Development of a new additive for improving machinability of PM steels

Tableau d'honneur de la Faculté des études supérieures et postdoctorales, 2017-2018Bien que la métallurgie des poudres (MP) soit connue comme un méthode de fabrication aux cotes presque finales, un volume ignificatif de pièces MP nécessitent que l’on ait recours à une opération d’usinage. Les opérations d'usinage secondaires sont habituellement requises pour la conformité dimensionnelle ou la production de caractéristiques géométriques compliquées qui ne peuvent pas être obtenues par le procédé de pressage. Cependant, en raison de la présence de porosité, l'usinabilité des pièces en aciers MP est difficile en comparasion aux aciers corroyés et peut ajouter 20% ou plus au coût total de fabrication de ces pièces. Parmi les diverses mesures connues pour améliorer l'usinabilité des aciers MP, l'utilisation d'additifs d'usinage, soit pré-mélangés, soit préalliés, est de loint la méthode la plus utilisée. Il existe des dizaines d'éléments et de composés différents qui peuvent améliorer l'usinabilité à différents niveaux. Néanmoins, leurs effets négatifs sur d'autres propriétés des aciers MP tels que les propriétés mécaniques et la résistance à la corrosion rendent leur utilisation peu intéressante. Dans cette étude, des particules de graphite libre sont présentées comme un nouvel additif qui non seulement améliore significativement l'usinabilité des aciers MP, mais le fait sans affecter de façon notable les propriétés mécaniques et la résistance à la corrosion. Il a été démontré qu'il est possible d'obtenir des particules de graphite libres dans un acier MP par enrobage de celles-ci. Cet enrobage permet d’empêcher le graphite de diffuser dans la matrice de fer pendant le frittage. Dans cette étude, des particules de graphite enrobées de nickel ont été recouvertes de cuivre par le procédé de cémentation. Un traitement thermique a ensuite été réalisé sur ce nouveau matériau afin d’obtenir un revêtement plus uniforme. Les résultats des essais de caractérisation mécanique sur des échantillons frittés (FC-0208) contenant des particules prémélangées de graphite enrobées de cuivre / nickel, soit traitées thermiquement ou non, montrent que ce nouvel additif ne détériore pas les propriétés mécaniques statiques et dynamiques des aciers MP. De plus, la résistance à la corrosion des échantillons contenant cet additif se révèle être la même que celle des échantillons sans additif. Les effets de l’additif non traité thermiquement et traité thermiquement sur l'usinabilité des aciers MP ont également été caractérisés en utilisant un opration de perçage. Les résultats obtenus montrent que ce nouvel additif peut améliorer significativement l'usinabilité en réduisant la force de coupe requise.Although powder metallurgy (PM) is known as a near-net-shape fabrication method, noticeable amount of PM parts need some sort of machining. Secondary machining operations are usually required for dimensional conformance or producing complicated geometrical features that cannot be achieved at the compaction stage. However, due the presence of porosity, machinability of PM steels is difficult compared to wrought steels and can add 20% or more to the overall fabrication cost of PM parts. Thus, improving machinability of PM steels can definitely reduce their production costs. Among the various measures known to improve machinability of PM steels, addition of machining aids, either as admixed or pre-alloyed, is the most popular one. There are tens of different elements and compounds that can improve machinability at different levels. Nevertheless, their negative effects on other properties of PM steel components, such as mechanical properties and corrosion resistance, make their utilization somewhat limited. In this study, free graphite particles are introduced as a new additive that not only significantly improve machinability of PM steels, but also does not affect the mechanical and corrosion properties. It was found that it is possible to have free graphite particles in a PM steel, sintered using conventional sintering conditions, by coating the graphite particles. This coating can prevent graphite from diffusing into the iron matrix during sintering. In this research, nickel coated graphite particles were coated with copper through cementation process. A heat treatment was then performed on this newly developed material to have a more uniform single layer coating. The results of mechanical characterization tests on the copper steel sintered samples containing admixed copper/nickel coated graphite particles, either in the form of non-heat-treated or heat-treated, showed that this new additive does not deteriorate static and dynamic mechanical properties of PM steels. Moreover, the corrosion resistance of the samples containing copper/nickel coated graphite was found to be the same as samples without additive. The effects of non-heat-treated and heat-treated copper/nickel coated graphite on machinability of PM steels were also characterized using drilling test. It was seen that this new additive can significantly improve machinability through reducing the required cutting force

