Technological features of the production of welded beds from prefabricated base parts

The work is devoted to the problem of fatigue strength of welded-cast joints as applied to the operating conditions of body parts of machines. Such operating conditions are characterized by non-uniformity of intensity and concentration of the load on parts and assemblies during the operation of the equipment. This heterogeneity of the load actualizes production of precisely welded-cast base parts for metalworking equipment beds. This is of considerable technological and economic interest. The aim of the work is to study the strength of welded-cast bearing structures in relation to the work of beds of heavy lathes. Unalloyed medium-carbon structural steel 35L and steel of ordinary quality MCT3 in the form of rolled products were used as the main materials for research. The research methods are presented. The study of the structure and properties of the welded joint made it possible to assess the technical feasibility of using the studied metals in the manufacture of welded-cast bearing structures. It has been established that welding of steel castings with rolled steel causes significant structural and mechanical heterogeneity. The influence of processing technology on the nature of formation of the structure of welded-cast joints is presented. The influence of heat treatment on the value of the hardness of the welded seam and the heat-affected zone was investigated. The study of the fatigue resistance of welded-cast specimens was carried out in relation to the operating conditions of joints undergoing vibration loads at normal temperatures, which can be classified as fatigue with a symmetric load cycle. It was found that the use of heat treatment of welded-cast specimens significantly reduces the mechanical heterogeneity of the joint along the seam and the heat-affected zone. Based on the results of studying mechanical characteristics, the choice of technology for the production of welded-cast joints is justified.

Dynamic Load Cycle Effects on PEMFC Stack CO Tolerance under Fuel Recirculation and Periodic Purge

This work presents first experimental evidence on the effects of dynamic load cycle on PEM fuel cell system CO tolerance, a topic which to date has not been comprehensively investigated. The experiments were performed with a 1 kW fuel cell system employing components, design, and operation conditions corresponding to automotive applications. To distinguish between the load cycle and other factors affecting the CO tolerance, the experiments were repeated with static and dynamic load cycles, as well as with pure and CO contaminated fuel. The measurement data showed that dynamic load cycle improves the CO tolerance in comparison to static load with the same average current density. Moreover, the cell voltage deviation data indicated that the difference could be explained by higher electrochemical CO oxidation rate under the dynamic load cycle. These results allow us to estimate the effect of the load cycle on CO tolerance and understand its origins, thus giving valuable input for fuel quality standardization and fuel cell system development work.

Design of High Power Regenerative Battery Discharger System for Nuclear Power Plant

In a Nuclear Power reactor, safety loads are backed by standby battery system. The healthiness of the battery is very essential requirement and prominent attention is given to availability and reliability of battery supply in nuclear plants. Hence regular monitoring and testing the performance of the battery is a prime requirement. The capacity and load cycle discharge testing of the battery is done annually and the current system employed is to discharge the battery current through resistor banks, which results in unusable power consumption and is uneconomical. The growing trend in power electronics field has given the new technology of regenerating the dissipated power to grid. This paper proposes a high power electronic regenerative technology with high efficiency, low harmonics to pump the dc power to the grid. Though, it is available at lower rating in industry, the paper proposes a high power regenerative discharge system. The topology selected is interleaved boost converter interfaced to a three phase grid connected inverter. The challenges involved are high power operation, steep current discharges with a minimal interference to the normal plant operation power supplies during the regeneration. This paper also presents the system design and simulation results.

Compression Behavior of Hybrid Tubes for Lightweight Steel Structures

This research shows the results of an experimental investigation carried out on the compression behavior of hybrid steel tubes formed by two concentric steel tubes and four different fillers of non-metallic material interposed between both tubes: polyurethane foam, polyurethane, epoxy and a cement-based mortar. The tests show that the incorporation of a resistant filler in the double tube allows it to improve its mechanical behavior by allowing a second load cycle. Furthermore, the strain energy absorbed during the two cycles led to the conclusion that the epoxy-filled tube absorbed more energy per unit of weight than the other resistant fillers.

