A comparison between traditional ZnO-(modified Matsuoka
system, [ZnO]) and SnO2-based varistors (98.9%SnO211%
CoO10.05%Nb2O510.05%Cr2O3, [SCNCr]) regarding their
mechanical properties, finite element (FE) modeling, and macroscopic
response with current pulse is presented in this work.
The experimental values of the elastic (static and dynamic) modulus
and bending strength are given. Both the static and the dynamic
modulus were two times higher for SnO2 (B200 GPa) with
respect to ZnO (B100 GPa). A similar behavior was found for
the bending strength, confirming the superior mechanical properties
of SCNCr associated with a homogeneous microstructure.
The finite element analyses yielded the most appropriate
thickness/diameter aspect ratio (H/D), while thermomechanical
stress is minimized. The values of (H/D) were lower for the
SCNCr in comparison with the ZnO-based varistors, allowing
the production of smaller pieces that can resist the same
thermomechanical stress. Finally, preliminary analyses of the
macroscopic failures for samples treated with degradation pulses
of 8/20-ls type allowed to confirm the absence of failures due to
cracking and/or puncture in the SCNCr. The absence of these
failures originates from the good thermomechanical propertiesPeer reviewe