Papers by Keyword: Cryogenic

Abstract: We have demonstrated an integrated 3.3 kV 4H-SiC vertical planar bidirectional (BD) conventional (Conv) power DMOSFET in common-drain (CD) configuration using two commercially available power DMOSFET dies and study its operation down to 77 K (-196 °C) to evaluate its cryogenic static and switching performance. The BD conduction and blocking are achieved down to 77 K. The measured specific on-resistance (R_ON,sp) of the BD MOSFET at room temperature (RT) is 26 mΩ-cm², approximately twice that of the unidirectional device. It increases by 54% when cooled to 77 K due to a substantial increase in channel and possibly JFET on-resistance components. In addition, the extracted specific switching losses (E_ON,sp and E_OFF,sp) increases by 33% (13%) at 195K (–77 °C) and by 83% (88%) at 77 K, relative to their RT values. These increases are primarily attributed to the substantial rise in R_ON,sp at 77 K. As a result, the implemented BD Conv DMOSFET exhibits degradation in both on-state and switching performance under cryogenic operation, driven mainly by the significant increase in channel and JFET resistance components.

Abstract: The global growth of discarded end-of-life tires (ELT) is leading to a significant challenge of waste management. Many of these tires are incinerated or exported to countries with less stringent environmental regulations, exacerbating pollution and wasting resources. Until now, the main destinations for recycled rubber have been flooring, rubberized pavements, infill for synthetic turfs and moulded goods. The increasing necessity for the industry to adopt more sustainable products and processes by incorporating recycled materials, needs to be supported by innovative solutions. The present paper introduces a recycled rubber material, characterized by different certified laboratory tests performed to evaluate the mechanical and physical performance of a virgin rubber compound combined with different content levels of rubber powders derived from ELT, and with different particle sizes and production methods. There is extensive research on the ELT management systems and the various methods for recycling rubber from end-of-life tires, but limited studies on the impact of particle size and the influence of content of recycled rubber powders, added in new rubber compounds suited for performance-demanding applications. Based on the laboratory test results and the case study presented in this paper, it was possible to conclude that this recycled material can be incorporated into new rubber compounds, without compromising the performance. Numerous studies examine methods for recycling rubber from end-of-life tires, assessing their progress and limitations. Some focus on well-documented processes such as reclaiming, devulcanization, and surface modification, while others explore long-studied applications like rubberized concrete and rubber-modified asphalt. There is limited available information and published studies on the influence of particle size and content levels of recycled rubber powders that can be incorporated into new rubber compounds, for various applications such as new tires, conveyor belts, gaskets and profiles.

Abstract: In the last few decades, non-traditional machining has increased the efficiency of the machining process. One of the most prevalent non-traditional methods of milling is through the use of an EDM process. Traditional machining methods can't easily machine materials with a complicated profile or hardness that EDM can handle. The industrial sector makes extensive use of EDM. Cryogenically treated copper electrodes and regular copper electrodes were used to conduct an experiment on an EN24 material using varied input parameters, such as electrode rotation, gap voltage, and discharge current. Electric discharge machining was used in a study. The Taguchi method is used to design experiments. Three input parameters were employed in an orthogonal L16 array to find an optimal value for each of the three components. OC (overcut), TWR (Tool wear rate), and Ra (surface roughness) are the three output variables. The S/N ratio can be used to determine the best values and relative relevance of each of these factors using a statistical analysis of variance (ANOVA) table. Additionally, the overcut, tool wear rate, and surface roughness of traditional and non-traditional EDM are examined. For the deep cryogenic and non-traditional machining method, conventional and non-traditional electric discharge machining methods were found to have optimal or dominant factors for the TWR and Ra.

Abstract: Thermal conductivity measurements of high-strength AA 7115 cryogenic thermal conductivity under various circumstances of solution and ageing were made using a one-dimensional steady state method. Structural analysis is also used to examine the heat conductivity of the alloy. Aluminum alloy's thermal conductivity decreased linearly as the temperature lowered. The thermal conductivity at various temperatures was reduced by a considerable 35 percent after the solution was applied. The thermal conductivity of the fluid was dramatically lowered after deep cryogenic treatment. In contrast, the ageing process improved the thermal conductivity succeeding solution-deep cryogenic therapy or solution. There were many point flaws in the lattice that increased electrical scattering, which resulted in a decrease in heat conductivity. After severe cryogenic treatment, thermal conductivity dropped even further because of the larger in size of Aluminum - Copper precipitates and raised dislocation density. Raise in thermal conductivity cause by increase in number of fine secondary phase particles precipitating with time. Thermal conductivity of aluminium alloy can be employed to study deep cryogenic treatment methods at low temperatures.

