difference in temperature increase can be explained as follows.
Due to the limited thermal conductivity of ferritic–pearlitic steels
and the high strain localization in the gauge it is assumed that
the thermal energy related to the local heating is mainly trans-
ferred to the surface of the gauge. Hence, it appears that a speci-
men design with a larger surface of the gauge is favorable.
However, this effect should be reduced or even negligible for mate-
rials with higher thermal conductivity, like copper. Moreover, the
characteristic frequencies for both designs also decrease with
increasing displacement amplitude.