Determination of equivalent transversely isotropic material parameters for sheet-layered lamination stacks

•Accurate transversely isotropic material parameters of bonded lamination stacks.•Material parameter determination ab initio by different homogenization methods.•High material parameter sensitivity to the interlaminar varnish stiffness and thickness.•Varnish thickness measurement by laser scanning microscopy and nanoindentation.•Proving the capability with the help of a numerical and experimental modal analysis. This paper covers the accurate prediction of equivalent homogenized material parameters for sheet-layered lamination stacks, which are located in rotors and stators of electric motors. Modeling the structural and dynamic behavior of these parts is a challenging task due to the special layered design of these stacks, with a huge influence of the applied joining technology, here a full-surface bonding. For the derivation of equivalent transversely isotropic material parameters, three procedures, namely the rule of mixture, an analytical and numerical homogenization, are compared eventuating in only minor differences between them. The investigations show that rather the input parameters for these averaging methods, i.e. the individual material parameters of each layer, are crucial for an accurate modeling. Experimental tests are carried out on coated sheet laminations to determine the initially unknown bonding varnish thickness with two different measurement methods, the 3D laser scanning microscopy and instrumented indentation testing, resulting in almost equivalent and reasonable values. The capability of the ab initio deduced material parameters is demonstrated by comparing an experimental and numerical modal analysis of a sample lamination stack showing an almost perfect agreement. By this, it is also revealed that a varnish Young’s modulus measured by nanoindentation is overestimated from a macroscopic point of view. Damping parameters of a bonded lamination stack are determined with the help of the experimental modal analysis showing a relatively low damped system.