EC-GMR array with rotating current excitation for multilayered riveted structures inspection


The challenge in detecting crack under fastener heads (CUF) in a multi-layered aircraft structure poses the need for advanced NDE technology. Our previous work has presented the feasibility of eddy current (EC) technology using giant magnetoresistive (GMR) sensors in detecting 2nd layer hidden cracks in layered aircraft components. An EC-GMR inspection system has been developed to directly measure the normal component of magnetic flux density associated with eddy currents induced inside the specimen. However, a major limitation of current sensor system is in detecting cracks that are parallel to the direction of induced currents. This paper presents a new design using orthogonal excitation coils for generating a rotating uniform current, which provides uniform sensitivity to cracks emanating in all orientations around fastener sites. The design and inspection using the orthogonal coil probe and GMR sensor is presented using a simulation model. Several candidate designs for the orthogonal coil configuration will be presented using the simulation model. The detection of cracks in all radial directions around aluminum and steel fasteners are validated numerically and experimentally.

2014 Review of Progress in Quantitative Nondestructive Evaluation