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Träfflista för sökning "LAR1:ltu srt2:(2020);pers:(Prakash Braham)"

Sökning: LAR1:ltu > (2020) > Prakash Braham

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1.
  • Gebretsadik, Daniel, et al. (författare)
  • Friction and wear characteristics of PA 66 polymer composite/316L stainless steel tribopair in aqueous solution with different salt levels
  • 2020
  • Ingår i: Tribology International. - : Elsevier. - 0301-679X .- 1879-2464. ; 141
  • Tidskriftsartikel (refereegranskat)abstract
    • Friction and wear behaviour of a PA 66 composite with 25% glass fibre reinforcement sliding against a 316L stainless steel have been investigated using different aqueous solutions under mixed/boundary lubrication. The aqueous solutions used are deionized water, seawater, seawater without group II metal salts, solution of dissolved Group II metal salts and solution of group II metal salts and NaHCO3. Lower friction and wear was obtained when lubricated with seawater. However, when deionized water or salt solutions without group II metal salts is used, increased wear was observed. The lower friction and wear in seawater solution is due to group II metal ions and bicarbonate ions that facilitate formation of the sparingly soluble carbonates that act as a lubricating tribofilm.
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2.
  • Hultqvist, Tobias, 1991-, et al. (författare)
  • Transient analysis of surface roughness features in thermal elastohydrodynamic contacts
  • 2020
  • Ingår i: Tribology International. - : Elsevier. - 0301-679X .- 1879-2464. ; 141
  • Tidskriftsartikel (refereegranskat)abstract
    • Understanding the influence of surface roughness in elastohydrodynamically lubricated (EHL) contacts is essential to improve durability and friction performance of machine elements employing non-conformal contacting surfaces. In this work, the transient event of a surface feature passing through a thermal EHL line contact operating under different sliding conditions is investigated with the purpose of providing a deeper understanding of surface roughness influence. This is achieved by solving the EHL problem in space and time. It was seen that sliding influences the temperature rise in the contact significantly, especially in the vicinity of the asperity. However, due to the characteristic behaviour of EHL contacts, the local temperature rise mainly influence the film thickness during exiting of inlet perturbations and the asperity.
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3.
  • Ji, Zhengjia, et al. (författare)
  • Mechanical and tribological properties of nanocomposites incorporated with two-dimensional materials
  • 2020
  • Ingår i: Friction. - : Springer. - 2223-7690 .- 2223-7704. ; 8, s. 813-846
  • Forskningsöversikt (refereegranskat)abstract
    • In recent years, attempts to improve the mechanical properties of composites have increased remarkably owing to the inadequate utilization of matrices in demanding technological systems where efficiency, durability, and environmental compatibility are the key requirements. The search for novel materials that can potentially have enhanced mechanical properties continues. Recent studies have demonstrated that two-dimensional (2D) nanomaterials can act as excellent reinforcements because they possess high modulus of elasticity, high strength, and ultralow friction. By incorporating 2D nanomaterials in a composite, 2D nanomaterial-based composites (2DNBCs) have been developed. In view of this, a critical review of recent mechanical and tribological studies based on 2DNBCs has been undertaken. Matrices such as polymers, ceramics, and metals, as well as most of the representative 2D nanomaterial reinforcements such as graphene, boron nitride (BN), molybdenum disulfide (MoS2), and transition metal carbides and nitrides (MXenes) have been included in this review. Their preparation strategies, intrinsic mechanical properties, friction and lubrication performances, strengthening mechanisms, influencing factors, and potential applications have been comprehensively discussed. A brief summary and prospects are given in the final part, which would be useful in designing and fabricating advanced 2D nanocomposites in the future.
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4.
  • Johansson, Jens E., et al. (författare)
  • Improving Hypoid Gear Oil Pitting Performance through Friction Reduction
  • 2020
  • Ingår i: Tribology Transactions. - : Taylor & Francis. - 1040-2004 .- 1547-397X. ; 63:2, s. 280-295
  • Tidskriftsartikel (refereegranskat)abstract
    • Earlier studies have shown that the load-dependent friction behavior of various gear oils can affect their pitting performance; that is, low friction resulted in a long pitting life. These studies were limited, however, to test methods and running conditions quite different from those occurring in actual gear transmissions. In the present study, a more gear-like twin-disc machine with test specimens and running conditions relevant for gear contacts was used to investigate whether the same trends could be found. To analyze this possible correlation, the first step was to prepare a set of hypoid gear oils and to test their friction performance to compare various ways of improving friction behavior but also to form an understanding of why their friction performance varied. The second step was to test the pitting performance of the oils. The pitting results could then be compared to the friction properties of the oils to analyze the correlation. Other possible mechanisms behind the formation of pits are also discussed. The results show that for the oils included, the antiwear and extreme-pressure additive package and the base oil type affect friction. The results further show that additive combinations and/or base oils that result in low friction lead to enhanced pitting performance.
