Characterization of the Fatigue Behaviour of Low Carbon Steels by Means of Temperature and Micromagnetic Measurements

Abstract

Investigations on low carbon (non- and low-alloy) steels were conducted in form of load increase tests (LIT) and constant amplitude tests (CAT) to find the correlation among material behaviour, mechanical load, and the type of NDT method. With the help of preprogrammed load-free sequences, the thermal impact on magnetic Barkhausen noise (MBN) measurement can be avoided, so that the cyclic deformation properties of material responses can be interpreted more precisely. The results indicate differences between the change in temperature and the MBN-derived variable during LITs and CATs regarding the demonstration of the incubation stage and the cyclic hardening behaviour.

Short-Time Fatigue Life Estimation for Heat Treated Low Carbon Steels by Applying Electrical Resistance and Magnetic Barkhausen Noise

“…The second LIT had a connection problem in the ER measurement, so that the data points were unfortunately lost (from σa = 230 MPa onwards), but this does not change or disturb any further steps. It can be seen in Figure 11 that the plastic portion of both materials generally increase, but at certain stage, the MBN signal falls, as already shown in [37]. The data point from the second LIT covered the elastic-plastic region and gives an idea of the choice of the stress amplitudes for the upcoming CATs.…”

“…To characterize the microstructure-based fatigue behavior in detail, the change in temperature ∆T, the change in MBN signal ratio ∆ϕ MBN and the change in electrical resistance ratio ∆ϕ R were calculated from the measurands. Technical specifications of the IR camera, the MBN sensor, as well as the preparation of the fatigue specimens, are already introduced in [37].…”

“…The later extracted feature "change in MBN signal ratio" ∆ϕ MBN was derived from the peak value of the pre-processed MBN signals I max [37] with an arbitrary unit in the time domain. It is the mean value calculated from three cycles in the middle of the excitation window.…”

“…All calculated plastic material responses derived from the three aforementioned measuring techniques are presented: the change in temperature, ∆T; the change in MBN signal ratio, ∆ϕ MBN ; and the change in electrical resistance ratio, ∆ϕ R . As described in [37], the tests were not performed with continuous load, but with inserted load-free sequences. The progress of ∆T p -N curves are shown in a continuous way, while the mean values from each load step of ∆T p , ∆ϕ MBN,p and ∆ϕ R,p are emphasized with dots of different shapes.…”

“…In addition to ER, micromagnetic-based methods can also be used in this context, such as eddy current testing, incremental permeability, Fourier analysis of the tangential 2 of 21 magnetic field, and magnetic Barkhausen noise (MBN) [27]. More papers in this field regarding the MBN technique [28][29][30][31][32][33][34][35][36] has already been introduced in [37].…”