Waleed K. Ahmed

Half-metallicity and optoelectronic properties of V-doped zincblende ZnS and CdS alloys

In this paper, spin-polarized density functional calculations on the structural, electronic, optical and magnetic properties of the zincblende structure of the Zn1−xVxS and Cd1−xVxS alloys at x = 0.25 in the ferromagnetic (FM) ordering has been investigated. The study is accomplished using the full-potential (FP) linearized augmented plane wave plus local orbital (LAPW+lo) self-consistent scheme of calculations. To incorporate the exchange correlation component in the total energy calculations of the crystal, Perdew–Burke and Ernzerhof (PBE) parameterization for the generalized gradient approximation (GGA) and GGA+U are employed. Basically, for both alloys, to address their structural properties, we calculated their equilibrium lattice constants, bulk moduli as well as pressure derivatives. In general, from the analysis of the obtained electronic band structure of these alloys, the half-metallic nature of Zn0.75V0.25S and nearly half-metallic nature of the Cd0.75V0.25S alloy are demonstrated. The plotted density of states (DOS) curves project spin-exchange splitting energy Δx(d) and Δx(pd) as generated by V-3d states. It has been clearly evident that the effective potential results for the spin-down case are more striking than for the spin-up case. In order to describe the magnetic behavior of these alloys, the exchange constants N0α (valence band) and N0β (conduction band) as well as the magnetic moment values are estimated. The calculated results of the magnetic moment show that the main source in the reduction of the local magnetic moment of V in the alloys in comparison with its free value is a p–d orbital hybridization and partial transfer to nonmagnetic sites of (Zn, S) and (Cd, S) in Zn0.75V0.25S and Cd0.75V0.25S alloys. In addition, a study concerning optical properties, such as the refractive index, reflectivity and absorption coefficients is performed to determine their potential for optical and optoelectronic devices.

Development of Nanocement Mortar as a Construction Material

The present research examined the compressive and flexural strength of nanocement mortar by using micro cement, micro sand, nanosilica and nanoclay in developing a nanocement mortar which can lead to improvements in ferrocement construction. The measured results demonstrate the increase in compressive and flexural strength of mortars at early stages of hardening. In addition, the influence of heating on compressive strength of cement mortar. General expressions to predict the compressive strength, modulus of rupture for the developed nanocement mortar in the present work are proposed.

Studying structural, electronic and optical properties of zinc-blende Ga1−x Al x P at normal and under pressure by means of first principle

Structural, electronic and optical properties of the zinc-blende Ga1−x Al x P ternary alloys with their ordered AlP and GaP binary compounds have been investigated, using the full potential linearized augmented plane wave method in conjunction with the density functional theory. The total energies are carried out to calculate the lattice constant, bulk modulus and its pressure derivative of the zinc-blende AlP, GaP binary compounds and their corresponding ternary Ga1−x Al x P solid solutions for the compositions (x = 0.25, 0.50 and 0.75). The band gap energies and the optical properties of these materials are investigated at normal pressure condition as well as under high pressure levels. The estimated results obtained from this work are justified, discussed and compared with the experimental data and other available theoretical works.

Thermal Performance of Ferrocement Green Building System

Urban development is a key consumer of energy, a ferrocement structural system based on generic services facilities is introduced and prefabricated cavity walls/and roofs within the structural system present a series of possibilities for the solution of building construction at maximum reduction of the electrical energy. The energy required to run the building using the proposed ferrocement construction system is determined and the possibility of using the renewable energy production rather than energy depleted is presented.

Adsorption of Bilirubin Toxin in Liver by Chitosan Coated Activated Carbon Prepared from Date Pits

The aim of this work was to develop activated carbon (AC) from date pit powder and evaluate its adsorption efficiency of bilirubin toxin. In order to increase the adsorption capacity of bilirubin, an increase in the surface area is necessary. This increase was achieved through pyrolysis technique and to further increase the absorption capacity of AC when coated with chitosan gel, which contains several groups on its chains that act as interaction sites. Results indicated that the presence of the AC lead to a decrease in bilirubin content and the more the AC added to the sample, the faster the rate of adsorption as well as the higher the capacity of adsorption. A 0.3 M AC concentration shows a 0.82 left over bilirubin fraction after 16 h, while a 0.1 M AC concentration shows a 0.9 bilirubin fraction after the same interval of time. Contact time is another factor that also contributed to the increase in adsorption of bilirubin. It was seen that chitosan coated AC shows an increase in adsorption percentage from about 25% to 96% when left for a longer period of time.

