HK1160926B - Pulse-echo method with determination of the leading body geometry - Google Patents

Description

Pulse echo method with determination of the geometry of the precursor

The present invention relates to a pulse echo method for ultrasonic material inspection and a related device. This relates to an acoustic method for detecting material defects, in which ultrasound is used. Ultrasound examination belongs to a non-destructive examination method. It is thereby also possible to inspect the component in the mounted state, for example a support element of an aircraft. Ultrasonic inspection is a suitable inspection method for finding internal and external defects in acoustically conductive materials (to which most metals belong), for example in the case of welds, forgings, castings, semi-finished products or pipes. In engineering, an important task for the quality control of components is, for example, the safety of personnel transport devices or pipelines (e.g., pipelines for hazardous substances). Laid rails are conventionally inspected by test trains. Therefore, efforts are made to improve the reliability and accuracy of the method.

As with all inspection methods, ultrasonic inspection is standardized and performed according to criteria, for example, non-destructive inspection of forged parts made of steel according to DIN EN 10228-: ultrasonic inspection of castings composed of ferrite and martensitic steels, which is incorporated herein by reference. Suitable inspection devices and methods are known for the non-destructive inspection of workpieces by ultrasound. Reference is made in general to the specialist book Werkstoffpruefung mitrasfill, by J.and H.Krautkr (ISBN-13: 978-3-540-15754-0, 5 th edition (1996), Springer (Berlin)).

This method is generally based on the reflection of ultrasound on boundary surfaces. An ultrasonic head or probe is mainly used as a sound source, which radiates in a frequency range of 10kHz to 100 MHz. In the pulse echo method, the ultrasound head does not emit continuous radiation, but rather emits very short acoustic pulses, the duration of which is 1 μ s and less. The pulses emitted by the transmitter pass through the workpiece to be examined at the relevant speed of sound and are reflected almost completely at the solid-air boundary surface. The ultrasound head is usually not only able to transmit pulses but also to convert incoming pulses into electrical measurement signals, which then also operate as a receiver. The time required for the acoustic pulse to pass from the transmitter through the workpiece and back again is measured by means of an oscilloscope and a computer unit as an analysis unit. In this way, for example, the thickness of the workpiece can be checked, given the speed of sound c in the material. The core of such a probe is at least one ultrasonic transducer, for example in the form of a piezoelectric element. It is also known, for example from WO 2007/144271, to generate and receive ultrasound pulses using a phased array of a plurality of individually excitable ultrasound transducers in a fixed arrangement.

The transducer or transducers are usually coupled to the workpiece to be examined in the case of a wedge-shaped matching layer (also referred to as front conductor) which is/are, for example, usually composed of a thermoplastic composition, such as methyl methacrylate (PMMA). On the front conductor, there is a coupling surface via which the sound generated by the ultrasonic transducer or transducers can be coupled into the workpiece to be examined, wherein the wedge shape causes the sound to be incident obliquely into the workpiece. The front conductor and the piezoelectric element or elements are usually arranged in a housing which is closed on one side and has a coupling opening on the other side, through which ultrasound emitted by the acoustic coupling surface can exit.

For coupling between the workpiece and the probe (i.e. the lead body), a coupling medium, for example a paste (solvent), glue, water or oil, is applied to the surface of the workpiece to be examined. The probe is typically used to traverse the surface to be inspected. This can be done manually, mechanically or automatically (e.g. within a production line). In the latter case, the test piece is usually immersed in a suitable liquid (immersion bath technique) or is moistened in a defined manner for the purpose of transmitting the acoustic signal.

Knowledge of the dimensions of the front conductor in connection with the ultrasonic examination is important, for example, for the precise location of workpiece defects and/or the determination of workpiece dimensions. Furthermore, the geometry of the front conductor has a strong influence on the ultrasound examination by the so-called AVG method, in particular when the latter is carried out by means of a probe which permits electronic adjustment of the angle of incidence. In the case of a wedge-shaped front conductor, the dimensions relevant for the ultrasonic examination are, for example, the wedge angle alpha and the distance d between the coupling face of the front conductor (that is to say the boundary face adjoining the workpiece to be examined) and the midpoint of the face covered by the transducer on the opposite boundary face of the front conductor.

