• 복식문화연구
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• 제21권6호
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• pp.967-973
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• 2013

During high speed sewing, the needle thread is exposed to dynamic loading, short strike loading, inertia forces, friction, rubbing, force of check spring, bending, pressure, friction, impact, shock and thermal influence. The dynamic thread loading/tension alters throughout the stitch formation cycle and along its passage through the machine. The greatest tensile force occurs at the moment of stitch stretching, when the take up lever pulls for required thread length through the tension regulator. These stresses act on the thread repeatedly and the thread passes 50-80 times through the fabric, the needle eye and the bobbin case mechanism, before getting incorporated into the seam, which result in upto 40% loss in tensile strength of the sewing thread. This damage in the sewing thread adversely affects its processing and functional performance. In this paper, the contribution of dynamic loading, passage through needle and fabric, and bobbin thread interaction in the loss in tensile properties has been studied. It is observed that the loss in tensile properties occurs mainly due to the bobbin thread interaction. Dynamic loading due to the action of take up lever also causes substantial loss in tenacity and breaking elongation of cotton threads.

• 한국군사과학기술학회지
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• 제10권1호
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• pp.144-149
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• 2007

Behaviour of a thread joint of a rocket motor case show complex structural characteristics. Pre-torque must be applied to the threads to prevent the loosening of the interface from the additional pressure load. During the pressurization of the rocket motor case, the jointing face may be opened if the pre-torque were not set properly or the structure may be failed if the local concentrated stress exceeds the strength of the material. In this paper, the structural behaviour of a thread joint of a rocket motor case were analyzed by the finite element method and the results were compared to the experimental ones. A method to set a pre-torque for a thread joint were proposed to ensure the structural safety.

• 한국정밀공학회지
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• 제16권4호통권97호
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• pp.122-128
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• 1999

Bolted joint assembly for nuclear power plants consists of various components : cover plate, retainer plate, manway flange, gasket and stud bolts/nuts. To guarantee the soundness of the joint, it is important to prevent leakage through the gasket and reduce the stress concentration factor at the thread root. In this paper, Submodeling technique for the finite element method is proposed to accurately compute three dimensional contact stresses which govern the sealing performance and the maximum contact stresses at the threads root. For verification of global solutions used as boundary conditions of submodel solution, the stresses on the cover plate and the manway flange are measured by strain gages when internal pressure is applied to the bolted joint assembly. The numerical results are compared with the experimental results.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2003년도 춘계학술대회
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• pp.1366-1371
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• 2003

Molecular dynamics (MD) simulations are conducted to investigate the thermophysical characteristics and the stability of liquid threads for various conditions. A cylindrical thread in the simulation domain is made of Lennard-Jones molecules. The surface tension of liquid threads can be determined from local densities, local normal and transverse components of the pressure force. In order to understand the effects of thread radii on surface tensions, the Tolman equation is modified on the basis of the cylindrical coordinates for prediction of surface tensions. Surface tensions calculated from the MD simulation agree with the prediction from the modified Tolman equation. In addition, surface tensions decrease linearly with increasing system temperature. For a binary system, the surface tension decreased linearly compared to that for a pure system with increasing binary ratio of solute molecules which have relatively large value of the affinity coefficient. For a fixed binary ratio, the surface tension increased slightly with the affinity coefficient and the maximum value appear around where the affinity coefficient is 1.5 and decreased rapidly for upper value of 1.5. In addition, the critical wavelengths of perturbations are proven to be directly proportional to the equimolar dividing radii of the liquid threads.

• 대한조선학회논문집
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• 제51권3호
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• pp.259-264
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• 2014

Tip vortex cavitation (TVC) is important for naval ships and research vessels that require raising the cavitation inception speed to maximum possible values. The concepts for alleviating the tip vortex are summarized by Platzer and Souders (1979), who carried out a thorough literature survey. Active control of TVC involves the injection of a polymer or water from the blade tip. The main effect of such mass injection (both water and polymer solutions) into the vortex core is an increase in the core radius, consequently delaying TVC inception. However, the location of the injection port needs to be selected with great care in order to ensure that the mass injection is effective in delaying TVC inception. In the present study, we propose a semi-active control scheme that is achieved by attaching a thread at the propeller tip. The main idea of a semi-active control is that because of its flexibility, the attached thread can be sucked into the low-pressure region closer to the vortex core center. An experimental study using a scale model was carried out in the cavitation tunnel at the Seoul National University. It was found that a flexible thread can effectively suppress the occurrence of TVC under the design condition for a model propeller.