Mechanical properties of nano-cement mortar: Compression and tension

The present research examines the compressive and tension strength of nano cement mortar by using micro cement, micro sand, nano silica and nano clay in developing a nano-cement mortar which can lead to improvements in concrete construction. The results have shown an increase in both the compressive and tensile strength of mortar at early stages of hardening. For testing purpose, 50 mm cubes and 250×50×10 mm prisms were cast and tested for determining the compressive and tensile strength of nano-cement mortar. The parameters that were taken consideration during the investigation were micro sand, micro cement, nano silica, developed nano clay and naphthalene sulphonate as super- plasticizers. It has been concluded that the measured results demonstrate significant increase in the tensile strength of the developed mortar. Accordingly, an empirical equation is formulated for the tensile strength prediction.

LEFM to Investigate the Impact of Deteriorated Particles in Composite Material

Due to its distinguished properties especially being isotropic, particulate reinforced composite is considered as one of the attractive material for wide range of applications, where the relatively low manufacturing cost is a desirable advantage. In the present analysis, deteriorated particles embedded in particulate reinforced composite have been investigated. The impact of the fractured particles is studied through the principles of fracture mechanics using finite element method. Mainly the stiffness variation of the composite due to the presence of the fractured particles is mainly predicted, since it is considered as an important factor especially from the view point of the damage-tolerant design of composite structures. A representative volume element (RVE) has been selected to represent the particulate composite with different particle volume fractions. It is important to point out that based on a previous investigation and comparison between two and three dimensional finite element analysis for a particulate reinforced composite, two-dimensional, plane strain finite element analysis is used to estimate the stresses and deformation that taken place. Uniaxial tensile stress perpendicular to the crack face of the fractured particle has been applied to the representative volume element. Due to symmetry of the studied geometries, quarter of the representative volume element is modeled via finite element method with a consistent mesh as possible to maintain reliable results. Linear elastic fracture mechanics (LEFM) is adopted through estimating stress intensity factor (SIF) of the cracked particles. Basically, the investigation covers the assessment of fractured particles with different crack lengths, where the particle’s stiffness is considered as a substantial parameter in the analysis in combination with others. Moreover, various particles volume fractions are taken into account to figure out their influence on the effective Young’s modulus of the representative volume element chosen for the studied cases. Multiple point constraints (MPC) technique is adopted in the finite element model to calculate the effective stiffness of the fractured particle. In general, it has been shown that there is a considerable influence of the deteriorated particles on increasing stress intensity factor levels at the crack tip as long as the crack length increases with respect to the particle size, and this basically depends on the stiffness ratio of the matrix/particle considered in the analysis. In the other hand, it has been noticed that a significant reduction in the effective stiffness of the particulate composite which is calculated based on the modeled representative volume element as a function of the crack length.Copyright

Thermal response of a ferrocement cavity wall under direct fire

AbstractOne of the main challenges for building designs is to provide comfort to its occupants at a low cost. The present investigation aims to study the performance of a ferrocement cavity wall under heating by means of applying direct fire to two ferrocement leaves with a space in between to be filled with insulation material. The main parameters considered in the present investigation are the fire temperature at its core and the space between the two ferrocement leaves. All leaves were subjected to direct fire for 2 hours. The performance of the ferrocement cavity wall was observed by reading an infrared thermometer instrument and examining the crack patterns on the wall panel. It is concluded that increasing the cavity wall space affected the degree of insulation, while the degree of insulation is not affected by the type of insulation material. It is also concluded that hair cracks appeared on the surface of the ferrocement leave facing the fire when the temperature reached 1300°C with the core of th...

