Non-destructive testing: A systems approach

© Fraunhofer IKTS
Microshaping of fine-scaled piezoceramics for high-frequency ultrasonic transducers.
© Fraunhofer IKTS
Acoustic emission sensor for active and passive structure monitoring.
© Fraunhofer IKTS
PCUS® pro Multi for automated ultrasonic testing.

Ultrasonic methods

 

Ultrasonic methods are some of the most frequently used methods for non-destructive testing. Fraunhofer IKTS combines years of experience in materials testing with unique capabilities in the field of ultrasonic technologies. As a developer of industrial ultrasonic testing systems, Fraunhofer IKTS offers sensors, testing electronics, software, simulation and modeling services, and an accredited test lab for validation and verification of ultrasonic methods – which truly makes it a one-stop shop for ultrasonics.

 

Ultrasonic sensors

At the heart of every testing system are the sensors. Fraunhofer IKTS develops sensors optimally adapted to the given geometries, materials, and acoustic parameters.

Technical details

  • High-performance ultrasonic transducers for use on fiberreinforced composites (high- and low-frequency, focused/ unfocused, single-element or segmented)
  • Dice-and-fill composites
  • Soft-mold composites for frequencies of 5–30 MHz with max. transducer dimensions of 10 x 10 mm
  • Screen-printed ultrasonic transducers for mass-produced compact sensor systems with 5–30 MHz and max. transducer dimensions of 100 x 100 mm
  • Focused ultrasonic phased array probes
  • High-sensitivity phased array probes
  • High-frequency probes (100–250 MHz)
  • High-temperature probes (up to 200 °C)
  • Acoustic emission sensors

 

Ultrasonic electronics

© Fraunhofer IKTS
Mobile testing system for wheel set shafts with longitudinal bores using electronics and software from Fraunhofer IKTS (source: Arxes-Tolina).

To get the full potential out of the sensors, Fraunhofer IKTS offers the PCUS® pro series of powerful modular electronics. The portfolio extends from simple manual ultrasonic testers to fully automated ultrasonic testing systems.

Technical details

  • Modular and customizable
  • Compact and energy-efficient
  • Meets respectively relevant parts of ultrasonics standard DIN EN 12668
  • Suitable for single oscillators as well as single- and multichannel testing electronics up to arrays
    (up to 128:128)

 

Ultrasonic software

Software has become fundamental to the development of testing systems for industrial application. It must be innovative and quickly available without compromising flexibility to allow future changes and extensions. PCUS® pro Lab is a modular software suite that quickly and flexibly creates solutions for the given testing task. The software supports parameterization for actuator and sensor control, visualization, and evaluation. Data organization and management take place in the flexibly adaptable revision system. In addition, the suite can be fully integrated into existing manufacturing concepts within the scope of Industry 4.0.

Technical details

  • Intuitive operation via a modern, accessible, and easily adaptable user interface
  • Professional implementation of customer-specific requirements through a modular parameterization, test procedure, and analysis concept
  • Mapping of complex test requirements to any geometries
  • Real-time display of volume images during data acquisition

 

Simulation and modeling

Nowadays simulation techniques are essential for optimizing ultrasonic testing systems and developing new measurement methods. They enable the physical plausibility of a method to be tested and the best possible measurement and probe parameters to be determined even before the first measurement setup is actually realized. This saves time and money in the development and leads to testing systems with clearly improved performance parameters.

Technical details

  • Numerical ultrasonic solver (EFIT) developed in-house
  • Wave physics simulation
  • Consideration of diffraction, interference, mode conversion, multiple scattering, etc.
  • I sotropic and anisotropic, homogeneous and heterogeneous materials
  • Solids and liquid media
  • 2D and 3D models
  • Time signals, wavefield snapshots, video animations

Services offered

  • Development of customer-specific sensors
  • Measurement and characterization of probes
  • Development of software for special applications up to complete
    testing systems conforming to DIN EN 12668
  • Development of testing electronics for simple manual testing
    systems up to automated ultrasonic testing systems
  • Development of user-specific simulation tools
  • Scientific consulting with simulation-supported feasibility
    and optimization studies
  • Interpretation of results
  • Demonstration and training

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© Fraunhofer IKTS
Simulated vibration behavior of ceramic tubes for battery applications.
© Fraunhofer IKTS
Ultrasonic goniometer HUGO measuring surface property gradients.

