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Papers by Bernhard Reitinger

IOP Conference Series: Materials Science and Engineering

The mandatory Non-Destructive Testing (NDT) by the aerospace industry for both present and future... more The mandatory Non-Destructive Testing (NDT) by the aerospace industry for both present and future generation hybrid aircraft using thick composite structures poses many challenges for traditional inspection techniques. Laser Ultrasonic Testing (LUT) deployed by a robot for inspection of modern aerospace composite components shows good promise. It is a non-contact method offering the possibility of fast scan times without the need for couplant. This paper presents the latest work-in-progress for the design and development of the system developed by the ACCURATe consortium. ACCURATe is an ongoing H2020 Clean Sky 2 part funded project to develop a laser ultrasound based NDT system prototype for fast and contactless testing of large carbon fibre reinforced polymer (CFRP) aircraft structures. The approach is based on a non-contact laser generated and detected pulsed ultrasound technique with delivery of both the laser ultrasound excitation and detection pulses through flexible optical fi...

Materials

In Wire and Arc Additive Manufacturing (WAAM) and fusion welding, various defects such as porosit... more In Wire and Arc Additive Manufacturing (WAAM) and fusion welding, various defects such as porosity, cracks, deformation and lack of fusion can occur during the fabrication process. These have a strong impact on the mechanical properties and can also lead to failure of the manufactured parts during service. These defects can be recognized using non-destructive testing (NDT) methods so that the examined workpiece is not harmed. This paper provides a comprehensive overview of various NDT techniques for WAAM and fusion welding, including laser-ultrasonic, acoustic emission with an airborne optical microphone, optical emission spectroscopy, laser-induced breakdown spectroscopy, laser opto-ultrasonic dual detection, thermography and also in-process defect detection via weld current monitoring with an oscilloscope. In addition, the novel research conducted, its operating principle and the equipment required to perform these techniques are presented. The minimum defect size that can be iden...

AIP Conference Proceedings, 2014

In the continuous casting process the avoidance and rapid detection of occurring solidification c... more In the continuous casting process the avoidance and rapid detection of occurring solidification cracks in the slab is a crucial issue, in particular for the maintenance of a high quality level in further production processes. Due to the elevated temperatures of the slab surface a remote sensing non-destructive tool for quality inspection is required, which is also applicable for the harsh industrial environment. In this work the application of laser ultrasound (LUS) technique during the continuous casting process in industrial environment is shown. The proof of principle of the detection of the centered solidification cracks is shown by pulse-echo measurements with laser ultrasonic equipment for inline quality inspection. Preliminary examinations in the lab of different casted samples have shown the distinguishability of slabs with and without any solidification cracks. Furthermore the damping of the bulk wave has been used for the prediction of the dimension of the crack. With an adapted “synthetic apert...

Easy-to-handle non-destructive testing methods for components are getting more and more important... more Easy-to-handle non-destructive testing methods for components are getting more and more important to achieve “zero failure production”. Especially in the aerospace industry, the responsible quality managers have to follow a strict 200% testingapproach. This means, a full-faced checking of the part is performed by an automated NDT system as the first step of the procedure. Areas that show deviations from the reference dataset are marked as so-called „findings“. In a second step a qualified auditor needs to evaluate these findings on a PC-monitor as „ok“, „defect“ or „ignore“. Finally, these rated findings are required to be again validated by manual NDT measurements on the real component. This rather unintuitive workflow requires a change of the perspective between the graphically illustrated dataset on a monitor and the real component, which is not only a further source of errors but also leads to focusing on the defective areas only. With the advancement in headsets, cameras, and t...

2021 48th Annual Review of Progress in Quantitative Nondestructive Evaluation

We demonstrate the determination of the Poisson’s ratio of steel plates during thermal processing... more We demonstrate the determination of the Poisson’s ratio of steel plates during thermal processing based on contact free laser ultrasound measurements. Our method utilizes resonant elastic waves sustained by the plate, provides high amplitudes, and requires only a moderate detection bandwidth. For the analysis, the thickness of the samples does not need to be known. The trend of the measured Poisson’s ratio reveals a phase transformation in dual-phase steel samples. While previous approaches based on the measurement of the longitudinal sound velocity cannot distinguish between the ferritic and austenitic phase above 770°C, the shown method can. If the thickness of the samples is known, the method also provides both sound velocities of the material. The gained complementary information could be used to analyze phase composition of steel from low temperatures up to its melting point.