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5.
  • Meng, Yonggang, et al. (författare)
  • A review of recent advances in tribology
  • 2020
  • Ingår i: Friction. - : Springer. - 2223-7690 .- 2223-7704. ; 8, s. 221-300
  • Forskningsöversikt (refereegranskat)abstract
    • The reach of tribology has expanded in diverse fields and tribology related research activities have seen immense growth during the last decade. This review takes stock of the recent advances in research pertaining to different aspects of tribology within the last 2 to 3 years. Different aspects of tribology that have been reviewed including lubrication, wear and surface engineering, biotribology, high temperature tribology, and computational tribology. This review attempts to highlight recent research and also presents future outlook pertaining to these aspects. It may however be noted that there are limitations of this review. One of the most important of these is that tribology being a highly multidisciplinary field, the research results are widely spread across various disciplines and there can be omissions because of this. Secondly, the topics dealt with in the field of tribology include only some of the salient topics (such as lubrication, wear, surface engineering, biotribology, high temperature tribology, and computational tribology) but there are many more aspects of tribology that have not been covered in this review. Despite these limitations it is hoped that such a review will bring the most recent salient research in focus and will be beneficial for the growing community of tribology researchers.
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6.
  • Moghaddam, Pouria Valizadeh, et al. (författare)
  • Dry sliding wear of nanostructured carbide-free bainitic steels : Effect of oxidation-dominated wear
  • 2020
  • Ingår i: Wear. - : Elsevier. - 0043-1648 .- 1873-2577. ; 454-455
  • Tidskriftsartikel (refereegranskat)abstract
    • The microstructure has a profound impact on sliding wear behaviour. This paper aims to understand the effect of carbide-free bainitic microstructure on oxidation-dominated wear in a self-mated dry sliding contact and compare the results with quenched and tempered martensitic microstructure. The results show improved wear resistance of the carbide-free bainitic steel austempered at low temperature. Hence, the retained austenite content of the carbide free bainitic microstructure is not the only indicator of excellent wear resistance. Compared to tempered martensitic microstructure, the carbide-free bainite offers a higher resistance against the formation of brittle white etching layer during the sliding wear. In summary, the formation of a thin and mechanically stable compositional mixed layer on top of the surface together with a hard underlying substrate are the main reasons behind the improved wear performance of carbide-free bainitic steel austempered at low temperature.
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7.
  • Moghaddam, P. Valizadeh, et al. (författare)
  • Effect of retained austenite on adhesion-dominated wear of nanostructured carbide-free bainitic steel
  • 2020
  • Ingår i: Tribology International. - : Elsevier. - 0301-679X .- 1879-2464. ; 150
  • Tidskriftsartikel (refereegranskat)abstract
    • Sliding wear performance of carbide-free bainitic steel is significantly affected by microstructure. This investigation is an attempt to find a correlation between microstructure and wear resistance of carbide-free bainitic steel and compare the results with that of a conventional tempered martensitic microstructure. Under predominantly adhesive wear conditions, carbide-free bainitic microstructure with the highest amount of retained austenite offers the best wear resistance. This is mainly attributed to the more pronounced work hardening and TRIP-effect of carbide-free bainitic microstructure austempered at higher temperature. Therefore, higher initial bulk hardness is not the only indicator of wear resistance. Moreover, when both oxidation and adhesion are active, a microstructure with an optimum content of retained austenite and bainitic ferrite shows the highest wear resistance.
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8.
  • Moghaddam, P. Valizadeh, et al. (författare)
  • Influence of fracture toughness on two-body abrasive wear of nanostructured carbide-free bainitic steels
  • 2020
  • Ingår i: Wear. - : Elsevier. - 0043-1648 .- 1873-2577. ; 460-461
  • Tidskriftsartikel (refereegranskat)abstract
    • This study aims to understand the effects of toughness and hardness on two-body wear of nanostructured carbide-free bainitic steels. For this purpose, three different steel grades were austempered at 250 °C to obtain carbide-free bainitic microstructures with different mechanical properties. The mechanical properties were determined in terms of fracture toughness and hardness. The wear tests were carried-out at three different loads with two different types of abrasive papers. The results show that a carbide-free bainitic steel with an optimum combination of hardness and fracture toughness exhibits the highest wear resistance. It has been seen that hardness is not the only parameter in determining the abrasive wear resistance and retained austenite has a beneficial effect on two-body abrasive wear.
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9.
