Affiliations: [a] Institute of Theoretical and Applied Mechanics,
Academy of Sciences of the Czech Republic, Prosecká, The Czech
Republic | [b] Faculty of Mechanical Engineering, University of West
Bohemia, Univerzitní, Pilsen, The Czech Republic
Correspondence:
[*]
Corresponding author: L'ubomír Gajdoš, Institute
of Theoretical and Applied Mechanics, Academy of Sciences of the Czech
Republic, 76, 190 00 Prague 9, Prosecká, The Czech Republic. E-mail:
[email protected]
Abstract: 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 ΔR – σ
and ΔL – σ records.
