In the present investigation, we successfully fabricate a hybrid polymer nanocomposite containing epoxy/polyester blend resin and graphene nanoplatelets (GNPs) by a novel technique. A high intensity ultrasonicator is used to obtain a homogeneous mixture of epoxy/polyester resin and graphene nanoplatelets. This mixture is then mixed with a hardener using a high-speed mechanical stirrer. The trapped air and reaction volatiles are removed from the mixture using high vacuum. The hot press casting method is used to make the nanocomposite specimens. Tensile tests, dynamic mechanical analysis (DMA) and thermogravimetric analysis (TGA) are performed on neat, 0.2 wt %, 0.5 wt %, 1 wt %, 1.5 wt % and 2 wt % GNP-reinforced epoxy/polyester blend resin to investigate the reinforcement effect on the thermal and mechanical properties of the nanocomposites. The results of this research indicate that the tensile strength of the novel nanocomposite material increases to 86.8% with the addition of a ratio of graphene nanoplatelets as low as 0.2 wt %. DMA results indicate that the 1 wt % GNP-reinforced epoxy/polyester nanocomposite possesses the highest storage modulus and glass transition temperature (Tg), as compared to neat epoxy/polyester or the other nanocomposite specimens. In addition, TGA results verify thethermal stability of the experimental specimens, regardless of the weight percentage of GNPs.

This paper presents the disturbance and uncertainty suppression by using the nonlinear disturbance observer and an extended state observer for a nonlinear active magnetic bearing system. Otherwise, the chattering free is assured by a fuzzy controller, where the fixed sliding mode surface boundary is regulated by fuzzy boundary layer. The stability of the system is guaranteed by Lyapunov condition. First, the nonlinear disturbance observer is presented to estimate the disturbance from outside of the system. Second, the system parameter variations are estimated by an extended state observer with the construction via the estimated disturbance value. Third, the proportional–integral–derivative sliding mode surface has been constructed due to the chattering values that appear from the high-frequency switching control values. Fourth, these chattering values are reduced by using a Mamdani fuzzy logic control. The proposed control methodology was given by the MATLAB simulation. The overshoot value that is equal to zero, narrow settling time, and the average distance tracking error value which is quite small are archived.

This paper aims to present secure communication based on master and slave Lorenz chaotic systems. To apply a form of the linear synchronization control method, the mathematical models of master and slave systems were reformed into Takagi-Sugeno (T-S) fuzzy systems. First, the Lorenz chaotic system was completely changed to the form of the T-S fuzzy model with two sublinear systems and two boundary fuzzy membership functions. Second, a newly adaptive disturbance observer (ADOB) was proposed with a high convergent speed for the synchronization system, which was based on the basic nonlinear disturbance observer. Third, adaptive sliding-mode control (ASMC) has been constructed to synchronize the master and slave systems of a secure communication system. The stability of the proposed control algorithms was shown by solving the Lyapunov condition with the support of Young's inequality. The synchronization of two nonidentical chaotic Lorenz systems was utilized to encrypt and decrypt the data. Transmitted and decrypted signals are used to show that the proposed algorithms are adequate for the secure communication system. To confirm the originality and power of the proposed algorithms, secure communication between two computers was implemented perfectly through an internet router and electronic circuit communication scenarios.