Search results

The purpose of this paper is to investigate the deposition of uniform, adherent and crack‐free Ni‐P thin films on carbon fibres using the electroless deposition technique.

Before applying the electroless process, the carbon fibre surfaces must be subjected to several treatment processes to remove the organic binder, etching and surface metallization. The surface morphology of the Ni‐P coatings was assessed using a scanning electron microscope (SEM). The chemical compositions of Ni‐P layers were identified by energy dispersive X‐ray analysis (EDS). The bond strength of the coated layer was determined by measuring the electrical resistance at the fibre/coating interface. The magnetic properties of the fibres were estimated using a hysteresis diagram. The tensile performance of single fibres coated by Ni‐P has been investigated with respect to coating thickness.

Pre‐treatment processes are used to improve the adhesion of Ni‐P layers and to obtain homogeneous coatings. The influence of plating parameters (temperature, pH and time) on the coating thickness of the Ni‐P layer was investigated. It was found that the coating thickness increased as the pH value, plating time and the temperature of the bath increased. The results revealed that a complete and uniform Ni‐P coating on fibre could be obtained at optimum conditions 85°C, pH 6, for 60 min, and the results indicated that the P content in the electroless deposit is approximately 3.4 wt%. The tensile strength values are improved significantly after coating and increased by 3‐5 times with increasing of coating thickness from 0.3 to 2 μm.

The results presented in this work are an insight into understanding of the deposition and adherence of Ni‐P thin films on carbon fibre using the electroless technique and behaviour of the coated fibre.

The newsvendor problem is fundamental to many operations management models. The problem focuses on the trade-off between the gains from satisfying demand and losses from unsold products. The newsvendor model and its extensions have been applied to various areas, such as production plan and supply chain management. This chapter examines the study about newsvendor problem. In this research, there is a review of the contributions for the multiproduct newsvendor problem. It focuses on the current literature concerning the mathematical models and the solution methods for the multiitem newsvendor problems with single or multiple constraints, as well as with the risks. The objective of this research is to go over the newsvendor problem and bring into comparison different newsvendor models applied to the flower industry. A few case studies are described addressing topics related to the newsvendor problem such as discounting and replenishment policies, inventory inaccuracies, or demand estimation. Three newsvendor models are put into practice in the field of flower selling. A full database of the flowers sold by an anonymous retailer is available for the study. Computational experiments for practical example have been conducted with use of the CPLEX solver with AMPL programming language. Models are solved, and an analysis of different circumstances and cases is accomplished.

The paper's aim is to predict numerically the contact temperatures between two rough sliding bodies and to compare with the experimental results.

An elastic contact algorithm is used to analyze the normal contact between two nominally smooth surfaces. The algorithm evaluates real contact area using digitized roughness data and the corresponding contact pressure distribution. Using finite element method a steady state 3D temperature distribution at the interface between the sliding bodies is obtained. Using infrared (IR) imaging technique, experiments were carried out to measure the contact temperature distribution between rough rubbing bodies with a systematic variation of surface roughness and operating variables.

Contact temperature distributions over a wide range of normal load, sliding velocity and surface roughness have been obtained. It was seen that the maximum contact temperature expectedly increases with surface roughness (S_a values), normal load and sliding velocity. The results also indicate that the “hot spots” are located exactly at the positions where the contact pressures are extremely high. Temperatures can be seen to fall drastically at areas where no asperity contacts were established. The temperature contours at different depths were also plotted and it was observed that the temperatures fall away from the actual contact zone and relatively high temperatures persist at the “hot spot” zones much below the contact surface. Finally it is encouraging to find a good correlation between the numerical and experimental results and this indicates the strength of the present analysis.

Experimental accuracy can be improved by using a thermal imaging camera that measures emissivity in situ and uses it to find the contact temperature. The spatial resolution and the response time of the camera also need to be improved. This can improve the correlation between numerical and experimental results.

One of the major factors attributed to the failure of sliding components is the frictional heating and the resulting flash temperatures at the sliding interface. However, it is not easy to measure such temperatures owing to the inherent difficulties in accessing the contact zone. Besides, thermal imaging techniques can be applied only with such tribo‐pairs where at least one of the contacting materials is transparent to IR radiation. In practice, such cases are a rarity. However, the good correlation observed between the numerical and experimental results in this work would give the practicing engineer a confidence to apply the numerical model directly and calculate contact temperatures for any tribo‐material pairs that are generally seen around.

A good correlation between the numerical and experimental results gives credence to the fact that the numerical model can be used to predict contact temperatures between any sliding tribo‐pairs.

The purpose of this study is to investigate the effect of the incorporated zirconia (ZrO₂) nanoparticles on the performance of the deposited layer Ni–Cu alloy on steel sheet.

