Properties Of Epoxy Resin Based Quantum Tunneling Composites

The polymer matrix composites based on Quantum tunneling effect conduction mechanism are metal filler composite polymer materials with excellent piezoresistive property, which have broad applying prospect. The nickel powder with spiky structure can generate quantum tunneling effect. It will make epoxy resin with sensitive piezoresistivivity when it is composited with epoxy resin as a functional component. The nickel powder can also improved the mechanical, electrical conductivity performance of epoxy resin effectively. In this thesis, the mechanical, electrical and piezoresistive performances of epoxy resin based quantum tunneling composites (QT/EPC) are systematically investigated. The main research contents and results are as follows:(1) QT/EPC with nickel powder volume content of 0%,4%,5%,6%,7%,8%,9%,10%, 12%,16%,22%,25.54% were prepared by simple mechanical mixing the epoxy resin and the nickel powder. Then an axial compressive damage test to QT/EPC was performed. The change rules of compression yield strength, elastic modulus, Poisson ratio of QT/EPC with different contents of nickel powder were investigated. Finally, the mechanics constitutive model of QT/EPC were build up. The research results show that the yield strength of QT/EP composites with different contents of nickel powder are improved compared to pure epoxy except the composites with the nickel powder content of 22 vol.%., the elastic modulus increased, and the Poisson ratio declined.(2) The static resistance of QT/EPC with different contents of nickel powder was tested. The effect of nickel powder content and resistance measurement on the resistance of the composites was discussed. The conductive mechanism was also investigated. The research results show that the resistance of QT/EPC presents a non-linear decrease with the increase of nickel powder content. The resistance of QT/EPC is mainly affected by the nickel powder spacing, the area percentage of particles per unit area, the extent of damage of spiky structure, and the impact of pore structure. The effect degree of contact resistance on the resistance of the composites changes as 'N' shapes.(3) The effect of nickel powder content and resistance measurement on the piezoresistive property of the composites was discussed, and the piezoresistive mechanism of QT/EPC was also investigated. The research results show that the composites with nickel powder content of 7vol% have the highest piezoresistivite sensitivity. The strain and stress sensitivities can achieve 34.5 and 0.644% MPa-1, respectively. Piezoresistive sensitivity of QT/EPC measured by two-electrode method is larger than that measured by four-electrode method, but the piezoresistive property of QT/EPC measured by two-electrode is unstable. The high loading speed leads to fast deformation of the specimen, thus causing the conductive network inside instability and the resistance of composites increases without loading. When the composites are subjected to low stress amplitude (less than 27% of the yield ultimate stress), the resistivity change curve is non-linear, When the composites are subjected to high stress amplitude (exceed 30% of the yield ultimate stress), the fractional change of resistivity remains unchanged at the highest stress amplitude. The resistivity change curves reach plateau. The composites appear creep and resistance creep when they are subjected to multiple cyclic loading. However, the resistance creep of the composites is not obvious when the composites are subjected to constant loading.