Uniaxial ACFM detection system for metal crack size estimation using magnetic signature waveform analysis

•A single-axis ACFM detection system is able to estimate the crack dimensions.•A characteristic surface is developed based on different parameters of crack.•The crack depths can be inversed by a fitted polynomial interpolation formula.•The system provides a straightforward and fast crack sizing detection procedures. A single-axis alternating current field measurement (ACFM) detection system is proposed for crack size estimation. A single tunneling magneto-resistive (TMR) sensor is used to detect Bz signal, which is able to determine both the length and depth of a crack simultaneously. First, a theoretical analysis is presented to evaluate the crack length and especially depth using Bz signature waveform. The underlying physics principle is supported using a finite element analysis (FEA) method. In the simulation, the cracks with various lengths and depths are analyzed for a given crack width, and corresponding Bzmax values are obtained. Next, a Bzmax characteristic polynomial surface is developed, which can be represented by a fitted polynomial interpolation equation. The crack depth can be inversed by this equation with reference to the measured Bzmax value and crack length. Finally, real ACFM experiments are conducted to demonstrate that the crack lengths and depths can be readily estimated.