensor in the cavity, the acoustic wave sensor can be attached to the cavity by a groove top. These dimensions and features also avoid spurious frequencies in the raw data acquired by the sensor, making the device robust.

[0044] In one embodiment, the contact element is attached to a first end of a housing, the housing extending between the first end and the second end. The portion of the housing extending between the first end and the second end can have a diameter or width of 1 to 10 cm, particularly 4 to 7 cm. The length of the portion of the housing extending between the first end and the second end can be 5 to 15 cm, particularly 7 to 10 cm. Such a housing is compact and can be easily and safely held in one hand.

[0045] Advantageously, the device does not comprise an actuator or impactor. This prevents vibrations generated by the actuator or impactor from propagating inside the device, for example along the housing, and affecting the measurement data. However, the inspection system may also comprise an actuator or impactor in addition to the inspection device. The actuator or impactor may be attached to an impactor housing. In an embodiment, the impactor housing may be attached to the inspection device, preferably at a defined distance, in particular by providing a damping element between the impactor housing and the housing of the inspection device, to prevent vibrations from the impactor from reaching the sensors and adversely affecting the measurement data.

[0046] In a preferred embodiment, the inspection device further comprises a communications module, in particular a Bluetooth® transmitter or other wireless transmitter, configured to transmit raw data indicative of the acoustic waves measured by the acoustic wave sensor, which is received by processing means, such as a laptop or tablet computer, and processed according to the method described above.

[0047] As is clear from the described features, such an inspection device has a wide range of applications. In particular, such a device can be used for data acquisition for IE as well as PIT. This allows the user to inspect not only pile-like structures but also plate-like structures, while only purchasing, carrying, and maintaining one device.

[0048] Further preferred embodiments are set forth in the dependent claims as well as in the following description. [Brief explanation of the drawings]

[0049] The invention will be better understood, and further objects thereof will become apparent, from the following detailed description, which refers to the accompanying drawings. [Figure 1] FIG. 1 is a perspective view of an inspection device according to an embodiment of the present invention. [Figure 2] FIG. 2 shows the elements of the test device of FIG. 1 in an open state. [Figure 3] FIG. 3 shows a cross section of the inspection device of FIG. [Figure 4] FIG. 4 shows a portion of the inspection device of FIG. 1 in an open state. [Figure 5] FIG. 5 shows a detailed cross-section of the inspection device of FIG. [Figure 6] FIG. 6 illustrates an inspection apparatus and system according to an embodiment of the present invention. [Figure 7] FIG. 7 is a flow diagram of an NDT inspection method according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0050] 1 is a perspective view of an embodiment of the testing device of the present invention. The device comprises a housing 1, for example made of plastic. For ease of use, and in particular for ease of grip, the housing 1 is provided with a knob 12, for example in the shape of a Swiss cross, which is preferably made of plastic or rubber. Furthermore, the housing 1 is provided with a fastening part 11, for example in the form of a loop, for attaching a ribbon used to securely hold the device.

[0051] Various control and input / output elements are located on a top side 17 of the housing, opposite a bottom side 18 with contact elements (not shown in FIG. 1 ). Typically, the device can include a button 13 configured to switch the device on and off. The button 13 may further be configured to control an acoustic wave sensor (not shown in FIG. 1 ), and in particular, the button 13 may be configured to activate the acoustic wave sensor and initiate a measurement. This has the advantage, compared to other measurement activation methods, such as measuring while the device is powered on, that only relevant data is acquired, simplifying data processing. In particular, during processing, it is no longer necessary to define a time window within which relevant data is located.

[0052] Generally, the device may include an indicator, e.g., an LED, configured to indicate the operating state of the device, such as "on" or "measure." Such an indicator may be included on button 13. Preferably, button 13 facilitates one-button control of the device, as described above.

[0053] On the top side 17, the device further comprises a Bluetooth® module 14 and a USB connector 15, which together function as communication modules, for example for transmitting the measured raw data to a processing unit. The USB connector 15 can also be used to charge the rechargeable battery that powers the device. Such a rechargeable battery (see Figure 2) can be replaced by opening the housing 1 using a knob 16.