It is known that the connection between the ultrasonic transducer and the front body is constructed in a releasable manner in order to be able to change the examination conditions, such as the angle of incidence, during the ultrasonic examination of the workpiece, depending on the workpiece geometry to be examined and/or the desired examination direction in the workpiece, etc. Furthermore, it is known to store data specific to the leading wedge in a non-volatile memory connected to the leading wedge and to read this data and transmit it to an analysis unit during the ultrasound examination. This is disclosed, for example, in DE 3327526a1, which however proves to be very complex in practice, since data communication is required between the front conductor and the evaluation unit. In this way, a defective mounting (for example a twisted mounting direction) of the front conductor on the ultrasonic transducer cannot be detected.

Furthermore, it has been shown that: the dimensions of the front conductor change due to wear, in particular due to the frequently used, thermoplastic and therefore often very soft compositions and the often mostly manual displacement of the front conductor over the surface of the workpiece to be examined. Therefore, it is necessary to verify the size of the front conductor in relation to the ultrasonic examination. It is known from DE 3327526a1 to check the dimensions of the front conductor. This is achieved by the back wall echo of a special calibration body, which can be arranged adjacent to the coupling surface of the front body. This is comparatively complex and has an adverse effect on the accuracy of the measurement due to the change in the calibration body and the coupling between the calibration body and the precursor body.

Furthermore, DE 3441894a1 discloses the determination of the thickness dimension in a workpiece by means of back wall echoes of the workpiece.

Against this background, the inventors of the present invention have set themselves the task of providing an improved, more precise pulse echo method, in which the ultrasound-examination-relevant dimensions of the precursor are measured comparatively simply and, if appropriate, taken into account in the analysis of the ultrasound examination.

This object is achieved by a method according to claim 1 and by an apparatus according to claim 12. Advantageous embodiments are the subject matter of the dependent claims.

In a method for non-destructive ultrasonic inspection, at least one ultrasonic pulse is emitted into a workpiece to be inspected by means of at least one ultrasonic emitter. The invention is not limited in terms of the workpiece, but rather is generally constructed of acoustically conductive materials. The ultrasonic pulse is reflected at the boundary surface, for example at its back wall and at discontinuities in the workpiece. The reflected ultrasound is received by means of at least one ultrasound receiver and the associated signals are analyzed. The recorded signals are shown, for example, in a time-dependent or position-dependent view, for example, by means of an oscilloscope or a computer program product running on a computer having a display device. The location-dependent views are linked, for example, by speed of sound versus time-dependent views. The ultrasound penetrates a front conductor in its propagation from the transmitter to the workpiece and on its way back from the workpiece to the receiver, which is arranged between the workpiece and the transmitter or the receiver.

The method is characterized in that at least one step is provided before, during or after the aforementioned inspection of the workpiece, which is used to determine the dimensions of the front conductor relevant to the ultrasonic inspection, such as the thickness of the front conductor and/or the angle of its boundary surface. In this step, the travel time of at least one ultrasonic pulse generated by the ultrasonic transmitter, reflected on the boundary surface of the front conductor and received by the ultrasonic receiver is determined. In other words, the propagation time of the back-wall echo of the leading wedge is determined, for example by means of the speed of sound and/or the distance between the transmitter and the receiver. At least one dimension of the front conductor associated with the ultrasound examination is determined from the measured travel time. The terms transmitter and receiver may be interpreted functionally. In a further embodiment of the invention, it is therefore provided that the transducer acting on the transmitter also serves as a receiver for the ultrasound pulses previously transmitted by it. Alternatively, other transducers spaced from the transmitter may be used as receivers. In a simple embodiment of the method according to the invention, the determination of the current dimension of the front conductor can be used to verify its dimensional stability.

