Nabeel H. Alharthi

Chemical and structural analyses of the graphene nanosheet/alumina ceramic interfacial region in rapidly consolidated ceramic nanocomposites:

Graphene nanosheets (GNS) reinforced Al2O3 nanocomposites were prepared by a rapid sintering route. The microhardness and fracture toughness values of the resulting nanocomposites simultaneously increased due to efficient graphene nanosheet incorporation and chemical interaction with the Al2O3 matrix grains. The properties enhancement is attributed to uniformly dispersed graphene nanosheet in the consolidated structure promoted by high surface roughness and ability of graphene nanosheet to decorate Al2O3 nanoparticles, strong GNS/Al2O3 chemical interaction during colloidal mixing and pullout/crack bridging toughening mechanisms during mechanical testing. The GNS/Al2O3 interaction during different processing stages was thoroughly examined by thermal and structural investigation of the interfacial area. We report formation of an intermediate aluminum oxycarbide phase via a confined carbothermal reduction reaction at the GNS/Al2O3 interface. The graphene nanosheet surface roughness improves GNS/Al2O3 mechanical attachment and chemical compatibility. The Al2O3/GNS interface phase facilitates efficient load transfer, thus delaying failure through impediment of crack propagation. The resulting nanocomposites, therefore, offer superior toughness.

Preparation of TiO2 incorporated polyacrylonitrile electrospun nanofibers for adsorption of heavy metal ions

This paper describes the adsorption of lead and cadmium ions from an aqueous solution using a composite of titanium dioxide (TiO2)-incorporated polyacrylonitrile (PAN) electrospun nanofibers. Adsorption capacities and the mechanical response of the PAN/TiO2 composite electrospun nanofibers are investigated at different weight percentages of TiO2 (0.5, 1.0, 2.0, and 5.0xa0wt.%). The adsorption capacities of the composite PAN/TiO2 (2.0 and 5.0xa0wt.%) for Pb(II) and Cd(II) are remarkably increased by approximately 114 and 47%, respectively, compared to those of pure PAN electrospun nanofibers. Moreover, the adsorption of Pb(II) and Cd(II) by PAN/TiO2 nanofibers reaches an equilibrium within 60xa0min, and the process can be described using the nonlinear pseudo-second-order kinetic model. The adsorption isotherm study can be represented by the Langmuir model, which suggests the homogeneous distribution of monolayer adsorptive sites on the composite nanofiber surface. Furthermore, the ultimate tensile strength and ductility of all nanofiber membranes are measured through a uniaxial tension test. Mechanical tests reveal a reduction in the tensile strength of the PAN/TiO2 composite nanofibers with increase in TiO2 amount due to the possible formation of agglomerates and voids in the nanofiber structure.

Physical, mechanical, chemical and thermal properties of nanoscale graphene oxide-poly methylmethacrylate composites

The purpose of this laboratory study was to formulate and characterize the graphene oxide-poly(methyl methacrylate) resin composite with an intended use as bone cement. Graphene oxide was fabricated through ultrasonication route. The autopolymerization resin (Eco Cryl Cold, Protechno, Vilamalla Girona, Spain) was used to prepare the specimens of required dimensions for different testing parameters. The control group (C-group) was prepared as such. However, for GO1-group, 0.024u2009wt/wt.-% of graphene oxide was incorporated in a resin matrix and GO2-group was a composite with 0.048u2009wt/wt.-% of graphene oxide in a resin matrix. TEM examination of graphene oxide sheets demonstrated them in the range of ∼500u2009nm to ∼2u2009µm. The mechanical properties were characterized using three-point bending and wear resistance, while material properties were assessed through transmission electron microscope, scanning electron microscopy, Fourier-transform infrared spectroscopy, Raman spectroscopy, X-ray diffraction, differential scanning calorimetry and thermo-gravimetric analysis. The results suggest that 0.024u2009wt/wt.-% and 0.048u2009wt/wt.-% of loading of GO have no effect on the physiochemical characteristics. However, thermal characteristics might slightly be improved. According to the analysis of variance results (pu2009<u20090.05, nu2009=u20095), wear resistance and bending strength of both GO1 and GO2 groups significantly improved compared to C-group. The bending strength of GO2 improved to 87.0u2009±u20097.2u2009MPa from 65.9u2009±u200911.5u2009MPa of C-group. Scanning electron microscopy examination of the fractured surface demonstrated granule like structure where the graphene oxide sheets might be covered inside PMMA. The use of GO-PMMA composites favorably enhances the mechanical properties of bone cement.

Experimental and Numerical Study of Texture Evolution and Anisotropic Plastic Deformation of Pure Magnesium under Various Strain Paths

The deformation behavior and texture evolution of pure magnesium were investigated during plane strain compression, simple compression, and uniaxial tension at room temperature. The distinctive stages in the measured anisotropic stress-strain responses and numerically computed strain-hardening rates were correlated with texture and deformation mechanisms. More specifically, in plane strain compression and simple compression, the onset of tensile twins and the accompanying texture-hardening effect were associated with the initial high strain-hardening rates observed in specimens loaded in directions perpendicular to the crystallographic c-axis in most of the grains. The subsequent drop in strain-hardening rates in these samples was correlated with the exhaustion of tensile twins and the activation of pyramidal slip systems. The falling strain-hardening rates were observed in simple compression and plane strain compression with loading directions parallel to the c-axis where the second pyramidal slip systems were the only slip families that can accommodate deformation. For uniaxial tension with the basal plane parallel to the tensile axis, the prismatic and second pyramidal slips are the main deformation mechanisms. The predicted relative slip and twin activities from the crystal plasticity simulations clearly showed the effect of texture on the type of activated deformation mechanisms.

Prediction of Cutting Conditions in Turning AZ61 and Parameters Optimization Using Regression Analysis and Artificial Neural Network

All manufacturing engineers are faced with a lot of difficulties and high expenses associated with grinding processes of AZ61. For that reason, manufacturing engineers waste a lot of time and effort trying to reach the required surface roughness values according to the design drawing during the turning process. In this paper, an artificial neural network (ANN) modeling is used to estimate and optimize the surface roughness (Ra) value in cutting conditions of AZ61 magnesium alloy. A number of ANN models were developed and evaluated to obtain the most successful one. In addition to ANN models, traditional regression analysis was also used to build a mathematical model representing the equation required to obtain the surface roughness. Predictions from the model were examined against experimental data and then compared to the ANN model predictions using different performance criteria such as the mean absolute error, mean square error, and coefficient of determination.