Failure Analysis in Hybrid Composite Laminates Using Acoustic Emission and Microscopy

Fiber Reinforced Plastic (FRP) composite materials are widely used in many applications especially in aircraft manufacturing because they offer outstanding strength to weight ratio compared to other materials such as aluminum alloys. The use of hybrid composite materials is potentially an effective cost saving design while maintaining strength and stiffness requirements. In this work, Woven Carbon Fibers (WCFs) along with Unidirectional Glass Fibers (UDGFs) are added to a an aerospace-rated epoxy matrix system to produce a hybrid carbon and glass fibers reinforced plastic composite plates. The manufacturing method used here is a conventional vacuum bagging technique and the stacking sequence achieved consists of a symmetric and balanced laminate (±451WCF, 03UDGF, ±451WCF) to simulate the layup usually adopted for helicopter composite blades constructions. Then, tensile static tests samples are cut according to ASTM standard using a diamond blade and tested using a servohydraulic test machine. Acoustic Emission (AE) piezoelectric sensors (transducers) are attached to the samples surface using a special adhesive. Stress waves that are released at the moments of various failure modes are then recorded by the transducers in the form of AE hits and events (a burst of hits) after they pass through pre-amplifiers. Tests are incrementally paused at load levels that represent significant AE hits activity which usually corresponds to certain failure modes. The unbroken samples are then thoroughly investigated using a high resolution microscopy. The multi load level test-and-inspect method combined with AE and microscopy techniques is considered here to be an innovation in the area of composite failure analysis and damage characterization as it has not been carried out before. Results are found to show good correlation between AE hits concentration zones and the specimens damage location observed by microscopy. Waveform analysis is also carried out to classify the damage type based on the AE signal strength energy, frequency and amplitude. Most of the AE activity is found to initiate from early matrix cracking that develops into delamination. Whereas little fiber failure activity has been observed at the initial stages of the load curve. The results of this work are expected to clear the conflicting reports reported in the literature regarding the correlation of AE hits characteristics (e.g. amplitude level) with damage type in FRP composite materials. In addition, the use of a hybrid design is qualitatively assessed here using AE and microscopy techniques for potential cost savings purposes without jeopardizing the weight and strength requirements as is the case in a typical aircraft composite structural design.Copyright

An Experimental Investigation on the Shear Strength of Ferrocement Reinforced With Hexagonal Mesh

Ferrocement is characterized by fine diameter mesh reinforcement, and size of mesh opening, and the surface area per unit volume of mortar may be as much as ten times that in conventional reinforced concrete. The behavior of ferrocement is characterized by volume fraction of the fibers Vfx and Vfy in x and y directions and the specific surfaces of the mesh SLx and SLy. An experimental investigation on the shear strength of ferrocement plate reinforced with hexagonal mesh is carried out. Ferrocement square plate specimens were cast and tested. A total of 24 simply supported square plates (500×500mm) having mortar with cement/ sand proportions 1: 2 and 1: 3 by weight have been cast and tested under ‘patch’ load varying the number of mesh layers, the plate thickness, the size of the mesh opening and the arrangement and orientation of the mesh. Woven hexagonal mesh has been used. All plate specimens have been tested with their edges simply supported over a span of 450mm in two directions. During tests, central patch loads of size 100×100mm at the center of each plate specimens were applied to the models through a universal testing machine of 250 ton capacity. Having located the specimens within its support, series of patch load increments were then applied to the plate up to failure loads. The plate behavior has been presented in the form of the first cracking load Pcr and the ultimate load Pu which is the total patch load at failure. It was observed that the first cracking load is influenced by the ultimate mortar strength and not much affected by volume content of reinforcement. The slope of the curves at collapse indicates that the load carrying capacity is highly influenced by the steel volume content and the tensile strength of the mesh reinforcement while the contribution of mortar is negligible. The failure loads in the plates with closely spaced wires were higher as compared to the plates with widely spaced wires. There is an increase in the value of failure load Pu for the plate specimens with orthogonally oriented mesh layers as compared to the specimens with twin layers. An important conclusions regarding the plate behavior are drawn and expression to estimate the first cracking load is proposed. A comparison of the first cracking load values with those obtained using the proposed expression. It is seen that the proposed expression gives a reasonable estimate of the first cracking load.Copyright