Title / Author(s) / Keywords
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Publication | Date |
 Application Note: Ultrasonic Steel Weld Testing SONOTEC GmbH 58, Halle, Germany NEWS
| NDT.net Journal
| 2019-12 |
 New Dual SONOAIR & COBOT Setup - Roadshow USA SONOTEC GmbH 58, Halle, Germany NEWS
| NDT.net Journal
| 2019-11 |
 Ultrasonic Thickness Testing of Reinforced Rubber Conveyor Belts Ultrasonic Solutions SONOTEC GmbH 58, Halle, Germany NEWS
| NDT.net Journal
| 2019-10 |
Einflussgrößen bei der Bestimmung von Eigenspannungen mit Ultraschall J. Pohl1 18, V. Prautzsch1, P. Holstein2 17, A. Bodi2 10, C. Pick3 2 1Hochschule Anhalt 11, Köthen, Germany 2SONOTEC GmbH 58, Halle, Germany 3MBQ Qualitätssicherung GmbH 3, Hettstedt-Walbeck, Germany
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Die Bestimmung der Eigenspannung in Materialien beruht auf der sehr genauen Bestimmung von Schallgeschwindigkeiten, die technisch als präzise Laufzeitmessung realisiert wird. Die akusto-elastischen Koeffizienten der Werkstoffe und die Ausgangsschallgeschwindigkeiten stellen den Grundzusammenhang zwischen den Mess- und den Zielgrößen dar. Die hochaufgelöste und reproduzierbare Messung der Schallgeschwindigkeit wird entscheidend durch Prüfsystemeigenschaften und die Kenntnis der Werkstoffe bestimmt. Es werden akusto-elastische Koeffizienten verschiedener Werkstoffe in ihrer Beeinflussung durch herstellungs- beziehungsweise verarbeitungstechnische Einflüsse vorgestellt und diskutiert.
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| DGZfP 2019 Session: Zustandsüberwachung | 2019-08 |
Detection of delamination and impact damage in multilayered lightweight materials T. Gautzsch1 4, A. Bodi1 10, M. Lucas2 3, R. Steinhausen3 13, M. Kiel3 12 1SONOTEC GmbH 58, Halle, Germany 2SONOTEC US Inc., Islandia, NY, USA 3Forschungszentrum Ultraschall Halle gGmbH 15, Halle, Germany
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A variety of lightweight composite materials are used in aerospace construction. Most common are multiple layers of aluminum with adhesive interfaces of different thicknesses, GFRP sandwich structures with and without honeycomb cores and glass fiber reinforced aluminum. The material properties of all materials are highly dependent on the integrity of all adhesive and matrix structures. These can be impaired by impacts, production problems, physical stress or aging.
Air-coupled ultrasonic testing (ACUT) can be a method for non-destructive quality control for semi-finished composite materials as well as products. Additionally, it can be applied for maintenance testing of parts to find impact and stress damage.
We will present a case study on the detection, measurement and evaluation of delamination in multi-layered aluminum bonds with up to 4 sheets of aluminum in various thicknesses. The aviation-specific specimen is measured in through-transmission with ACU with multiple frequencies, filters and averages with classic piezocomposite as well as phased-array ACU transducers. Delamination and flaws can be found in every adhesive layer. Depending on the composite thickness, different frequencies have to be applied.
| AeroNDT 2018 Session: Ultrasonics 1 | 2019-03 |
A new approach to air-coupled broadband measurement Effective testing of composite laminates by using a new multi-element transducer R. Steinhausen1 13, M. Kiel1 12, A. Bodi2 10, T. Gautzsch2 4 1Forschungszentrum Ultraschall Halle gGmbH 15, Halle, Germany 2SONOTEC GmbH 58, Halle, Germany
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Due to the large variety of possible flaws (e.g. air inclusions, delaminations, gluing errors, impurities, kissing bonds) different methods than the established measurement methods of
metal bonds have to be used for the inspection of composite laminates. Depending on the type of discontinuity the requirements of the inspection task are very diverse and time
consuming. Due to the differences in the lateral and axial dimensions of defects and the attenuation varieties it is necessary to measure as broad-banded as possible. Typical bandwidths as implemented in contact testing methods cannot be used in air-coupled ultrasonic testing at the moment.
