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- Ghasemi, Rohollah, 1983-
(författare)
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Tribological and Mechanical Behaviour of Lamellar and Compacted Graphite Irons in Engine Applications
- 2015
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- There has been much discussion about the beneficial uses of lamellar graphite iron in piston rings–cylinder liner systems, where a good combinations of both thermal and tribological properties are essential. The excellent tribological performance of lamellar iron under such sliding conditions is principally associated with lubrication behaviour of the graphite particles which are distributed as lamellas throughout the matrix. During sliding, graphite particles are extruded and smeared onto the counterfaces, act as solid lubricating agents and form a thin graphite film between the sliding surfaces. Although this process especially, during the running-in period significantly changes the sliding wear response of the components, the exact mechanism behind of this phenomenon has rarely been discussed in previous studies.It is tribologically beneficial to keep the graphite open, particularly in applications where the scuffing issues do matter. In this thesis, the main causes involved in closing the graphite lamellas are discussed, with a focus on matrix plastic deformation that occurs during sliding. In first step, the relationship between graphite lamellae orientation and plastic deformation was investigated. To do so, two piston rings, belonging to the same two-stroke marine engine operated for different periods of time, were selected and compared to the unworn sample. The worn piston rings displayed a substantial decrease in both frequency and area fraction of the graphite lamellas. Most of the lamellas were closed as a result of plastic deformation of matrix. This happening was caused mainly by the interaction between abrasive particles and metallic matrix. Additionally, it was found that graphite lamellas parallel or near-parallel to the sliding direction exhibited maximum closing tendency under sliding condition.In next step, to have a better understanding of the graphite film formation mechanism and matrix deformation role in closing the graphite lamellas, microindentation and microscratch testing were performed on typical lamellar iron. The qualitative results showed a similar mechanism involving in graphite contribution to lubricate the sliding surfaces. Moreover, microindentations made nearby the graphite lamellas demonstrated that the deformation of the matrix causes the formation of cracks in the centre of the graphite lamellas, compressing and then extruding the graphite from its natural position, irrespective of the lamellas′ size. Furthermore, it was found that subsurface graphite orientation had a large influence on the extrusion behaviour, in that, for graphite lamellas oriented towards the indenter, the effect was observed more pronounced.Furthermore, an improved fully ferritic solution strengthened compacted graphite iron was produced for future wear studies. The effects of different Si levels and section thicknesses on tensile properties and hardness were investigated as well. The influence of Si content and section thickness on mechanical properties was revealed by improving the materials strength and slightly enhancing the hardness through increasing Si content. Besides, Si addition up to 4.5 wt% significantly affected the strength and elongation to failure of cast samples.
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| 2. |
- Belov, Ilja, et al.
(författare)
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Simulation and Experimental Methodology for Virtual Prototyping of Annealed Industrial Coils
- 2023
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Ingår i: Heat Transfer Engineering. - : Taylor & Francis. - 0145-7632 .- 1521-0537. ; 44:4, s. 353-367
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Tidskriftsartikel (refereegranskat)abstract
- The finite element three-dimensional transient model of the annealing process, including conductive and convective heat transfer in an aluminum (Al) coil was developed, implemented, and validated. It combines winding force dependent effective radial thermal conductivity model and the novel convective heat transfer modeling methodology. Experimental validation of the finite element model was performed for two industrial coils having different dimensions, strip thickness and crowning depth. The general agreement between the predicted and measured temperatures for most of the probes was better than 10% at the target material temperature. A series of measurements were configured and performed to supply both the input and validation data for the simulations. The effect of the additional wetted area on the convective heat transfer at the coil base was quantified. The guidelines on the virtual prototyping of the Al coil annealing process were provided, which can be of interest for the process designers.
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| 5. |
- Matsushita, Taishi, et al.
(författare)
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Influence of contact pressure on the thermal contact conductance of layered metallic sheets
- 2022
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Ingår i: High Temperatures-High Pressures. - : Old City Publishing. - 0018-1544 .- 1472-3441. ; 51:1, s. 63-82
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Tidskriftsartikel (refereegranskat)abstract
- For the optimisation of the annealing process of aluminium coils, simulation of the process is often performed. To simulate the process with higher accuracy, reliable input parameters are required, and thermal conductivity (thermal contact conductance) is one of them. In the present study, a method to measure the thermal conductivity and thermal contact conductance of metallic sheets were developed based on the steady-state comparative longitudinal heat flow. The apparatus was built with a compression test machine, and thus it allows to control the pressure to the sample and carry out the measurements at different contact pressure. An equipped heater allows to heat the sample to 573 K. To evaluate the thermal conductance at the interface, a thermal resistance network model was applied. The measurements were carried out with an aluminium alloy (AA3003 sheets). In addition to the thermal contact conductance measurements, the surface roughness of the sheets was also investigated. The semi-empirical equation for the relationship between thermal contact conductance and contact pressure was obtained based on the measurement results.
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| 6. |
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| 7. |
- Awe, Samuel A., et al.
(författare)
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Development of new Al-Cu-Si alloys for high temperature performance
- 2017
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Ingår i: Advanced Materials Letters. - : VBRI Press. - 0976-3961 .- 0976-397X. ; 8:6, s. 695-701
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Tidskriftsartikel (refereegranskat)abstract
- In a quest to develop new light metal alloys that can perform excellently at elevated-temperatures (from 300°C to 400°C), a ternary eutectic Al-Cu-Si alloy was exploited to gain a deeper understanding of the alloy system and its suitability for high temperature applications. The alloys studied, with chemical composition of Al-27%Cu-5%Si (by weight percent) with Ni addition in the range of 0 to 1.5%wt, were cast in a rapid solidification casting technique. The solidification characteristics of the alloy was studied using the Thermo-Calc software. Microstructures were characterized in a scanning electron microscope coupled with energy dispersive spectrometry (SEM-EDS). Finally, the elevated-temperatures tensile properties of the alloys were investigated. Comparing the microstructures and mechanical properties of these Al-Cu-Si(-Ni) alloys with conventional Al-Si alloy A319, the refined microstructure with dispersed Ni intermetallic particles formed in the as-cast Al-Cu-Si(-Ni) alloys deliver improved elevated temperature properties. In particular, the yield strength and ultimate tensile strength of the new alloy with 1.5% Ni at 400?C were observed to be 220% and 309% higher, respectively, than for conventional A319 alloy.
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| 8. |
- Belov, Ilja, et al.
(författare)
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Effect of fillets on heat transfer in a rheocast aluminium heatsink
- 2016
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Ingår i: 2016 17th International Conference on Thermal, Mechanical and Multi-Physics Simulation and Experiments in Microelectronics and Microsystems (EuroSimE). - : IEEE. - 9781509021062
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Konferensbidrag (refereegranskat)abstract
- The effect of fillets formed between the base and plate fins of rheocast aluminium heatsinks on the thermal resistance of the heatsinks has been quantified by simulation. Simulation methodology, including sequential optimization has been developed in order to determine hotspot distributions where the fillets have the maximum effect. Combination of different fillet dimensions with various base thickness levels and aluminium alloys having inhomogeneous thermal conductivity have been investigated. For the studied cases, the effect of fillets on heatsink thermal resistance differs from negligible to 6%. The results would guide thermal designers on contribution of fillets to the heat transfer in multi-fin heatsinks for natural convection.
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