Mahir H. Es-Saheb

Highly Ordered Mesoporous Tungsten Oxides with a Large Pore Size and Crystalline Framework for H2S Sensing

An ordered mesoporous WO3 material with a highly crystalline framework was synthesized by using amphiphilic poly(ethylene oxide)-b-polystyrene (PEO-b-PS) diblock copolymers as a structure-directing agent through a solvent-evaporation-induced self-assembly method combined with a simple template-carbonization strategy. The obtained mesoporous WO3 materials have a large uniform mesopore size (ca. 10.9 nm) and a high surface area (ca. 121 m(2)  g(-1)). The mesoporous WO3-based H2S gas sensor shows an excellent performance for H2S sensing at low concentration (0.25 ppm) with fast response (2 s) and recovery (38 s). The high mesoporosity and continuous crystalline framework are responsible for the excellent performance in H2S sensing.

Elastic plastic analysis of bonded composite repair in cracked aircraft structures

Three-dimensional and nonlinear finite element method is used to estimate the performance of the bonded composite repair of metallic cracked aircraft structures by analyzing the J integral and the plastic zone size around the crack tips for single and double symmetric patches. Several calculations have been realized to extract the plasticized elements around the crack tip. The obtained results show that, the double symmetric patch has a considerable beneficial effect on the repair performance compared to the single patch. A correction factor was introduced to the calculated values of the SIF for single patch in order to compensate for the effect of the plastic zone in the un-patched face of the repaired structure.

Template synthesis of metal tungsten nanowire bundles with high field electron emission performance

One-dimensional (1D) metal nanowires are of great importance for nanodevices due to their distinctive optical, electronic and mechanical properties. Here, for the first time, we report a simple H2 reduction-assisted hard-templating approach to fabricate metallic tungsten (W) nanowire bundles by using mesoporous silica SBA-15 as a template. The metal W nanowires with a length of 300–500 nm and diameter of 5–8 nm have long-range regularity over large areas because of their inter-wire pillar connections. Each nanowire has body-centred cubic (bcc)-W crystalline structure with a [110] preferential growth direction. As a field electron emitter, the W nanowires bundles show a low turn-on field of 4.1 V μm−1, a high field enhancement factor up to 3563 and good field emission stability (with a fluctuation below 5% over 32 h).

Post-Heat Treatment and Mechanical Assessment of Polyvinyl Alcohol Nanofiber Sheet Fabricated by Electrospinning Technique

Polyvinyl alcohol (PVA) sheets based nanofibers were produced by electrospinning technique. Postheat treatment of the produced PVA sheets with temperatures both below and above Tg to improve the mechanical properties of this material is conducted. The morphology, microstructures, and thermal degradation of the nanofibers sheets produced were investigated using scanning electron microscopy (SEM), transmission electron microscope (TEM), and thermal gravimetric analysis (TGA). Produced nanofibers are compact, and entangled with each other, with diameters from around 150 to 210. Some mechanical characteristics of the successfully produced PVA sheets, and heat-treated, are then conducted and assessed employing uniaxial tensile tests at different speeds ranging from 1 mm/min to 100 mm/min. The tensile test results obtained show that the PVA sheets are strain rate sensitive with increasing strength as the speed (i.e., strain rate) increases. The yield tensile stress ranges from 2.411 to 6.981 MPa, the ductility (i.e., elongation percent) from ∼21 to 60%, and Young modulus ranges from 103 to 0.137 KPa. However, for heat-treated samples, it is found that the yield strength increases almost by ∼35–40% more than the values of untreated cases with values reaching up to about 3.627–9.63 MPa.

Mass Gain Estimation Between Double and Single-Bonded Composite Repairs for Inclined Cracks in Aircraft Structures

Repair of cracked components by an adhesively bonded composite patch has gained acceptance in aerospace structures. The advantages of the double symmetric repair compared to the single one are well known. These advantages permit a significant reduction of the stress intensity near the repaired defect. In this study, a new approach was used to determine the advantage of the double symmetric patch: it is the determination of the mass gain obtained by the use of the double patch if the two techniques (single and double patches) give the same stress intensity at the crack tip. The mass gain was estimated numerically using the three-dimensional finite element method for repaired inclined cracks. The obtained results show that the mass gain eventually obtained by the use of the double patch can be very significant.

Specific crack enthalpy as material characterization parameter

Abstract In this study, the specific crack enthalpy (damage), considered a material characterization parameter according to crack layer theory, is discussed. The crack region and its accompanying damage become a crack layer. Fatigue crack propagation experiments were conducted on HT60 and HT80 steel. The specific enthalpy γ* of fracture due to ductile crack propagation in steel HT60 and HT80 has been calculated. The energy release rate and damage coefficients were determined at different stress ratios varying from R = 0.04 to 0.8. The crack layer translational resistance moment R1 has been determined. Because interpreting the data of crack propagation on two types of steel in the light of this theory reveals reasonable similarity, the need to set up experiments specifying the limitations and applicability of the theory is essential.