Effect of current density on the porous silicon preparation as gas sensors**

In this study, porous silicon (PSi) was used to manufacture gas sensors for acetone and ethanol. Samples of PSi were successfully prepared by photoelectrochemical etching and applied as an acetone and ethanol gas sensor at room temperature at various current densities J= 12, 24 and 30 mA/cm2 with an etching time of 10 min and hydrofluoric acid concentration of 40%. Well-ordered n-type PSi (100) was carefully studied for its chemical composition, surface structure and bond configuration of the surface via X-ray diffraction, atomic force microscopy, Fourier transform infrared spectroscopy and photoluminescence tests. Results showed that the best sensitivity of PSi was to acetone gas than to ethanol under the same conditions at an etching current density of 30 mA/cm2, reaching about 2.413 at a concentration of 500 parts per million. The PSi layers served as low-cost and high-quality acetone gas sensors. Thus, PSi can be used to replace expensive materials used in gas sensors that function at low temperatures, including room temperature. The material has an exceptionally high surface-to-volume ratio (increasing surface area) and demonstrates ease of fabrication and compatibility with manufacturing processes of silicon microelectronics.

On the hygrothermal properties of sandcrete blocks produced with sawdust as partial replacement of sand

In Nigeria, sawdust is continuously generated in large quantities as waste but majorly under-utilised, a situation which causes serious environmental problems and health hazards when managed improperly. This work focussed on production and assessment of hygrothermal properties of solid core sandcrete blocks in which sand is partially replaced with sawdust at 0%, 10%, 20%, 30%, and 40% loading levels. Experiments were conducted on block samples made with untreated sawdust (USD) and on those similarly produced but with treated sawdust (TSD). The results showed that the blocks with USD content are capable of decreasing wall heat transmission load and improve energy efficiency of building envelopes better than their counterparts produced with TSD. In terms of compliance with standard bulk density and water absorption requirements, incorporation of USD or TSD at 20% or 10% level respectively, was found to be optimum for partial sand substitution in the studied block samples in order to suit the functional requirements of building structure and interior space. Since sawdust is cheaply and commonly available in vast amount, utilising it in sandcrete block production is a promising way of minimising its disposal problems while enhancing the development of safe, affordable, and sustainable housing.

Structural response and sensitivity analysis of granular and asphaltic overlayment track considering linear viscoelastic behavior of asphalt

This study investigated the structural response of granular and asphaltic overlayment of rail track considering the linear viscoelastic behavior of asphalt. The calculation of the tensile strains at the bottom of the asphalt layer, the compressive stresses at the top of the subgrade layer, and the service life of the granular and the asphaltic overlayment rail track were conducted using the KENTRACK software. Furthermore, the sensitivity analysis by changing different factors was studied in this paper. The results of this study indicate that the asphaltic overlayment rail track structure has a much longer predicted service life than the granular rail track. It was also shown that the sub-grade compressive stress is more sensitive to the change in subgrade modulus than the change in ballast-sub-ballast-asphalt layer thickness and the change in binder type, respectively. In addition, the asphalt tensile strain is more sensitive to the change in asphalt layer thickness than the change in subgrade modulus and the change in binder type, respectively. These findings also enhance our understanding that subgrade compressive stress and asphalt tensile strain in the asphaltic overlayment track are more sensitive to the change in asphalt layer thickness than the change in binder type.

Impact strength of surface treated SS316L wires reinforced PMMA**

Stainless steel 316L (SS316L) as a significant bio-material, their wires were used to support the PMMA matrix. Two simple and low-cost surface pretreatments for SS316L wires were performed to enhance denture impact strength: mechanical scratching (treating SS316L wires with SiC powder inside a rotating container) and electrochemical anodizing. Three mechanical scratching samples for different periods of 60, 90 and 120min were prepared. Anodizing technique conditions were: Ethylene glycol with perchloric acid as an anodizing solution, 15V supplying and graphite rod as an anode. Anodizing process involved three pretreating periods of 15, 20, and 30min. All the prepared samples had dimensions of 65 × 10 × 3 mm. SEM technique showed different morphology nature involved holes, scratches and pores with a density of 104/μm2 and a crack length of 60μm. The PMMA reinforced with scratched stainless steel 316L wire surface for 120 min presented the highest impact strength value (42 kJ/m2) with (450.91%) increment. Anodizing samples showed a fluctuating behavior of samples with enhancing in the impact strength of anodizing wire for 20min of about 26.99 kJ/m2, which is still lower than that for scratched samples in average.

Unmanned aerial vehicle evasion manoeuvres from enemy aircraft attack

One of the most important problems associated with the combat use of unmanned aerial vehicles remains to ensure their high survivability in conditions of deliberate countermeasures, the source of which can be both ground-based air defence systems and fighter aircraft. For this reason, the study and optimization of evasive manoeuvres of an unmanned aerial vehicle from an enemy aircraft attack remains relevant. Based on the game approach, the authors of this paper propose an algorithm for guaranteeing control of the trajectory of an unmanned aerial vehicle, which ensures its evasion from an enemy air attack. The study of the influence of tactically significant indicators of the manoeuvrability of an unmanned aerial vehicle on the effectiveness of the evasion manoeuvre was carried out. The model predictions are presented, reflecting the degree of influence of unmanned aerial vehicle manoeuvring capabilities on achieving a positional advantage when solving the problem of evading air enemy attack.

