Interlaminar fracture toughness of carbon/flax fiber hybrid composite

Abstract

The application of carbon fiber reinforced composites (CFRP) was limited by their poor delamination resistance. However, the hierarchical microstructure of flax fibers could help to improve the interlaminar properties of the composite. Therefore, the interlaminar fracture toughness of CFRP composites can be improved by hybridized flax with carbon fibers. In this study, the carbon/flax fiber hybrid composites (CFFRP) were manufactured by moulding process. The mode Ⅰand mode Ⅱ interlaminar fracture toughnesses of CFFRP composites were studied by double cantilever beam (DCB) and end-notched flexure (ENF) tests, and were compared with those of CFRP composites. The results show that the Mode Ⅰinterlaminar fracture toughness of CFFRP composite is 1.29 kJ/m2, which is about 3.5 times higher than that of CFRP composites (0.37 kJ/m2). The Mode Ⅱinterlaminar fracture toughness is 1.09 kJ/m2 and is about 23.86% higher than that of CFRP composites (0.88 kJ/m2). The interlaminar fractured surfaces of CFRP and CFFRP composites are observed with the aid of scanning electron microscopy (SEM). From the microscopies of the fractured CFRP specimens it can be seen that pure delamination by the peeling of carbon fibers from epoxy resin is obtained for CFRP composites. The surfaces of carbon fibers were relatively clean and few epoxy resin fragments attached. The weak interfacial properties between carbon fiber and epoxy resin cause a lower GⅠc for CFRP composites. On the contrary, from the observation of SEM photographs of flax fiber layers in the interlaminar fractured CFFRP composites, fiber breakage, fiber peeling and fiber entanglement are founded. On the fractured carbon fiber layer, there are some flax fibers tangling with carbon fibers. These multi-scale failure modes due to the unique microstructure of the flax fibers may make the crack propagation become difficult and thus lead to the GⅠc and GⅡc increased for CFFRP composites than those of CFRP composites.

Keywords

• hybrid composite
• flax fiber
• interlaminar fracture toughness
• scanning electron microscopy (sem)