Structural Retrofitting of Corroded Reinforced Concrete Beams Using Bamboo Fiber Laminate

Corrosion creates a significant degradation mechanism in reinforced concrete (RC) structures, which would require a high cost of maintenance and repair in affected buildings. However, as the cost of repairing corrosion-damaged structures is high, it is therefore pertinent to develop alternative eco-friendly and sustainable methods. In this study, structural retrofitting of corroded reinforced concrete beams was performed using bamboo fiber laminate. Three reinforced normal weight concrete beams were produced, two of which were exposed to laboratory simulated corrosion medium, and the remaining one sample served as control. Upon completion of the corrosion cycle, one of the two corroded beams was retrofitted externally with a prefabricated bamboo fiber laminate by bonding the laminate to the beam surface with the aid of an epoxy resin. The three beams were subjected to loading on a four-point ultimate testing machine, and the loads with corresponding deflections were recorded through the entire load cycle of the beams. Finally, the mass loss of embedded steel reinforcements was determined to measure the effect of corrosion on the beams and the steel. The result showed that corroded beams strengthened with bamboo laminates increase the bearing capacity. Using a single bamboo laminate in the tensile region of the corroded beam increased the ultimate load capacity of the beam up to 21.1% than the corroded beam without retrofit. It was demonstrated in this study that the use of bamboo fiber polymer for strengthening destressed RC beams is a more sustainable approach than the conventional synthetic fibers.

Investigation of Viral Load Cycle Threshold Values in Patients with SARS-CoV-2 Associated Pneumonia with Real-Time PCR Method

Introduction: In this study, we aimed investigate the relationship of SARS-CoV-2 viral load cycle threshold (Ct) values with pneumonia. Methodology: A total of 158 patients in whom SARS-CoV-2 was confirmed in upper respiratory tract (URT) samples with molecular method and who had computed tomography (CT) of the chest, between April 2020 and June 2020 were included in this retrospective cross-sectional study. Results: Mean age of 158 PCR positive patients was 45.22 ± 17.89 and 60.8% of them were male. Pneumonia was detected in 40.5% of the patients on their chest CT. A weak but significant correlation was found between SARS-CoV-2 Ct value detected with PCR in analysis of oropharyngeal/ nasopharyngeal (OP/NP) samples and chest CT score (Pearson’s r: 0.197, p = 0.01). No correlation was found between the first detected viral load Ct value and age, gender and mortality. There was no significant correlation between chest CT score and mortality. While the areas remaining under ROC curve for Ct value in analysis of OP/NP samples in prediction of chest CT score ≥ 1, ≥ 5 and ≥ 10 were 0.564, 0.640 and 0.703 respectively. Conclusions: We found that the amount of SARS-CoV-2 viral load (inverse relationship with Ct) detected in OP/NP samples of patients with COVID-19 pneumonia did not reflect the increasing severity of pulmonary lesions on chest CT. Although primary target of SARS-CoV-2 is all epithelial cells of the respiratory tract we believe studies comparing viral loads in lower respiratory tract samples are needed to determine the severity of pulmonary disease.

Heat Treatment Consideration in Structural Simulations of Machine Elements: Analysis of a Starter Clutch Barrel

Consideration of heat treatment in simulations of structural components and its impact on predictions of behaviour during operation is analysed here. An automotive machine element with a complex geometry and dynamic load is analysed rather than a standard laboratory specimen under controlled conditions. The heat treatment analysis of a starter clutch barrel has been performed in DANTE followed by a structural analysis in ANSYS 2019 R3 during operation simulating a load cycle due to the start of an internal combustion engine. The heat treatment simulation consisted of carburisation, quenching and tempering. First, the carbon content and its distribution have been simulated. Next, the hardness of the starter clutch barrel and its distribution have been analysed with respect to the carbon distribution and hardness-dependent material properties of the AISI/SAE 4142 steel. Finally, the stress field after the heat treatment and during the operation of the starter clutch barrel has been thoroughly evaluated and compared to the simulation without the consideration of the heat treatment. Results of the simulation show that the heat treatment introduces favourable compressive stresses at the critical location of the starter clutch barrel and reduces the effective amplitude of the equivalent stress during the operation. Furthermore, the results of the simulation prove that heat treatment should be considered already during the early stages of the R & D process as it can have a decisive effect on the operational behaviour of the structural component. Moreover, a non-consideration of the heat treatment can lead into erroneous conclusions regarding the suitability of machine elements.