Taguchi‐based analysis of polyamide 6/acrylonitrile–butadiene rubber/nanoclay nanocomposites: The role of processing variables

Applying the Taguchi method of experimental design, we prepared various polyamide 6 (PA6)/acrylonitrile butadiene rubber (NBR)/nanoclay nanocomposites under different processing conditions by melt mixing in an internal mixer. The effects of the processing variables, including the rotor speed, chamber temperature, and mixing order on the morphology, that is, the rubber particle size and interlayer distance, and the mechanical properties, that is, the tensile modulus and impact strength, were then investigated. As demonstrated with the Taguchi approach, the lower temperature associated with higher rotor speeds improved the mechanical properties of the 90/5/5 PA6/NBR/nanoclay systems. However, it was revealed that the mixing order did not affect the mechanical properties for the assigned composition. Hence, the simultaneous mixing of all the ingredients is seemingly the simplest way of mixing to obtain the desired mechanical properties. These results were confirmed with transmission and scanning electron microscopy observations and X‐ray diffraction measurements. Image analysis corresponding to the mean particle size of the NBR constituent was also performed. The optimum processing condition to achieve the appropriate mechanical properties is ultimately predicted by the Taguchi analysis and corresponded to a chamber temperature of 230°C and a screw speed of 80 rpm. Moreover, the simultaneous mixing of all of the ingredients was suggested for convenience. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 820‐828, 2013     

Influence of Diisocyanate Structure on the Synthesis and Properties of Ionic Polyurethane Dispersions

A number of aqueous polyurethane dispersions based on polytetramethylene glycol (PTMG), 1,4-butanediol (1,4-BDO), dimethylol propionic acid (DMPA) and diisocyanates of differing structures such as toluene diisocyanate (TDI), diphenylmethane diisocyanate (MDI), isophorone diisocyanate (IPDI), and dicyclohexylmethane diisocyanate (H₁₂MDI) were prepared. IR Spectroscopy was used to check the end of polymerization reaction and also the polymer characterization. The effects of diisocyanate structure on the particle size, contact angle, mechanical and thermal properties of the emulsion-cast films were studied. Average particle size of prepared polyurethane emulsions change by different diisocyanate based polyurethane. TDI based PU shows higher average particle size and contact angle than the others. Tensile strength, hardness, and elongation at break were higher in the case of MDI based polyurethane. Thermal property and thermal stability is also affected by variation of diisocyanate molecular structure.     

The microstructure,hardness and tensile properties of a new super high strength aluminum alloy with Zr addition

This research is based on the addition of zirconium to a new super high strength Al–12.24Zn–3.25 Mg–2.46Cu alloy. The results showed that Zr addition decreases average grain size (approximately 20%), forms rosette-like microstructure and introduces proper distribution of the second phases. In addition, due to the presence of Al₃Zr particles in Zr-refined specimen, the area fraction of recrystallized regions decreased by 65% as compared with unrefined specimen. Furthermore, tensile strength, yield strength and particularly elongation values of the extruded refined sample were enhanced nearly 34%, 25% and 1850%, respectively, when compared with not-extruded unrefined one. Microstructural observations and fractographic examinations of the fractured surfaces of several extruded specimens indicated dimple-like mechanism while the presence of coarse eutectic constituent was responsible for brittle mode of fracture in not-extruded specimens.     

Effect of Al on the hydrogenation characteristics of nanocrystalline Mg powder

We have fabricated nanocrystalline Mg–Al powders with nominal Al compositions of 4 and 8 at% by the electrodeposition technique and have compared their hydrogenation characteristics with those for a commercially available pure Mg powder. It is elucidated that interestingly the amount of Al incorporated in MgH₂ increases with decreasing the hydrogenation temperature. This observation indicates that the magnesium hydride phase has a limited solubility for aluminum and the supersaturation of hydride with Al is attributed to the slower mobility of aluminum at low temperatures. The rejection of Al during hydride formation is shown to result in a higher fraction of the intermetallic phase, thus reducing the hydrogen capacity. It is suggested that the presence of the intermetallic phase prior to hydrogenation enhances the hydride nucleation rate, which further decreases the hydrogen capacity in comparison to pure Mg.     

