Sensitivity analysis of the non-destructive evaluation of micro-cracks using GMR sensors

• Subregion FE-simulation of micro-crack for magnetic flux leakage evaluation.
• Subregion FE-simulation of sensitivity distribution with respect to local permeability changes.
• Verification of GMR model and identification of measurement uncertainties based on measurement data.
• Discussion of the ability of micro-crack identification with GMR sensors based on sensitivity analysis.
• Discussion of GMR measurement uncertainties based on sensitivity analysis.

Micro-cracks in a magnetized ferromagnetic material cause stray fields that can be observed using giant magnetoresistive (GMR) sensors. This work investigates the applicability of GMR sensors to the non-destructive evaluation of micro-cracks via the observation of stray fields. For this purpose, our measurement setup is assessed using a fast new sensitivity analysis based on adjoint states, employing the finite-element method. A model for the GMR sensor is developed and verified. We are able to resolve micro-cracks with an opening of 3 μm and a depth of 30 μm. GMR positioning inaccuracies are analyzed.