Abstract
Steel rope wires represent the main bearing components of bridges whose long-term operation depends on loading conditions, corrosion attack, and/or pre-stressing. Corrosion attack especially can remarkably reduce the effective cross-sectional area, which in turn over-stresses the wires and redistributes stress to the neighboring wires. The premature collapse of many bridges is very often caused by wire rupture as a result of their poor corrosion protection. For these reasons, various processes—such as galvanizing, phosphating, etc.—have been applied to steel wires to increase their resistance against corrosion. However, these processes can alter the microstructure, especially in the near-surface regions. The Barkhausen noise technique has been already reported as a suitable technique for investigating corrosion extent and true pre-stress in the steel rope wires. This study reports that non-homogeneity of the surface state of wires undergoing different surface treatment makes it more difficult to assess the true stress state and increase the uncertainty of Barkhausen noise measurement. Barkhausen noise signals are correlated with metallographic and SEM observations as well as microhardness measurements. The non-homogeneity of the surface state of wires is also investigated by the use of chemical mapping and linear chemical analyses.
Highlights
Magnetic Barkhausen noise (MBN) is a function of the stress state [1], its variation [2] as well as microstructure of ferromagnetic bodies [3]
This study investigates how the non-homogeneity in the surface state affects relationships among the tensile stress and MBN parameters extracted from the raw MBN signals
The main role of the MBN technique can be viewed as monitoring true pre-stress
Summary
Magnetic Barkhausen noise (MBN) is a function of the stress state [1], its variation [2] as well as microstructure of ferromagnetic bodies [3]. MBN refers to the irreversible and discontinuous jumps of domain walls (DWs) [4] whose sudden displacement, initiated by altering the magnetic field, produces electromagnetic (as well as acoustic) pulses [5] These pulses can be detected on the free surface using a suitable pick-up coil. It is well known that DWs align with the direction of tensile stress and contribute to the increasing magnitude of MBN pulses, producing higher MBN emission, whereas compressive stress aligns DWs in the direction perpendicular to the direction of the stresses, which in turn decreases MBN [6] This behavior explains the sensitivity of MBN against the different magnitudes and regimes of stresses and has been already reported [7]. This study investigates how the non-homogeneity in the surface state affects relationships among the tensile stress and MBN parameters extracted from the raw MBN signals
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