Dynamic behavior of short aramid fiber‐filled elastomer composites

Short fiber reinforcement is a suitable way to improve the tribological properties of elastomers. However, rubbers products are often exposed to highly dynamic mechanical loadings. Hereby it is crucial to study the change in dynamic behavior due to the addition of short fibers. Therefore, these properties were investigated in terms of dynamic mechanical thermal analysis, heat build‐up (HBU), and fatigue crack growth resistance under cyclic loadings for two different rubber compounds. A peroxide cured ethylene–propylene–diene rubber (EPDM) and a sulfur cured natural rubber (NR) compound were chosen and reinforced with two types of short aramid fibers. It was found that the short fibers could contribute to the improvement in the crack growth resistance, HBU, and the dynamic mechanical behavior of the composites depending on the testing conditions. POLYM. ENG. SCI., 54:2958–2964, 2014. © 2014 Society of Plastics Engineers     

Plasma-sprayed composite coatings with reduced friction coefficient

The study analyses the tribological properties of a composite plasma sprayed with Al₂O₃-3TiO₂ mixed in various proportions with CaF₂, which is known as a solid lubricant. The coatings were plasma-sprayed in air and were tested using a pin-on-disc tribological set-up. The tests enabled to study their wear resistance and determine the coefficient of friction on the basis of friction force obtained in the course of continuous measurement at a set load. Experiments were optimized by the use of the two-level experiment design aimed at finding the optimal content of CaF₂ in the composite. The influence of the spraying parameters on the coefficient of friction, hardness and surface roughness was determined by means of regression analysis. Metallographical studies of the plasma-sprayed composite were conducted with the use of a scanning microscope with an energy dispersion spectrometer (EDS).     

Monte Carlo simulations of I2- (CO2)16 and I2- (N2O)16 clusters. Minimum energy structures and solvation energy

Structures of the I2- (CO2)16 and I2- (N2O)16 clusters have been studied along the dissociation path of the halide ion. Minimum energy structures and solvation energies have been estimated. The influence of the electrostatic interaction on the I2- charge distribution and the structure of the solvation shell has been discussed. It has been shown that the small dipole moment of the N2O molecule does not have much influence on the cluster properties, and the large quadrupole moments of both solvent clusters give the major contribution into electrostatic interactions. The structure of the clusters is more sensitive to different potential models than to the dipole moment of the N2O molecule.     

A Computer Simulation Study of Short-Range Order in Metastable hcp Phase of Solid Nitrogen

A quenched disordered phase of solid nitrogen has been studied in the temperature region where a dynamical crossover is observed between nearly free rotations and activated tumbling motion. The orientational dynamics of the molecules is fast enough to be simulated using the Monte Carlo Metropolis algorithm and Molecular Dynamics. However, these methods become non-ergodic at very low temperature where formation of a glassy state could be observed. The crystal structure below the crossover temperature remains hcp with the molecular orientations frustrated due to the incompatibility of the strong quadrupolar interactions with the hexagonal lattice. For this reason, quenched nitrogen at low temperature seems to be a good candidate for a glassy crystal model.