Graphenes have aroused great interest among the scientists lately, due to their special physical properties which are supposed to be transferred to composite materials [1,2,3,6]. Some polymers show low mechanical properties which can be improved by adding various types of materials [9,13]. Using nanoparticles, an enhancement of mechanical, thermal and electrical properties can be obtained, even for small contents of additives [10,11,12,14,15,16]. The evaluation of mechanical properties of polymer composites with graphene can be achieved relying on the three-point bending tests [4]. This work presents a few conclusions resulting from the three points bending tests of the polyester composites with graphene and graphite [7,8].
Graphene oxide and graphite filled polyester composites were prepared by using conventional melt-mixing methods in order to improve tribological performance of polyester. It was investigated friction stability, microhardness, friction coefficient, and specific wear rate of the composites in details. It was found that the presence of graphite and graphene oxide influenced friction coefficient and wear rate of the composites. Graphene oxide decreased wear rate with increasing of test speed and graphite decreased wear rate for composite for all speeds. Tribological performance of the polyester/graphene composites is mainly attributed to bigger thermal conductivity for graphene, which can easily dissipate the heat which appears during the friction process at bigger forces. The positive influence of graphite on coefficient of friction (COF) of the composites is the result of the clivage of graphite layers during the loadings due to van der Waals weak bonds between the graphite layers.
Mechanical behaviour law for thermoplastic polymers was established on the basis of phenomenological models. This work is intended to examine whether a constitutive equation used for thermoplastic polymers could be applied in case of their composites. G’Sell-Jonas model gave good results when used for the prediction of stress-strain characteristics at high strain rate, for semi-crystalline polymers subjected to mechanical tests. Data obtained through compressive test of polyphenylene sulphide (PPS) composites were processed by a numerical algorithm based on G’Sell-Jonas constitutive equations. Besides, a comparative analysis of experimental results and numerical model was done. The study showed clearly a good agreement between experimental and numerical results.
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