چكيده به لاتين
The mechanical properties of polymers can be significantly improved when a small amount of nanoparticles is properly added to polymers. Adding of some small of graphene platelets considerably improves the creep behavior of polymers. Considering the research gap in this field, the purpose of the present research is to study and predict the creep behavior of graphene/epoxy nanocomposites. The present research consists of experimental, analytical and numerical investigations. An experimental program was conducted to assess the present analytical and numerical models. It was observed in experimental investigations that the addition of 0.1, 0.25, 0.5 and 1 wt.% graphene platelets to epoxy resulted in an increase the creep resistance of epoxy by 16, 28, 32 and 11 percent, respectively in 30 minutes. In analytical section, the Halpin-Tsai and Mori-Tanaka analytical micromechanical models were modified in this research for the first time to predict the creep behavior of nanocomposites. The present method can predict the total strain of polymer nanocomposites reinforced by graphene platelets. In the present method, the creep modulus of graphene/epoxy nanocomposites was predicted and the total strain of nanocomposites was obtained having the creep modulus of polymer and the elastic properties of graphene platelets. The results obtained showed that the modified H-T model predictions were more compatible with the experimental results at low filler contents (< 0.25 wt.%) in comparison with the modified M-T model, whereas, the modified M-T model was more reliable at high filler contents (> 0.25 wt.%). A combined finite element and micromechanics method was also presented in this research. The creep behavior of nanocomposites was modeled using a finite element software by considering the chemical bonds between the graphene and the polymer as beams and mechanical connectors. The numerical model of the creep behavior of a representative volume element of nanocomposites was presented for the first time via this method. The present method predicts the creep modulus and total strain of graphene/epoxy nanocomposites considering the random distribution of graphene platelets. The interphase between the graphene and the polymer was considered in the finite element model. The relative difference of the total strain obtained by the X-FE-M model and the experimental result was about 7.5% at 30 min. This indicates the accuracy of the proposed model and the applied assumptions.
