Multi-layer continuum model for adhesive FM 300-2 in end-notched flexure carbon laminate

Abstract

The current investigation analyses the un-stable crack initiation of an adhesively bonded End Notched Flexure (ENF) specimen by means of a continuum damage formulation, based on the Bazant's crack model, to reproduce accurately the load response and the fracture process zone of the adhesive. The specimen consisted of carbon fibre reinforced polymer adherends and two sheets of FM 300-2 adhesive films. The need of this implementation arose from experimental observations of normal transverse damage mechanisms at the bondline during the crack initiation. The damage model was based on a multi-layer configuration of the adhesive meso-structure that accounted for two damage activation functions in the normal and shear transverse directions. The results demonstrated the capability of the model to predict closely the force drop in the load–displacement curve of the ENF test. Different multi-layer configurations were studied following proper meso-structure simplification of the adhesive to use elastic and damage-capable layers in a correct order and thicknesses. The rise of the modelled shear strength allowed for keeping enough stored strain energy contributed to the low triaxiality stress in the bondline. Finally, the results demonstrated a significant influence of the layers modelling the knitted carrier to the local mechanisms of tensile fracture because of the normal transverse deformations. Unclassified. Based on Foreground information under EDA Contract No B.PRJ.RT.670 covering the Ad Hoc Project entitled “PATCHBOND II”.