Processing conditions and final mechanical properties of polymer nanocomposites are affected by their interfacial layers behavior. However, it is impossible to determine directly the properties of these layers by dynamic rheometry tests. In this work, the interfacial layers properties are evaluated for polystyrene containing silica nanoparticles by the concept of glass-transition temperature shift. The samples were prepared via solutionmixing method and dynamic rheometry was used to determine the viscoelastic behavior of filled polymers in the melt state. This initial step showed that addition of silica particles increased the glass-transition temperature. By preference, decrease in the filler particle size lead to a drastic increase in the glass-transition temperature and interfacial layer volume fraction due to relatively high surface area of the small filler particles. Then, in the next step, the viscoelastic properties of interfacial layer have been evaluated on the basis of the properties of neat polystyrene using temperature-frequency superposition law. For this purpose, the shift factor was calculated from the glass-transition temperature of the sample with maximum filler content. Finally, the effect of immobilized interfacial layer on the viscoelastic properties of the polymer nanocomposite samples has been estimated.

In this study, control of the airflow by the direct current (DC) electrical discharge with bare electrodes has been investigated in different velocity regimes. The discharge characteristics of the plasma model are obtained numerically. An induced electrohydrodynamic (EHD) force on neutral flow was characterized based on momentum transfer from charged particles. The change in the incident flow parameters was studied by applying Navier-Stokes (N-S) equations, considering source terms arising from a weakly ionized plasma. The effect of the discharge on the lowand high-speed flow was simulated in this study. It was concluded that the changes of the velocity profile, airflow pressure, and oblique shock wave could be attributed to the EHD force from a nonthermal plasma to the incoming airflow. It was seen that the incident airflow is accelerated also by the induced EHD force. Our results show that the most important mechanism in the plasma-based flow control is the momentum transfer from the electrical discharge to the incident flow and that the gas heating has no significant role. K E Y W O R D Selectrical discharge, flow control, plasma actuator

This paper attempts to describe the fatigue response of a foam the core sandwich composite with unsymmetrical carbon/glass face sheets under tension-tension cyclic loading. The laminate is a critical element of the structure of a light full composite airplane which was determined through the stress analyses for numerous load cases. The face sheets, over a PVC foam the core, consist of two similar woven E-glass fibers following unidirectional carbon fibers with epoxy resin. Extensive fatigue data were generated for the S-N diagram of this laminate. Based on the static FEM analyses, two designs for the configuration of foam to solid laminate bonding zone have been investigated. Hence, the effects of using each of these different proposed designs have been determined. The damage events causing final failure were traced during fatigue tests. Four distinct damage events were found. Two of them were initiated and propagated in the foam the core, which could result in lower dispersion in comparison with other composite materials, because of foam the core homogeneity. The first damage event in the core is crack initiation and propagation along thickness, followed by the second damage event, which is crack propagation parallel to the length of the gauge. The parallel crack length is shortened by increasing the load ratio.

This study represents an effort to predict the bearing strength, failure modes, and failure load of bolted joints in foam-core sandwich composites. The studied joints have been used in a light full composite airplane. By using solid laminates, a new design for the joint zone is developed. These solid laminates include a number of glass plies with total thickness equal to core thickness. The effect of solid laminate size and interface angle of foam-solid laminate in the bonding zone on the bearing strength, failure loads and type of modes are investigated. The numerical study is performed using 3D FEM in ANSYS commercial code. Tsai-Wu failure criterion is used in the failure analysis. The results indicate that the most important parameter in the proposed joint zone design is the foam-solid laminate interface angle which plays an important role on the value of failure criterion (damage) in the bonding zone. Also, the use of squared shaped solid laminate as compared with a circular laminate will decrease the criterion value significantly. Finally, the influence of solid laminate size and interface angle on the buckling strength was discussed. As obtained through eigenvalue buckling analysis, the increase of solid laminate size or interface angle could result in considerable higher buckling strength.

Equal Channel Angular Pressing (ECAP) is one of the methods of refining and fine-graining metal materials. In this research, ECAP operation was performed on samples of 5182 alloy in 1 to 4 passes at ambient temperature. After implementation of the specimens through ECAP, prepared to obtain mechanical properties such as hardness, tensile, and metallography. The results of these experiments showed that the mechanical properties of the packed materials through ECAP have improved compared to the normal state. Using a scanning microscope, it was observed that the average grain size decreased from 131 μm in the initial state to 745 nm after the ECAP process after the fourth pass. The results of the hardness test also showed a 213% increase compared to normal. The increase in yield stress after 4 passes is about 3 times. Finally, the crack growth of these materials under fatigue loading was compared with the non-ECAP mode by creating a suitable pre-crack. It was observed that crack growth is faster in ECAP materials and the failure surface is smoother compared to normal. Also, the deviation of the crack from its path in microstructure materials is less than normal. Finally, by comparing the Experimental results of crack growth with the results of numerical analysis, the accuracy of the numerical results is validated and confirmed.