Statistical evaluation of the Barkhausen Noise Testing (BNT) for ground samples

The Barkhausen Noise Testing (BNT) is a non-
destructive method for investigation many of
ferromagnetic material features. The most common
application is monitoring of so-called grinding burns
caused by introducing locally high temperature while
grinding. Other features, such as microstructure, residual
stress changes, hardening depth, etc., can be monitored as
well. Nevertheless, because the BNT is a method based on
a complex magneto-electric phenomenon which still
needs more scientific investigations an understanding, it is
not standardized yet. Therefore, there is a need for
studying of traceability and stability of the measurement
method. The aim of this study was to carry out statistical
analysis of the ferromagnetic samples after grinding
processes by the use of BNT. The first part of the
experiment was to grind samples in different facilities
(Sweden and Finland) with similar grinding parameters,
different grinding wheels, and different hardness. The
second part was to evaluate measured BNT parameters in
order to determine significant factors affecting BNT signal
value. The measurement data from the samples were divided
into two different batches according where they were
manufactured. Both grinding batches contained
measurement data from three different appraisers. The
main feature for calculation was the RMS value from the
Microscan direct results. The first processing step was to
normalize the RMS values for all the measurements. The
standard analysis of variance (ANOVA) was applied for
the normalized dataset. The ANOVA analysis showed that
a significant impact on the BNT signal value has grinding
parameters, while the other investigated factors (e.g.
measurer) are negligible. The reasons of that are discussed
at the end of the paper.