Interlaminar Mechanical Properties and Toughening Mechanism of Highly Thermally Stable Composite Modified by Polyacrylonitrile Nanofiber Films

This work concentrated on the interlaminar mechanical properties and toughening mechanism of carbon fiber-reinforced bismaleimide resin (CF/BMI) composites modified by polyacrylonitrile (PAN) nanofiber films. The PAN nanofiber films were prepared by electrospinning. End-notched flexure (ENF) and short-beam strength tests were conducted to assess the mode II fracture toughness (G(IIc)) and interlaminar shear strength (ILSS). The results showed that the G(IIc) and ILSS of PAN-modified specimens are 1900.4 J/m(2) and 93.1 MPa, which was 21.4% and 5.4% higher than that of the virgin specimens (1565.5 J/m(2) and 88.3 MPa), respectively. The scanning electron microscopy (SEM) images of the fracture surface revealed that the PAN nanofiber films toughen the composite on two scales. On the mesoscopic scale, the composite laminates modified by PAN formed a resin-rich layer with high strength and toughness, which made the crack propagate across the layers. At the microscopic scale, the crack propagation between two-dimensional nanofiber films led to constant pull-out and breakage of the nanofibers. As a result, the interlaminar fracture toughness of the composite laminates improved.