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Abstract

Nondestructive material condition monitoring and assessment is accomplished by placing, mounting, or scanning magnetic and electric field sensors and sensor arrays over material surfaces. The material condition can be inferred directly from material property estimates, such as the magnetic permeability, dielectric permittivity, electrical property, or thickness, or from a correlation with these properties. Hidden cracks in multiple layer structures in the presence of fasteners are detected by combining multiple frequency magnetic field measurements and comparing the result to characteristic signature responses. The threshold value for indicating a crack is adjusted based on a high frequency measurement that accounts for fastener type. The condition of engine disk slot is determined without removal of the disk from the engine by placing near the disk a fixture that contains a sensor for scanning through the slot and means for recording position within the slot. Inflatable support structures can be placed behind the sensor to improve and a guide can be used to align sensor with the slot and for rotating the disk. The condition of an interface between a conducting substrate and a coating is assessed by placing a magnetic field sensor on the opposite side of the substrate from the coating and monitoring at least one model parameter for the material system, with the model parameter correlated to the interfacial condition. The model parameter is typically a magnetic permeability that reflects the residual stress at the interface. Sensors embedded between material layers are protected from damage by placing shims on the faying surface. After determining the areas to be monitored and the areas likely to cause sensor damage, a shim thickness is determined and is then placed in at least one area not being monitored by a sensor. The condition of a test fluid is assessed through a dielectric sensor containing a contaminant-sensitive material layer. The properties of the layer are monitored with the dielectric sensor and correlated to contaminant level.

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