No abstract

The paper presents experimental results concerning the variation of microplastic limit (MPL) during fatigue as determined by the measurement of changes in inductanceLof specimens made from normalized low-C steel CSN 411375. Some indications have been obtained that MPL varies during fatigue with dislocation density. This was proved by nanoindentation, X-ray diffraction and transmision electron microscopy.

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 limit 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. resistance and inductance). Measurements were performed on normalized low-C steel CSN 411375, and the microplastic limit was determined by evaluating the ΔRσ and ΔLσ records.