Enhanced fracture toughness of nanostructured carbon‐fiber reinforced poly(urethane‐isocyanurate) composites at low concentrations

Carbon fiber reinforced poly(urethane‐isocyanurate)‐nanosilica composites CF‐(PUI‐NS) were manufactured by means of the vacuum‐assisted resin transfer moulding technique (VARTM) at very low NS concentrations (0–4 wt%). The high strain to failure of the PUI matrix (>7%) affected tensile tests by CF reorientation. Both the tensile strength and strain to failure were highly dependent on its kinematics. CF(PUI‐NS) caused an increase of the static toughness with a maximum improvement of tensile strain to failure and modulus of +28.8% and +39% at 1 wt% and 2 wt% of NS, respectively. The interlaminar shear strength (G_IC) of the composites showed both a deterioration of ?12.9% and an improvement of +9.9% for NS concentrations of 1 wt% and 4 wt%, respectively. Regardless of the G_IC value, all of the composites prepared with NS presented secondary maxima of the force versus displacement plots, indicating a substantial arrest of the crack propagation velocity after delamination started. Fractographic analysis revealed several features, such as fiber pull‐out, bridging as well as river patterns whereas the composites prepared with NS behaved in a more ductile fashion due to the presence of river patterns and a reduced fiber pull‐out. POLYM. ENG. SCI., 58:1241–1250, 2018. © 2017 Society of Plastics Engineers