• 대한치과교정학회지
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• 제45권5호
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• pp.268-272
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• 2015

Clear thermoplastic retainers have been widely used in daily orthodontics; however, they have inherent limitations associated with thermoplastic polymer materials such as dimensional instability, low strength, and poor wear resistance. To solve these problems, we developed a new type of clear orthodontic retainer that incorporates multi-layer hybrid materials. It consists of three layers; an outer polyethylenterephthalate glycol modified (PETG) hard-type polymer, a middle thermoplastic polyurethane (TPU) soft-type polymer, and an inner reinforced resin core. The resin core improves wear resistance and mechanical strength, which prevent unwanted distortion of the bucco-palatal wall of the retainer. The TPU layer absorbs impact and the PETG layer has good formability, optical qualities, fatigue resistance, and dimensional stability, which contributes to increased support from the mandibular dentition, and helps maintain the archform. This new type of vacuum-formed retainer showed improved mechanical strength and rate of water absorption.

• 반도체디스플레이기술학회지
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• 제6권2호
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• pp.5-10
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• 2007

According to the advantageous features of flash memory, its exploitation and application in mobile and ubiquitous related devices as well as voluminous storage devices is being increased rapidly. The inherent properties that are determined by configuration of flash memory unit might restrict the promising expansion in its utilization. In this paper, we study policies based on threshold values, instead of using global search, in order to satisfy our objective that is to decrease the necessary processing cost or penalty for recycling of flash memory space at the same time minimizing the potential degradation of performance. The proposed cleaning methods create partitions of candidate memory regions, to be reclaimed as free, by utilizing global or dynamic threshold values. The impact of the proposed policies is evaluated through a number of experiments, the composition of the optimal configuration featuring the methods is tested through experiments as well.

• 한국공작기계학회논문집
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• 제10권5호
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• pp.25-30
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• 2001

The purpose of this investigation is experimentally to clarify the machinability and optimum tool geometry on milling of hardened STD11 steel. In the finish process office milling of high hardened STD11 steel by CBN tool, the optimum tool shape is suggested, which can minimize the tool fracture and chipping by impact. It is measured that cutting farce, tool wear and surface roughness generated during single-insert face milling using various geometric CBN tools. It has been found that the optimal chamfer angle of CBN tool is about -$25^{\circ}C$ and the suitable chandler width is 0.2mm. The nose radius of tool is the most excellent at 1.2mm in the viewpoint of tool wear and surface roughness.

• 한국기계가공학회지
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• 제20권2호
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• pp.120-125
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• 2021

Phylon molds are widely used for injection molding of foams used in shoe outsoles. Injection pylon molds are usually prepared by first casting the aluminum alloy and then applying an anodized coating to improve durability. This study was carried out to examine the durability of aluminum phylon molds. The aluminum materials used in this study were A771, A6061, and AC4C, and their mechanical properties were compared. Specimens for anodic oxidation tests were prepared with coating thicknesses of approximately 10 and 40 ㎛. We tried to select the optimum material and coating thickness suitable for fabricating phylon injection molds. Among the three materials, A6061 exhibited the best tensile, wear, and impact properties. The difference in the wear resistance between the soft- and hard-anodized coatings was insignificant.

• International Journal of Advanced Culture Technology
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• 제9권2호
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• pp.130-135
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• 2021

Because of the COVID-19 epidemic, many countries have made the obligation to wear masks normal. Wearing masks in public places has become a must. At present, wearing a mask to participate in sports makes it very common. People seek to gain health through exercise but ignore the potential respirato-ry health threat. That is, wearing a mask will cause a decrease in oxygen content in the body. This neg-ative impact becomes more prominent as the wear-ing time and oxygen consumption increase. To pro-tect people from viruses and enjoy a healthy life. This paper proposes a breathing pattern that im-proves blood oxygen saturation while wearing a jogging mask and walking. Namely, shouting breathing pattern. Use a pulse oximeter to measure the blood oxygen saturation of running at different speeds and compare the normal breathing pattern and the shouting breathing pattern. The results show that the shouting breathing pattern has a sig-nificant improvement in the blood oxygen satura-tion of low-speed walking and medium-speed jog-ging.