Furthermore, the geometry data of the front conductor relating to the ultrasound examination are provided in the ultrasound examination analysis without a structurally complex data exchange or a time-consuming manual data input between the analysis unit and the front body. Furthermore, wear-induced deviations can be determined by approximately simultaneous measurements. The measurement of the propagation time of the back wall echo through the front conductor does not require a calibration body. This simplifies the verification and its accuracy and enables field verification as well. It will be clear to the skilled person that the accuracy of the determination can be improved by repeating the steps for the dimensioning, the sound propagation folding back and/or by using other transducers, i.e. acoustic paths.

According to a further preferred embodiment, the front conductor is uncoupled during the step for determining at least one dimension of the front conductor. "uncoupled" is to be understood in the sense of the present invention as: the lead is not acoustically coupled to the workpiece to be inspected. For example, it is coupled to air. Thus, the coupled workpiece has no effect on the ultrasound propagation in the front conductor. In particular, when using a back wall echo, the coupling into the air increases the reflectivity and thus the accuracy of the determination due to the large change in the acoustic impedance when the front conductor transitions into the surrounding air. For this reason, an uncoupled state can in principle be understood to mean that the coupling surface adjoins any medium, the latter having an acoustic impedance which differs greatly from the material of the front conductor, so that preferably total internal acoustic reflection of the test sound occurs in the front conductor.

The dimensions are preferably calculated by means of the shortest acoustic path, which is obtained geometrically or by means of digital simulation, corresponding to the respective travel time.

Furthermore, according to a preferred embodiment, in the step for determining at least one dimension of the front conductor relevant to the ultrasonic examination, the propagation times of the back-wall echo obliquely impinging on the coupling surface adjoining or to be adjoining the workpiece and the propagation times of the at least one back-wall echo perpendicularly impinging on the coupling surface are measured. It can be shown that with a simple geometric design of the front conductor, in particular in the case of a wedge or in the case of two parallel boundary surfaces intersecting the sound propagation, calculations can be carried out with a low propagation time measurement, for example, with knowledge of the distance of the ultrasound transmitter from the ultrasound receiver only. Preferably, the method is therefore used in front conductors that are wedge-shaped or have two plane-parallel faces. The shortest acoustic path of the ultrasound can thus be determined from the propagation time by simple geometric calculations when dimensioning.

In a preferred embodiment, a phased array of selectively excitable ultrasound transducers, each of which serves as an ultrasound receiver or ultrasound transmitter, is used for carrying out the method. The use of a phased array opens up the possibility of easily matching the acoustic radiation to the geometry and/or attenuation of the preamble by the number and/or position selection of the selectively excitable transducers, so that the transmitted ultrasound pulses actually reach the receiver. Preferably, the phased array comprises more than two selectively excitable transducers.

In the step for determining at least one dimension of the front conductor in connection with the ultrasound examination, it is preferred to use the outermost ultrasound transducer of the phased array to improve the measurement accuracy.

Preferably, the determined dimensions of the precursor are taken into account when analyzing the signals from the ultrasonic examination of the workpiece, in order to be able to determine the position of the discontinuity with respect to the position of the transmitting and/or receiving transducer, for example, with greater accuracy.

This process is particularly useful in the case of precursors composed of thermoplastic compositions, in particular crosslinked polystyrene interpolymers (e.g. Rexolite)) A structured precursor is particularly suitable in the case, since it is subject to increased wear and thus to a continuous and strong change in its dimensions.

When analyzed in the step for determining the relevant dimensions of the front conductor, the signals of the receiving transducers of the phased array can be triggered for rising edges or zero crossings of the pulse echo in order to determine the propagation time. But surprisingly it has been shown that: this method is preferably used because the accuracy can be improved when triggering on the pulse peak of the received pulse echo. The analysis can be carried out, for example, in an excitation unit (not shown) which is formed separately from the probe. The digital and, if appropriate, analog excitation electronics required for exciting the phased array for transmitting the ultrasound pulses can also be combined by means of the excitation unit into a common excitation and evaluation unit.