We describe an efficient implementation of such an inspection with significantly improved results compared to conventional systems. It is based on a new multi-element air ultrasonic
transducer. Each of the elements has different frequencies. The overlapping sound beams of the individual elements allow generating a broad-band signal which can be additionally
steered inside the material as it is well-known from phased-array UT.
The new transducer increases the bandwidth considerably by an in-phase simultaneous activation of all elements. In order to operate such an ultrasonic transducer a special senderreceiver
electronic is necessary. As the individual transducer elements have to be activated simultaneously the system must have at least as many channels as the ultrasonic transducer. Additionally all channels with different frequencies have to be activated with a very high time accuracy relative to each other.
The evaluation takes place under consideration of the dispersive properties of the inspected test objects with respect to the interdependency with ultrasound. Frequency-dependent
properties like attenuation as well as geometry characteristics such as scattering behavior at interfaces cause a change in the measured ultrasonic signal. Accordingly, it is possible to
achieve new contrast mechanisms. An increase of the effective bandwidth by combining a multi-element air-coupled ultrasonic transducer and a multi-channel measurement system
allow gaining more information of the sample in only one measurement cycle. This accelerates the measurement of different frequencies drastically and eliminates uncertainties during the alignment of transducers with different frequencies.
| NDT Canada 2018
| 2018-10 |
Phased-Array-Prüfköpfe für die koppelmittelfreie Ultraschallprüfung A. Mück1 9, S. Scheunemann2 2 1SONOTEC GmbH 58, Halle, Germany 2Forschungszentrum Ultraschall Halle gGmbH 15, Halle, Germany
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Die kontaktfreie Prüfung mittels luftgekoppeltem Ultraschall hat insbesondere aufgrund der Anwendung neuartiger Kompositmaterialien in den vergangenen Jahren enorm an Bedeutung gewonnen. Dem wesentlichen Vorteil des Verzichts auf ein Koppelmittel wie Wasser steht der Nachteil der hohen Verluste bei der Schallübertragung durch die Luft gegenüber. Diese erschweren eine Interpretation der Testergebnisse. Aus diesem Grund sind Verbesserungen des Prüfsystems und der einzelnen Komponenten notwendig.
Ein vielversprechender Ansatz ist die Anwendung der Phased-Array-Technik in der koppelmittelfreien Prüfung. Durch den Einsatz mehrkanaliger Ultraschallprüfköpfe und -geräte ist es möglich, das Schallfeld an die jeweilige Anwendung anzupassen und dadurch den Prüfprozess zu verbessern. Diese Technik wird seit mehreren Jahrzehnten bereits erfolgreich in der Medizin und industriellen Materialprüfung angewandt. Dennoch sind bisher nur wenige Systeme für die koppelmittelfreie Prüfung verfügbar. Ein Grund dafür ist, dass sich der Aufbau von Luftschallprüfköpfen stark vom Aufbau von Kontakttechnik- oder Tauchtechnikprüfköpfen unterscheidet. Das erfordert eine Adaption des Phased-Array-Konzepts an das Design von Luftschallprüfköpfen.
Im Vortrag werden neu entwickelte Phased-Array-Prüfköpfe für die koppelmittelfreie Ultraschallprüfung vorgestellt. Die Eigenschaften der Prüfköpfe, bezogen auf die Ultraschallerzeugung, wurden ausführlich untersucht und entsprechende Ergebnisse vorgestellt. Techniken wie die elektronische Fokussierung des Schallstrahls können auf dieser Basis angewandt und die Leistungsfähigkeit mit herkömmlichen einkanaligen Prüfköpfen verglichen werden. Abschließend werden die Möglichkeiten der neuen Prüfsysteme anhand von Anwendungsbeispielen demonstriert.
