• Journal of the Korean Society of Propulsion Engineers
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• v.23 no.2
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• pp.111-117
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• 2019

An experimental study on the welding part of a heat transfer plate that constitutes the lightweight and high efficiency recuperator is presented in this paper. In particular, to find out the service life of the welded part, fatigue characteristics were determined through experiments. Experiments were carried out on two materials (STS347, AL20-25 + nb), which are selected as the material of the recuperator; further, the specimens were manufactured through the methods used for actual fabrication and the standards recommended by ASTM. To evaluate the mechanical properties of the specimens at room and high temperature, MTS-810 was used in a high-temperature furnace. The tensile test was carried out at room and high temperatures for each specimen. The fatigue test was carried out by setting the load ratio corresponding to 50%, 40%, 30%, 20%, and 10% of the tensile strength at the stress ratio of 0.1. Finally, the fatigue life characteristics obtained by the experiment were compared with the stresses owing to the load generated in the operating conditions of the recuperator, and the lifetime of the welds was evaluated to prepare for the operation time required by the UAV.

• Aerospace Engineering and Technology
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• v.13 no.2
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• pp.160-166
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• 2014

The shutoff valve of a Liquid Rocket Engines (LRE) controls the flow of propellant between turbo-pump and combustion devices of LRE using pilot pressure and spring force. The shutoff valve is closed when the pilot pressure is removed from the diaphragm type actuator. During designing process of life cycle is when should be analyzed according to the characteristics of forces with respect to the opening and closing of diaphragm actuator. A valve has been designed to adjust the control pressure which is required to open a poppet and to determine the working fluid pressure at which a valve starts to close. During flow capacity test under room temperature as a part of life cycle tests, the leakage in diaphragm was occurred due to the leakage of sheet welding sections. The operating cycle of the diaphragm type actuator is about 61 times with 22 MPa of pilot pressure.

• The Journal of Korean Academy of Prosthodontics
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• v.40 no.5
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• pp.470-483
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• 2002

The purpose of this study was to investigate further the mechanics of failure of magnets used for denture retention. Dyna magnets were retrived from denture that had failed after 34 months of clinical use. The magnets were observed and sectioned in order to analyse with high resolution scanning electron microscope. From this study, corrosion behaviors of used magnetic attachment were analysed. The results were as follows ; 1. In Nd-Fe-B based magnetic materials, the erosion-corrosion was started at ununiformed part of stainless steel cover. 2. Corrosion was initiated at weared stainless steel surface and then magnetic materials were spalled by corrosive solution. 3. Spatting was occurred in Nd-Fe-B magnet materials due to corrosion products and then corrosion rate was increased drastically. 4. Corrosion started from ununiformed stainless steel surface as well as welded zone. In conclusion, the failure of magnets may occur by either breakdown of the welding or breakdown of the encapsulating material. So, it is considered that the corrosion problem of dental magnetic materials could be solved to some extent with surface treatment of dental magnetic materials.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.27 no.5
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• pp.713-723
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• 2003

In this study, a state of art review of existing residual stress analysis techniques and representative solutions is presented in order to develope the residual stress analysis procedure for fitness-for-service (FFS) assessment of welded structure. Critical issues associated with existing residual stress solutions and their treatments in performing FFS are discussed. It should be recognized that detailed residual stress evolution is an extremely complicated phenomenon that typically involves material-specific ther-momechanical/metallurgical response, welding process physics, and structural interactions within a component being welded. As a result, computational procedures can vary significantly from highly complicated numerical techniques intended only to elucidate a small part of the process physics to cost-effective procedures that are deemed adequate for capturing some of the important features in a final residual stress distribution. Residual stress analysis procedure for FFS purposes belongs to the latter category. With this in mind, both residual stress analysis techniques and their adequacy for FFS are assessed based on both literature data and analyses performed in this investigation.

