A conductive contact between laminations is often represented by one resistance in a fault-loop calculation. That simplification can fail if resistance changes with applied load, temperature, electrical excitation or previous contact history. The model then predicts current using a value that may describe only one state.
The first comparison should follow the contact through loading and unloading. A force sweep in one direction alone cannot reveal whether the contact returns to its initial electrical condition.
Specify the resistance being measured
Identify the contact and the measurement terminals. Sheet resistance, lead resistance and additional contacts can enter the observed voltage. Use a qualified arrangement that separates the intended contact contribution where the geometry permits, and document contributions that cannot be isolated.
For a linear operating region, R = V/I, with volts, amperes and ohms. If the voltage-current relation is nonlinear, a single ratio depends on the selected operating point. A local differential slope and a finite V/I ratio are different model quantities.
Loading branch
Increase the selected mechanical load through justified states and record actual force, displacement, temperature and electrical response. Nominal pressure requires a defined contact area; the true conductive micro-contact area may remain unknown. Retain the force-based description when an area assumption is unsupported.
Unloading branch
Repeat corresponding observations while removing load. Compare the two branches at the same stated force and electrical condition. A difference indicates history dependence but does not alone identify whether it comes from changed contact area, coating damage, trapped debris or another mechanism.
Re-established reference
Return to the initial measurement state and examine whether the electrical response recovers. Inspect the contact surfaces or representative retained samples where appropriate. Any irreversible change needs separate attribution before it is built into a model law.
Avoid confusing geometry with film behavior
Growing conductive contact area and a changed insulating film can both lower measured resistance. Their implications differ. Use independent surface or mechanical evidence to narrow the explanation. An electrical trace alone should not be described as proof of film breakdown.
The selected electrical measurement must not create an uncontrolled new contact condition. Its excitation and containment belong in a qualified laboratory procedure, particularly when the object is an intentionally abnormal contact.
Use the curve to define the model’s domain
Compare fault-loop predictions with measured states over the load and temperature range relevant to the investigation. If one constant resistance reproduces the required behavior within demonstrated uncertainty, retain the simpler model with that range stated.
If it does not, use a supported state- or history-dependent representation, or report a sensitivity envelope. Do not fit a smooth nonlinear curve beyond the observed states and call it material data. The practical result is a pressure-history record showing when the constant-resistor approximation is adequate and where it conceals a changing current path.
Carry contact hysteresis into the heating estimate
Use 0.23 mm nominal sheet thickness [1] and assume a loop area of 20 sheet thicknesses × 100 mm = 460 mm². With assumed uniform normal flux of 1.0 T peak at 50 Hz, Erms is 0.1022 V. Assume negligible inductance and contact-dominated total resistance of 0.10 Ω during loading but 0.20 Ω at the same force during unloading. Total loop heating is then E²/R = 0.1044 W and 0.0522 W, a twofold difference. A single resistance would hide that history effect. Measure both branches at controlled temperature and electrical excitation, separating lead and sheet contributions and their uncertainty [2]. Faraday induction supplies the voltage relation [3]. The assumed field is normal to this loop; main rolling-direction flux is not automatically linked.
Manufacturing controls. Contact area, burr shape, coating disruption, clamp history and contamination govern the resistance state. Do not turn a fitted force curve into a universal CRGO material property or extrapolate beyond the tested interface conditions.
References
- Nippon Steel Corporation, Grain-Oriented Electrical Steel Sheets, catalogue D004je_03_202004, 2020, Specifications; Size and Form Tolerances.
- JCGM, JCGM 100:2008, Evaluation of measurement data — Guide to the expression of uncertainty in measurement, 2008.
- Zhao, X. et al., Magnetostrictive Properties of the Grain-Oriented Silicon Steel Sheet under DC-Biased and Multisinusoidal Magnetizations, Materials 12, 2156, 2019, sections 2.1 and 2.3; DOI: 10.3390/ma12132156.