Electronic Service Quality, Product Type, and Impulse Online Buying; A Field Experiment

Impulse buying is an unintended and persuasive purchasing behavior. It is estimated that 40% of online buying is due to impulse behavior (Chan, Cheung, and Lee 2017). Despite the increasing importance of online buying for businesses, our understanding of the topic is limited in two ways. First, online buying and impulsiveness are understudied. Although impulse buying has been studied extensively, it has received limited attention in online settings (Akram et al. 2018). The majority of the published papers in an online context are focused on rational and planned buying behavior rather than impulse behavior (Liao et al. 2016). Second, a limited number of factors and their effect on customer behavior have been studied in online shops (Ladhari 2010). Extant literature examined the impact of the design of online shops, types of products, and the presentation of products on customers’ impulse buying behavior. The emphasis of past research is on the technical aspects of a website rather than overall electronic service quality (ESQ). There are different ESQ factors, including operational related factors (e.g., shipping, return policies, etc.), seller related factors (ratings), and pricing related factors (billing accuracy) that are neglected in the past studies. To address the two mentioned gaps, we study customers’ impulse online buying behavior through the identification of critical ESQ parameters that affect customer decisions. We focus on the impulse online buying behavior of customers and use cognitive emotion theory to analyze the behavior of customers in response to the ESQ stimulus provided by online shops. To develop the research, we conduct a comprehensive literature analysis to identify ESQ factors and to develop a research model underlying customers’ impulse online buying behavior. We will conduct a field experiment and an online survey to explore the effect of different factors on impulse buying behavior of online buyers. We will collect data from customers of two online shops on eBay. Each of these stores has multiple products from different product categories. The data will be analyzed based on the design of experiment (DOE) and appropriate structured equation modeling methods. The findings of this research can have important implications for practitioners. The identified ESQ factors assist online shops in enhancing their performance efficiently by focusing on and investing in areas with practical importance

Predictive analytics in agribusiness industries

Agriculturally related industries are routinely among the most hazardous work environments. Workplace injuries directly impact labor-market outcomes including income reduction, job loss, and health of the injured workers. In addition to medical and indemnity costs, workplace incidents include indirect costs such as equipment damage and repair, incident investigation time, training new personnel for replacement of the injured ones, an increase in insurance premiums for the year following the incidents, a slowdown of production schedules, damage to companies’ reputation, and lowering the workers’ motivation to return to work. The main purpose of incident analysis is the derivation and development of preventative measures from injury data. Applying proper analytical tools aimed at discovering the causes of occupational incidents is essential to gain useful information that contributes in preventing those incidents in future. Insight gained from the analyses of workers’ compensation data can efficiently direct preventative activities at high-risk industries. Since incidents arise from a combination of factors rather than a single cause, research on occupational incidents must go deeper into identifying the underlying causes and their relationship through applying more comprehensive analyses. Therefore, this study aimed at identifying underlying patterns in occupational injury occurrence and costs using data mining and predictive modeling techniques instead of traditional statistical methods. Utilizing a workers’ compensation claims dataset, the objectives of this study were to: investigate the use of predictive modeling techniques in forecasting future claims costs based on historical data; identify distinctive patterns of high-cost occupational injuries; and examine how well machine learning methods work in finding the predictive relationship between factors influencing occupational injuries and workers’ compensation claims occurrence and severity. The results lead to a better understanding of injury patterns, identification of prevalent causes of occupational injuries, and identification of high-risk industries and occupations. Therefore, various stakeholders such as policymakers, insurance companies, safety standard writers, and manufacturers of safety equipment can use the findings of the study to plan for remedial actions and revise safety standards. The implementation of safety measures by agribusiness organizations can prevent occupational injuries, save lives, and reduce the occurrence and cost of such incidents in agricultural work environments