Acoustic methods

 

Special elastodynamic methods

Like ultrasonic methods, acoustic methods utilize elastodynamic interactions in an object to yield information about the condition of the object. This is frequently connected with acoustic signal radiation. Acoustic resonance testing is a wellknown and widely applied method for detection of cracks in parts such as ceramic utensils.

Scientists at IKTS supplement this initially purely empirical approach with experimental and theoretical model-based vibration analysis. Special elastodynamic methods cover a wide range of methods from the scalar acoustic waves until several 100 MHz linear and nonlinear bulk elastic waves. Thus, mechanical stresses can be determined from the relationship between the velocity of elastic wave propagation and mechanical stress. Focused very-high-frequency ultrasonics enables volume imaging with microscopic resolution (scanning acoustic microscopy, or “SAM” for short) to be performed on opaque objects.

If the application requires it, the methodology is modified to solve the given problems. One example of this is SAM tomography, which delivers a spatial representation similar to that provided by x-ray CT for tasks that are difficult for ultrasonics. Another recent development is imaging of surface microstructures via grazing elastic waves that are optically scanned.

The available standard equipment does not always permit use of novel methods. When necessary, IKTS scientists can develop suitable equipment and make it available to customers.

Application fields

  • Fast whole-part defect analysis
  • Determination of surface gradients in mechanical properties and stress states
  • Verification of layer adhesion, inhomogeneities, and cracks

Services offered

  • Methods development and adaptation for individual test conditions
  • Development and validation of adapted measurement systems
  • Service provision and consulting

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© Fraunhofer IKTS
Monitoring of structural damage in thermally loaded parts via acoustic emission and high-temperature strain measurement.
© Fraunhofer IKTS
3D acoustic emission location plot for creep damage localization.

Acoustic emisson analysis

Fraunhofer IKTS provides acoustic emission analysis for damage detection of structural components during fatigue tests or under operational load by fast and reliable localization of sound emitting regions, e.g., due to crack growth. The position of the damage can be determined by the travel time of ultrasonic waves from damage to the sensors of the network. Furthermore, detailed signal processing allows the evaluation and the classification of the damage. The results from acoustic emission analysis offer detailed information which can be used for the focused application of conventional NDT methods and allows better load control during structural testing.

Acoustic emission testing is well suited for static and dynamic tests on fiber composite parts. These materials produce strong acoustic emissions when fiber breaks and delamination occur. In dynamic fatigue tests, the high level of noise from the surroundings and the acoustic properties of the composite materials might decrease the detectability and therefore lead to challenges. To face them and to ensure a wider applicability of acoustic emission, IKTS offers an acoustic measurement system with high measurement dynamics and sophisticated damage evaluation and localization algorithms. The system also supports the storage and the evaluation of complete waveforms. If used during fatigue testing, the distributions of acoustic emission parameters supply information about the structural state and allow to adjust the load conditions if needed.

Technical details

  • High variability of acoustic emission measurement system due to modular structure of 4-channel sensor nodes
  • Adaptation of in-house hardware and software to the given measurement task

Application fields

  • Development of light-weight structures
  • I ntegrity testing of light-weight structures under specific loading and environmental conditions

Services offered

  • Accompanying measurements for static and dynamic structural fatigue tests (from coupons to large structures)
  • Supply of measuring equipment
  • Specific system and sensor design
  • On-site installation of measurement systems
  • Support in evaluation of recorded signals
  • Employment of high-resolution NDT methods after location of defects and customer-specific development of acoustic measurement systems

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© Fraunhofer IKTS
Development of eddy current sensors for special applications, e.g., composite materials.

Electromagnetic methods

 

High-frequency eddy current methods

The eddy current method is an electromagnetic technique for non-destructive testing of metals and non-conductive or weakly conducting materials such as plastics or ceramics. It has become a key technology for quality assurance, especially in the field of light-weight construction – for all areas from the aerospace and automotive industries to energy technology – because of its high speed, operation without a coupling medium, no requirements regarding radiation protection, and ease of integration into industrial manufacturing processes.

The so-called high-frequency eddy current technique and imaging impedance spectroscopy in the frequency range of 100 kHz to 100 MHz used to analyze weakly conducting material classes such as carbon fibers and carbon fiber composites were developed at Fraunhofer IKTS. Methods knowhow covers the entire production chain – from simulation and sensors, manipulation, and electronics to device construction. Customer requirements are consistently converted to adapted measurement and testing solutions.

The EddyCus® device plattform from Fraunhofer IKTS meets the growing requirements of the light-weight construction industry and can also cater to the needs for eddy currentbased techniques for quality assurance in other areas.

