Simulation of steel/epoxy laminates for electric engines or generators: Part 1 - Characterization and modeling of coating films based on waterborne epoxy varnishes

Waterborne epoxy varnishes are essential for electrical steel laminates used in
electric engines or generators. Two varnish formulations based on bisphenol-A-
diglycidylether and dicyandiamide with an epoxy equivalent weight (EEW) of
~ 500 and ~ 900 g/mol were investigated. Thin specimens were prepared by con-
secutive coating and solvent evaporation followed by final curing. Glass transi-
tion temperatures (T g) of 89 °C (EEW-900) and 101 °C (EEW-500) were deduced
by dynamic mechanical analysis (DMA). The lower T g value was attributed to
the higher EEW and a lower network density. Moreover, master curves along
with Williams–Landel–Ferry and Prony series parameters were generated. By
digital image correlation (DIC)-assisted tensile testing of single epoxy films at
temperatures from 30 to 150 °C, a significant drop in tensile modulus from 2600
to 10 MPa and a rise in Poisson’s ratio from 0.35 to 0.47 was ascertained. The
implemented finite element model (FEM) showed a good agreement with the
experimental data.