In respect to economization of energy and raw materials the avoidance and real-time detection of ... more In respect to economization of energy and raw materials the avoidance and real-time detection of defects is a crucial issue in the continuous casting process. Those defects may occur during solidification of aluminum and beco m noticeable as bulk cracks as well as surface or near-surface cracks. Similarly, in furt her production processes the maintenance of a high quality level in high performance aluminum alloys for aerospace and automotive industry is also a fundamental topic. Th erefore, a non-destructive remote sensing testing tool for quality inspection duri g early stage of production is required. In this work the laser ultrasound (LUS) technique is demonstrated for qu ality inspection of semi-manufactured aluminum products. In LUS high energ y short laser pulses illuminate the sample. A fraction of the pulse energy is absorbed at the sample surface, causes local heating and thermal expansion, and induces br oadband ultrasonic waves which propagate through the sample. Those wa...

Generally, the elastic material properties (e.g. Young’s modulus and Poisson ratio) in steel and ... more Generally, the elastic material properties (e.g. Young’s modulus and Poisson ratio) in steel and cast iron are assumed to be unaffected by hardening processes in commo n literature. Only the hardness is presumed to alter, while the elastic properties keep cons tant. As the results of traditional and FEM (finite element method) static and dynamic stress calculations di rectly depend on the accuracy of these properties they are highly crucial. We show that the elastic properties get considerably mo dified during the hardening process. The change in Young’s modulus was up to 4%. An increase in hardness was associated with a decrease of the Young’s modulus. This effect was measured in steel alloys, a s well as in cast iron. Measurements were performed utilizing a picosecond-laser an d a photorefractive interferometer. Subsequently, the elastic properties were calculated from the recorded signals and the known density of the materials. As the measurements are performed conta ctless, futu...

Structural Control and Health Monitoring

Journal of Imaging

In conventional photoacoustic tomography, several effects contribute to the loss of resolution, s... more In conventional photoacoustic tomography, several effects contribute to the loss of resolution, such as the limited bandwidth and the finite size of the transducer, or the space-dependent speed of sound. They can all be compensated (in principle) technically or numerically. Frequency-dependent acoustic attenuation also limits spatial resolution by reducing the bandwidth of the photoacoustic signal, which can be numerically compensated only up to a theoretical limit given by thermodynamics. The entropy production, which is the dissipated energy of the acoustic wave divided by the temperature, turns out to be equal to the information loss, which cannot be compensated for by any reconstruction method. This is demonstrated for the propagation of planar acoustic waves in water, which are induced by short laser pulses and measured by piezoelectric acoustical transducers. It turns out that for water, where the acoustic attenuation is proportional to the squared frequency, the resolution li...

The optical generation of ultrasound is based at low power levels on the thermoelastic effect, wh... more The optical generation of ultrasound is based at low power levels on the thermoelastic effect, which is the generation of elastic waves by transient surface heating with a laser pulse. At high power level the laser source operates in the ablation regime by vaporizing a small amount of surface material. The radiated field of such a source resembles a monopole radiating in all directions of the half space. Laser ultrasonics uses one laser with a short pulse for the generation of elastic waves and another one, a long pulse or continuous laser, coupled to an optical interferometer for the detection of ultrasound. This technique enables a completely contactless measurement of elastic constants. As the laser pulse generates bulk as well as surface acoustic waves (SAW) both can be used for non-contact material characterization. Short laser pulses were used to generate bulk waves in continuous fiber reinforced aluminium or magnesium. With an optical interferometer the run-time of these wave...

The International Journal of Advanced Manufacturing Technology

Many industrial sectors face increasing production demands and the need to reduce costs, without ... more Many industrial sectors face increasing production demands and the need to reduce costs, without compromising the quality. The use of robotics and automation has grown significantly in recent years, but versatile robotic manipulators are still not commonly used in small factories. Beside of the investments required to enable efficient and profitable use of robot technology, the efforts needed to program robots are only economically viable in case of large lot sizes. Generating robot programs for specific manufacturing tasks still relies on programming trajectory waypoints by hand. The use of virtual simulation software and the availability of the specimen digital models can facilitate robot programming. Nevertheless, in many cases, the virtual models are not available or there are excessive differences between virtual and real setups, leading to inaccurate robot programs and time-consuming manual corrections. Previous works have demonstrated the use of robot-manipulated optical sens...