Abstract: In past few decades, natural fibers which are viable and abundant in nature are the emerging trends in material science as reinforcement for polymer matrix materials and they are the commute for the non-biodegradable, non-renewable and high-density synthetic fibers. Plant-based fibers such as banana, hemp, kenaf, PALF, jute, and coir has been used as reinforcement in a polymer matrix for the applications in consumer goods, furniture’s, civil and automotive structures and low-cost housing structures. The natural fibers used in this study are Hemp and Jute fibers which are finding increasing in the composite material as reinforcements. The main objective of the current work is to examine the mechanical properties of hybrid fibers (hemp and jute) reinforced epoxy composites under room temperature and at cryogenic temperature. From this study, it is clear that tensile, flexural and impact properties of polymer composites are greatly influenced by cryogenic temperature and its properties vary with respect to the extent of cryogenic treatment. The specimens are immersed in liquid nitrogen for the duration of 15, 30, 45 and 60mins and later it is subjected for tensile, flexural and impact properties. The maximum tensile strength of 21.13MPa, flexural strength of 51.95MPa and Impact strength of 8.935kJ/m² is obtained for an untreated specimen and its value start to decrease as curing time increases. At cryogenic temperature, the material comes harder and loses its ductile property and become brittle due differ in thermal expansion coefficient of matrix and fiber material

Abstract: In this paper, some preliminary experimental investigations have been reported for analysing the machining performance characteristics viz. Material Removal Rate (MRR) & Tool Wear Rate (TWR). Electrical Discharge Machining (EDM) of Inconel-718 alloy via helical threaded cryogenically treated rotary copper tool electrode is conducted. Impact of machining factors viz. peak current (I_p), pulse-on time (T_on), tool rotation (N_t) & hole depth (h) were investigated using Taguchi’s L₉ (3⁴) Orthogonal Array (OA). Optimum arrangements of factors for greatest MRR & least TWR were found in current study. Results predicts that I_p & N_t are two most affecting machining factors that affects MRR. Whereas I_p & T_on are two most affecting machining factors that affects TWR.

Abstract: MgB₂ superconductor with relatively high critical temperature (Tc=40 K) has been developed for possibilities utilization in various practical applications such as Magnetic Resonance Imaging. In order to enhance the process, the material was prepared by Powder-In-Tube (PIT) method, while the superconducting properties was improved by incorporating 0 wt.%, 10 wt.% and 20 wt.% SiC nanoparticles into MgB₂ structure. This study aimed at analyzing the effect of sintering temperature on the microstructure, resistivity and phase of Fe-sheathed MgB₂ superconducting wires. Three different compositions of MgB₂ powders were inserted into Fe tube with inner ø of 4 mm and outer ø of 6 mm. This tube was then rolled and drawn into a ø 2.5 mm wire. Wire samples with three different compositions of SiC were heat treated at 600°C and 800°C respectively. All samples were characterized to analyze the morphology, resistivity and crystal structure. X-ray diffraction (XRD) analysis showed that some Mg may react with SiC to form MgSi and with oxygen to form MgO. Scanning electron microscope (SEM) images revealed that with no addition of SiC, MgB₂ was formed and dispersed uniformly in wire, but with 10 wt.% and 20 wt.% SiC nanoparticles, the whisker morphology was observed resulting in degradation of the superconducting properties.

Abstract: The Selective Laser Melting (SLM) process has been proved as the most effective method among Additive Manufacturing (AM) technologies to produce hard, dense and strong metallic structures with intricate shapes and profiles from wide range of metallic alloys. The SLM generated structures from 17-4PH stainless steel high strength alloys involve layer by layer building up through laser melting of successively deposited powder layers. Therefore, the mechanical properties of such structures need to be thoroughly checked and investigated before putting these materials to practical applications. This research mainly investigates the cryogenic impact properties of SLM generated 17-4PH specimen. These characteristics are very important in applications requiring high strength customized structures that could maintain their mechanical properties at sub-zero temperatures. The experimental analysis proves that SLM is a very reliable technology to produce high strength metallic structures and these specimens can function efficiently in extreme conditions.

Abstract: Machinability of aerospace material, Inconel 625 through Wire cut electrical discharge machining has been performed and compared using Taguchi’s Orthogonal L18 (2¹*3⁵). Normal diffused and cryogenic treated diffused wires are being used as a tool electrode to investigate the effects of machining parameters viz. tool electrode, peak current, pulse on time, pulse off time, wire feed and wire tension on the response MRR. The present study resulted that cryogenic treated tool electrode give better performance in comparison to normal wire electrode assisting in improving stock removal and less electrode wear. Pulse on time and peak current are observed as the most influenced parameter. Scanning Electron Microscopy (SEM) studies has been conducted and presented.

Abstract: We present a comparative study of the electrical characteristics of different 1200V commercial SiC power MOSFETs at cryogenic temperatures down to 77 K. As compared to conventional silicon power MOSFETs, SiC MOSFETs show very different operating characteristics at low temperatures which is due to unique material and design parameters used in SiC MOSFETs. Of particular interest is a non-linear mixed triode/pentode-like I-V characteristic exhibited by all SiC MOSFETs at 77 K, which is demonstrated to be due to short channel effects in the constituent JFET.