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Micro-plastic limit of low-carbon steel CSN 41 1375 as determined by the measurement of electrical impedance
Summary
This study demonstrated that the microplastic limit of low-carbon steel can be determined using electrical impedance measurements, exploiting the relationship between magnetic permeability changes and dislocation pile-up formation during tensile loading. Electrical impedance measurement provides a practical non-destructive method for assessing the fatigue threshold of steel components in service.
It is generally accepted that not all cyclic stresses below the fatigue limit are non-damaging. Particularly in spectrum loading, the inclusion of some cyclic stresses below the fatigue limi can reduce the fatigue life of a component. It is believed that the boundary between damaging and non-damaging stresses is the so-called micro-plastic limit (MPL) defined as a macro-stress at which dislocation pile-up stresses begin to obstruct the magnetic domains in rotation to the direction of the tensile stress. This paper shows that MPL can be determined from changes in magnetic permeability during tensile loading. In our work, changes in magnetic permeability were measured indirectly - by measuring changes in electrical impedance (a.c. resistence and induktance). Measurements were performed on normalized low-C steel CSN 411375, and the microplastic limit was determined by evaluating