Materials Science Forum

State of the art of in-situ analysis on grain structure of metals during thermal and stress treat... more State of the art of in-situ analysis on grain structure of metals during thermal and stress treatment is done by observation of the probe in a thermomechanical treatment system. Potential analysis methods are high energy x-ray scattering (e.g. in a synchrotron) or laser-ultrasonics (LUS). The most commonly used thermomechanical system, is the so called “Gleeble” from Dynamic Systems Inc., which is able to heat and load the material in a quite fast manner with extremely high heating rates, very high forces and fast force changes. There is a wide area of research and applications, though, where these capabilities are not fully required, a less complex deformation-and quenching dilatometer would often be sufficient. In this paper we will show the implementation of a LUS system in such a dilatometer and compare it to the “all inclusive” Gleeble system, pointing out benefits and downsides on different aspects, like the technical specifications, the needed footprint and more. A sketch of ...

Nondestructive Testing and Evaluation

2011 IEEE International Ultrasonics Symposium, 2011

ABSTRACT We investigate numerically and experimentally the negative refraction of surface acousti... more ABSTRACT We investigate numerically and experimentally the negative refraction of surface acoustic waves in two-dimensional phononic crystals in the MHz range. We performed high-performance time-domain simulations of propagating broadband surface acoustic waves with the Finite Element Method (FEM) and spatio-temporal imaging by means of pulsed optical excitation and interferometric detection. Experimental and numerical evidence is found for negative refraction from surface wave focusing at particular frequencies after wave propagation through a parallel-sided phononic crystal layer. Obliquely incident plane waves on a phononic crystal were also investigated by numerical simulations. The transmitted waves show a clear shift of the wave front at particular frequencies, providing further evidence for negative refraction of the surface acoustic waves.

IOP Conference Series: Materials Science and Engineering

The mandatory Non-Destructive Testing (NDT) by the aerospace industry for both present and future... more The mandatory Non-Destructive Testing (NDT) by the aerospace industry for both present and future generation hybrid aircraft using thick composite structures poses many challenges for traditional inspection techniques. Laser Ultrasonic Testing (LUT) deployed by a robot for inspection of modern aerospace composite components shows good promise. It is a non-contact method offering the possibility of fast scan times without the need for couplant. This paper presents the latest work-in-progress for the design and development of the system developed by the ACCURATe consortium. ACCURATe is an ongoing H2020 Clean Sky 2 part funded project to develop a laser ultrasound based NDT system prototype for fast and contactless testing of large carbon fibre reinforced polymer (CFRP) aircraft structures. The approach is based on a non-contact laser generated and detected pulsed ultrasound technique with delivery of both the laser ultrasound excitation and detection pulses through flexible optical fi...

Materials

In Wire and Arc Additive Manufacturing (WAAM) and fusion welding, various defects such as porosit... more In Wire and Arc Additive Manufacturing (WAAM) and fusion welding, various defects such as porosity, cracks, deformation and lack of fusion can occur during the fabrication process. These have a strong impact on the mechanical properties and can also lead to failure of the manufactured parts during service. These defects can be recognized using non-destructive testing (NDT) methods so that the examined workpiece is not harmed. This paper provides a comprehensive overview of various NDT techniques for WAAM and fusion welding, including laser-ultrasonic, acoustic emission with an airborne optical microphone, optical emission spectroscopy, laser-induced breakdown spectroscopy, laser opto-ultrasonic dual detection, thermography and also in-process defect detection via weld current monitoring with an oscilloscope. In addition, the novel research conducted, its operating principle and the equipment required to perform these techniques are presented. The minimum defect size that can be iden...