[0054] 1, the button 13, the Bluetooth module 14, and the USB connector 15 are located on the top side 17 of the housing for easy access and ease of use of the device. However, each of these elements, especially the button 13, can also be located elsewhere, such as on a side wall of the housing 1 intermediate the top side 17 and the bottom side 18.

[0055] Figure 2 shows the inspection device of Figure 1 with the side walls of the housing 1 removed. In particular, only the bottom 23 and top 24 of the housing 1 are shown, thus revealing the internal elements of the device. The device comprises a contact element 2, which in this embodiment has a plate-like shape and a substantially circular cross section in the horizontal plane. The contact element 2 is made of steel and is configured to mechanically couple to a test object for measuring acoustic waves.

[0056] The contact element 2 is attached to the housing 1, in particular to the bottom 23, by means of a fixing element 21 that is screwed to the housing. Preferably, the contact element 2 is attached to the housing via a damping element (see e.g. Fig. 5) and is mechanically decoupled from the housing as described above.

[0057] The device further comprises a battery 22 as a power source, for example a rechargeable battery as described above.

[0058] Figure 3 shows a cutaway view of the device with the same elements as described above, in particular how the fastening part 11 is formed by a recess in the housing 1 and a small rod passing through the recess, thereby forming a loop for attaching, for example, a ribbon.

[0059] The contact element 2 has a protrusion that protrudes from the housing 1, in particular from the bottom 23 of the housing, for example by at least 2 mm. The protrusion may have a rounded or conical shape, which ensures a good connection between the contact element and the test piece.

[0060] Furthermore, the contact element 2 comprises a cavity 25 in the form of a slot for mounting an acoustic wave sensor (not shown in FIG. 3 ), the shape and dimensions of which are preferably adapted to those of the acoustic wave sensor, typical dimensions being given above.

[0061] 4 shows the bottom 23 of the housing with the contact element 2 and the acoustic wave sensor 3 mounted on a flexible carrier 31 in a slot in the contact element 2. The sensor 3 is a MEMS acceleration sensor, which has high sensitivity and a wide frequency range as described above. Alternatively, the sensor 3 may be a different type, for example a piezoelectric sensor, configured to sense acoustic waves in a relevant frequency range, for example for testing plate-like and pile-like specimens, as described above.

[0062] Preferably, the sensor 3 is mounted entirely within the cavity 25. In other words, no part of the sensor 3 protrudes from the cavity 25. Furthermore, the sensor 3 is fixedly glued to the cavity, in particular to at least one side wall of the cavity parallel to the impact direction of the contact element 2. This can be achieved in particular by a grove top covering the sensor 3 and the cavity 25. Such a method of mounting the sensor 3 to the contact element 2 prevents the sensor 3 from picking up spurious frequencies, i.e. signals that are not indicative of acoustic waves in the test piece, for example from vibrations of the sensor 3 itself or of the carrier 31.

[0063] The carrier 31 has leads that connect to the acoustic wave sensor 3, in particular connecting the sensor 3 to the communication module and the battery. The carrier 31 is preferably flexible, e.g. a flexprint, as this can minimize the transmission of spurious vibrations, e.g. from the housing, through the carrier to the sensor 3.

[0064] Figure 5 shows a cutaway bottom view of the device of the previous figure. The contact element 2 is attached to the bottom 23 of the housing via the fixing element 21. For this purpose, the contact element 2 is provided with a circumferential projection 33, which is held to the housing, in particular to the bottom 23, by the fixing element 21. Generally, the projection 33 may not extend over the entire circumference of the contact element 2, but may cover only a portion of the circumference. Alternatively, the contact element 2 may be provided with a number of protrusions adapted to attach the contact element 2 to the housing.

