26.04.2015 Views

Electromagnetic Testing

Create successful ePaper yourself

Turn your PDF publications into a flip-book with our unique Google optimized e-Paper software.

Q.7.6 Subsurface discontinuities located in thick or multilayered aircraft<br />

structures could be detected by:<br />

A. low frequency sinusoidal continuous wave instruments.<br />

B. high frequency sinusoidal continuous wave instruments.<br />

C. pulsed systems.<br />

D. A or C.<br />

Answer to a Mistake – a mistake make is a good lesson learned.<br />

D.J. Hagemaier discussed low frequency eddy current inspection of aircraft structures for<br />

subsurface discontinuity detection in an article published in Materials Evaluation in 1982. A low<br />

frequency (100Hz to 1000Hz) technique can be used to locate cracks in thick or multiple layer,<br />

bolted or riveted aircraft structures. Again, models are constructed with artificial cracks and their<br />

responses are compared to responses in the actual test object. Most of these examinations are<br />

performed using single or multifrequency sinusoidal alternating current processes. Pulsed eddy<br />

current systems, if available, might also be used for crack detection in thick structures.<br />

Charlie Chong/ Fion Zhang

Hooray! Your file is uploaded and ready to be published.

Saved successfully!

Ooh no, something went wrong!