AIP Conference Proceedings, 2014

In the continuous casting process the avoidance and rapid detection of occurring solidification c... more In the continuous casting process the avoidance and rapid detection of occurring solidification cracks in the slab is a crucial issue, in particular for the maintenance of a high quality level in further production processes. Due to the elevated temperatures of the slab surface a remote sensing non-destructive tool for quality inspection is required, which is also applicable for the harsh industrial environment. In this work the application of laser ultrasound (LUS) technique during the continuous casting process in industrial environment is shown. The proof of principle of the detection of the centered solidification cracks is shown by pulse-echo measurements with laser ultrasonic equipment for inline quality inspection. Preliminary examinations in the lab of different casted samples have shown the distinguishability of slabs with and without any solidification cracks. Furthermore the damping of the bulk wave has been used for the prediction of the dimension of the crack. With an adapted “synthetic apert...

Easy-to-handle non-destructive testing methods for components are getting more and more important... more Easy-to-handle non-destructive testing methods for components are getting more and more important to achieve “zero failure production”. Especially in the aerospace industry, the responsible quality managers have to follow a strict 200% testingapproach. This means, a full-faced checking of the part is performed by an automated NDT system as the first step of the procedure. Areas that show deviations from the reference dataset are marked as so-called „findings“. In a second step a qualified auditor needs to evaluate these findings on a PC-monitor as „ok“, „defect“ or „ignore“. Finally, these rated findings are required to be again validated by manual NDT measurements on the real component. This rather unintuitive workflow requires a change of the perspective between the graphically illustrated dataset on a monitor and the real component, which is not only a further source of errors but also leads to focusing on the defective areas only. With the advancement in headsets, cameras, and t...

2021 48th Annual Review of Progress in Quantitative Nondestructive Evaluation

We demonstrate the determination of the Poisson’s ratio of steel plates during thermal processing... more We demonstrate the determination of the Poisson’s ratio of steel plates during thermal processing based on contact free laser ultrasound measurements. Our method utilizes resonant elastic waves sustained by the plate, provides high amplitudes, and requires only a moderate detection bandwidth. For the analysis, the thickness of the samples does not need to be known. The trend of the measured Poisson’s ratio reveals a phase transformation in dual-phase steel samples. While previous approaches based on the measurement of the longitudinal sound velocity cannot distinguish between the ferritic and austenitic phase above 770°C, the shown method can. If the thickness of the samples is known, the method also provides both sound velocities of the material. The gained complementary information could be used to analyze phase composition of steel from low temperatures up to its melting point.

In respect to economization of energy and raw materials the avoidance and real-time detection of ... more In respect to economization of energy and raw materials the avoidance and real-time detection of defects is a crucial issue in the continuous casting process. Those defects may occur during solidification of aluminum and beco m noticeable as bulk cracks as well as surface or near-surface cracks. Similarly, in furt her production processes the maintenance of a high quality level in high performance aluminum alloys for aerospace and automotive industry is also a fundamental topic. Th erefore, a non-destructive remote sensing testing tool for quality inspection duri g early stage of production is required. In this work the laser ultrasound (LUS) technique is demonstrated for qu ality inspection of semi-manufactured aluminum products. In LUS high energ y short laser pulses illuminate the sample. A fraction of the pulse energy is absorbed at the sample surface, causes local heating and thermal expansion, and induces br oadband ultrasonic waves which propagate through the sample. Those wa...

Generally, the elastic material properties (e.g. Young’s modulus and Poisson ratio) in steel and ... more Generally, the elastic material properties (e.g. Young’s modulus and Poisson ratio) in steel and cast iron are assumed to be unaffected by hardening processes in commo n literature. Only the hardness is presumed to alter, while the elastic properties keep cons tant. As the results of traditional and FEM (finite element method) static and dynamic stress calculations di rectly depend on the accuracy of these properties they are highly crucial. We show that the elastic properties get considerably mo dified during the hardening process. The change in Young’s modulus was up to 4%. An increase in hardness was associated with a decrease of the Young’s modulus. This effect was measured in steel alloys, a s well as in cast iron. Measurements were performed utilizing a picosecond-laser an d a photorefractive interferometer. Subsequently, the elastic properties were calculated from the recorded signals and the known density of the materials. As the measurements are performed conta ctless, futu...

