Synergistic Toughening in Ternary Silica/Hollow Glass Spheres/Epoxy Nanocomposites

Herein, the fracture toughness of ternary epoxy systems containing nanosilica and hollow glass microspheres (HGMS) is investigated. The experimental measurements reveal synergistic fracture toughness in some hybrid compositions: The incorporation of 10 phr of HGMS and nanosilica alone modify the fracture toughness of epoxy by 39% and 91%, respectively. However, use of 10 phr hybrid modifier can enhance the fracture toughness of the resin up to 120%. Observations reveal different toughening mechanisms for the blends i.e., plastic deformation for silica nanoparticles and crack bifurcation for HGMS. Both of these toughening mechanisms additively contribute to the synergism in ternary epoxies

A refined finite element method for stress analysis of rotors and rotating disks with variable thickness

In this paper, a refined finite element method (FEM) based on the Carrera unified formulation (CUF) is extended for stress analysis of rotors and rotating disks with variable thickness. The variational form of the 3D equilibrium equations is obtained using the principle of minimum potential energy and solved by this method. Employing the 1D CUF, a rotor is assumed to be a beam along its axis. In this case, the geometry of the rotor can be discretized into a finite number of 1D beam elements along its axis, while the Lagrange polynomial expansions may be employed to approximate the displacement field over the cross section of the beam. Therefore, the FEM matrices and vectors can be written in terms of fundamental nuclei, whose forms are independent of the order of the beam theories. The validity and capabilities of the presented procedure are investigated in a number of numerical examples, and some conclusions are reported and compared well with the analytical and 3D finite element solutions. The results obtained by the 1D CUF models are in close agreement with the reference solutions. Moreover, it is verified that the innovative procedure presented in this paper can be used as an accurate tool of structural analysis for complex rotors to reduce the computational costs

Study of synergistic toughening in a bimodal epoxy nanocomposite

Toughening of epoxy with different types of modifiers produces a bimodal blend that might show better fracture resistance in comparison with single-modified ones. In this research, bimodal epoxy formulations including mixtures of glass microsphere and silica nanoparticles are explored for possible synergistic toughening. The influence of composition on the glass transition temperature (T-g), tensile characteristics, and fracture toughness (K-IC) is investigated. Interestingly, a synergism in fracture toughness is observed when mixtures of modifiers were incorporated. For the fixed overall modifier content, K-IC is higher when the volume fraction of glass microsphere is lesser than the volume fraction of nanosilica. Fractographs reveal that glass microsphere increases the toughness of epoxy matrix by crack pinning/bridging mechanisms. On the other hand, nanosilica enhances the toughness by increase in plastic deformation via shear banding/particle debonding. Interestingly, the origin of synergistic toughness in bimodal epoxies is the interaction between the glass microsphere and crack-tip damage zone which provides comprehensive stable crack deflection within the nanosilica-toughened epoxy. This mechanism results in a mixed-mode crack growth that reduces the strain energy release rate in bimodal formulations