[0065] 5, an O-ring 32, for example made of rubber, is arranged between the contact element 2 and the housing, in particular the bottom 23 of the housing. Such an O-ring forms a damping element and is adapted to damp vibrations propagating through the damping element, in particular from the housing. In other words, the damping element mechanically decouples the contact element 2 from the housing at least to some extent, for example at least 50% or 90%. Furthermore, the O-ring 32 serves as a sealing element to protect the inside of the device, in particular making the housing splash-proof and dust-proof.

[0066] Opposite the protrusion 33, another O-ring 34 is arranged to separate and mechanically decouple the contact element 2 from the fixing element 21. This other O-ring 34 avoids spurious frequencies due to external vibrations, e.g. vibrations from the housing, being measured by the acoustic wave sensor. Generally, the other O-ring 34 may not be necessary, and one O-ring 32 may be sufficient as a damping element, for example if the fixing element 21 itself exhibits damping properties.

[0067] Generally, the above-described features contribute to making the inspection device sensitive to acoustic waves in a wide frequency range, e.g., 0-35 kHz, particularly 100 Hz-20 kHz. Therefore, such an inspection device can be used not only to inspect plate-like specimens using, for example, the IE method and algorithm, as described above, but also to inspect pile-like specimens using, for example, the PIT method and algorithm.

[0068] FIG. 6 illustrates an embodiment of an inspection system. The inspection system includes an inspection device 5, such as the one described above. Generally, the inspection device 5 includes an acoustic wave sensor 51 configured to measure acoustic waves by mechanically contacting a test specimen 4. As described above, the test specimen 4 can have various shapes, such as a board or a stake, and can be made of various materials, such as concrete, metal, or wood. To acquire data using the sensor 51, the device 5 is typically held against the surface of the test specimen, for example, by hand, to ensure a particularly good connection. For PIT, a putty or gel is preferably applied between the inspection device 5, particularly its contact element, and the test specimen surface to ensure a good connection. For IE measurements, the contact element typically requires dry-point contact, i.e., pressing against the test specimen surface without the use of a couplant such as putty or gel.

[0069] The system further comprises a processing unit 6 configured to receive and process the raw data from the device 5. Such a processing device may be, for example, a laptop or tablet computer, which is convenient for use in the field or at a testing site. Alternatively, the processing unit 6 may be integrated into the device 5. Preferably, the device 5 comprises a communication module 52, such as a Bluetooth transmitter, configured to transmit the raw data to a communication module 63 of the processing unit 6. Alternatively, the device 5 and the processing unit 6 may be connected by a cable, or the processing unit 6 may be integrated with the inspection device 5, i.e., located in the same housing.

[0070] Preferably, the processing unit 6 comprises a first processing means 61 for executing a first processing algorithm, such as the IE algorithm, as described above, and a second processing means 62 for executing a second processing algorithm, such as the PIT algorithm. The first and second processing means 61, 62 can be implemented, for example, as two separate or one common CPU or FPGA.

[0071] Furthermore, the processing unit 6 may comprise a display 64 connected to the first and second processing means 61, 62 and configured to display a graphical representation of the raw or processed data to a user. In particular, the processing unit 6 may be configured to perform the method as described above with respect to Figure 7 and further detailed below.

[0072] Such inspection systems have the advantage, among other things, that they can be used to examine specimens of different shapes and materials by applying different types of analysis to the raw data, for example, in the time domain or frequency domain. Therefore, users only need one inspection system, i.e., one inspection device and processing unit, to perform NDT inspections on-site or at a test site. This is more convenient than traditional solutions that require at least two inspection devices, saving time and money.

[0073] 7 illustrates an embodiment of a method for NDT inspection of a specimen that can be implemented by the system described above. In a preparation step S1, the system is set up. This includes powering on the inspection device, establishing communication between the device and a processing unit, and contacting the inspection device with the specimen at a measurement position.

[0074] In step S2, raw data representing the acoustic waves propagating through the test piece is received by the processing unit from the inspection device. The acoustic waves typically include reflected waves, e.g., single or multiple reflections, which, as described above, can be used to gain insight into the test piece. In particular, the acoustic waves are generated by an impactor, e.g., a hand hammer, that applies an impact at an impact location near the measurement location, e.g., at a distance of 4-50 cm, particularly 5-10 cm from the measurement location.