 

Technical details

  • Frequency range: up to 100 MHz
  • Special sensors for fiber composite materials
  • Eddy current system for individual system integration (integration kit)
  • 2D and 2.5D eddy current scanning systems
  • Robot-based eddy current systems for freeform parts Application fields
  • Characterization of fiber layers and material properties of carbon fiber composites
  • Testing of ceramics and metals
  • Monitoring of hardening reactions in epoxy resins

Services offered

  • Development and setup of customer-specific testing systems, including sensors, hardware, software, and manipulator technology

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© Fraunhofer IKTS
Testing weld seams on frame structures by means of micromagnetic Barkhausen noise.

Mikromagnetic Barkhausen noise

The micromagnetic Barkhausen noise technique is a surface characterization method that can only be used on ferromagnetic materials. The Barkhausen effect represents the interaction between an induced electromagnetic field and the component microstructure. It is especially useful for detecting stress and fatigue, but it can also be used for detecting residual austenite and cementite. Barkhausen noise is also the only non-destructive method other than x-ray diffraction that can be used to determine internal stresses independently of the microstructure.

Barriers to use of this method in practice can mainly be attributed to the large size and inflexibility of the sensors, the extreme sensitivity of the testing systems to parasitic effects, and the extensive calibration. Fraunhofer IKTS has developed smaller, more compact, and more robust test equipment to overcome these barriers. The technology is now less sensitive to environmental effects. In addition, special sensors allow for wider use and the calibration requirements can be considerably reduced through a complex algorithm.

Technical details

  • Application with standard sensors or, alternatively, with multi-axis sensors or current excitation
  • Transfer of raw data (integral, maximum, mean value, coercive field strength, etc.)
  • Alternative transfer of calibrated materials properties (hardness, stress, retained austenite, cementite, etc.)
  • Measurement services as well as conceptual design and setup of customized test equipment and/or sensors

Application fields

  • Outdoor deployment in rugged environmental conditions
    with laboratory instruments and robust manual test equipment

  • Materials characterization during the manufacturing process
  • Evaluation of stress state in large-scale industrial plants and
    buildings

Services offered

  • Development of customized sensors and test equipment
  • Rental of testing systems
  • Training
  • Testing services

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© Fraunhofer IKTS
Examination of an electronic assembly using high-resolution x-ray laminography.
© Fraunhofer IKTS
X-ray CT of a single-handed pocket watch, manufactured around 1600 (exhibit item on display at Staatliche Kunstsammlungen Dresden).

X-ray methods

 

Micro-computed tomography

Industrial micro-computed tomography (micro-CT) is an established method of analysis for technical and scientific applications and is increasingly established in the investigation of artistic and cultural goods. It is ideal for visualizing air inclusions, cracks, and other material inhomogeneities in objects of any shape. Micro-CT enables non-destructive three-dimensional examination of objects with a high spatial resolution.

Fraunhofer IKTS has a micro-CT system that can be adapted to customer requirements. This makes it possible to investigate objects ranging from miniature electronic components to large art objects and fossils.

Technical details

  • 225 kV microfocus x-ray tube
  • 2048 x 2048 pixel area detector
  • Spatial resolution: max. 1 μm
  • Specimen size: max. 60 cm (greatest extension)
  • Specimen weight: max. 6 kg

Application fields

  • Materials and product development for electronics industry and medical technology
  • Examination of mass-produced parts
  • Examination of archaeological finds and art objects

High-resolution CT laminography


High-resolution computed laminography (HRCL) is a new x-ray tomography method that was developed at Fraunhofer IKTS. With it, small regions of especially large-area and planar circuit substrates can be investigated non-destructively at a high resolution. With a modified measurement setup and an optimized reconstruction algorithm, the challenges associated with high-resolution investigation of circuit boards with size restrictions by micro-CT were eliminated. Now, for example, control boards for automotive or power electronics and embedded systems can be analyzed non-destructively without any need for sample preparation.

Technical details

  • 225 kV microfocus x-ray tube
  • 2048 x 2048 pixel area detector
  • Spatial resolution: max. 900 nm
  • Specimen size: max. 60 cm (greatest extension), larger for examination of subareas
  • Sample weight: max. 6 kg

Application fields

  • Fast visualization of cracks in bond pads for electronic components on substrates
  • Examination of systems embedded in CFRP plates

X-ray diffraction

Fraunhofer IKTS utilizes the x-ray diffraction (XRD) method to determine the compositions of material mixtures. In this method, an incident x-ray beam is diffracted by ordered structures such as crystals or quasi-crystals and the diffraction intensity distribution is measured.