• 한국정밀공학회지
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• 제13권7호
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• pp.36-44
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• 1996

Drilling tests were carried out austempered ductile cast iron(ADI) to clarify the factors influencing the drilling characteristics of ADI material. The machinability of material was evaluated using high speed steel drill and cobalt contained drill of 6mm diameter. The spheroidal graphite cast iron materials were austemized at 900 .deg. C for 1 hour and then wear was kept at 375 .deg. C for 2 hours. Austempered ductile cast iron contains a great deal of retained austenite which contribustes to an improvement of impact strength. In this paper, machinability of ADI was invastigated by drilling experimentation. The results obtained are as follows:a) Flank wear incresses logarithmically with the increases of cutting time and proportionally with the increases of cutting force. b) Drilling hole number of about 2 times can be educed more step feed than ordinary feed due to the high hardness of ADI material and hardness increasing ascribed to the martensite of retained austenite.

• Tribology and Lubricants
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• 제39권5호
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• pp.167-172
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• 2023

Titanium alloys are widely recognized among engineering materials owing to their impressive mechanical properties, including high strength-to-weight ratios, fracture toughness, resistance to fatigue, and corrosion resistance. Consequently, applications involving titanium alloys are more susceptible to damage from unforeseen events, such as scratches. Nevertheless, the impact of microscopic damage remains an area that requires further investigation. This study delves into the microscopic wear behavior of α-titanium crystal structures when subjected to linear scratch-induced damage conditions, utilizing molecular dynamics simulations as the primary methodology. The configuration of crystal lattice structures plays a crucial role in influencing material properties such as slip, which pertains to the movement of dislocations within the crystal structure. The molecular dynamics technique surpasses the constraints of observing microscopic phenomena over brief intervals, such as sub-nano- or pico-second intervals. First, we demonstrate the localized transformation of lattice structures at the end of initialization, indentation, and wear processes. In addition, we obtain the exerted force on a rigid sphere during scratching under linear movement. Furthermore, we investigate the effect of the relaxation period between indentation and scratch deformation. Finally, we conduct a comparison study of nanoindentation between crystal and amorphous Ti substrates. Thus, this study reveals the underlying physics of the microscopic transformation of the α-titanium crystal structure under wear-like accidental events.

• 한국의류학회지
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• 제29권6호
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• pp.837-846
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• 2005

The purpose of this study is to suggest a standard of guidance for testing the performance and safety of motorcycle jacket with built-in airbag. The method of testing were as follows: The effects of the motorcycle jacket with built-in airbag are experimentaly investigated according to neck injury of FMVSS 208. The experiment consists of the crash simulation test by shield and the impact test. The head and neck injuries are evaluated based on industrial standards. Also, the displacements of the head and neck and chest are observed by film analysis. Using the results of the crash simulation test, neck injury$(N_ij)$ is discussed and the peak chest deflection of the results of the impact test, chest injury is pursued. Neck injury$(N_ij)$ of the result of the crash test show that the chance of a serious wound is $18\%$ if rider wear the R&D motorcycle jacket with built-in airbag(Type A). Chest injury is expected by peak chest deflection of the result of the impact test. The result of the peak chest deflection show that the reduction effect in chest injury of Type A motorcycle jacket is $10.3\%$.

• 한국철도학회:학술대회논문집
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• 한국철도학회 2003년도 춘계학술대회 논문집
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• pp.706-711
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• 2003

This paper describes EDM testing, Magnetic particle testing and Ultrasonic testing results of carbody structure for EMU. Carbodys are subject to vibration, impact and wear which can cause severe defects leading to a fatal accident. The purpose of the test is to prove the endurance of Korean EMU for the commercial operation.

• 열처리공학회지
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• 제30권1호
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• pp.17-20
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• 2017

Mechanical properties of STD61 steel are compared with those of carburized STD61 steel when both are quenched and tempered in vacuum heat treatment. Mechanical properties of carburized STD61 steel are improved better than STD61 steel in hardness, tensile strength, impact energy and wear resistance.