LAUSR

Abstract 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.