Mechanical performance investigation of lignocellulosic coconut and pomegranate / LDPE biocomposite green materials

Biocomposites have been implemented in various industrial applications. However, it is necessary to demonstrate their desired mechanical performance aspects for the near future green products. The aim of this work is to study the efficiency of utilizing both coconut and pomegranate lignocellulosic fiber as green reinforcement types for the low-density polyethylene, LDPE. Desired mechanical performance trends are investigated for the green composites including the tensile strength, tensile modulus, and elongation to break properties as a function of various reinforcement configurations. This was performed to properly optimize the reinforcement conditions to obtain desirable mechanical characteristics of such types of bio-composites for more sustainable functional attributes. Results have demonstrated that the best tensile strength for the coconut/PE was achieved at 20wt.% case with 8.2 MPa, and the best regarding this property for the pomegranate/PE was at 30wt.% with a value close to 8.3 MPa. Moreover, obvious inverse relationship between strength and strain for the coconut composite type was revealed at both low and high fiber contents. It was also noticed that the 20wt.% coconut-based composite has demonstrated the best optimal values of tensile strength and tensile modulus simultaneously. But no reinforcement condition was found for pomegranate/LDPE as an optimal for these mechanical properties concurrently.

Mechanical properties and microstructural characteristics of rotary friction welded dissimilar joints of rolled homogeneous armor steel and medium carbon steel

Distinct materials are used for the construction of battle tanks used in defense sectors. The hull and turret of the battle tanks are made up of rolled homogeneous armor steel (also known as armor steel). The inner portions like the driver cabin and control room are covered with medium carbon steel. Hence, the dissimilar joint between these materials is unavoidable in the battle tank construction. Conventional fusion welding processes like manual metal arc welding, gas metal arc welding, and gas tungsten arc welding are preferred to join the dissimilar metals. However, the high heat input nature of these processes will create hydrogen induced cracking, high residual tensile strain, and HAZ softening, etc. To minimize these issues, solid state welding processes were adopted. In the present study, mechanical properties and microstructural characteristics of rotary friction welded dissimilar joint of armor steel and medium carbon steel was analyzed. The ultimate tensile strength of the dissimilar joint is around 775 MPa and the failure occurred at the medium carbon steel side. The impact toughness value of dissimilar joints is higher than medium carbon steel and lower than armor steel. The microstructure across the dissimilar joint has distinct features and a complex pattern was observed at the weld interface.

Design and optimization of differential capacitive micro accelerometer for vibration measurement

This paper deals with the design and optimization of a differential capacitive micro accelerometer for better displacement since other types of micro accelerometer lags in sensitivity and linearity. To overcome this problem, a capacitive area-changed technique is adopted to improve the sensitivity even in a wide acceleration range (0–100 g). The linearity is improved by designing a U-folded suspension. The movable mass of the accelerometer is designed with many fingers connected in parallel and suspended over the stationary electrodes. This arrangement gives the differential comb-type capacitive accelerometer. The area changed capacitive accelerometer is designed using Intellisuite 8.6 Software. Design parameters such as spring width and radius, length, and width of the proof mass are optimized using Minitab 17 software. Mechanical sensitivity of 0.3506 μm/g and Electrical sensitivity of 4.706 μF/g are achieved. The highest displacement of 7.899 μm is obtained with a cross-axis sensitivity of 0.47%.

Mechanical behavior of thin-walled steel under hard contact with rigid seabed rock: Theoretical contact approach and nonlinear FE calculation

This work aims to investigate the mechanical behavior of steel-plated structures under a raking incident and to quantify the effect of the mesh size in nonlinear finite element (NLFE) analysis. To conveniently comprehend nonlinear phenomena, i.e., the grounding which takes place in this work, a series of theoretical contact formulations was defined. In the main analysis, raking, which is a part of the grounding scenario, was strictly assumed as contact between a tanker, which was assumed to have thin-walled steel, and a seabed rock in the form of a solid obstruction. Designed raking scenarios were calculated using the FE method by using the nonlinear phenomena of the material behavior in the calculation. The findings of this work indicated that the possibility of expanding the recommended mesh size in FE simulation should be evaluated by quantifying the behavior of structural responses, such as energy, the force damage pattern, and acceleration, subjected to a variety of applied meshing techniques. The results concluded that a notable difference occurred when the mesh size was more than 132 mm (ratio 11 based on the plate dimension in this work), and this size is strictly recommended to be used for calculation of the element length-to-thickness (ELT) ratio. Assessment in time simulation showed that applying larger mesh sizes will reduce the simulation time but increase the maximum values of the crashworthiness parameters, i.e., energy, force, acceleration, and displacement.

A mechanochemical preparation, properties and kinetic study of kaolin–N, P fertilizers for agricultural applications**

Solvent-free ball milling was used to activate kaolin, a trioctahedral clay material, with diammonium phosphate[(NH4)2HPO4] to serve as a fast-acting phosphorus and nitrogen releasing fertilizer. Different tests on a mixture of 3:1 weight ratio of kaolin: (NH4)2HPO4 were performed to analyze the level of incorporation of (NH4)2HPO4 in the kaolin and the degree of liberation of NH 4 + {\rm{NH}}_4^ + and PO 4 3 − {\rm{PO}}_4^{3 - } ions into solution. The experimental mill speeds were varied from 200 to 700 rpm rotational rates for a fixed period of 2 hours. Several milling periods of 1, 2, and 3 h. were studied at the fixed milling speed of 600 rpm. To explain the properties of activated materials and to understand the purpose behind the simpler disintegration of phosphorus, several analytical methods such as FT-IR, TGA-DTG and Ion chromatography (IC) were used. The proposed procedure was environmentally friendly, and it helped to maintain a balanced supply of nitrogen and phosphorus fertilizer for agriculture's long-term development by offsetting some of the existing high-cost chemical fertilizer. The results demonstrated that the mechanochemical reaction could yield an intercalated form of kaolin that is a transmitter of N and P sources in fertilizers.