Mechanics of Epoxy Nanocomposites: A Study on the Synergy of the Reinforcements

In this study, manufacturing and mechanical characterisation are performed on halloysite nanotube (HNT) reinforced epoxy composite, carboxyl-terminated butadiene-acrylonitrile (CTBN) rubber-added epoxy composite, and both HNT- and CTBN-rubber-added epoxy composites. It is aimed to explore the effects of HNT and CTBN rubber inclusions individually and the synergistic effects of HNT and CTBN rubber inclusions on the epoxy-based composite material. To achieve this, the mechanical characterisation of the epoxy matrix composite is performed numerically and experimentally. To investigate the viscoelastic behaviour, the samples are subjected to tensile and three-point bending tests at different strain rates (%1, %5, and %10 strain per minute) and to Charpy impact tests. The internal structures of samples are observed using the scanning electron microscope (SEM). Results demonstrate that 1% HNT reinforcement increases the elastic modulus by 15% (from 599 to 688 MPa in tensile tests) while 10% CTBN rubber reduces stiffness by 38% but increases elongation at break by 48%. Hybrid composites (H10R05) achieve balanced properties with 16% higher stiffness than pure rubber systems while maintaining 44% higher ductility than pure epoxy. Charpy impact tests show that 10% rubber increases fracture energy by approximately 85% compared to pure epoxy, while HNT provides modest improvements. All samples exhibit strain-rate-dependent behaviour, with elastic modulus increasing 10-16% from quasi-static to dynamic loading rates. Numerical modelling using the Mori-Tanaka, Halpin-Tsai, and finite element homogenisation (FEH) methods successfully predicts experimental trends, with FEH showing the highest accuracy (deviations <5%). This study provides valuable insights into designing composite materials with balanced mechanical properties through multi-reinforcement strategies.