DE
| DGZfP 2018 Session: Luftultraschall | 2018-09 |
Luftgekoppelter Ultraschall – Vorstellung neuer Ansätze im Bereich der koppelmittelfreien Prüfung F. Schönberg1 , R. Steinhausen2 13, M. Pfeiffer3 2, A. Bodi1 10, T. Gautzsch1 4 1SONOTEC GmbH 58, Halle, Germany 2Forschungszentrum Ultraschall Halle gGmbH 15, Halle, Germany 3IMA Materialforschung und Anwendungstechnik GmbH 15, Dresden, Germany
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Luftultraschallprüfverfahren gewinnen heute immer mehr an Bedeutung. Dies liegt in erster Linie an der Möglichkeit einer „koppelmittelfreien“ Prüfung und den damit verbundenen Vorteilen. Gleichzeitig entwickeln sich auch die Anlagentechnik und die Ultraschallwandler immer weiter. Die Luftultraschallprüfung kommt dabei überwiegend in der Prozesskontrolle in Produktionsketten zum Einsatz und ist ideal für die Prüfung von Materialien und Strukturen wie Verbundwerkstoffe, Verklebungen, Wabenstrukturen oder Schaumverbünde geeignet. So kann ein umfangreiches Spektrum an Prüfaufgaben wie Grenzflächendetektion, das Nachweisen von Inhomogenitäten oder die Detektion von Fremdkörpereinschlüssen abgedeckt werden.
Unser Beitrag soll einen Überblick über die Entwicklungen im Bereich der Luftultraschallprüfung geben und diese am Beispiel konkreter Prüfaufgaben vorstellen.
DE
| DGZfP 2018 Session: Luftultraschall | 2018-09 |
Genaue Laufzeitmessungen P. Holstein1 17, A. Bodi1 10, J. Pohl2 18, C. Pick3 2, B. FISCHER4 3 1SONOTEC GmbH 58, Halle, Germany 2Fachbereich EMW; Hochschule Anhalt 11, Köthen, Germany 3MBQ Qualitätssicherung GmbH 3, Hettstedt-Walbeck, Germany 4XARION Laser Acoustics GmbH 4, Wien, Austria
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Laufzeitmessungen bilden die Grundlage für eine Reihe von wichtigen Verfahren für die Anwendung von Ultraschall sowohl in der zerstörungsfreien Prüfung, der Prozessmesstechnik oder auch in der Medizintechnik. Durch Steigerung der Messgenauigkeit ergeben sich neue Möglichkeiten.
Die Bestimmung von Materialeigenschaften, Abmessungen, Spannungszuständen auf der Basis von Ultraschallverfahren erfordert zum Teil eine sehr hohe Auflösung. Unterschiedliche Materialklassen verlangen dabei aufgrund ihrer dispersiven und Dämpfungseigenschaften variable Lösungen mit verschiedenen Frequenzen und angepasster Prüftechnik sowie modifizierter Signalverarbeitung.
DE
| DGZfP 2018 Session: Poster mit Kurzpräsentation | 2018-09 |
A new approach to air-coupled broadband measurement Effective testing of composite laminates by using a new multi-element transducer R. Steinhausen1 13, M. Kiel1 12, A. Bodi2 10, T. Gautzsch2 4 1Forschungszentrum Ultraschall Halle gGmbH 15, Halle, Germany 2SONOTEC GmbH 58, Halle, Germany Composite materials, Defects, Transducers, Ultrasonics
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Due to the large variety of possible flaws (e.g. air inclusions, delaminations, gluing errors, impurities, kissing bonds) different methods than the established measurement methods of metal bonds have to be used for the inspection of composite laminates. Depending on the type of discontinuity the requirements of the inspection task are very diverse and time consuming. Due to the differences in the lateral and axial dimensions of defects and the attenuation varieties it is necessary to measure as broad-banded as possible. Typical band-widths as implemented in contact testing methods cannot be used in air-coupled ultrasonic testing at the moment.
We describe an efficient implementation of such an inspection with significantly improved results compared to conventional systems. It is based on a new multi-element air ultrasonic transducer. Each of the elements has different frequencies. The overlapping sound beams of the individual elements allow generating a broad-band signal which can be additionally steered inside the material as it is well-known from phased-array UT.
The new transducer increases the bandwidth considerably by an in-phase simultaneous activation of all elements. In order to operate such an ultrasonic transducer a special sender-receiver electronic is necessary. As the individual transducer elements have to be activated simultaneously the system must have at least as many channels as the ultrasonic transducer. Additionally all channels with different frequencies have to be activated with a very high time accuracy relative to each other.
