Experimental Investigation of Mechanically Coupled Composite Specimens in the ENF Test Configuration

Abstract

This paper reports an experimental study on the mode II interlaminar fracture of carbon/epoxy multidirectional (MD) laminates as well as on composite laminates with specific stacking sequence exhibited mechanical couplings. The aim of the analysis was to determine the mode II critical strain energy release rate (c-SERR, GIIC) and an applicability of the data reduction schemes. Specimens were subjected to the end notched flexure (ENF) test. During the experiment the applied load and the load point displacement were registered. Additionally, the crack onset and all propagation values were observed and marked on the specimens edges. Moreover, the acoustic emission (AE) data were registered. The values of the mode II c-SERR were obtained with assumptions of the Direct Beam Theory (DBT) and Corrected Beam Theory (CBT). The experiment proved that the fracture toughness depends on the specimen delamination interface. For the asymmetric laminates, the mode II c-SERR reached significantly greater values for those specimens where the bending-extension coupling (BE) occurred.