[0075] In step S3, the user may be explicitly offered different options for processing the raw data, in particular a first and a second processing algorithm. In this case, the user may select one of the processing algorithms depending on, for example, the geometry and / or material of the specimen. Alternatively, the applicable processing algorithm may be automatically selected based on characteristics of the raw data, such as frequency content or determined travel times. In another embodiment, no selection of processing algorithms may be possible, for example, because the raw data is processed by both the first and second processing algorithms.

[0076] Step S4 involves the actual processing of the raw data by at least one of the first and second processing algorithms.

[0077] In optional step S5, the processed data and, e.g., raw data, may be displayed to a user, e.g., via a GUI on a display of the processing unit. Preferably, the processing and display occurs in real time, e.g., with a time delay of less than 10 seconds, or even less than 1 second, before receiving the raw data. Thus, a user can directly evaluate the data acquired in the field and, if necessary, discard and repeat the measurement. In particular, the method may include displaying the raw data and / or the processed data to a user in the time domain and the frequency domain, e.g., simultaneously.

[0078] Additionally, the method can include user-adjustable processing steps, such as filtering and windowing steps, to improve signal quality and obtain better results, e.g., more accurate estimates of the specimen thickness or length, or more information about defects within the specimen. The invention disclosed in this specification includes the following aspects. <Aspect 1> A method for non-destructively inspecting a test piece using acoustic waves, comprising: (S2) receiving raw data indicative of acoustic waves propagating through the test piece (4) from an inspection device (5) located at a measurement position in mechanical contact with the test piece (4); (S3) providing an option to process the raw data by at least first and second processing algorithms; (S4) processing the raw data with at least one of the first and second processing algorithms; Including, the first processing algorithm includes deriving information about the test object (4) from multiple reflections of the acoustic wave; the second processing algorithm includes deriving information about the test object (4) from the travel time of a single reflection of the acoustic wave. method. <Aspect 2> the first processing algorithm comprises, in particular, determining a frequency spectrum of the raw data by applying a Fourier transform to the raw data; 2. The method of embodiment 1. <Aspect 3> the first processing algorithm comprises using frequency components of the raw data having frequencies up to at least 15 kHz, in particular up to at least 20 kHz; 3. The method of embodiment 1 or 2. <Aspect 4> the first processing algorithm includes determining dominant frequency components in the frequency spectrum; 4. The method of embodiment 2 or 3. <Aspect 5> receiving raw data from the inspection device (5) from a plurality of different measurement locations; collecting a data set including the dominant frequency components for each measurement location; In particular, displaying said dataset as a heatmap; 5. The method of embodiment 4, further comprising: <Aspect 6> detecting a dominant frequency component that deviates from other dominant frequency components in the data set; In particular, attributing the deviating dominant frequency components to defects located at the corresponding measurement locations; 6. The method of embodiment 5, further comprising: <Aspect 7> the first processing algorithm includes determining a thickness of the test specimen (4) based in particular on the dominant frequency component; In particular, the test piece (4) has a plate-like shape in which the acoustic waves propagate laterally relative to the plate-like shape. 7. The method according to any one of embodiments 1 to 6. <Aspect 8> the second processing algorithm includes evaluating the raw data in the time domain; 8. The method according to any one of embodiments 1 to 7. <Aspect 9> the second processing algorithm comprises using frequency components of the raw data having frequencies up to 10 kHz, in particular above 100 Hz; 9. The method according to any one of embodiments 1 to 8. <Aspect 10> the second processing algorithm includes determining a length of the test specimen (4) based on the travel time; In particular, the test body (4) has a pile-like shape in which the acoustic wave propagates along an extension line of the pile-like shape in the longitudinal direction. 