The evaluation takes place under consideration of the dispersive properties of the inspected test objects with respect to the interdependency with ultrasound. Frequency-dependent properties like attenuation as well as geometry characteristics such as scattering behavior at interfaces cause a change in the measured ultrasonic signal. Accordingly, it is possible to achieve new contrast mechanisms. An increase of the effective bandwidth by combining a multi-element air-coupled ultrasonic transducer and a multi-channel measurement system allow gaining more information of the sample in only one measurement cycle. This accelerates the measurement of different frequencies drastically and eliminates uncertainties during the alignment of transducers with different frequencies.
| ECNDT 2018 Session: Composite Material - UT | 2018-08 |
Adaptive Data Compression of Ultrasound Data for Long-term Data Acquisition and Trend Evaluation P. Holstein1 17, S. Seitz2, A. Tharandt1 4, C. Probst1 12, R. Tetzlaff2 1SONOTEC GmbH 58, Halle, Germany 2Institute of Circuits and Systems; Dresden University of Technology (TU Dresden) 78, Dresden, Germany Data processing, Leak detection, Ultrasonics
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Data compression technologies such as MP3 are extensively used for audio technologies.
There are two objectives: to maintain the quality of the original sound and two compress the data as much as possible. The degree of compression depends strongly from the signal character. The information of pure harmonic signals can be much better compressed than by considering noisy signals.
The ultrasound produced by processes in industry is used for maintenance purposes since some decades. On the one hand there are many signals with noisy character. Examples are leakage noise, jet noise, the noise of friction in bearings and gears. On the other hand there are signals with dominantly repeating impulses such as bearing faults (cracks or spalled areas) or arcing during electrical discharge. For both types of data different compressing rates has to be found.
Traditionally, ultrasound data for maintenance are evaluated by means of narrow band techniques such as heterodyning the ultrasound signal in the audible range, thereby a data reduction can be achieved.
In order to avoid the loss of real physical information, an ultrasound broadband technology has been introduced in order to consider the complete frequency range leading to a considerably increased data rate. Long-term recordings of service data would generate a huge amount of data on short time scales. Furthermore, the broadband technologies requires new approaches to make the signal audible. A vocoder technique has been modified in this contribution in order to compress the ultrasound data in real-time to a bandwidth which is compatible to the listening capabilities of testing persons. The spectra of compressed data can be used for the interpretation of measuring data. The degree of loss with respect to the information content has been estimated in comparison to the original uncompressed signal. Furthermore, ultrasound data – original and the compressed audible data – has been taken by applying pattern recognition techniques based on Cellular Neural Networks which will be exemplified by means of maintenance related data.
Authors:
Peter Holstein, Andreas Tharandt, Christian Probst
(SONOTEC Ultraschallsensorik Halle GmbH)
Ronald Tetzlaff, Steffen Seitz, Jens Müller
(Institute of Circuits and Systems, TU Dresden
| ECNDT 2018 Session: Data Processing - UT | 2018-08 |
2018-08 ECNDT 2018 Ultrasonic Inspection, Transducers Phased array probes for non-contact UT A. Mück 9 SONOTEC GmbH 58, Halle, Germany Phased arrays, Sensors, Ultrasonics
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Non-contact air-coupled ultrasonic testing has grown in importance during the last years especially due to the application of new composite materials. The main advantage of waiving couplants like water is set against the disadvantage of high coupling losses, which make the interpretation of testing results more complicated. Therefore improvements in the testing system and its components are necessary.
A promising approach is the application of the phased array technique to the contact-free ultrasonic testing. By using probes with multiple elements and a multi-channel instrument it is possible to adapt the ultrasonic sound field to the application as well as improving testing processes. This technique is introduced and has proved its performance in industry and medicine since decades. However, only a few systems are available for the use of non-contact testing. One reason is, that the design of non-contact probes differs from conventional probes. An adaption of the concepts of phased array probes to the design of such probes is necessary.
The novel SONOSCAN CF400 series includes a piezocomposite transducer of Ø20 mm. The mean frequency is 400 kHz. In the standard type the transducer is curved, leading to a focal distance of 50 mm. Typically these transducers are used in transmission technique, which gives an optimum distance of transmitter and receiver of 100 mm. A shorter focal distance cannot be achieved by a stronger bending of the transducer due to material limits.
