Measuring system and evaluation method of DC and AC magnetostriction behaviour to investigate 3.2% SiFe GO electrical steels

Abstract

A high precision magnetostriction tester was developed for 100 × 500 mm conventional GO and HiB electrical steel samples. Length changes were measured by means of a laser displacement meter, having a detection limit of ± 10 nm, corresponding to Δl/ l ≈ 1.5 × 10 −8 in relative measure to the magnetised length of l = 470 mm. The AC characteristic was quantified by the peak-to-peak magnetostriction λ( B) p-p vs. induction curves. For a simple characterisation of the induction dependence of DC magnetostriction three new parameters are proposed. The first one is the maximum value of magnetostriction, defined as λ s( B) = lim λ ( B → Bs ), when the induction tends to the saturation. The second one is the slope of the curve at the inflection point, d/d B{ λ( B)} max, characterising the highest speed of sign change of magnetostriction. The third one is the zero intercept point of the slope line — drawn to the point of inflection — on the X axis, the B o = B m( λ = 0). The results obtained on HiB 0.30 mm thick samples have confirmed a straight syntony between the above defined DC and AC magnetostrictive characterisation, which was previously demonstrated using the DC technique, referring to the DC measurement at opened magnetic circuit arrangement.