The aim was to produce Ni–Cu–ZrO₂ nanocomposite coatings by electrodeposition technique and estimate the influence of ZrO2 nanoparticles on the performance of Ni–Cu alloy. The surface morphologies and chemical compositions of the deposited layers were assessed using scanning electron microscopy and energy-dispersive X-ray analysis, respectively. Nanoindentation was used as a well-advanced technique for measuring microhardness and Young’s modulus values of different coatings. The corrosion resistance in 3.5 per cent NaCl solution of electrodeposited films has been investigated.

The main conclusion is that the surface morphologies of Ni–Cu–ZrO2 nanocomposite coatings were fine granular compared with Ni–Cu alloy. The corrosion behavior illustrated that the incorporation of ZrO₂ nanoparticles with Ni–Cu film improved the corrosion resistance. Significant improvement was also demonstrated in the hardness of nanocomposite coatings.

The optimized industrial use of steel-coated Ni–Cu alloy with super properties. Consequently, a social benefit can be associated with the reduction in the corrosion rate and increases the microhardness and Young’s modulus.

The results presented in this work are an insight into understanding the incorporation of ceramic reinforcement with metal or alloy films (matrix) on carbon steel using the electrodeposition technique. The development of corrosion resistance of Ni–Cu alloys has been considered as a promising behavior. In this work, a consistent assessment of the results achieved on laboratory scale has been conducted.

This paper aims to report a study of the influence of tungsten carbide (WC) nanoparticles on corrosion resistance properties of electroless nickel–phosphorus (Ni–P) coatings in NaCl solution.

The morphology of Ni–P–WC nanocomposite coatings was observed by scanning electron microscopy (SEM). The anodic polarization curves, electrochemical impedance spectra (EIS) and weight loss measurements were used to study the corrosion resistance properties of Ni–P–WC nanocomposite coatings in NaCl solution.

The WC nanoparticles content in the coatings increased with the increase of its concentration in the bath, and the WC nanoparticles are uniformly distributed in Ni–P alloy matrix. The results showed that the incorporation of WC nanoparticles elevated the corrosion resistance properties of Ni–P alloy matrix.

This study shows that the corrosion resistance was improved by the addition of WC nanoparticles to the Ni–P alloy matrix.

This paper aims to investigate the mechanism of spur gears running-in and to solve the lubrication problems of teeth running-in.

The elastohydrodynamic lubrication (EHL) model considering solid particles was established by applying multi-grid and multiple-grid integration methods to the numerical solution.

In the region where debris settle, transient pressure increases sharply, and a noticeable increase in the running-in load causes a remarkable increase in both the centre and maximum pressures and a slight increase in the minimum film thickness. Roughness wavelength makes a considerable difference to the minimum film thickness at double-to-single tooth transient. A considerable increase in rotation velocity can cause a remarkable reduction in both the centre and maximum pressures but an amazing increase in the minimum film thickness. The effects of roughness amplitude on the maximum pressure are considerably distinct.

Research on EHL of spur gears in the running-in process considering solid particles, surface roughness and time-variant effect is meaningful to practical gears running-in. Thermal effect can be included in the next study.

The analysis results can be applied to predict and improve lubrication performance of the meshing teeth.

The aim is to reduce gears’ manufacture and running-in costs and improve economic performance.

The EHL model that considers solid particles was established. The Reynolds equation was deduced taking the effects of solid particles into account. The EHL of spur gears running-in was investigated considering the time-variant effect, surface roughness, running-in load and rotation speed.

This paper aims to coat ternary composite NiBP-graphite films by Dynamic Chemical Plating “DCP” technique with a growth rate of at least 5 μm/h, which makes this technique a worthy candidate for production of composite films. Electroless nickel plating method can be used to deposit nickel–phosphorous and nickel–boron coatings on metals or plastic surface. However, restrictions such as toxicity, short lifetime of the plating-bath and limited plating rate have limited applications of conventional electroless processes.

DCP is an alternative for producing metallic deposits on non-conductive materials and can be considered as a modified electroless coating process. Using a double-nozzle gun, two different solutions containing the precursors are sprayed simultaneously and separately onto the surface. With this technique, NiBP-graphite films are fabricated and their corrosion and tribological properties are investigated.

With a film thickness of 2 μm, tribological analysis confirms that these coatings have favorable anti-friction and anti-wear properties. Corrosion resistance of NiBP-graphite composite films was investigated, and it was found that graphite incorporation significantly enhances corrosion resistance of NiBP films.

DCP is faster and simpler to perform compared to other electroless deposition techniques. Using a double-nozzle gun, metal salt solution and reducing agents are sprayed to the surface, forming a deposit. Previously, coatings such as Cu, Cu-graphite, Cu-PTFE, Ni-B-TiO2, Ni-P, Ni-B-P and Ni-B-Zn with favorable compactness and adherence by DCP were reported. In this paper, the authors report the application of the DCP technique for depositing NiBP-PTFE nanocomposite films.

