• Korean Journal of Metals and Materials
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• v.50 no.4
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• pp.271-279
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• 2012

9-12% Cr steels have been used in thermal power plants which repeat start and stop operations. Major factors of fatigue life are temperature, frequency, stress ratio, holding time, microstructure, and environment. Normally, fatigue life decreases at high temperature, low frequency, high stress ratio, and long holding time conditions. A Mod.9Cr-1Mo steel, called G91, was developed at ORNL (Oak Ridge National Laboratory, USA) and was adopted as a high-temperature structural material in the ASME Code in 2004. However, its low-cycle fatigue and fatigue crack growth characteristics have been rarely studied. In this work, we have investigated the low-cycle fatigue crack growth behaviors of G91 steel under various test conditions in terms of temperature and stress ratio. As temperature and stress ratio increase, the crack growth rate becomes faster and striation distance also increases. On the other hand, the number of branch cracks decreases.

• Architectural research
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• v.8 no.1
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• pp.57-68
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• 2006

Global competition and reduced project life cycle ultimately puts greater performance requirements on the capital project delivery systems used to maintain competitiveness. Despite continuing improvements in delivery cycle time, business owners of facilities continue to demand greater improvements in project delivery cycle time. Therefore, it is very important to investigate the various techniques and methods leading to reduction in project cycle time and also identify the applicability of identified techniques and methods. This paper introduces reduction techniques identified through literature review (i.e, Schedule Reduction Techniques (SRTs), Management Techniques (MTs), and Construction Institute Industry (CII) Best Practices (BPs). In order to collect applicability of these techniques under different project phases (Pre-project planning (PPP), Design (D), Material Management (MM), Construction (C), and Start-up (SU)), the Essence Applicability Matrices (EAM) is used.

• Journal of Electrical Engineering and Technology
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• v.13 no.4
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• pp.1578-1585
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• 2018

This work investigates two different motor drive technologies, switched reluctance motor (SRM) and induction motor (IM). They are designed optimally to meet the desired performances for electric scooters. The comparison of both motors is described in terms of performances and material cost. With the similar constraint, induction motor performs slightly better than switched reluctance motor. But this must be traded-off with higher weight and cost. Both drive systems are, however, suitable for electric scooter application. Finally, the range simulations are conducted on a European urban driving cycle, ECE15 driving cycle and a more realistic cycle, Bangkok driving cycle. The e-scooter ranges are varied from 36 to 109 km depending on driving cycle, motor technology and number of passengers.

• Nuclear Engineering and Technology
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• v.40 no.7
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• pp.581-592
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• 2008

In this study, a conceptual pyroprocess flowsheet has been devised by combining several dry-type unit processes; its applicability as an alternative fuel cycle technology was analyzed. A key point in the evaluation of its applicability to the fuel cycle was the recovery yield of fissile materials from spent fuels as well as the proliferation resistance of the process. The recovery yields of uranium and transuranic elements (TRU) were obtained from a material balance for every unit process composing the whole pyroprocess. The material balances for several elemental groups of interest such as uranium, TRU, rare earth, gaseous fission products, and heat generating elements were calculated on the basis of the knowledge base that is available from domestic and foreign experimental results or technical information presented in open literature. The calculated result of the material balance revealed that uranium and TRU could be recovered at 98.0% and 97.0%, respectively, from a typical PWR spent fuel. Furthermore, the anticipated TRU product was found to emit a non-negligible level of $\gamma$-ray and a significantly higher level of neutrons compared to that of a typical plutonium product obtained from the PUREX process. The results indicate that the product from this conceptual pyroprocessing should be handled in a shielded cell and that this will contribute favorably to retaining proliferation resistance.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.28 no.4
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• pp.333-342
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• 2004

Tensile and low cycle fatigue (LCF) tests on prior cold worked 316L stainless steel were carried out at various temperatures from room temperature to 650$^{\circ}C$. At all test temperatures, cold worked material showed the tendency of higher strength and lower ductility compared with those of solution treated material. The embrittlement of material occurred in the temperature region from 300$^{\circ}C$ to 600$^{\circ}C$ due to dynamic strain aging. Following initial cyclic hardening for a few cycles, cycling softening was observed to dominate until failure occurred during LCF deformation, and the cyclic softening behavior strongly depended on temperature and strain amplitude. Non-Masing behavior was observed at all test temperatures and hysteresis energy curve method was employed to describe the stress-strain hysteresis loops at half$.$life. The prediction shows a good agreement with the experimental results.