10. The method according to any one of embodiments 1 to 9. <Aspect 11> generating the acoustic waves at an impact location on the test specimen (4), in particular by impacting the test specimen with an impactor; 11. The method of any one of embodiments 1 to 10, further comprising: <Aspect 12> The generating of the acoustic waves includes striking the test piece (4) by hand, in particular with an impact hammer; 12. The method of embodiment 11. <Aspect 13> generating the acoustic waves includes activating an automatic impactor to strike the test specimen (4); In particular, the impact location is located at a known distance from the measurement location; especially, determining the speed of sound in the test body (4) based on the known distance; 12. The method of embodiment 11, further comprising: <Aspect 14> repeatedly generating the acoustic wave at the impact location, thereby generating a plurality of raw signals; In particular, averaging the raw signals at one measurement location before determining the travel time; 14. The method of any one of aspects 11 to 13, further comprising: <Aspect 15> an inspection device (5) having an acoustic wave sensor (3, 51); A means (6) adapted to carry out the steps of the method according to any one of aspects 1 to 14; in particular first processing means (61) adapted to execute said first processing algorithm and second processing means (62) adapted to execute said second processing algorithm; An inspection system comprising: <Aspect 16> A computer program comprising instructions for causing an inspection system according to aspect 15 to perform the steps of the method according to any one of aspects 1 to 14. <Aspect 17> An inspection device for the inspection system according to embodiment 15, comprising: a housing (1); a contact element (2) protruding from said housing (1) and including a cavity (25); an acoustic wave sensor (3, 51) mounted within the cavity (25); An inspection device comprising: <Aspect 18> The contact element (2) has a plate-like shape. An inspection device according to embodiment 17. <Aspect 19> The contact element (2) is made of a single piece of metal, in particular steel, 19. The inspection device according to embodiment 17 or 18. <Aspect 20> The part of the contact element (2) that protrudes from the housing (1) has a conical or rounded shape, In particular, the protrusion of the contact element (2) protrudes from the housing (1) by at least 2 mm. 20. The inspection device according to any one of aspects 17 to 19. <Aspect 21> the contact element (2) is mechanically decoupled from the housing (1) via a damping element (32, 34), in particular at least one O-ring or a damping adhesive, between the contact element (2) and the housing (1); 21. The inspection device according to any one of aspects 17 to 20. <Aspect 22> the contact element (2) comprises a protrusion (33) which is held in a corresponding notch in the housing (1); In particular, the protrusions (33) extend from the circumferential sides of the contact element (2), 22. The inspection device according to any one of aspects 17 to 21. <Aspect 23> The protrusion (33) is held in the notch by the damping element (32, 34), in particular by at least one or two O-rings. 23. The inspection device according to claim 22. <Aspect 24> The diameter of the contact element (2) is between 10 mm and 50 mm, in particular between 20 mm and 30 mm; 24. The inspection device according to any one of aspects 17 to 23. <Aspect 25> the acoustic wave sensor (3, 51) is attached, in particular glued, to a wall of the cavity (25) extending along the impact direction of the contact element (2); An inspection device according to any one of aspects 17 to 24. <Aspect 26> The acoustic wave sensor (3, 51) is attached to the cavity by a globe top. An inspection device according to any one of aspects 17 to 25. <Aspect 27> The cavity (25) has a slot-like shape, In particular, the cavity (25) has a width of 5 mm or less and a length of at least 10 mm. 27. The inspection device according to any one of aspects 17 to 26. <Aspect 28> The acoustic wave sensor (3, 51) is a MEMS or piezo type acceleration sensor, in particular a capacitive MEMS acceleration sensor; 28. The inspection device according to any one of aspects 17 to 27. <Aspect 29> said acoustic wave sensor (3, 51) is arranged on a flexible carrier (31) or wire, in particular a flex print; In particular, the flexible carrier (31) extends along the impact direction of the contact element (2). An inspection device according to any one of aspects 17 to 28. <Aspect 30> The raw data representing the acoustic waves measured by the acoustic wave sensor (3, 51) covers a frequency range from zero to at least 15 kHz, in particular a frequency range of at least 20 kHz; 30. The inspection device according to any one of aspects 17 to 29. <Aspect 31> a communication module (14, 15, 52), in particular a Bluetooth transmitter, configured to transmit raw data representative of the acoustic waves measured by said acoustic wave sensor (3, 51); 31. The inspection device according to any one of aspects 17 to 30. <Aspect 32> The contact element (2) is attached to a first end (18) of the housing (1); The housing (1) extends between the first end (18) and the second end (17); The portion of the housing (1) extending between the first end and the second end has a diameter of between 1 cm and 10 cm and a length of between 5 cm and 15 cm. 32. The inspection device according to any one of aspects 17 to 31. <Aspect 33> The device does not include an actuator or impactor. 33. The inspection device according to any one of aspects 17 to 32.

