| 1. |
- Ahmadkhaniha, Donya, et al.
(författare)
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Study of the process parameters influence on crack formation in laser alloying of grey cast iron
- 2024
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Ingår i: Optics and Laser Technology. - : Elsevier. - 0030-3992 .- 1879-2545. ; 179
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Tidskriftsartikel (refereegranskat)abstract
- This study aimed to investigate the influence of process parameters on crack formation in laser alloying or cladding of grey cast iron. For this purpose, the effects of laser power and feeding rate of Ni-based alloying powders were examined. The microstructure and hardness of the coating and the interface of the coating with cast iron (bonding zone) were studied. The results showed that the dilution ratio is crucial in crack formation, explaining the challenges in achieving a defect-free laser alloying coating on cast iron. The higher dilution ratio of laser alloying resulted in higher dissolved carbon and bigger (Nb, Ti)C carbides formation than in laser cladding coatings. In this study, cracks appeared in the coating due to the combination of the high amount of carbide in the layer and a sharp hardness gradient at the interface with the cast iron substrate. An empirical relation was proposed for dilution ratio as a function of specific energy density, which combined the most critical process parameters on crack formation.
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| 2. |
- Aladov, V ,A., et al.
(författare)
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A study of thermal regime in the high-power LED arrays
- 2018
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Ingår i: St. Petersburg Polytechnical University Journal: Physics and Mathematics. - : Polytechnical Univ Publishing House. - 2405-7223. ; 11:3, s. 39-51
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Tidskriftsartikel (refereegranskat)abstract
- Thermal resistance and temperature distribution for high-power AlGaInN LED chip-on-board arrays were measured by different methods and tools. The p-n junction temperature was determined through measuring a temperature-dependent forward voltage drop on the p-n junction, at a low measuring current after applying a high heating current. Furthermore, the infrared thermal imaging technique was employed to obtain the temperature map for the test object. A steady-state 3D computational model of the experimental setup was created including temperature-dependent power dissipation in the LED chips. Simulations of the heat transfer in the LED array were performed to further investigate temperature gradients observed in the measurements. Simulations revealed possible thermal deformation of the assembly as the reason for the hot spot formation. The bending of the assembly was confirmed by surface curvature measurements.
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| 5. |
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| 6. |
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| 7. |
- Belov, Ilja, et al.
(författare)
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A thermal conductivity model for grey iron
- 2024
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Ingår i: International Journal of metalcasting. - : Springer. - 1939-5981 .- 2163-3193. ; 18:3, s. 2107-2117
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Tidskriftsartikel (refereegranskat)abstract
- Thermal conductivity is an important property for many iron cast components, and the lack of widely accepted thermal conductivity model for cast iron, especially grey cast iron, motivates the efforts in this research area. The present study contributes to understanding the effects alloy microstructure has on thermal conductivity. A thermal conductivity model for a pearlitic cast iron has been proposed, based on the as-cast alloy composition and microstructural parameters obtained at different solidification rates. According to the model, available parallel heat transfer paths formed by connected graphite flakes across eutectic cells are determined by the space between dendrite arms. The uncertainties both for model inputs and for validation measurements have been estimated. Sensitivity analysis has been conducted to result in better understanding of the model behaviour. The agreement between modelled and measured thermal conductivities has been achieved within 5% on the average for the investigated samples.
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| 8. |
- Belov, Ilja, et al.
(författare)
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A thermal conductivity model for lamellar and compacted graphite irons
- 2024
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Ingår i: International Journal of metalcasting. - : Springer. - 1939-5981 .- 2163-3193.
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Tidskriftsartikel (refereegranskat)abstract
- Thermal conductivity is an important property for cast components produced from different types of cast iron. Development of a general widely-accepted thermal conductivity model for compacted and lamellar graphite irons poses a research challenge. The present study extends the modeling approach introduced earlier for pearlitic lamellar graphite iron toward compacted graphite iron and ferritic lamellar graphite iron. The proposed thermal conductivity model of the bulk material is based on the alloy microstructure and Si segregation between eutectic cells and non-cell regions, at the main assumption that the heat paths in the eutectic cells are formed by connected graphite phases surrounded by ferrite phases. The overall thermal resistance of these heat paths is determined by the hydraulic diameter of the interdendritic region. The uncertainties both for the modeled and for experimentally derived thermal conductivities have been estimated. The importance of considering the Si segregation in the model has been discussed. For the investigated samples, the agreement between modeled and measured thermal conductivities has been achieved within 4% on the average, at the same value of the single fitting parameter found for pearlitic, pearlitic–ferritic lamellar, and compacted graphite iron alloys. The results contribute to the understanding of the material microstructure effects on the cast iron thermal conductivity.
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| 10. |
- Belov, Ilja, et al.
(författare)
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Application of CFD Modelling for Energy Efficient Humidity Mangement of an Electronics Enclosure in Storage under Severe Climatic Conditions
- 2008
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Ingår i: International Conference on Thermal, Mechanical and Multi-Physics Simulation and Experiments in Microelectronics and Micro-Systems, 2008. - : IEEE. - 9781424421275 ; , s. 430-437
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Konferensbidrag (refereegranskat)abstract
- A CFD modelling methodology including experimental validation has been developed and applied for investigation of anti-moisture measures in a non- hermetic electronics enclosure containing a number of printed circuit boards, and placed in a severe storage environment. In the climatic test the temperature and the relative humidity have been varried from +33degC to +71degC and from 14% to 80%, respectively. Enclosure heater solutions have been parametrically studied by simulation. A heating strategy involving various power levels has been determined, which is just sufficient to maintain the internal relative humidity below 60%, thereby reducing the risk for dew formation on the electronics assembly.
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