Based on this probe the SONOSCAN CF400 3E type with the same transducer dimension has been developed. The electrode was constructed as an annular array with 3 equal-sized elements. By applying an appropriate delay law the focal distance has been adjusted to 10 mm. The focal width has been measured with 4 mm. The corresponding sound field is shown in Figure 1.
The advantage of electronic focussing phased array probes against conventional probes can be found in applications, where the distance between transmitter and receiver is limited by external restrictions. Because of interference in the near field of the probe, the presentation of scans using conventional probes will include artefacts. Phased array probes will avoid these.
| ECNDT 2018 Session: Ultrasonic Inspection, Transducers | 2018-08 |
Single-Sided Contact-Free Ultrasonic Testing – A New Air-Coupled Inspection Technology for Weld and Bond Testing M. Kiel1 12, R. Steinhausen1 13, A. Bodi2 10, M. Lucas2 3 1Forschungszentrum Ultraschall Halle gGmbH 15, Halle, Germany 2SONOTEC GmbH 58, Halle, Germany Ultrasonic Testing (UT), Composites, Weld, Bond, Contact-free, Air-coupled
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The automotive industry profits of many fully automated processes during its fabrication stages. Most of the processes are performed by robots just like all typical welding processes. To achieve quality requirements testing is necessary. It is recommended that a radiation and contact-free nondestructive testing method is applicable. This ensures a maximum testing speed and a minimum of necessary safety provisions, preparations or post-processing of the test objects.
Two special testing scenarios will be discussed using single-sided air-coupled ultrasonic testing. A main advantage is the contactless measurement without the application of any oil or water using high-power ultrasonic pulses. In addition to common transmission mode testing, we present a pitch-catch-technique using Lamb-waves. The influence of geometry effects and the importance of high bandwidth will be discussed.
The first test specimen are edge-to-edge laser-welded metal sheets as used for instance in automotive production processes. The goal of a better quality assurance is the immediate control of the welding process. Accordingly, for future testing systems it is recommended to implement the work tool and the testing sensor into the welding robot. The aim of the testing is to monitor the complete performance of the welding and to record interruptions of the weld seam or any reduction of the laser energy. Any discontinuity within the sound path leads to changes of the ultrasonic signal. Due to the fact that the non-welded plates should have no defects, changes of the signal indicate directly a change of the weld seam.
The second test samples are adhesive bonds found in composite material structures such as combinations of metal sheets and carbon fiber reinforced plastics (CFRP). The mechanical stability, lifetime and performance of such composite structures strongly depends on the quality of the bond. Air-coupled ultrasonic testing is a promising nondestructive method for the characterization of these bonds. In transmission mode the absence of glue acts as an additional interface within the test object which strongly reduces the transmitted ultrasound wave. Glue application errors can be detected easily.
| APCNDT 2017 Session: Ultrasonic Testing 9 | 2018-03 |
 Corrosion Measurement at Refineries with the SONOWALL 70 SONOTEC GmbH 58, Halle, Germany
NEWS
| NDT.net Journal
| 2018-02 |
Einseitige Luftultraschallprüfung von Blechverbindungen - Eine Sache der Geometrie M. Kiel1 12, R. Steinhausen1 13, A. Bodi2 10 1Forschungszentrum Ultraschall Halle gGmbH 15, Halle, Germany 2SONOTEC GmbH 58, Halle, Germany
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In der Produktion von Halbzeugen für Massengüter ist das Fügen von Metallwerkstoffen häufig vollautomatisiert und robotergeführt. Zwar ist gewünscht, dass der Prozess durch die Automatisierung stets gleich abläuft, die Gewissheit darüber kann aber immer nur eine anschließende Prüfung der Werkstücke liefern.