In a further preferred embodiment of the method according to the invention, the size of the precursor determined in the context of the method according to the invention is taken into account in the analysis of the examination result. This may be relevant in particular for material examinations when using phased arrays for generating ultrasound pulses, in particular in the case of phased arrays which are excited in the field of ultrasound examinations so that the angle of incidence to the workpiece is adjusted electronically and controllably. For example, reference is made in the present context to patent applications DE 102008037173, DE 102008002445 and DE 102008002450 of the same applicant, which are combined with a generalization of the so-called AVG method for inspection devices with electronically adjustable angles of incidence. The disclosure of which is incorporated herein in its entirety by reference. Whereas, relatedly, the dimensions of the wedge-shaped front conductor can also be varied with respect to the varying wedge angle alpha, whereby the change in the angle of incidence in the material to be examined is likewise directly obtained. If the thickness dimension of the front conductor changes, this leads to a changed injection time in the test object, which is relevant when measuring the propagation time and thus determining the relevant position. In the case of a tapered front conductor, this also results in a change of the coupling input position. All the aforementioned parameters are automatically compensated for when the phased array is activated and/or taken into account when the examination results are evaluated, even in a preferred development of the method according to the invention. These particular method implementations can be implemented in particular in the excitation and evaluation unit described above.

In a further embodiment, the method further comprises a step for determining a reference point of the front conductor, for example an edge of the front conductor, to which the ultrasonic examination of the workpiece is to be fixed, for example in that it is finally arranged flush with an edge of the test body and the back wall echo of the test body is examined.

The invention further relates to a device for carrying out the method according to at least one of the advantageous embodiments described above. The device comprises at least one ultrasonic transmitter for transmitting at least one ultrasonic pulse into the workpiece to be examined, wherein the ultrasonic pulse is reflected in a boundary surface in the workpiece. Furthermore, at least one ultrasonic receiver for receiving the reflected ultrasound, an evaluation unit for evaluating the relevant signals and a front conductor are provided, which is arranged between the workpiece and the transmitter such that the ultrasound passes through the front conductor. The device is characterized in that an ultrasound receiver and an ultrasound transmitter are fixedly or releasably arranged on the front conductor for carrying out the steps for determining the geometry of the front conductor. In this step, the travel time of at least one ultrasonic pulse generated by the ultrasonic transmitter, reflected on the boundary surface of the front conductor and received by the ultrasonic receiver or a further ultrasonic receiver is measured and at least one dimension of the front conductor relevant to the ultrasonic examination is determined therefrom. In other words, the propagation time of at least one back wall echo of the leading wedge is determined. The terms receiver and transmitter are to be interpreted functionally. In a further embodiment according to the invention, the method is therefore designed such that: the transducer acting as a transmitter also acts as a receiver for the ultrasonic pulses previously transmitted by it. Alternatively, other transducers spaced apart from the transmitter may be used as receivers. By determining the current dimensions of the front conductor, its wear can be monitored and/or the accuracy of the ultrasound examination performed with the device can be improved. Furthermore, the ultrasound examination is provided with ultrasound examination-related geometric data of the front conductor without structurally complex data exchange between the evaluation unit and the front conductor or without elaborate manual data input. Furthermore, the deviation caused by the losses is reliably determined by an approximately simultaneous measurement. Since the travel time measurement of the back wall echo of the front volume is performed, a separate calibration volume is no longer required. This simplifies the detection and its accuracy and enables field verification if necessary.

The invention is explained below with reference to schematic drawings, as related geometrical calculations and preferred embodiments, without being limited to what is shown and described.