Physical simulation of hot deformation, and microstructural evolution for 42CrMo4 steel prior to direct quenching

 Direct quenching and tempering (DQ-T) of hot rolled steel section has been widely used in steel mill for the sake of improvement of mechanical properties and energy saving. Temperature history and microstructural evolution during hot-rolling plays a major role on the properties of direct quenched and tempered products. The mathematical and physical modeling of hot forming processes is becoming a very important tool for design and development of required products as well as to predict the microstructure and the properties of the components. These models were mostly applied to predict austenite grain size (AGS), dynamic, meta-dynamic and static recrystallization in the rods immediately after hot rolling and prior to DQ process. In this paper the hot compression tests were carried on 42CrMo4 steel in the temperature range of 900 - 1100°C and the strain rate range of 0.05 - 1 s- 1 in order to study the high temperature softening behavior of the steel. For the exact prediction of flow stress, the effective stress - effective strain curves were obtained from experiments under various conditions. On the basis of experimental results, the dynamic recrystallization fraction (DRX), AGS, hot deformation and activation energy behavior were investigated. It was found that the calculated results were in a good agreement with the experimental flow stress and microstructure of the steel for different conditions of hot deformation.     

Postbuckling analysis of piezoelectric multiscale sandwich composite doubly curved porous shallow shells via Homotopy Perturbation Method

In this study postbuckling behaviors of multiscale composite sandwich doubly curved piezoelectric shell with a flexible core and MR layers by employing Homotopy Perturbation Method in hygrothermal environment has been investigated. By using Reddy third shear deformable theory the face sheets and third-order polynomial theory of the flexible core the strains and stresses are obtained. A mathematical model for the multiscale composite layered shell with a flexible core and magnetorheological layer (MR) that incorporates the nonlinearity of the in-plane and the vertical displacements of the core is assumed. Three-phase composite shells with polymer/Carbon nanotube/fiber and polymer/Graphene platelet/fiber either uniformly or non-uniformly based on different patterns according to Halpin–Tsai model have been considered. The governing equations of multiscale shell have been derived by implementing Hamilton’s principle. Meanwhile, simply supported boundary conditions are employed to the shell. For investigating correctness and accuracy, this paper is validated by other previous researches. Finally, different parameters such as temperature rise, various distribution patterns, magnetic fields and curvature ratio are considered in this article. It is found these parameters have significant effect on the frequency–amplitude curves.

     

Hybrid modelling of machine tool axis drives

The x-axis dynamics of a milling machine where the workpiece and saddle are mounted on supporting slides is considered. A permanent magnet motor, lead screw, ball nut and bearings are employed as the machine, traverse actuator mechanism. Hybrid, distributed–lumped parameter methods are used to model the machine tool x-axis drive system. Inclusion of the spatial configuration of the drive generates the incident, travelling and reflected vibration signature of the system. Lead screw interactive torsion and tension loading, which is excited by cutting and input disturbance conditions, is incorporated in the modelling process. Measured and results from simulation exercises are presented in comparative studies enabling the dynamic characteristics of the machine to be identified under, no load and with the application of cyclic, cutting force disturbances. The effect of the lead screw length, cutting speed and hence the load disturbance frequency are examined and the resulting performance accuracy is commented upon.     

An analytical solution for static stability of multi-scale hybrid nanocomposite plates

An analytical answer to the buckling problem of a composite plate consisted of multi-scale hybrid nanocomposites is presented here for the first time. In other words, the constituent material of the structure is made of an epoxy matrix which is reinforced by both macro- and nanosize reinforcements, namely, carbon fiber (CF) and carbon nanotube (CNT). The effective material properties such as Young’s modulus or density are derived utilizing a micromechanical scheme incorporated with the Halpin–Tsai model. To present a more realistic problem, the plate is placed on a two-parameter elastic substrate. Then, on the basis of an energy-based Hamiltonian approach, the equations of motion are derived using the classical theory of plates. Finally, the governing equations are solved analytically to obtain the critical buckling load of the system. Afterward, the normalized form of the results is presented to emphasize the impact of each parameter on the dimensionless buckling load of composite plates. It is worth mentioning that the effects of various boundary conditions are covered, too. To show the efficiency of presented modeling, the results of this article are compared to those of former attempts.