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- Beitrag zu einem Tagungsband (7) (entfernen)
Schlagworte
- Reconstruction (3)
- Electromagnetic testing (2)
- Finite element method (2)
- Spherical defects (2)
- Superconducting wires (2)
- Eddy Current Testing (1)
- Eddy current testing (1)
- FEM (1)
- GMR (1)
- GMR-Sensor-Array (1)
Visualization of material defects - modern approaches in acoustical and electrical NDE-methods
(2008)
Increasing demands in materials quality and cost effectiveness have led to advanced
standards in manufacturing technology. Especially when dealing with high quality
standards in conjunction with high throughput quantitative NDE techniques are vital to
provide reliable and fast quality control systems. Fast NDE-systems using a high degree
of automatisation can be used for both determining the degree of integrity of the
components under test and indicating a change of production parameters as well.
However, independently of the applied NDE method and the underlying physical
principle a reliable visualisation of hidden defects within the component under test is
based on a sufficient high signal to noise ratio (SNR) and a high spatial resolution. In this
talk we illuminate two standard NDT methods such as Ultrasonic Testing and Eddy
Current Testing and show their physical principles also discussing the interaction
between sound waves or induced eddy currents with different kinds of material defects.
This introduction substantiates the attainable SNR and spatial resolution of both methods
with respect to defect sizing and defect classification. As a first future prospect we report
on the SAFT-algorithm to improve SNR and spatial resolution paving the way for a flaw
sizing approach in ultrasonic inspection. As a second modern NDE approach we
represent the use of small magnetoresistance sensor arrays for EC testing of Al-laser
welds or for testing superconducting wires. The high sensitivity and small extent of GMR
sensors results in a remarkably SNR and spatial resolution offering new visualisation
techniques for defect localisation, defect characterization and tomography-like mapping
techniques.
Increasing demands in materials quality and cost effectiveness have led to advanced
standards in manufacturing technology. Especially when dealing with high quality standards in
conjunction with high throughput quantitative NDE techniques are vital to provide reliable and fast
quality control systems. In this work we illuminate a modern electromagnetic NDE approach using a
small GMR sensor array for testing superconducting wires. Four GMR sensors are positioned around
the wire. Each GMR sensor provides a field sensitivity of 200 pT/√Hz and a spatial resolution of
about 100 µm. This enables us to detect under surface defects of 100 µm in size in a depth of 200 µm
with a signal-to-noise ratio of better than 400. Surface defects could be detected with a SNR of up to
10,000. Besides this remarkably SNR the small extent of GMR sensors results in a spatial resolution
which offers new visualisation techniques for defect localisation, defect characterization and
tomography-like mapping techniques. We also report on inverse algorithms based on either a Finite
Element Method or an analytical approach. These allow for accurate defect localization on the µm
scale and an estimation of the defect size.
The determination of magnetic distortion fields caused by inclusions hidden in a
conductive matrix using homogeneous current flow needs to be addressed in multiple tasks of
electromagnetic non-destructive testing and materials science. This includes a series of testing
problems such as the detection of tantalum inclusions hidden in niobium plates, metal inclusion in
a nonmetallic base material or porosity in aluminum laser welds. Unfortunately, straightforward
tools for an estimation of the defect response fields above the sample using pertinent detection
concepts are still missing. In this study the Finite Element Method (FEM) was used for modeling
spherically shaped defects and an analytical expression developed for the strength of the response
field including the conductivity of the defect and matrix, the sensor-to-inclusion separation and the
defect size. Finally, the results also can be useful for Eddy Current Testing problems, by taking the
skin effect into consideration.