A conductometric study on the effect of solvent upon complex formation between kryptofix22dd with Ho3+ metal cation in organic solvents

The complexation reaction between Ho3+ cation with macrocyclic ligand kryptofix22DD was studied in ethyl acetate (EtOAC), methanol (MeOH), propylene carbonate (PC), tetrahydrofuran (THF) at different temperatures by coductometric method. Kryptofix22DD forms a 1:1 complex with Ho3+ cation. The stability of (kryptofix22DD.Ho)3+ complex changes with the type of the organic solvents and also with temperature. The stability constant of the complex in the non-aqueous solvents varies in order: EtOAC ≥ THF > PC ≥ MeOH. By plotting the van’t Hoff diagrams, the values of standard thermodynamic parameters such as enthalpy (∆H°c), entropy (∆S°c) and Gibbs free energy (ΔG°C), for formation of (kryptofix22DD.Ho)3+ complex were obtained. The results showed that the entropy and enthalpy of complexation reaction between kryptofix22DD with Ho3+ metal cation depend on the nature of the solvents.               KEY WORDS: Kryptofix22DD, Ho3+ cation, Organic solvents, Complexation, Conductometry Bull. Chem. Soc. Ethiop. 2019, 33(2), 277-284.DOI: https://dx.doi.org/10.4314/bcse.v33i2.

Modeling Dendritic Solidification using Lattice Boltzmann and Cellular Automaton Methods

This dissertation presents the development of numerical models based on lattice Boltzmann (LB) and cellular automaton (CA) methods for solving phase change and microstructural evolution problems. First, a new variation of the LB method is discussed for solving the heat conduction problem with phase change. In contrast to previous explicit algorithms, the latent heat source term is treated implicitly in the energy equation, avoiding iteration steps and improving the formulation stability and efficiency. The results showed that the model can deal with phase change problems more accurately and efficiently than explicit LB models. Furthermore, a new numerical technique is introduced for simulating dendrite growth in three dimensions. The LB method is used to calculate the transport phenomena and the CA is employed to capture the solid/liquid interface. It is assumed that the dendritic growth is driven by the difference between the local actual and local equilibrium composition of the liquid in the interface. The evolution of a threedimensional (3D) dendrite is discussed. In addition, the effect of undercooling and degree of anisotropy on the kinetics of dendrite growth is studied. Moreover, effect of melt convection on dendritic solidification is investigated using 3D simulations. It is shown that convection can change the kinetics of growth by affecting the solute distribution around the dendrite. The growth features of twodimensional (2D) and 3D dendrites are compared. Furthermore, the change in growth kinetics and morphology of Al-Cu dendrites is studied by altering melt undercooling, alloy composition and inlet flow velocity. The local-type nature of LB and CA methods enables efficient scaling of the model in petaflops supercomputers, allowing the simulation of large domains in 3D. The model capabilities with large scale simulations of dendritic solidification are discussed and the parallel performance of the algorithm is assessed. Excellent strong scaling up to thousands of computing cores is obtained across the nodes of a computer cluster, along with near-perfect weak scaling. Considering the advantages offered by the presented model, it can be used as a new tool for simulating 3D dendritic solidification under convection

Factor Analysis and Yield Optimization of a Billet Manufacturing Process: A Case Study

A Thesis Presented to the Faculty of the College of Business and Technology Morehead State University in Partial Fulfillment of the Requirements for the Degree Master of Science by Fatemeh Davoudi Kakhki on April 22, 2016