This paper seeks to develop a reliable simulation technique and experimental equipment applicable to thermal analysis of disk brakes. The application is focused on safety issues arising in coal mines and other hazardous explosive environments.

The experimental rig provides data on the friction power generated by the disk‐pad pair for a user‐defined squeezing force program. The developed software predicts the temperature field in the brake and pad. The code is based on the finite volume approach and is formulated in Lagrangian coordinates frame.

In the circumferential direction advection due to the rotation of the disk dominates over the conduction. The energy transfer problem could be formulated in a Lagrange coordinates system as 2D. A novel approach to the estimation of the uncertainty of numerical simulations has been proposed. The technique is based on the GUM methodology and uses sensitivity coefficients determined numerically. Very good agreement of simulated and measured values of temperature in the brake has been found.

The results apply for simple disk and pad geometries for which the correlations of the Nusselt number versus Reynolds and Prandtl are known. Moreover, the model should not be used in the last braking period where the assumption of negligible circumferential conduction is not applicable. Though the code models a situation of constant rotation speed, the deceleration profile of the disk can readily be accounted for. The next step of the research should be to couple the heat conduction in the brake with CFD simulation of the surrounding air.

The highest temperature in the system is at the pad‐disk interface. The depth of penetration of the temperature into the disk is relatively low. The heat dissipation from the disk is controlled by convection.

The novelty of the paper is in the simplified and robust simulation model of the brake, the concept of the experimental rig and the methodology of uncertainty assessment. The developed methodology can be useful to researchers and industry involved in safety investigations and determining safety standards, specifically in explosive atmospheres. It may also be of interest to the automotive industry.

The purpose of this paper is to investigate the effect of TiO₂ nanoparticle content on the corrosion behavior of Ni‐Cr/TiO₂ nanocomposite coatings applied by pulse‐reverse electroplating.

Ni‐Cr/TiO₂ nanocomposite coatings with various contents of TiO₂ nanoparticles were electrodeposited by pulse‐reverse method from a bath containing TiO₂ nanoparticles to be codeposited and citric acid as the complexing agent. The surface morphology and the composition of coatings were studied by scanning electron microscopy (SEM) equipped by energy dispersive X‐ray system (EDS). The corrosion performance of coatings in the 0.5 M NaCl as a corrosive solution was investigated by potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) methods.

It was found that the surface of Ni‐Cr/TiO₂ nanocomposite coatings showed a finer structure that was more uniform and compact in appearance than was that of Ni‐Cr coatings. The incorporation of TiO₂ nanoparticles in the alloy coating matrix improved the corrosion performance of the coatings and the higher content of nanoparticles gave better corrosion resistance.

Applying the Ni‐Cr coatings by the pulse‐reverse plating method eliminated cracks that were a problem in the Ni‐Cr alloy coating structure. Furthermore, the corrosion resistance was improved by the addition of TiO₂ nanoparticles to the alloy matrix. This paper reports the optimum plating conditions that gave the better corrosion performance.

The purpose of this paper is to propose a simple physical evaporation route in which catalyst‐free zinc oxide (ZnO) nanoscrewdrivers were deposited on silicon (Si) (111) substrates.

Prior to the deposition, the Si (111) wafer was cut into pieces of 2×2 cm². Then, the wafers were dipped for 1 min into mixture buffered oxide etchant to remove native oxide. Then, the samples were rinsed in an ultrasonic bath cleaned with boiling acetone, ethanol, and de‐ionized (DI) water for 10 min. Lastly, the wafers were rinsed in 25 ml DI water in stirred and then were blown dry with nitrogen. In this technique, the starting material is high‐purity metallic zinc (Zn) powder (99.99 per cent pure). Following, the Zn films were then annealed under air environment in the furnace at 500°C for 1 h deprived of any catalysts.

These ZnO samples were studied by scanning electron microscopy, high‐resolution X‐ray diffraction (HR‐XRD), and photoluminescence (PL) spectroscopy. Atomic force microscope (AFM) images were applied to ascertain surface morphology of produced ZnO nanoscrewdrivers. XRD pattern confirmed that the ZnO nanoscrewdrivers were of polycrystalline structure in universe with a hexagonal close packed type and c‐axis is perpendicular to the substrate. The peak at 34° correspond to the reflection planes of ZnO(002) crystallographic plane is perceived. The AFM surface images disclosed that the surfaces of produced ZnO thin films are not smooth. The PL spectrum of as‐synthesized nanoscrewdrivers shows a UV emission peak at 380 nm and a broad green emission peak at 500 nm.

The paper reports on a simple physical evaporation route, ZnO nanoscrewdrivers were synthesized via the thermal evaporation of the high‐purity Zn powders and annealed at 500°C under air atmosphere without introducing any hetero‐metal catalysts or other carrier gases approach.