Fracture mechanical characterization of mica-filled epoxy glass composites under monotonic and cyclic loading

Abstract

Stator insulations comprised of mica-filled epoxy glass composite materials are of paramount importance for the reliability of high-voltage rotating machines. The present work deals with the fracture mechanical characterization of the winding insulation under conditions of monotonic and cyclic loading. The identification and quantification of the weak interfaces in the material that will most likely result in the initiation and propagation of defects are investigated in detail. Material specimens are processed from insulation tapes, and tests are conducted under mode I, mode II and mixed mode (Fixed Ratio Mixed Mode) loading to characterize the weak interface. The influence of resin content on the strength of the weak interface is also investigated. The results give an indication of the delamination mechanism and a measure of the critical energy release rate in the insulation materials.