Effect of short multi-walled carbon nanotubes on the mode I fracture toughness of woven carbon fiber reinforced polymer composites

•The GIc of CFRP composites evaluated using three data reduction methods was the same.•The GIc of CFRP composites increased with increasing the S-MWCNT-COOH amount.•A model was developed based on pull-out process of a short CNT from an epoxy matrix.•Idealized load–displacement curves of CFRP composites were proposed using LEFM. The present study experimentally and theoretically investigated the effects of short multi-walled carbon nanotubes on the mode I fracture toughness of woven CFRP composites. COOH-functionalized short multi-walled carbon nanotubes (S-MWCNT-COOH) with three different amounts of 0.5, 1, and 1.5 wt% (by weight) of epoxy resin/hardener mixture were used. In total, 32 test specimens were fabricated and tested. The mode I fracture toughness was performed under double cantilever beam (DCB) test, and was evaluated using three different data reduction methods: modified beam theory method (MBT), compliance calibration method (CC), and modified compliance calibration method (MCC). The test results with the addition of 0.5, 1, and 1.5 wt% S-MWCNT-COOH showed 1.6, 31.0, and 31.7% increase on average, respectively, of the mode I fracture toughness of the CFRP composites. The mode I fracture toughness evaluated using the three data reduction methods of MBT, CC, and MCC was almost the same. Furthermore, an analytical model was constructed using the trilinear curves based on bridging law describing the pullout force–displacement response of short CNTs from an epoxy matrix, and the predicted results showed good agreement with the experimental results. Finally, idealized load–displacement curves of the CFRP composites were proposed based on the linear elastic fracture mechanics (LEFM) using initiation fracture toughness, and the predictions showed good agreement with the experimental curves.