Dr. habil. Martin Spies, Physicist, Materials Scientist, is affiliated to the Fraunhofer Institute for Industrial Mathematics ITWM, Kaiserslautern, Germany.

Dr. Spies has studied Physics at the Universities of Saarland and Kaiserslautern as well as Materials Science at University of Houston, Texas. In 2001, he has been awarded the academic Venia Legendi in the field of Nondestructive Testing at University of Saarland, Saarbruecken. Dr. Spies is based in Germany’s Fraunhofer Society since the late 1980s. Finally heading the Simulation working group of the Fraunhofer Institute for Nondestructive Testing IZFP in Saarbruecken, he joined the mathematics institute ITWM in October 2007.

His particular research interest is in simulation-assisted ultrasonic NDT on the basis of physical models; the Ultrasonic Imaging working group at ITWM, uniting research fellows and PhD students as well, engages in imaging techniques with specific emphasis on defect testing and materials characterization. Research is concentrating on complex NDT problems such as the inspection of anisotropic and/or inhomogeneous media or highly attenuating structural materials. R&D projects are carried out with various academic and industrial partners on the national as well as international level.

Dr. Spies is currently a member of the counselling board of the German Society for Nondestructive Testing DGZfP and actively participating in various DGZfP committees of experts.
 

Abstract

Synthetic Aperture Focusing Technique (SAFT) and Time-of-Flight Diffraction Technique (TOFD)Ultrasonic Imaging – Past and Present

The determination of defects in materials and components using nondestructive testing and enhanced evaluation techniques is widely applied in many industrial areas. The safe operation of structures, appliances or vehicles requires permanent or periodic inspection of relevant parts and components. Depending on the size of flaws to be detected and depending on the material to be inspected the choice of the proper nondestructive method is made. Inspections with regard to cracks in the surface or near-surface regions are usually based on magnetic or liquid penetrant examination procedures or ultrasonic methods with special techniques. In order to find defects in the bulk of materials, radiographic or ultrasonic techniques are used.

For ultrasonic inspection a variety of techniques such as single probe, tandem or pitch-and-catch as well as phased-array techniques are available. Reliable defect detection requires defined and reproducible scanning of the probes along the surface of the components. From the recorded ultrasonic rf-data, amplitude and time-of-flight information can be extracted and used for the assessment of a defect. However, such an evaluation will provide insufficient quantitative results in cases of complex defect geometries and/or unfavourable material properties.

Over the years, the Synthetic Aperture Focusing Technique SAFT has – not only for such complex applications – been successfully applied to improve the performance of ultrasonic testing. The algorithmic processing of the raw rf-data leads to a reduction of the microstructural noise signals and thus to an improvement of the signal-to-noise ratio of the defect echoes. For specific defect and component configurations, the Time-of-Flight Diffraction Technique TOFD has also been successfully applied for quantitative evaluation of crack sizes.

This contribution will review developments and applications of SAFT and TOFD with reference to representative examples from more than three decades. Recent inspection problems dealing with unfavourable defect and material properties such as the detection and sizing of stress corrosion cracks in austenitic steel components or the quantitative evaluation of defects in highly attenuating materials, also with reference to POD issues, will be additionally addressed.