• International Journal of Naval Architecture and Ocean Engineering
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• v.12 no.1
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• pp.868-880
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• 2020

One of the main concerns in the structural integrity of offshore pipelines is mechanical damage from external loads. Pipelines are exposed to fatigue failure in welded joints due to geometric discontinuity. In addition, fatigue loads such as currents, waves, and platform motions may cause significant plastic deformation and fracture or leakage within a relatively low-cycle regime. The 2007 ASME Div. 2 Code adopts the master S―N curve for the fatigue evaluation of welded joints based on the mesh-insensitive structural stress. An extension to the master S―N curve was introduced to evaluate the low-cycle fatigue strength. This structural strain method uses the tensile properties of the material. However, the monotonic tensile properties have limitations in describing the material behavior above the elastic range because most engineering materials exhibit hardening or softening behavior under cyclic loads. The goal of this study is to extend the cyclic stress-strain behavior to the structural strain method. To this end, structural strain-based procedure was established while considering the cyclic stress-strain behavior and compared to the structural strain method with monotonic tensile properties. Finally, the improved prediction method was validated using fatigue test data from full-scale girth-welded pipes.

• Nuclear Engineering and Technology
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• v.54 no.11
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• pp.4062-4071
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• 2022

Long-term aluminum (Al) corrosion tests were designed to investigate the condition that would generate severe Al corrosion and precipitation. Buffer agents of sodium tetraborate (NaTB), trisodium phosphate (TSP) and sodium hydroxide (NaOH) were adopted. The insulation materials, fiberglass and calcium silicate (Ca-sil), were examined to explore their effects on Al corrosion. The results show that significant precipitates were formed in both NaTB/TSP-buffered solutions at high pH. The precipitates formed in NaTB solution raise more concerns on chemical effects in GSI-191. A passivation layer formed on the surfaces of coupon in solution with the presence of insulations could effectively mitigate Al corrosion. The Fe-enriched intermetallic particles (IPs) embedded in coupon appeared to serve as seeds to readily induce precipitation via providing extra area for heterogeneous Al hydroxide precipitation. X-ray spectroscopy (EDS) and X-ray diffraction (XRD) analyses indicate that the precipitates are mainly boehmite (γ-AlOOH) and no direct evidence confirms the presence of sodium aluminum silicate or calcium phosphate.

• Transactions of Materials Processing
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• v.31 no.3
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• pp.117-123
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• 2022

In this study, a commercial AZ61 magnesium alloy is extruded at 300 ℃ and 400 ℃ and the microstructures, mechanical properties, and high-cycle fatigue properties of the extruded materials are investigated. Both extruded materials have a fully recrystallized microstructure with no Mg₁₇Al₁₂ precipitates. The average grain size and maximum basal texture intensity of the extruded material increase with increasing extrusion temperature. The material extruded at 400 ℃ (AZ61-400) has higher tensile yield strength and lower compressive yield strength than the material extruded at 300 ℃ (AZ61-300) because of the stronger basal texture of the former. Because of coarser grain size, the tensile elongation of AZ61-400 is lower than that of AZ61-300. Despite the differences in microstructures and tensile/compressive properties, the two extruded materials have the same fatigue strength of 110 MPa. This is because the finer grain size of AZ61-300 causes an increase in fatigue strength, but its weaker texture causes a decrease in fatigue strength. In both extruded materials, fatigue cracks initiate at the surface of fatigue specimens at all stress amplitudes tested.

• Journal of Korean Society of Environmental Engineers
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• v.38 no.8
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• pp.403-410
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• 2016

During expressway construction it has been input a lot of material, but it does not manage to estimate quantitatively. In this study, the total material requirement for construction of expressway, which separated direct material requirement and indirect material requirement each section was quantified by combining life cycle assessment (LCA) and material flow analysis (MFA). In the direct material requirement, sand 2.27E + 04 ton/km, limestone 1.02E + 04 ton/km and gravel 4.47E + 03 ton/km were required, in the indirect material requirement, gravel 2.75E + 04 ton/km, iron 9.80E + 03 ton/km and coal 9.74E + 03 ton/km were required. Material such as sand, limestone which has high direct material requirement is require of excess input prevention from construction site, and material such as iron, rare metals(chrome, nickel) and coal which has high indirect material requirement is require additional studies of resource management.

• KIEAE Journal
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• v.4 no.2
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• pp.49-56
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• 2004

This study intends to propose the fundamentals of 'Ecovillage' design by researching into the cycle system of material of 'Crystalwaters' which is having been in charge of a leading role of GEN since 1996 (GEN was formed in 1996) as Ecovillage in Australia. First, to secure the water resources, we can store up rain and the water of valley, and dam. Second, we are able to use the natural filter apparatus, do tree-planting of roof to gain better quality of water. Third, it is to save the energy as supplying water. For it, we make the best of a gravity that is one of the cycle principle of water. Forth, to build a Dam can make a site of scenic beauty, do the role of recreation place and provide against emergencies (a fire, drought) as well as make a mild climate. Fifth, it can reduce the environment load because of sewage and garbage as making it compost. This is possible by treating biologically using composting apparatus of the dry or wet process. Sixth, it is to reduce the environmental pollution as to discharge seperating a recycable waste, an organic matter being able to make it compost. Finally, first of all, environmentally friendly inhabitant consciousness from lifestyle and production style plays an importent part for water cycle and the ecological cycle of waste and sewage.