Structural Control and Health Monitoring

Journal of Imaging

In conventional photoacoustic tomography, several effects contribute to the loss of resolution, s... more In conventional photoacoustic tomography, several effects contribute to the loss of resolution, such as the limited bandwidth and the finite size of the transducer, or the space-dependent speed of sound. They can all be compensated (in principle) technically or numerically. Frequency-dependent acoustic attenuation also limits spatial resolution by reducing the bandwidth of the photoacoustic signal, which can be numerically compensated only up to a theoretical limit given by thermodynamics. The entropy production, which is the dissipated energy of the acoustic wave divided by the temperature, turns out to be equal to the information loss, which cannot be compensated for by any reconstruction method. This is demonstrated for the propagation of planar acoustic waves in water, which are induced by short laser pulses and measured by piezoelectric acoustical transducers. It turns out that for water, where the acoustic attenuation is proportional to the squared frequency, the resolution li...

The optical generation of ultrasound is based at low power levels on the thermoelastic effect, wh... more The optical generation of ultrasound is based at low power levels on the thermoelastic effect, which is the generation of elastic waves by transient surface heating with a laser pulse. At high power level the laser source operates in the ablation regime by vaporizing a small amount of surface material. The radiated field of such a source resembles a monopole radiating in all directions of the half space. Laser ultrasonics uses one laser with a short pulse for the generation of elastic waves and another one, a long pulse or continuous laser, coupled to an optical interferometer for the detection of ultrasound. This technique enables a completely contactless measurement of elastic constants. As the laser pulse generates bulk as well as surface acoustic waves (SAW) both can be used for non-contact material characterization. Short laser pulses were used to generate bulk waves in continuous fiber reinforced aluminium or magnesium. With an optical interferometer the run-time of these wave...

The International Journal of Advanced Manufacturing Technology

Many industrial sectors face increasing production demands and the need to reduce costs, without ... more Many industrial sectors face increasing production demands and the need to reduce costs, without compromising the quality. The use of robotics and automation has grown significantly in recent years, but versatile robotic manipulators are still not commonly used in small factories. Beside of the investments required to enable efficient and profitable use of robot technology, the efforts needed to program robots are only economically viable in case of large lot sizes. Generating robot programs for specific manufacturing tasks still relies on programming trajectory waypoints by hand. The use of virtual simulation software and the availability of the specimen digital models can facilitate robot programming. Nevertheless, in many cases, the virtual models are not available or there are excessive differences between virtual and real setups, leading to inaccurate robot programs and time-consuming manual corrections. Previous works have demonstrated the use of robot-manipulated optical sens...

Materials Science Forum

State of the art of in-situ analysis on grain structure of metals during thermal and stress treat... more State of the art of in-situ analysis on grain structure of metals during thermal and stress treatment is done by observation of the probe in a thermomechanical treatment system. Potential analysis methods are high energy x-ray scattering (e.g. in a synchrotron) or laser-ultrasonics (LUS). The most commonly used thermomechanical system, is the so called “Gleeble” from Dynamic Systems Inc., which is able to heat and load the material in a quite fast manner with extremely high heating rates, very high forces and fast force changes. There is a wide area of research and applications, though, where these capabilities are not fully required, a less complex deformation-and quenching dilatometer would often be sufficient. In this paper we will show the implementation of a LUS system in such a dilatometer and compare it to the “all inclusive” Gleeble system, pointing out benefits and downsides on different aspects, like the technical specifications, the needed footprint and more. A sketch of ...

Nondestructive Testing and Evaluation

2011 IEEE International Ultrasonics Symposium, 2011

ABSTRACT We investigate numerically and experimentally the negative refraction of surface acousti... more ABSTRACT We investigate numerically and experimentally the negative refraction of surface acoustic waves in two-dimensional phononic crystals in the MHz range. We performed high-performance time-domain simulations of propagating broadband surface acoustic waves with the Finite Element Method (FEM) and spatio-temporal imaging by means of pulsed optical excitation and interferometric detection. Experimental and numerical evidence is found for negative refraction from surface wave focusing at particular frequencies after wave propagation through a parallel-sided phononic crystal layer. Obliquely incident plane waves on a phononic crystal were also investigated by numerical simulations. The transmitted waves show a clear shift of the wave front at particular frequencies, providing further evidence for negative refraction of the surface acoustic waves.