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

Abstract 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 consecutive coating and solvent evaporation followed by final curing. Glass transition 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. Graphical Abstract