Claims

1. A method for non-destructively inspecting a test piece using acoustic waves, comprising: (S2) receiving raw data representing acoustic waves propagated through the test piece (4) from an inspection device (5) at a measurement position in mechanical contact with the test piece (4), the acoustic waves including frequency components between 100 Hz and 20 kHz; (S3) providing an option to process the raw data with at least first and second processing algorithms; (S4) processing the raw data with at least one of the first and second processing algorithms; Including, the first processing algorithm includes deriving information about the test object (4) from multiple reflections of the acoustic wave; the first processing algorithm includes determining a frequency spectrum of the raw data; the second processing algorithm comprises deriving information about the test object (4) from the travel time of a single reflection of the acoustic wave; the second processing algorithm includes evaluating the raw data in the time domain; The method comprises: receiving raw data from the inspection device (5) from a plurality of different measurement locations; collecting a data set for each measurement location; The method further comprises:

2. The method described in claim 1, wherein the frequency spectrum is determined by applying a Fourier transform to the raw data.

3. 3. The method of claim 1, wherein the first processing algorithm comprises using frequency components of the raw data having frequencies up to 20 kHz.

4. The method of any one of claims 1 to 3, wherein the first processing algorithm comprises determining dominant frequency components in the frequency spectrum.

5. The step of collecting the dataset comprises: collecting a data set including the dominant frequency components; displaying the dataset as a heat map; The method of claim 4, comprising:

6. detecting a dominant frequency component that deviates from other dominant frequency components in the data set; associating the deviating dominant frequency component with a defect located at the corresponding measurement location; The method of claim 5 further comprising:

7. the first processing algorithm includes determining a thickness of the specimen (4) based on the dominant frequency component; The method according to any one of claims 4 to 6, wherein the test body (4) has a plate-like shape in which the acoustic waves propagate transversely relative to the plate-like shape.

8. The method of any one of claims 1 to 7, wherein the second processing algorithm comprises using frequency components of the raw data having frequencies between 100 Hz and 10 kHz.

9. the second processing algorithm includes determining a length of the test body (4) based on the travel time; The method according to any one of claims 1 to 8, wherein the test specimen (4) has a pile-like shape in which the acoustic waves propagate along a longitudinal extension of the pile-like shape.

10. The method according to any one of claims 1 to 9, further comprising the step of generating the acoustic waves by impacting an impactor against the test piece (4) at an impact location on the test piece.

11. 11. The method of claim 10, wherein the step of generating acoustic waves comprises manually striking the test specimen (4) with an impact hammer.

12. the step of generating acoustic waves includes a step of activating an automatic impactor to strike the test specimen (4); the impact location is located at a known distance from the measurement location; The method of claim 10, further comprising determining the speed of sound in the test body (4) based on the known distance.

13. repeatedly generating the acoustic wave at the impact location, thereby generating a plurality of raw signals; averaging the raw signals at one measurement location before determining the transit time; The method of any one of claims 10 to 12, further comprising:

14. an inspection device (5) having an acoustic wave sensor (3, 51); Means (6) adapted to carry out the steps of the method according to any one of claims 1 to 13, a first processing means (61) adapted to execute the first processing algorithm and a second processing means (62) adapted to execute the second processing algorithm; An inspection system comprising:

15. A computer program comprising instructions for causing an inspection system according to claim 14 to carry out the steps of the method according to any one of claims 1 to 13.

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