INVESTIGATION OF TUNGSTEN SURFACE CARBIDIZATION UNDER PLASMA IRRADIATION

This paper presents the results of a study of the formation of a carbidized layer under various experimental conditions and the choice of optimal parameters for carbidization of a tungsten surface under plasma irradiation. To study the effect of the surface temperature of a tungsten sample and the duration of plasma irradiation, experiments were carried out at a sample surface temperature of 1300 °C and 1700 °C with an irradiation duration of 300–2400 s. Analysis of the research results showed that the maximum formation of W2C on the surface is observed at a test temperature of 1700 °C. At a temperature of 1300 °C, the phase composition of the carbidized layer depends on the duration of plasma irradiation. According to the literature analysis, the formation of WC occurs on the surface of tungsten, from which C diffuses into the particle and forms the underlying layer of W2C. With an increase in the ion fluence, depending on the irradiation time and the temperature of the sample surface, the diffusion of C into W accelerates, the WC content decreases, and W2C becomes the dominant carbide compound.

Modelling the Yield Stress of Fly-Ash Added Superplasticized Cement Paste at Different Temperatures Using Artificial Neural Network

Rheology is the science that concerns the flow of liquids, and the distortion of solids under an applied force. The study of the rheology of concrete determines the properties of fresh concrete. The rheological parameters are affected by temperature, stress conditions and several other factors. The main intention of this research is to model the rheological parameters of the fly ash incorporated cement with various types of superplasticizers exposed under different temperatures using an Artificial Neural Network. Test data were generated by performing rheological tests on cement paste at three distinct temperatures (15, 27, 35°C). Mixes were prepared using OPC, fly ash (15, 25, 35%) and superplasticizers of four different families. By conducting experiments, 252 data have been generated by modifying the combination of fly-ash, superplasticizer, and test temperature. Among the 252 data, 80% has been utilized for training and 20% is utilized for predicting the model’s accuracy. The input layer of the model consists of test temperature, the amount of fly ash replaced, cement and water content, and four different groups of superplasticizers. The cement paste’s yield stress was the output parameter of the model. The model generated data has been compared with the experimentally generated data to determine the accuracy of the model.Keywords: Rheology, Fly Ash, Superplasticizer, Temperature, ANN

Linking biodegradation kinetics, microbial composition and test temperature – Testing 40 petroleum hydrocarbons using inocula collected in winter and summer

Experiments linked temperature, biodegradation kinetics and microbial composition. Biodegradation kinetics and microbial composition were similar for summer and winter inoculum but markedly affected by test incubation.

Using Computational Modelling to Study Extensional Rheometry Tests for Inelastic Fluids

The present work focuses on the extensional rheometry test, performed with the Sentmanat extensional rheometer (SER) device, and its main objectives are: (i) to establish the modelling requirements, such as the geometry of the computational domain, initial and boundary conditions, appropriate case setup, and (ii) to investigate the effect of self-induced errors, namely on the sample dimensions and test temperature, on the extensional viscosity obtained through the extensional rheometry tests. The definition of the modelling setup also comprised the selection of the appropriate mesh refinement level to model the process and the conclusion that gravity can be neglected without affecting the numerical predictions. The subsequent study allowed us to conclude that the errors on the sample dimensions have similar effects, originating differences on the extensional viscosity proportional to the induced variations. On the other hand, errors of a similar order of magnitude on the test temperature promote a significant difference in the predicted extensional viscosity.

Tensile and shear strength for a self-drilling screw and transition of failure-modes and shear-strengths for self-drilling screwed connections at elevated-temperatures

PurposeThe purpose of this study is to clarify both tensile and shear strength for self-drilling screws, which are manufactured from high-strength, martensitic-stainless and austenitic stainless-steel bars, and the load-bearing capacity of single overlapped screwed connections using steel sheets and self-drilling screws at elevated temperatures.Design/methodology/approachTensile/shear loading tests for the self-drilling screw were conducted to obtain basic information on the tensile and shear strengths at elevated temperatures and examine the relationships between both. Shear loading tests for the screwed connections at elevated temperatures were conducted to examine the shear strength and transition of failure modes depending on the test temperature.FindingsThe tensile and shear strengths as well as the reduction factors at the elevated temperature for each steel grade of the self-drilling screw were quantified. Furthermore, either screw shear or sheet bearing failure mode depending on the test temperature was observed for the screwed connection.Originality/valueThe transition of the failure modes for the screwed connection could be explained using the calculation formulae for the shear strengths at elevated temperatures, which were proposed in this study.

The tribological performance of W-DLC in solid–liquid lubrication system addivated with Cu nanoparticles

Judicious selection of additives having chemical and physical compatibility with the DLC films may help improving the triboligical properties and durability life of DLC-oil composite lubrication systems. In this study, Cu nanoparticles were added to PAO6 base oil to compose a solid-liquid composite lubrication system with W-DLC film. The effects of nanoparticle concentration, test temperature and applied load on tribological performance were systematically studied by a ball-on-disk friction test system. The tribological results illustrated that Cu nanoparticles could lower the coefficient of friction (COF) and dramatically reduce the wear rates of W-DLC films. The optimal tribological behavior was achieved for the 0.1 wt.% concentration under 30 ℃ and the applied load of 100 N. The test temperature and applied load were vital influencing factors of the solid–liquid lubrication system. The bearing effect and soft colloidal abrasive film of spherical Cu nanoparticle contributed to the excellent tribological performance of the composite lubrication system under mild test conditions, meanwhile, the local delamination of W-DLC film and oxidation were the main causes of the friction failure under harsh test conditions. With test temperature and applied loads increase the degree of graphitization of the W-DLC film increased. In conclusion, there are several pivotal factors affecting the tribological performance of solid–liquid lubrication systems, including the number of nanoparticles between rubbing contact area, graphitization of the worn W-DLC films, tribofilms on the worn ball specimens and oxidation formed in friction test, and the dominant factor is determined by the testing condition.

Quasi-static perforation response of inter-ply hybrid polypropylene composites at various temperatures

This study is motivated by the lack of knowledge in the research of mechanical characterization of thermoplastic composites (TPCs) with additional fiber hybridization. To enhance the mechanical properties of long glass fiber-reinforced polypropylene (PP) composite, hybridization via alkaline-treated aramid and carbon fabrics is performed. High performance fabrics modified with 10 wt.% sodium hydroxide (NaOH) aqueous solution are incorporated into the PP composite as reinforcements. Herewith, four arrangements (hybrid composites) for two different reinforcements and two different stacking configurations and the monolithic composite are separately investigated in terms of quasi-static perforation behavior. Failure mechanisms are also evaluated at macro level by visual observations and micro scales through a scanning electron microscopy (SEM). The experimental results provide a basis for selecting fiber-enabled hybridization and lay-up configuration with improved perforation resistance. Moreover, the influence of test temperature is reported for three different values as 20°C, 60°C, and 100°C. Based upon the results, the maximum penetration force of hybrid configuration with single-layered aramid fabric reinforcements is approximately 15.5% higher than that of single-layered carbon fabric reinforcements at 60°C test temperature. It is further observed that the absorbed energy improves as the number of fabrics is increased in both aramid and carbon reinforcements. The test temperatures significantly affect the failure mechanisms of TPCs. A smaller damaged area at the penetrated faces of the hybrid structures is obtained by comparison with the monolithic TPCs.