Magnetoeleastic Probes to Detect Subsurface Cracking/Residual Stresses Beneath Coatings in Ferromagnetic Materials

High strength steel alloys (300M) used in navel aircraft engine and landing gear components are found to be highly susceptible to fatigue cracking, induced by the cyclic loading these structures are subjected to in service. Stress-induced cracking is found to initiate due to improper grinding and machining of the parts during fabrication. There is critical need for nondestrucive techniques which can detect both cracking and potential crack nucleation sites within these components. Current NDE procedures using MPI methods suffer from limited sensitivity to these cracks, on account of the coatings used above the ferromagnetic steel alloys for corrosion resistance. A novel hybrid probe and instrument is proposed to simultaneously detect both subsurface residual stresses and stress-induced cracking in coated and uncoated ferromagnetic structures. Modifications to make these dual measurements are proposed on probe designs developed recently by the authors to measure residual stresses in anti-friction bearings. In Phase I, we will develop these modifications and demonstrate system capabilities through simple experiments. A prototype for a portable, commercially viable system is planned to be developed and delivered in Phase II.