Investigations on the Interfacial reinforcing Mechanisms of Innovative Hierarchical-Structured FRPs by Nanoclays Incorporation

Abstract

Fiber reinforced polymers (FRPs) are being extensively applied to aerospace, aviation, automotive, marine, and civil construction industries due to their outstanding stiffness-to-weight and stiffness-to-weight ratio. However, unlike the isotropic materials like metals and ceramics, the mechanical properties on the transverse and through-thickness directions of the orthogonal anisotropic FRPs are inevitably inferior to that on the primary direction. The relatively weak interfacial and interlaminar strength and toughness can become disturbing factors during the FRP services, limiting the performance and application breakthrough. Incorporating nano-additives were proved as one effective method to ameliorate the interfacial and interlaminar properties in the last decades. Conventionally, the nano-additives were randomly dispersed in the matrix in most researches; and the comprehensive study regarding the distribution conditions is still limited yet. The objective of this dissertation is to investigate the interfacial toughening mechanism by the innovative hierarchical distribution of nanoclays amalgamating experimental, computational, and numerical approaches. Different-structured halloysite nanotubes (HNTs) were successfully synthesized using various methods, and the hierarchical distribution was realized by the electrophoresis deposition (EPD) technique. The optimal EPD parameters and the potential agglomeration problem during the Vacuum-assisted Resin Transfer Molding (VaRTM) fabrication process were explored. The stiffness properties regarding the different structures and distributions were computationally elaborated by implementing Eshelby-Mori-Tanaka micromechanical model with orientation averaging. The effect of the nanoscale nanoclays on the macroscale FRPs was investigated based on the homogenization principle. The damping properties by incorporating nanoclays were investigated via “interfacial shear hysteresis” mechanical approach with a parameter study. All computational and numerical results were verified with experimental works and were in substantial agreement at the aspects of tendency and magnitude. The hierarchical distributed nanoclays demonstrated enhancement on the interlaminar strength and toughness by selective reinforcing the vulnerable interfacial region. Moreover, the works in this dissertation are suitable to be utilized and referenced for other nanoclays/FRPs systems in the future.