Fraunhofer IKTS also uses XRD to determine internal stresses via the sin2y method. Here, the specimen is tilted by a certain angle y (psi) to a reflection. Measurements are performed at various points, which at least include the extremes (edges, corners, and middle), to yield the distribution of internal stresses in the specimen. Texturing affects the results obtained by numerous methods. Using the sin2y method reliable values are determined, if the layer to be investigated is not textured. For this reason, the pole figures are obtained for at least two different reflections at various points on the test object. The internal stress can then be derived from the determined peak positions.

Application fields

  • Determination of compositions of material mixtures and internal stresses within the scope of materials and product development
  • Root cause studies for part defects

 

X-ray line detector

X-ray line detectors are usually used to examine continuous streams of products or to avoid undesired scattering when the object size only permits linewise illumination. The L100 line detector developed at Fraunhofer IKTS is made using customer-specific ASICs and thus enables low-cost fabrication and diverse configurations – with no size restrictions. The novel detector also works with direct conversion. This yields higher resolutions and speeds than are obtained with conventional detectors. Thanks to the single-photon counting mode, the x-ray photon energies can also be evaluated. This enables “dual energy” applications, in which differentiation is made between materials in terms of composition.

Technical details

  • Line length: 102.4 mm
  • Resolution: 100 μm
  • Energy range: 30–200 keV and 2–40 keV
  • Scan speed: up to 50 m/s

Application fields

  • In-line quality assurance and materials classification for:
  • Food and pharmaceutical industries
  • Small parts/semi-finished product manufacturing

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© Fraunhofer IKTS
OCT cross-sectional image of a weld seam with air and particle inclusions.

Optical methods

 

Optical coherence - tomography

At Fraunhofer IKTS, optical coherence tomography (OCT) is used for three-dimensional detection and imaging of structures in various materials such as ceramics, plastics, glasses, glass fiber-reinforced plastics, and biological materials. The noninvasive tomographic imaging method enables visualization of the surface topographies and internal structures in scattering media. For this, the object to be investigated is irradiated with a low-coherence near-infrared light source and the scattered light is processed by a spectroscopic method.

OCT allows testing to be done in real time without direct contact with the specimen. Another advantage of OCT is its high measurement speed, which enables bulk specimens to be investigated in a matter of seconds. These advantages qualify it as an efficient, low-cost method for in-line defect detection (e.g., seal seam inspection) as well as for foreign object detection in bulk materials in various branches of industry. The measurement method can be adapted to diverse applications and optimized for specific requirements.

Technical details

  • 3D imaging method for semi-transparent materials
  • Measurement area: 40 x 40 cm
  • Resolution: < 10 μm
  • High penetration depth: 1–3 mm
  • High axial resolution: 0.5–15 μm
  • Non-invasive, non-contact measurement method
  • No ionizing radiation
  • More than 30 cross-sectional images per second

Application fields

Product testing and process monitoring for:

  • Plastics and packaging industry
  • Ceramics industry
  • Electronics industry
  • Additive manufacturing methods
  • Food industry
  • Roll-to-roll processes

Services offered

  • Static and dynamic layer thickness measurement
  • Three-dimensional structure visualization (surface and internal structure)
  • Development of customized testing systems
  • Improvement of measurement algorithms and image analysis
  • I ntegration into existing systems

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© Fraunhofer IKTS
Automated in-line testing system based on laser speckle photometry.

Laser speckle photometry

Time-resolved laser speckle photometry (LSP) is a new method that was developed at Fraunhofer IKTS to characterize part surfaces. It is based on evaluation of the temporal changes in speckle patterns formed due to mechanical or thermal excitation of the test objects. Excitation can originate from the process itself (e.g., heat generated by welding) or through deliberate input (e.g., of heat or mechanical stresses) during testing.

The non-contact method is characterized by a simple, robust design and low costs compared with those of competing measurement methods. The extremely short measurement times predestine it for in-line use in industrial production and for in-situ measurements within the scope of maintenance and repair work.

Laser speckle photometry is highly sensitive to out-of-plane and in-plane displacements. Compared with other techniques that concentrate on the distortion of the overall speckle patterns or of the fringes, laser speckle photometry measures the spatial and temporal dynamics of the speckles produced by changes in intensity of each pixel in the camera sensor. The interaction between the speckle dynamics and the specimen condition can be described by a correlation function. A customer-specific correlation model based on reference values, process conditions, and material characteristics is used to determine properties such as porosity, stresses, and defects.

