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Magneto-Resistive Array Development

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Magneto-Resistive Array DevelopmentSignificance

The nondestructive inspection of multi-layer airframe geometry is a significant challenge largely due to complexity of test geometry and deep lying defects. The test geometry includes configurations of aircraft skins, stringers, doublers, wing-splice with fasteners and deep lying cracks and corrosion.  Inspection of these complex samples needs to deal with a large number of variables associated with the test sample (material, size, thickness, edges, air gaps, etc.), experimental sensor system (frequency, waveform shape, harmonics, sampling intervals, circuit design etc.), and defect variables (length, width, volume, shape, distribution, orientation, etc.). Combination of these classes of variables encountered in any inspection makes the interpretation of the signals very challenging.

The availability of a fully validated computational model is valuable in designing an optimum sensor configuration as well as in signal interpretation. The model serves to predict and visualize the fields generated by the source in the test geometry, which in turn provides greater understanding of field-flaw and field-material interactions that influence the sensor measurements. The model can predict the sensor signal over a wide range of sensor and defect parameters, thereby yielding an optimized sensor design as well as procedures for interpreting complex signals.

Objective

Although we have previously verified that it is possible to detect 2nd and 3rd layer cracks using GMR sensors, several technological challenges remain to be addressed, such as crack orientation, penetration depth and inspection speed, considering the large area that should be inspected. The major objective of this study is to design a coil that is sensitive to cracks of all orientations and achieves rapid scanning/inspection ability. 

Approach

The project comprises of conducting systematic model-based investigations of defect and multi-layer sample geometry using a number of MR sensor configurations. Different coil configurations, including orthogonal coils and excitation waveforms are evaluated using the simulation model. In addition, sensors are built for experimental data acquisition on the samples that can be used for validating model predictions. Comparison of measurements with model predictions is performed to validate and optimize model parameters to improve the model accuracy.  The verified models would be used to predict the optimum parameters for eddy-current excitation and MR inspection of simulated aircraft geometry.