In a preferred embodiment of the method according to the invention, the workpiece, not shown in fig. 1, is subjected to an ultrasonic examination by the pulse echo method with the aid of the probe shown in fig. 1. For this purpose, in this embodiment, a phased array 1 of probes is used, which also applies to the dimensioning of the front conductor 4, as will be described later. The phased array 1 comprises a plurality (here 22) of selectively excitable acoustic transducers 2, 3. In ultrasound examinations, the acoustic transducers may be excited in a common in-phase manner, in a common but mutually phase-shifted manner, in a selective group manner, and so forth. The invention is not limited in terms of method steps in ultrasound examination and the person skilled in the art is responsible for selecting a correspondingly suitable excitation selection. The ultrasound generated by the transducers of the phased array 1 passes through a front conductor 4 made of thermoplastic material in order to penetrate into a workpiece which is arranged adjacent to a coupling face 5 of a wedge-shaped front conductor 4 (also referred to as "front wedge" in the following). It should be noted that: the speed of sound of the leading wedge 4 has a relatively strong temperature dependence. However, it is generally not necessary here to carry out a separate temperature measurement of the front conductor 4, since the speed of sound c in the front conductor is obtained directly as a result of the method according to the invention. Nevertheless, if the absolute value T of the temperature of the front conductor is advantageously known in addition to the speed of sound c in the case of a determination, the temperature of the front conductor can be inferred from the measured speed of sound c from the material table of the front conductor.

In order to improve the accuracy of the ultrasound examination, a step is proposed according to the invention for determining the dimensions of the front conductor 4 in connection with the ultrasound examination. This step can be performed before, after or during the ultrasound examination described above and repeated as many times as necessary.

In this step, ultrasound is also transmitted using the phased array 1. In addition, the leading wedge 4 is not coupled to the workpiece by its coupling surface 5, i.e., it remains uncoupled, but in particular, for example, coupled to air. This step comprises three single steps in this embodiment. In both steps, the respective back-wall echoes of the strongly diverging sound beams respectively generated by the outermost transducers 2 and 3 are received by these transducers and are then acoustically presentThe propagation time t is determined by means of the corresponding back-wall echo when the corresponding front conductor 4 is correctly struck on the coupling surface 5₁And t₂. This step can be performed with a delay in time, but can also be performed simultaneously. It should be noted that the shortest acoustic path for ultrasound is path d₁And d₂Which correspond to the respective perpendicular distances of the converters 2, 3 to the coupling surface 5. In a third substep, the propagation time t of the ultrasound from the transducer 3 as transmitter to the transducer 2 as receiver (or vice versa) is measured in the case of the formation of a back-wall echo, i.e. in the case of an oblique incidence on the coupling face 5. Shortest acoustic path e of ultrasound₁+e₂Is characterized in that the angle of incidence beta corresponds to the angle of emergence beta on the rear wall (coupling face 5).

In the case of thicker, for example, wedge-shaped front conductors, it can be advantageous if the detection of the back-wall echo on the uncoupled front conductor described above is not carried out with the aid of the sound beams of the individual transducers of the phased array, but rather a plurality of (adjacent) transducers of the phased array are combined, for example, at the right and left edges, in order to produce a sound beam with reduced divergence. Such a modified method implementation is also included in the method according to the invention.

From the three measured propagation times t, t₁、t₂The distance from a known or previously determined (invariable) transducer w may determine the speed of sound c in the leading wedge 4 as follows:

the distance d can thus be calculated as follows₁And d₂：

The slope angle of the leading wedge may be determined according to the following equation:

the average distance d, which is not shown in the drawing, corresponds to the distance between the coupling surface and the center point of the surface covered by the transducer 1 on the boundary surface of the front conductor 5 opposite the coupling surface, and is determined as:

with respect to the derivation of equation (1):

from the triangles Δ ABC and Δ BCD, e can be determined₁And e₂：

e₁And e₂The sum applies:

(6) e₁+e₂＝ct

with the above pair e₁And e₂Corresponds to:

