Stress detection and measurement in ferromagnetic metals using pulse electromagnetic method with U-shaped sensor

This paper proposed a pulse electromagnetic method (PEM) with a specially designed U-shaped sensor to detect and measure stress in ferromagnetic metals, which is derived from pulsed eddy current (PEC) and pulse magnetic flux leakage (PMFL). At first, theory behind PEM for tensile stress measurement has been analyzed. The influences of electrical conductivity and magnetic permeability of ferromagnetic material on sensor's response have been investigated through finite element method (FEM). Experimental system has been built and the experimental studies have been carried out to obtain the relationship between stress and extracted features from difference response of PEM U-shaped sensor. The excitation frequency has been optimized to improve the sensitivity. Both simulation and experimental results indicate that the proposed PEM can be used to measure and quantify the unidirectional tensile stress in ferromagnetic specimen due to the linear relationship in elastic deformation. The relationship between sensitivity and frequency is a reverse power function, and low frequency excitation has a higher sensitivity on stress measurement.