Heat generation during plunge stage in friction stir welding

This paper deals with the heat generation in the Al alloy Al2024-T3 plate under different rotating speeds and plunge speeds during the plunge stage of friction stir welding (FSW). A three-dimensional finite element model (FEM) is developed in the commercial code ABAQUS/Explicit using the arbitrary Lagrangian-Eulerian formulation, the Johnson-Cook material law and Coulomb’s Law of friction. The heat generation in FSW can be divided into two parts: frictional heat generated by the tool and heat generated by material deformation near the pin and the tool shoulder region. Numerical results obtained in this work indicate a more prominent influence from the friction-generated heat. The slip rate of the tool relative to the workpiece material is related to this portion of heat. The material velocity, on the other hand, is related to the heat generated by plastic deformation. Increasing the plunging speed of the tool decreases the friction-generated heat and increases the amount of deformation-generated heat, while increasing the tool rotating speed has the opposite influence on both heat portions. Numerical results are compared with the experimental ones, in order to validate the numerical model, and a good agreement is obtained

Comparation of mechanical behaviour of SiC sintered specimen to analysis of surface defects

This research examined SiC sintered specimens with high hardness and strength. This material is used to protect of projectile impact for military purposes. The testing procedure consists of structure examination obtained using XRD analysis, surface examination by SEM analysis and optical microscopy, examination of mechanical properties and density determination. Analysis confirmed surface irregularities characterized using image analysis. The sample is subjected to bending. Finite element modeling was used to simulate the behavior of sample subjected to bending in presence of critical damage on surface. It is confirmed that there is correlation between the largest irregularities determined on surface and measured strength of sample. Simulations show the significance of damage size. The size of damage on surface is considered to be the critical parameter for quality determination.Program and the book of abstracts available at: [https://dais.sanu.ac.rs/handle/123456789/175

Surface properties of magnetite in high temperature aqueous electrolyte solutions: A review

Deposits and scales formed on heat transfer surfaces in power plant water/steam circuits have a significant negative impact on plant reliability, availability and performance, causing tremendous economic consequences and subsequent increases in electricity cost. Consequently, the improvement of the understanding of deposition mechanisms on power generating surfaces is defined as a high priority in the power industry. The deposits consist principally of iron oxides, which are steel corrosion products and usually present in colloidal form. Magnetite (Fe3O4) is the predominant and most abundant compound found in water/steam cycles of all types of power plants. The crucial factor that governs the deposition process and influences the deposition rate of magnetite is the electrostatic interaction between the metal wall surfaces and the suspended colloidal particles. However, there is scarcity of data on magnetite surface properties at elevated temperatures due to difficulties in their experimental measurement. In this paper a generalized overview of existing experimental data on surface characteristics of magnetite at high temperatures is presented with particular emphasis on possible application in the power industry. A thorough analysis of experimental techniques, mathematical models and results has been performed and directions for future investigations have been considered. The state-of-the-art assessment showed that for the characterization of magnetite/aqueous electrolyte solution interface at high temperatures acid-base potentiometric titrations and electrophoresis were the most beneficial and dependable techniques which yielded results up to 290 and 200 degrees C, respectively. Mass titrations provided data on magnetite surface charge up to 320 degrees C, however, this technique is highly sensitive to the minor concentrations of impurities present on the surface of particle. Generally, fairly good correlation between the isoelectric point (pH(iep)) and point of zero charge (pH(pzc)) values has been obtained. All obtained results showed that the surface of magnetite particles is negatively charged in typical high temperature thermal power plant water, which indicates the low probability of aggregation and deposition on plant metal surfaces. The results also gave strong evidence on decline of pHiep and pHpzc with temperature in the same manner as neutral pH of water. The thermodynamic parameters of magnetite surface protonation reactions were in good agreement with each other and obtained using one site/two pK and mainly one site/one pK model. All collected data provided evidences for interaction between particles, probability of deposition and eventual attachment to the steel surface at various pH and temperatures and can serve as a foundation for future surface studies aimed at optimizing plant performances and reducing of magnetite deposition. In future works it would be indispensable to provide the surface experimental data for extended temperature ranges, typical solution chemistries and metal surfaces of power plant structural components and thus obtain entire set of results useful in modeling the surface behavior and control of deposition process in power reactors and thermal plant circuits. Moreover, the acquired results will be applicable and greatly valuable to all other types of power plants, industrial facilities and technological processes using the high temperature water medium

Bucket wheel excavator Integrity assessment of the bucket wheel boom tie-rod welded joint

The bucket wheel boom tie-rods are vital structural parts of the bucket wheel excavators (BWE) Their failures inevitably cause BWE collapse and are followed among other things by a substantial financial loss (millions of E) Non-destructive testing revealed a flaw in the butt welded Joint of the body and eye-plate of the bucket wheel tie-rod Its size exceeds the level allowed by current technical regulations An integrity assessment of the bucket wheel tie-rod has been carried out i e the remaining fatigue life has been determined based on the stress-state characteristics in the welded Joint and defined by experimental research in real working conditions The calculation results show that despite the excessive size of the internal flaw the welded Joint integrity is not compromised During periodical inspections of the welded joint in the past two years (BWE was put into operation in December 2007) changes that could compromise the structural integrity were not observed In this way by using a fail-safe philosophy design a considerable financial saving (ca 1 600 000 (sic)) was achieved while at the same time there was no threat to the worker s safety and life the safety of the machine and the production process in the open pit min