In der hier vorgestellten Prüfsituation handelt es sich um die Untersuchung einer laserunterstützten Stoßschweißnaht von Stahlblechen. Bei diesem Prozess wird ein hochenergetischer Laser verwendet, um Stahlbleche unterschiedlicher Dicke von 0,8 bis 1,6 mm miteinander zu verbinden. Derartige Verbindungen werden z.B. im Automobilbereich verwendet, um einen Übergang zwischen dickeren stabilen Konstruktionsteilen zu weniger beanspruchten Teilen geringerer Wandstärke zu schaffen. Die Qualität der Schweißnaht hängt von sehr vielen Parametern ab. Eine mögliche Fehlerquelle ist u.a. der kurzeitige Verlust der Laserleistung, was zu einer Unterbrechung der Schweißnaht führt.
Die einseitige Messanordnung besteht aus zwei Luftultraschallwandlern auf jeweils einer Seite der Schweißnaht. Die sich innerhalb der Bleche und über die Schweißnaht hinweg ausbreitende Lambwelle wird gemessen und analysiert. Die Anordnung der Wandler kann bedingt durch die einfache Geometrie zweier auf Stoß aneinander geschweißter Bleche so gewählt werden, dass keinerlei zusätzliche Abschattung der sich in Luft ausbreitenden Ultraschallwelle nötig ist. Das Verfahren ist demzufolge vollständig berührungslos. Die Ultraschallmessung kann direkt am Schweißroboter erfolgen, da nicht erst die Abkühlung der Bleche abgewartet werden muss.
In unserem Beitrag stellen wir die Möglichkeiten aber auch die Grenzen der Methode dar. Wir betrachten die Ergebnislage als Vergleich von Amplituden- und Laufzeitbewertung der Ultraschalldaten. Dabei werden sowohl das Auflösungsvermögen und die Empfindlichkeit der Messung als auch die Einflüsse der Wandlerjustage und die Anforderungen an die Roboterführung betrachtet. Die Einflüsse der unterschiedlichen Phasengeschwindigkeiten der Lambwelle beim Verschweißen von zwei unterschiedlich dicken Blechen sowie der Abweichung von der optimalen Prüfkopfführung werden in Hinblick auf die Robustheit der Bestimmung der Fehlergröße diskutiert.
DE
| DGZfP 2017 Session: Luftultraschall | 2017-09 |
2017-09 DGZfP 2017 Vorträge der Mitgliedergruppe B Neues Wanddickenmessgerät mit A-Bild und B-Bild-Funktion A. Bodi 10, M. Lucas 3 SONOTEC GmbH 58, Halle, Germany
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Das SONOWALL 70 ist ein portables Handgerät, bei dessen Entwicklung die Vereinfachung und Beschleunigung des Prüfvorganges, der Ausschluss möglicher Fehlerquellen sowie die übersichtliche Darstellung der Ergebnisse im Vordergrund stand.
Als erstes Prüfgerät aus dem Markt besitzt das SONOWALL 70 eine intelligente, kabellose Prüfkopferkennung. Die damit verbundene erweiterte Prüfkopfverwaltung ermöglicht die Hinterlegung prüfkopfspezifischer Daten. So können beispielsweise DAC-Kurven, Vorlauflängen und Seriennummern direkt im Prüfkopf gespeichert werden.
Neben den verschiedensten Anwendungen zur Wanddickenmessung kann das Gerät durch ein Upgrade zum Materialprüfgerät erweitert werden.
Dank seiner kompakten Größe, einem Gewicht von nur 990g trotz robustem Aluminiumgehäuse, dem hochauflösenden und entspiegelten Grafikdisplay sowie Schutzklasse IP 67 eignet sich das Gerät ideal für raue Prüfumgebungen.
Eine intuitive Bedienoberfläche, das klar strukturierte Menü und die Darstellung aller Menüpunkte in Volltext vereinfacht und beschleunigt die Geräteeinstellung und verringert das Risiko von Fehleinstellungen. Auf dem großformatigen 5“Zoll Grafikdisplay (800x480) kann der Prüfer alle für ihn relevanten Messwerte und Geräteeinstellungen wie Wanddicke, A-Bild und individuell angepasste Prüfparameter auf einen Blick erkennen.