Optimization of Anthocyanin Extraction from Saffron Petals with Response Surface Methodology

Optimum extraction conditions of anthocyanins from petals of saffron (Crocus sativus) using acidified ethanol as the solvent were revealed. The investigated factors were solvent to sample ratio (20:1–80:1), ethanol concentration (%), extraction temperature (25–45 °C), and time (8–24 h). Response surface methodology with Box–Behnken design was applied to determine optimum processing conditions leading to maximum extraction efficiency (mg cyanindin-3-glucoside/l). Obtained coefficients of variance showed that the linear effect of temperature was more pronounced for extraction yield than three other variables at 5 % level. Optimum extraction conditions that maximize the extracted anthocyanins were found to be a ratio of solvents to sample 20 ml/g, ethanol concentration of 25.02 %, temperature 25.8 °C, and extraction time 24 h which gave 1609.11 mg/l anthocyanins. A quadratic regression equation describing the effects of independent process variables on anthocyanin extraction from saffron petals can be used for finding optimum conditions to achieve desired extraction yield in similar conditions. © 2015, Springer Science+Business Media New York

A critical analysis of Iranian buy-back transactions in the context of international petroleum contractual systems

This research critically examines the Iranian petroleum contractual system from its birth to the present, and considers its future evolution. Initially, it reviews the development of oil contracts, from the early concessions until the annulment of all obligations as the result of two major events; the Nationalisation Movement and the Islamic Revolution of 1979. The constant policy struggle between the need for foreign funding and technology in the oil industry on one hand and the desire to avoid foreign exploitation on the other is analysed in terms of its impact on the current stance towards foreign investment and the formation of the present contractual model. The embodiment of this complex struggle is the buy-back contractual model that has found widespread use in Iranian petroleum transactions since 1989. This scheme is best described as a short term risk service agreement, whereby the foreign investor provides the funds for petroleum Exploration and Exploitation in exchange for a pre-defined, volume-based quantum of remuneration in case of successful production that serves to both compensate and reward the contractor. The adoption of this system is a compromise solution between the need for foreign capital, expertise and services on one hand and wariness of foreign involvement in natural resources on the other, as evident from the Constitutional limitations discussed later in this study. A crucial element of this arrangement is the transfer of the field's operation back to the National Iranian Oil Company following conclusion of the contract; a legal step which distinguishes buyback contracts from alternative systems that may be contrary to the Constitution. Both the structure and the comparative advantages of the buy-back have been discussed at length, with particular attention to the enabling laws and their flaws. Detailed analysis is devoted to the other major international contractual models, including a comparative evaluation of these alternative systems and their suitability for the Iranian oil industry, given the limitations of the Constitution. The buy-back system is scrutinised from both the foreign and the domestic perspective and the issue of whether revision of its terms or an alternative model would be more appropriate considering the grievances of all the participants. The extent to which the Iranian oil industry was and will be affected by increasing international pressure, particularly as the result of US Sanctions, was considered extensively. It appears that Iran is not yielding to such pressure but rather orienting itself towards alternative allies and continuing to sign contracts based on the buy-back. Particularly stringent examination of specific terms and conditions of buy-back has been conducted through a review of various oil fields so as to determine if the model's perceived flaws manifest themselves in reality. The finding of the analysis described above is that the buy-back contract as implemented in Iran is flawed on basis of the limiting nature of its provisions rather than by virtue of the model itself. A number of provisions, such as maximum contract length and method of remuneration, which are needlessly restrictive, are highlighted and the importance of modernising them in light of the current economic environment is noted. Based on the facts and findings throughout the study, the conclusion arises that evolutionary rather than revolutionary reforms are both required and viable, without undermining the current legal framework. Lastly, the study yields a practical recommendation as to the reforms most crucial to the preservation of Iran's attractiveness to investors, in light of the current economic, political and legal environment