Technical details

  • Can be used on all non-reflecting materials
  • Test chamber size: no restrictions, homogeneous illumination of areas of up to 100 x 100 mm, larger areas are examined by scanning
  • Lateral resolution: 10 μm (metals) to 100 μm (ceramics)
  • Measurement speed: 20 measurements/second, 30 images/minute

Application fields

  • Process monitoring of rapid manufacturing processes, e.g., in-line materials characterization in additive manufacturing processes
  • Structure monitoring (stresses and defects)
  • In-line monitoring of biotechnological processes

Services offered

  • Development of customized LSP-based testing systems
  • On-site measurement services
  • Measurement of electronic component geometries
  • Contract research

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Hardware module for pattern recognition.
© Fraunhofer IKTS
Robot-assisted measurement and AI-based data analysis extend the range of applications for NDT methods.

Advanced NDT

 


In the scope of Industry 4.0-related testing, a huge volume of process data is accumulated from different sources and must be analyzed. Suitable methods can be applied to obtain further information from already determined or additionally measured parameters. Fraunhofer IKTS optimizes established and new NDT methods to show customers how they can use this valuable information.

Pattern recognition

With pattern recognition, test objects can be classified by means of their measurement signals, for example, through actively or passively acquired acoustic signals, images, or other parameters such as temperature values. The main focus of pattern recognition is on giving these data a meaning, for example, “The gear is defect-free” or “The valve has reached 80 % of its lifetime”.

Fraunhofer IKTS has a wealth of experience in the field of pattern recognition. Developed algorithms have already been successfully tested and used in numerous applications, e.g., in mechanical engineering, automotive, glass, paper, textile, and watch- and clockmaking industries. In addition to a PC-based solution, an autonomous, modular device for mobile measurements has been developed for connection of various sensors or microphones.

Technical details

  • Independent of testing method as well as sensor measurement
    principle and type
  • Combination of different sensor data possible

Application fields

  • OK/NOK analysis
  • Service life prediction
  • Detection of cracks, inclusions, and impact damage
  • Wear monitoring
  • Condition monitoring of parts, machines, and plants
  • Monitoring of production processes

 

Machine learning

Machine learning, as a subarea of artificial intelligence, is the process of learning from an existing, usually large set of data. This process does not occur by “rote learning”, but by recognition of patterns and regularities in known examples, the training data. In the training process, generalized models are built and can be used to classify new, unobserved data.

Fraunhofer IKTS uses special machine learning processes such as deep learning for training of deep neural networks (DNNs), the expectation maximization (EM) algorithm for hidden Markov models (HMMs), or convex optimization for support vector machines (SVMs). Special training software enables easy learning of new models, e.g., for additional series of the same part or comparable parts.

Services offered

  • Recognition and training software
  • Hardware modules
  • Data analysis and evaluation
  • Customer-specific development of complete systems

 

NDT assistance systems

Another focus of Industry 4.0 is on assistance systems intended to support humans in dealing with technology. Fraunhofer IKTS is developing a cognitive user interface for the control of testing systems. This cognitive UI enables a natural dialog between the user and the testing system. Thus, the user does not have to have any prior knowledge or learn any special commands. The interface independently adapts to the tester’s way of working and the testing tasks. It also learns the individual user’s behavior and can be controlled via various communication options (e.g., voice, touch, and gestures). This can, for instance, help testers operate test equipment when access to the test specimen is impeded or environmental conditions pose a complication (e.g., radioactively contaminated surroundings). The cognitive user interface developed at Fraunhofer IKTS has the advantage of being autonomous. It requires neither an Internet connection nor a radio network. In addition, the hardware module does not use any resources from the test equipment. For absolute data security, data are only kept on the device and are, by default, not transferred to external servers or clouds from third-party providers. This also makes the interface suitable for confidential and local applications involving sensitive data.

Technical details

  • Can be used without radio network or Internet connection
  • No transmission of user speech input to third-party servers
  • Enables non-contact “hands and eyes free” communications

Application fields

  • Maintenance, repair and operation (MRO) in:
  • Large-scale technical infrastructures
  • Aerospace
  • Industrial and plant engineering
  • Human-machine interaction
  • Control of equipment and plants

Services offered

  • Recognition software
  • Hardware
  • Training software
  • Customer-specific development

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