• 한국압력기기공학회 논문집
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• 제11권2호
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• pp.6-12
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• 2015

In this study, the performance test was carried out under various operation conditions targeting four representing types of lubricant which are mostly used in nuclear power plants, and mutually compared the characteristic and performance of lubricant. Especially, introducing the concept of the thread friction coefficient (hereinafter, TFC), which makes the friction relation between the stem nut and stem screw dimensionless. The test was performed to compare the lubricant performance for the four kinds of lubricant (Texaco, Alvania, Mobilux, MOVLL). In a test of the room temperature stem, the TFC of MOV Long Life shows the lowest value, next to Alvania EP2, Texaco EP2, and Mobilux EP0 in that order. And in a test of the high temperature stem, the TFC of Texaco EP2 shows the lowest, next to MOV Long Life, Alvania EP2, and Mobilux EP0 in that order. From the test result of the aging condition, three types of lubricant (MOV LL, Texaco EP2, Alvania EP2) show similar patterns up to 36 months, but in 60 months, the TFC of lubricant are increased rapidly.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2003년도 추계학술대회논문집
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• pp.241-244
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• 2003

The productivity of hydroforming process can be increased by combining pre-forming process and post-forming process such as the bending, piercing and the embedding process. Therefore in this study, integrated studies on the hydro-embedding technology have been performed by analyzing the deformed mode of the tubes and the optimal process parameters. In the case of the embedding test the characteristics of the embedded parts, such as the shape of the screw tip, screw thread and shape of thread were investigated at various process conditions. To measure the clamping force between the embedded part and the tube, special measuring device was used.

• Elastomers and Composites
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• 제37권3호
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• pp.192-194
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• 2002

Polyester cord yarns have been treated in an atmospheric-pressure nitrogen plasma reactor in order to enhance their adhesion to rubber. A thin layer or the plasma was generated in the close vicinity of the yam surface using various types or surface discharge. To assess the effect of the plasma treatment on fiber surface properties, the cord thread/rubber matrix adhesion values measured using the untreated and threads cord threads were compared. The static and dynamic adhesion of the cord thread to rubber was characterized by using the standard Henley test. The dynamic adhesion values for the reference and plasma treated fiber were $7,3{\pm}1,2\;N$ and $83,5{\pm}3,5\;N$. The surface properties were investigated by scanning electron microscopy, infrared spectroscopy and electron spin resonance spectroscopy. It is concluded that both polar group interactions and increased surface area of the fibers are responsible for the improved adhesive strength.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2004년도 춘계학술대회 논문집
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• pp.206-209
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• 2004

In the hydroforming process the number of process can be reduced by combining pre-forming process and post-forming process such as the bending, piercing and the embedding process. Integrated studies on the embedding manufacturing technology have been performed by analyzing the deformed mode of the tubes and the optimal process parameters. In this study, a simulation model that can prove clamping force between the clamping element and tube has been investigated by FEM. The characteristics of the embedded parts, such as the shape of the screw tip, screw thread and shape of thread were investigated at various clamping element conditions.

• 한국압력기기공학회 논문집
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• 제15권1호
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• pp.62-70
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• 2019

The APR1400 reactor may be operated for a long time under high temperature and pressure conditions, causing damage to the stud holes and causing stud bolts and holes to stick. The present practice is to manually remove the anti-sticking agent and foreign matter remaining in the APR1400 reactor stud hole and to visually check the surface condition of the thread to check the damage status of the threads. In the case of the APR1400 reactor stud holes, manually cleaning the threads increases the risk of radiation exposure and operator's fatigue. To avoid this, the autonomous mobile robot is used to automatically clean the reactor stud holes. The purpose of this study is to optimize the cleaning performance of the mobile robot by looking at the behavior of the surface roughness of the stud surface cleaned by the brush attached to the mobile robot due to changes in brush material, thickness of wire, and rotation speed. A microscopic approach to the surface roughness of the flank is needed to investigate the effects of the newly proposed brush of the autonomous mobile robot on the thread holes. According to this experiment, it is reasonable to use STS brush rather than Carbon one. Optimal operating conditions are derived and the safety of APR1400 reactor stud holes maintenance can be improved.