Bucket wheel excavator Integrity assessment of the bucket wheel boom tie-rod welded joint

The bucket wheel boom tie-rods are vital structural parts of the bucket wheel excavators (BWE) Their failures inevitably cause BWE collapse and are followed among other things by a substantial financial loss (millions of E) Non-destructive testing revealed a flaw in the butt welded Joint of the body and eye-plate of the bucket wheel tie-rod Its size exceeds the level allowed by current technical regulations An integrity assessment of the bucket wheel tie-rod has been carried out i e the remaining fatigue life has been determined based on the stress-state characteristics in the welded Joint and defined by experimental research in real working conditions The calculation results show that despite the excessive size of the internal flaw the welded Joint integrity is not compromised During periodical inspections of the welded joint in the past two years (BWE was put into operation in December 2007) changes that could compromise the structural integrity were not observed In this way by using a fail-safe philosophy design a considerable financial saving (ca 1 600 000 (sic)) was achieved while at the same time there was no threat to the worker s safety and life the safety of the machine and the production process in the open pit min

Influence of Chitosan Coating on Mechanical Stability of Biopolymer Carriers with Probiotic Starter Culture in Fermented Whey Beverages

The aim of this study was to improve the mechanical stability of biopolymer carriers and cell viability with addition of chitosan coating during fermentation process and product storage. Dairy starter culture (1% (w/v)) was diluted in whey and mixed with sodium alginate solution and the beads were made using extrusion technique. The mechanical stability of coated and uncoated beads, the release behavior, and the viability of encapsulated probiotic dairy starter culture in fermented whey beverages were analyzed. The mechanical properties of the beads were determined according to force-displacement and engineering stress-strain curves obtained after compression testing. It was observed that addition of chitosan as a coating on the beads as well as the fermentation process increased the elastic modulus of the calcium alginate-whey beads and cell survival. The current study revealed that the coating did not significantly improve the viability of probiotics during the fermentation but had an important influence on preservation of the strength of the carrier during storage. Our results indicate that whey-based substrate has positive effect on the mechanical stability of biopolymer beads with encapsulated probiotics

Anodization of Ti-Based Materials for Biomedical Applications: a Review

Commercially pure titanium (cpTi) and titanium alloys are the most commonly used metallic biomaterials. Biomedical requirements for the successful usage of metallic implant materials include their high mechanical strength, low elastic modulus, excellent biocompatibility and high corrosion resistance. It is evident that the response of a biomaterial implanted into the human body depends entirely on its biocompatibility and surface properties. Therefore, in order to improve the performance of biomaterials in biological systems modification of their surface is necessary. One of most commonly used method of implant materials surface modification is electrochemical anodization and this method is reviewed in the present work. Aim of the presented review article is to explain the electrochemical anodization process and the way in which the nanotubes are formed by anodization on the metallic material surface. Influence of anodizing parameters on the nanotubes characteristics, such as nanotube diameter, length and nanotubular layer thickness, are described, as well as the anodized nanotubes influence on the material surface properties, corrosion resistance and biocompatibility

The effect of T4 heat treatment on the microstructure and corrosion behaviour of Zn27Al1.5Cu0.02Mg alloy

The effect of heat treatment on the microstructure and corrosion behaviour of Zn27Al1 5CuO 02Mg alloy was examined The alloy was prepared by melting and casting route and then thermally processed (T4 regime) Corrosion behaviour of the as-cast and heat treated alloy was studied in 3 5 wt % NaCl solution using immersion method and electrochemical polarization measurements The applied heat treatment affected the alloy microstructure and resulted in increased ductility and higher corrosion resistance of the heat treated alloy Electrochemical measurements of the corrosion rate at the free corrosion potential are in agreement with the results obtained using the weight loss method 2010 Elsevier Ltd All rights reserve

Effect of the pH of artificial saliva on ion release from commercially pure titanium

Due to their excellent characteristics, such as chemical inertness, mechanical resistance, low Young’s modulus, high corrosion resistance, and outstanding biocompatibility, titanium and its alloys are the most used metallic materials for biomedical applications. In dental practice, these materials have demonstrated success as biomedical devices which are used for repairing and replacing failed hard tissue. However, the oral cavity is constantly subjected to the changes in the pH value changes and such an environment is strongly corrosive for titanium dental implants. The objective of this study was to examine ion release from commercially pure titanium (cpTi) in artificial saliva with different pH values (4.0, 5.5 and 7.5). The concentrations of released titanium ions were determined after 1, 3 and 6 weeks using Inductively Coupled Plasma - Mass Spectrometry. The results indicate that the ion release from commercially pure titanium in the artificial saliva is dependent both on the pH of artificial saliva and duration of immersion. [Projekat Ministarstva nauke Republike Srbije, br. III46010 i br. ON 174004