Analysis of the end-notched flexure test configuration applicability for mechanically coupled fiber reinforced composite laminates

The paper deals with Finite Element Method derivations concerning the mode II critical strain energy release rate (GIIc) distribution along delamination front in mechanically coupled laminated composites subjected to the standardized end notched flexure test, described in the ASTM D7905 Standard. Different stacking sequences were studied in order to obtain six possible forms of coupling matrix B. This revealed possible problems in calculation and interpretation of the GIIc experimental results, while directly using the standardized data reduction scheme. For each sequence several fiber orientation angles were considered, such that a wide fan of possible tendencies in the behavior of coupled composites could be analyzed. The strongest deviation of the GII distributions was observed for the laminated beam models exhibiting simultaneous bending-extension/extension-twisting/shearing-bending coupling, i.e. when the coupling matrix took its BLT form. All simulations were performed in the Abaqus finite element software environment using the virtual crack closure technique. Indications for the experimental tests were formulated in the conclusions section.