Simultaneously strengthening, toughening, and damage monitoring of fiber reinforced composite by using a rigid/flexible hybrid modifier

Abstract Two‐phase hybrid modification has been used as an advanced method to improve the strength and toughness of composite. An interfacial modification strategy for simultaneous strengthening, toughening, and damage monitoring of glass fiber (GF)/epoxy composite is proposed by coating rigid multi‐walled carbon nanotubes (MWCNT) and flexible thermoplastic polyurethane (TPU) on the glass fiber surface. The fiber pull‐out and out‐of‐plane experiments were performed to investigate the interfacial modification effect of rigid/flexible hybrid modifier. The results show that the hybrid modifier with a MWCNT/TPU mass ratio of 3:1 (MT@GF‐3/epoxy composite) realizes the most significant enhancement. Specifically, in comparison to GF/epoxy composites, MT@GF‐3/epoxy composite has an increment of 36.52%, 60.96%, 29.56%, and 80.36% in interfacial shear strength (IFSS), transverse fiber bundle test (TFBT) strength, interlaminar shear strength (ILSS) and interlaminar fracture toughness ( G IC ), respectively, and a significant enhancement in impact resistance. The enhanced interfacial strength and toughness are attributed to the mechanical interlocking, deflection of cracks, and plastic stretching generated by MWCNT and TPU. Results show that the two modifiers interact in a mutually reinforcing way with regard to the strengthening/toughening effects. In addition, multiple mechanical tests confirm the MT@GF/epoxy composites have an excellent damage monitoring ability by recording the resistance change based on the MWCNT's conductive characteristics. This strategy for interfacial modification coating a rigid‐flexible MWCNT/TPU hybrid modifier would offer valuable guidance for improving the strength and toughness of glass fiber/epoxy composites, as well as monitoring and locating the damage. Highlights A rigid/flexible hybrid modifier is proposed for modifying the GF/EP composites. The modifier achieves the greatest enhancement at a 3:1 mass ratio of MWCNT/TPU. The mutual reinforcing mechanism between the rigid/flexible phases is analyzed. Damage monitoring is realized for the modified GF/EP composites.