  • Moghaddam, Pouria Valizadeh (författare)
  • On the role of microstructure in wear of nanostructured carbide-free bainitic steels
  • 2020
  • Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
    • The significance of steel production for the development of sustainable society and economy is immense. Today’s fast growing global economy poses an increasing demand for improving the properties of steel. The development of nanostructured carbide-free bainitic steel with an excellent combination of strength and toughness is an attempt to satisfy this global demand. During austempering, the precipitation of cementite can be suppressed by addition of approximately 1.5 wt% silicon and a duplex microstructure comprising of extremely fine aggregates of retained austenite and bainitic ferrite can be obtained. Owing to their excellent mechanical properties, these novel steels exhibit considerable potential to replace quenched and tempered bearing steel or pearlitic rail steel. In these applications, wear play a crucial role in determining the performance of the components. However, the majority of studies have been limited to mechanical properties of these steels but not much attention has been paid to their tribological behaviour. Notably, the role of retained austenite and bainitic ferrite on wear performance has not yet fully understood. Furthermore, machining process is an inevitable step in the manufacturing of metal products. During the machining, contact temperature can rise to several hundred degrees. However, high temperature tribological behaviour of these steels in conjunction with coated cutting tool has not yet been addressed. Therefore, the aim of the present research work is to gain a deeper understanding of the correlation between microstructure and tribological performance of carbide-free bainitic steels in various conditions.To achieve this aim, tribological behaviour of nanostructured carbide-free bainitic steels has been investigated under dry rolling/sliding, sliding and two-body abrasive wear conditions. A number of steel grades were austempered under a wide range of temperatures and durations to obtain different carbide-free bainitic microstructures. The results have been compared with that of quenched and tempered bearing steel. Moreover, high temperature tribological behaviour of carbide-free bainitic and 316L stainless steels during interaction with TiAlN PVD coating has also been studied under dry reciprocating sliding condition.The results show that a relatively higher retained austenite content and its stability enhance wear resistance under rolling/sliding condition. Moreover, wear performance of carbide-free bainitic steel has been found to be superior to that of the quenched and tempered bearing steel. However, under sliding condition, the effect of retained austenite on wear heavily depends on sliding speed. At low sliding speed and under adhesive-dominated wear condition, higher retained austenite content results in improved wear performance due to the higher work hardenability. In contrast, at high sliding speed where oxidative wear is dominant, a microstructure with the lowest content of retained austenite exhibits the highest wear resistance. The higher amount of bainitic ferrite provides a hard underlying substrate for a thin and mechanically stable compositional mixed layer and thereby enhances the wear resistance. The formation and microcracking of a brittle white etching layer of quenched and tempered steel is responsible for its inferior wear resistance. Under two-body abrasive wear conditions, higher retained austenite content leads to improved wear resistance. A microstructure providing an optimum combination of hardness and toughness shows the best abrasive wear resistance. During reciprocating sliding, the tribological response of carbide-free bainitic steel is altered with increasing temperature. Higher temperature results in severe material transfer from carbide-free bainitic steel to TiAlN coated cemented carbide. Furthermore, at elevatedtemperature, a porous oxide layer grows on the transferred materials and reduce friction coefficient.In summary, there is no simple and general relationship between microstructure and wear resistance. Depending upon the dominant wear mechanisms and operating conditions, retained austenite and bainitic ferrite affect the wear behaviour in radically different manners.
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10.
  • Torres, Hector, et al. (författare)
  • The tribology of Ag/MoS2-based self-lubricating laser claddings for high temperature forming of aluminium alloys
  • 2020
  • Ingår i: Wear. - : Elsevier. - 0043-1648 .- 1873-2577. ; 442
  • Tidskriftsartikel (refereegranskat)abstract
    • In recent years, the use of aluminium alloys in the automotive industry has gained significant attention due to their specific strength, corrosion resistance and recyclability. However, their forming at high temperature in processes like hot stamping is challenging due to the poor tribological behaviour of aluminium alloys, which is the source of severe adhesive wear and a poor surface quality of the finished product.In an effort to overcome these tribological problems, iron- and nickel-based self-lubricating laser claddings with the addition of solid lubricants such as silver and molybdenum disulfide have been evaluated under conditions representative of hot stamping against the aluminium alloy AA6082. It has been found that self-lubricating claddings decrease friction and counter body wear at high temperatures compared to alloys commonly used in forming tools such as grade 1.2367 steel. Furthermore, nickel-based self-lubricating claddings have shown a better tribological behaviour than their iron-based counterparts, due to the formation of a nickel-based sulfide layer on the counter body. It is thus expected that the implementation of self-lubricating claddings can improve the quality of the final product while reducing the need for added lubricant during the hot stamping of aluminium alloys.
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