A hand held magnetic camera system for real time crack inspection

Paramagnetic metals like aluminum alloys are used in aircraft due to their light weight. Magneto-optical eddy current imager (MOI) is a nondestructive magneto-optical technique that is used to inspect fatigue cracks and corrosion in the aluminum alloy of aged aircraft. Unfortunately, the quantitative distribution of distorted magnetic flux leakage (MFL) from crack tips is difficult to measure, and therefore, the shapes and sizes of cracks are difficult to evaluate quantitatively. Additionally, the inspected results vary significantly according to the skill level of the worker. Hand-held magnetic camera using Hall sensor array for crack inspection in paramagnetic materials is developed by research center for real time NDT. Distorted alternate currents (DAC) are produced around the crack tips when the sheet type induced current (STIC) is induced on the specimen in the hand-held magnetic camera system. The alternate MFL resulting from the DAC is detected using a Hall sensor array. The root-mean-squared MFL after the use of high pass filter is converted to a digital signal by an analog-to-digital converter (ADC). And it is stored in a computer, and processed by interface and operation software. An algorithm for the quantitative nondestructive testing and evaluation of cracks of different shapes and sizes on the aluminum alloy, Al7075, is proposed in this paper.