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- Electromagnetic testing (2)
- Finite element method (2)
- Spherical defects (2)
- Flux leakage testing (1)
- GMR (1)
- GMR-Sensors (1)
- Magnetic flux leakage (1)
- NDT (1)
- Reconstruction (1)
- Sensor arrays (1)
GMR sensors are increasingly used for magnetic surface inspection due to their high
sensitivity and high spatial resolution. In case of simple planar or cylindrical shaped
components, the GMR-based inspection procedure can be automated easily. In order to
reduce the inspection time we present a GMR-based NDT-system consisting of a yoke
and a coil as a local magnetization unit. This way the global magnetization step and, if
necessary, the corresponding demagnetization cycle can be avoided reducing the
number of working steps. Using a local probe we measured plates, bearings, and rails,
each of which containing real fatigue cracks and reference artificial cracks of different
depths and orientations. Cracks with a depth of 40 ìm could be resolved with a signalto-
noise ratio of about 20. A reduction of the measuring time can be obtained using a
sensor array. We present an optimized sensor array for nondestructive testing
application, where gradiometric arranged GMR layers were fabricated on a board with
up to 48 GMR sensors. Each sensor detects the vertical field gradient. In our example
the baseline was chosen to be 250 ìm which efficiently suppress external background
fields without losing sensitivity for the detection of surface breaking defects.
High-precision magnetic field sensors are of increasing interest in non destructive testing (NDT). In particular GMR-sensors (giant magneto resistance) are qualified because of their high sensitivity, high signal-to-noise ratio and high spatial resolution. We performed magnetic flux leakage measurements of artificial cracks with a GMR-gradiometer and a 3-axes GMR-magnetometer. Cracks of a depth of 44 μm still could be detected with a sufficient high signal-to-noise ratio. A semi-analytic magnetic dipole model was used for swiftly predicting magnetic stray fields. The reliable reconstruction based on measurements of artificial rectangular-shaped defects is demonstrated.