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| DGZfP 2017 Session: Vorträge der Mitgliedergruppe B | 2017-09 |
Schallemission in der Instandhaltung C. Probst 12, P. Holstein 17 SONOTEC GmbH 58, Halle, Germany Acoustic Emission (AE) DE
| DGZfP AE-2015
| 2017-04 |
Lecksuche und Dichtheitsprüfung mit Ultraschall - Neue Ansätze - C. Schreiber 2 SONOTEC GmbH 58, Halle, Germany Leak Testing (LT) DE
| DGZfP LT-2016
| 2017-04 |
New approaches to air-coupled ultrasound testing of composite lightweight materials R. Steinhausen1 13, M. Kiel1 12, C. Pientschke1 6, H. Münch2 9, A. Mück2 9, K. Hahn2 4 1Forschungszentrum Ultraschall Halle gGmbH 15, Halle, Germany 2SONOTEC GmbH 58, Halle, Germany Composite Materials
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The development of piezo-composites enables new possibilities for ultrasound transducers even in the frequency range of air-coupled ultrasound. In contrast to bulk ceramics as transducer material, the piezo-composite vibrates in the thickness mode. Thus, the diameter of the transducer is independent of the resonance frequency. This advantage opens up the field of air-coupled ultrasound testing (ACU) above 300 kHz. Additionally, the large area and the reduced lateral coupling of the piezo-composite material allow multi-channel electrode design for sound field forming.
We present a new design of ultrasound transducers with three annular electrodes in combination with a fully controllable three channel ultrasound testing system. The sound field is characterized with the ball reflector method in comparison to a standard single electrode transducer. An improvement of the lateral resolution is observed which is verified by scanning a test specimen with blind holes of different sizes as well as lightweight materials with imperfect bonding and delamination. Beside the smaller sound field diameter the near field length could be reduced from originally 70 to 25 mm which leads to an increase of intensity due to lesser losses in the air section. We could also show that the use of a three-electrodes receiver in combination with a multi-channel system (transmitter and receiver) leads to an additional increase of the resolution.
Furthermore, we developed a new approach to single-sided air-coupling measurement by means of multi-receiver method. This technique directly provides spatially resolved imaging of subsurface structures of lightweight materials. In contrast to other techniques, for example lamb waves or SAFT, no additional data processing is necessary. This leads to direct imaging of defects in intrinsically complex samples, as expected e.g. for honeycomb structures.
| WCNDT 2016 Session: Composite Materials | 2016-07 |
Acoustic methods for leak detection and tightness testing P. Holstein 17, M. Barth 2, C. Probst 12 SONOTEC GmbH 58, Halle, Germany Leak Testing
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Air tightness testing has importance in industrial environments where in compressed air systems leaks account for a high percentage of energy loss. These losses can effectively be reduced by locating and repairing of leaks. Furthermore, tightness is a criterion for the quality of different kinds of seals and joints. For leak detection and tightness testing acoustic methods (passive and active) can be applied. Variations of the technology enable access to different problems. The methods for leak detection can be graded up by the estimation of leak sizes and energetic losses. Similarly, slot size and length of tightness leaks are responsible for energetic losses in buildings (window and door seals) or for dysfunctions in technical systems such as cabins, heat exchangers and others.
Leaks can be found easily by means of traditional ultrasound leak detectors which operate in a narrow frequency band (e.g. 40 kHz). However, this simple technology is inadequate for quantitative estimations of leak and tightness losses. Therefore, new theoretically based approaches have been developed and experimentally exemplified. Sound will be created by passing of air through leaks (for high and low pressure as well). Compressed air exits an orifice generating a turbulent jet, which emits a broadband sound. Acoustic leak finder devices can localize these leaks. However, quantification of their size remains a crucial task (with respect to energy loss and priority of repair). From the point of view of aero-acoustical theory a quantification of fluid parameters of leak jets can only be achieved by evaluation of a broad frequency band (20 kHz to 100 kHz). A new testing procedure and evaluation algorithm for finding and quantification of leaks will be presented.
Tightness of many technical systems can be tested by means of actively transmitted (ultra-)sound. Again, quantification remains a demanding task. The sound field strongly depends on depth, width and geometry of an orifice and is affected by diffraction, reflection, transmission and interference. The method is discussed with respect to the quantification of leak size. It is shown which demands are to be met on the sound source and the generated acoustic fields.
| WCNDT 2016 Session: Leak Testing | 2016-07 |
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