Cohesive zone parameters to predict mixed-mode delamination in CFRP reinforced with hydroxyl functionalized MWCNTs: Experimental and numerical investigations

This study aims to determine the cohesive zone model (CZM) parameters for predicting the mixed-mode delamination of carbon fiber/epoxy composites reinforced with hydroxyl functionalized multi-walled carbon nanotubes (MWCNTs). The cohesive strengths of the composite laminate are measured through cross-tension and short beam shear (SBS) tests for opening (mode I) and shear (mode II) loading, respectively, for pristine composites and those reinforced with 0.1 wt%, 0.2 wt%, and 0.3 wt% of MWCNTs. Mode I fracture toughness is evaluated with the double cantilever beam (DCB) test, while mode II fracture toughness is evaluated using the end-notched flexure (ENF) test. The CZM parameters obtained from these experiments are used in a triangular cohesive law to model the mixed-mode failure responses for three different mixed-mode ratios (GII/G = 0.2, 0.3, and 0.4). Finite element (FE) simulation results show good agreement with the experimental findings. Finally, the failure interface is analyzed under a scanning electron microscope (SEM) to investigate the fracture mechanisms.