• Journal of the Korean Society for Nondestructive Testing
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• v.8 no.1
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• pp.12-21
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• 1988

The behaviour of pressure vessel made of SS41 steel was investigated during hydrotest. AE tests were carried out for the vessels in as-manufactured, V-notched and weld-cracked state using microcomputer-based AE instrumentation. The following results were obtained: 1) In the case of source location using cylindrical program, to minimize the error of source location, the difference of max. Delta T values measured from each sensor should be kept as small as possible. 2) When crack grew, AE event rate increased continuously but AE event from the inclusions occurred intermittently, so by analyzing event rate, the source of AE could be derived. 3) From the spot welding part of supporter, many events with low energy occurred independent of Kaiser effect, which could be confirmed by analyzing energy parameter. 4) The b-value from the tensile specimen of was lower than that from normal specimen and the b-value from crack propagation was lower than that from deformation, so by analyzing peak amplitude distribution, the source mechanism could be derived from the b-value.

• Transactions of Materials Processing
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• v.20 no.2
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• pp.110-117
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• 2011

The purpose of this work is to develop of a press forming process for mobile phone battery cover as an alternative to the current manufacturing process by laser welding. This press forming process consists of a combination of bending, side pressing and side bending operations. The dimensional error for each process was investigated by finite element(FE) analysis and the Taguchi optimization method. The spreading of the cover width in the side pressing process was adjusted by modifying the blank shape with a notch. The over-bending method was adopted to compensate the spring-back which occurs after bending. Forming experiments were performed to verify the reliability of the developed press forming process. In addition, the strength of the product was evaluated to verify the suitability of the battery cover manufactured with this new press forming process. The results of the forming experiments indicate that the dimensional accuracy of the battery cover is within the required tolerance. The strength of the battery cover was evaluated to 547N which is larger than required strength of 400N.

• Transactions of Materials Processing
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• v.19 no.8
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• pp.508-516
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• 2010

Thickening process in sheet metal forming is being increased to improve the strength as well as to reduce manufacturing process such as welding. This process can make it possible to obtain part locally thicker than that of initial sheet thickness. In this study, design method for manufacturing the component which has double sinks with local thickened wall is proposed. Deep drawing and upsetting processes are applied in order to form double sinks and thicken its walls. Used material is SPHC440 with the thickness of 2.0mm and initial blank size is determined on the basis of the final product. Distance between the center of double sinks and first drawing ratio to avoid fracture are the most significant factors during deep drawing. FE-analysis is implemented in order to determine the appropriate values. Progressive die is designed based on the proposed method and FE-analysis. As a result of experiment, locally thickened component can be manufactured, which has double sinks with the thickness about 3mm at the corner and wall.

• Design & Manufacturing
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• v.14 no.2
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• pp.49-55
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• 2020

Recently, when a new component of construction equipment is designed, a stamping process capable of producing parts having high appearance quality and precision has been gaining attention. However, in general, as it is developed based on existing parts made by welding metal sheets and tubes, frequent to die modification occurs, which increases the time and cost of developing new parts. Thus, it is necessary to reduce the cost by shortening the die development period. In this study, a stamping process was designed for the urea tank cover, which is a part for excavators, to reduce the die development period through sheet metal forming analysis. The stamping process was designed by determining the blank holding force after selecting the initial blank shape and size. The round value at the corner was modified such that formability is ensured. After selecting process parameters, the thickness reduction rate and spring-back effect were reviewed.

• Journal of the Korean Institute of Intelligent Systems
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• v.22 no.4
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• pp.481-486
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• 2012

This thesis examines the development and application of 'Health Monitoring System' which monitors periodically the state of a pipe of petrochemical plant by using magnetostrictive sensor technology. The existing guided-wave inspection methods cannot be applied to welding part inspection in pipe, and has a limit of precision when applied to general parts because of noise, reflected waves, and so on. This technology uses the information on displacement of a defect through periodic monitoring, which makes more precise inspection, and can be utilized very usefully in a petrochemical plant.

• Journal of the Korean Institute of Gas
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• v.2 no.4
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• pp.1-6
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• 1998

In order to increase design efficiency, it is required to design steam boiler pressure parts systematically considering daily start-stop operation and load variation. The objective of this research is to develope an integrated system for increasing design efficiency of boiler pressure parts. The developed system consists of three program modules: (1) flexibility design module for the header stub considering fatigue life, (2) fatigue limit calculation and life evaluation module for the thick-walled boiler pressure part under cyclic operation using TRD301 code, (3) drawing automation module for the header and drum producing design drawings, welding data and bill of materials.