60 Technik
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- Magnetic force microscopy (2)
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- Capacitive coupling (1)
- Data fusion (1)
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- Fatigue life evaluation (1)
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The service life of materials and components exposed to repeated mechanical loads is
limited, which is why the understanding of the damage evolution and estimating its fatigue life is of
high importance for its technical application. This paper shows how temperature and magnetic field
measurement methods can be used to describe the cyclic deformation behaviour of metallic materials
and to derive parameters from this, which are used in short-term methods to calculate the fatigue
life. Within the SteBLife (stepped-bar fatigue life) approach, only three to five fatigue tests with a
stepped fatigue specimen are required to determine a complete S–N or Woehler curve with scatter
bands for different failure probabilities. If only a trend S–N curve is required, the number of tests
can be reduced to a single fatigue test only. In the framework of this paper, these approaches will be
presented for normalised SAE 1045 (C45E) and quenched and tempered SAE 4140 (42CrMo4) steels.
Encapsulated magnetic nanoparticles are of increasing interest for biomedical applications.
However, up to now, it is still not possible to characterize their localized magnetic properties within
the capsules. Magnetic Force Microscopy (MFM) has proved to be a suitable technique to image
magnetic nanoparticles at ambient conditions revealing information about the spatial distribution
and the magnetic properties of the nanoparticles simultaneously. However, MFM measurements
on magnetic nanoparticles lead to falsifications of the magnetic MFM signal due to the topographic
crosstalk. The origin of the topographic crosstalk in MFM has been proven to be capacitive coupling
effects due to distance change between the substrate and tip measuring above the nanoparticle. In this
paper, we present data fusion of the topography measurements of Atomic Force Microscopy (AFM)
and the phase image of MFM measurements in combination with the theory of capacitive coupling in
order to eliminate the topographic crosstalk in the phase image. This method offers a novel approach
for the magnetic visualization of encapsulated magnetic nanoparticles.
Magnetic force microscopy (MFM) has become a widely used tool for the characterization of magnetic properties. However, the
magnetic signal can be overlapped by additional forces acting on the tip such as electrostatic forces. In this work the possibility to
reduce capacitive coupling effects between tip and substrate is discussed in relation to the thickness of a dielectric layer introduced
in the system. Single superparamagnetic iron oxide nanoparticles (SPIONs) are used as a model system, because their magnetic
signal is contrariwise to the signal due to capacitive coupling so that it is possible to distinguish between magnetic and electric force
contributions. Introducing a dielectric layer between substrate and nanoparticle the capacitive coupling can be tuned and minimized
for thick layers. Using the theory of capacitive coupling and the magnetic point dipole–dipole model we could theoretically explain
and experimentally prove the phase signal for single superparamagnetic nanoparticles as a function of the layer thickness of the
dielectric layer. Tuning the capacitive coupling by variation of the dielectric layer thickness between nanoparticle and substrate
allows the distinction between the electric and the magnetic contributions to the MFM signal. The theory also predicts decreasing
topographic effects in MFM signals due to surface roughness of dielectric films with increasing film thickness.