Abstract
High strength and toughness seems like intrinsic conflicts in mechanical properties of materials, including composites interfaces. To solve this problem, we constructed a hierarchically structured interphase in aramid composites via in-situ grafting and foaming of polyurea on fiber surface and penetrating epoxy resin into the pores. As differential scanning calorimeter (DSC) and atomic force microscopic (AFM) confirmed, soft porous polyurea filled rigid resin matrix generated numerous covalent bonded interfaces and formed “rigid-and-soft” interlocking stereoscopic interphase. Axial covalent bonds between fiber and polyurea, radial covalent bonds between polyurea and epoxy resin highly improved interfacial shear strength by 115.9%. Newly formed interfaces caused much higher energy consumption during interfacial failure is considered to enhance interfacial shear toughness (GⅠC) by 493.2%. Mathematical analysis and finite element analysis furtherly proved strengthening and toughening mechanisms, and we found the enhancement of GⅠC is also highly related to thickness of polyurea layer and pores’ sizes.
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