(7) ct sinβ＝d₁+d₂

use of the pair d₁And d₂Equation (2) of (a) yields:

by means of the cosine theorem of the triangle Δ BDE:

wherein:

(10) cos(180°-2β)＝2sin²(β)-1

using equations (4) and (9) yields:

this is obtained by means of equations (2), (8) and (11):

or correspond to:

thus, the wedge shown in the probeBy measuring the propagation times t, t in the case of a front conductor 4 at oblique incidence of the back-wall echo₁、t₂And the speed of sound c in the front conductor 4 is determined based on the distance w of the transmitter 3 and the receiver 2. The sound speed c thus determined accurately and actually present is used to calculate the vertical distance d of the receiver 2 or transmitter 3 from the coupling surface 5₁And d₂. This is then based on the analysis of the actual ultrasound examination and thereby increases the accuracy of its determination.

Claims (8)

1. A method for non-destructive ultrasonic testing, wherein at least one ultrasonic pulse is emitted into a workpiece to be tested by means of at least one ultrasonic emitter (3) and the ultrasonic pulse is reflected at a boundary surface in the workpiece, the reflected ultrasonic sound is received by means of at least one ultrasonic receiver (2) and the associated signals are evaluated, and the ultrasonic sound penetrates a front conductor (4) which is arranged between the workpiece and the emitter or receiver and is releasably connected to the ultrasonic emitter and receiver, wherein the method comprises determining at least the front conductor (4) which is associated with ultrasonic testingOne dimension (alpha, d)₁，d₂) Wherein the propagation time of at least one ultrasonic pulse generated by the ultrasonic transmitter (3), reflected on the boundary surface (5) of the front conductor (4) and received by the ultrasonic receiver (2) is measured and at least one dimension (alpha, d) of the front conductor (4) relevant for the ultrasonic examination is determined therefrom₁，d₂) Characterized in that at least one dimension (alpha, d) associated with the ultrasound examination is determined for the front conductor (4)₁，d₂) Is not coupled and is used to determine at least one dimension (alpha, d) of the front conductor (4) relevant to the ultrasound examination₁，d₂) In which the propagation time of a back-wall echo obliquely impinging on a coupling surface (5) to be adjoined to the workpiece is measured and the propagation time of at least one back-wall echo perpendicularly impinging on the coupling surface (5) is measured, and a phased array (1) of selectively excitable ultrasonic transducers (2, 3) each serving as an ultrasonic receiver or an ultrasonic transmitter is used and is used for determining at least one dimension (alpha, d) of a front conductor (4) relevant for ultrasonic inspection₁，d₂) Is triggered by the pulse peak of the received pulse echo, and the determined dimension (alpha, d) of the preamble (4)₁，d₂) This is taken into account when analyzing the signals in the ultrasonic examination of the workpiece.

2. Method according to claim 1, characterized in that said dimensions (alpha, d)₁，d₂) By means of the shortest acoustic path (d) corresponding to the respective travel time, obtained by geometric or digital simulation₁，d₂，e₁，e₂) To calculate.

3. A method according to claim 1 or 2, characterized in that in performing the method, the speed of sound c in the front conductor is determined.

4. A method according to claim 1 or 2, characterized in that the phased array (1) comprises more than two selectively energizable ultrasound transducers (2, 3).

5. Method according to claim 1 or 2, characterized in that at least one dimension (alpha, d) related to the ultrasound examination is determined for the front conductor (4)₁，d₂) Using the outermost ultrasound transducers (2, 3) of the phased array (1).

6. Method according to claim 1 or 2, characterized in that the front conductor (4) used is wedge-shaped or has two plane-parallel faces.

7. Method according to claim 1 or 2, characterized in that the front conductor (4) used consists of a thermoplastic composition.

8. The method according to claim 7, characterized in that the front conductor (4) used consists of a cross-linked polystyrene interpolymer.