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임희식,김태형,박경채 대한용접접합학회 2003 대한용접·접합학회지 Vol.21 No.2
Metal matrix composites(MMC) consist of metal matrix into which is distributed a second solid phase. The normal intension is to develop a material with superior mechanical properties (for example increased toughness, stiffness and wear resistance) compared to those inherent in the matrix component. In this study, WC-12%Co/low carbon steel MMC overlays have been prepared by Gas Metal Arc Welding(GMAW) according to feeding rate of WC-12%Co grit. The macro and microstructures were examined using optical microscopy (OM) and scanning electron microscopy(SEM) each other. The characteristics of hardness and wear resistance have been investigated. WC-12%Co/low carbon steel MMC overlays which have been taken good beads without porosity and cracks were manufactured by method of GMAW. Matrix of overlayed surface was seen as fish bone and faceted dendrite structures. It was known that structures were iron tungsten carbides, Fe$_{6}$W$_{6}$C which have been occurred by melting of WC-12%Co grits. After MMC had been tested by block-roll wear test it was known that WC-12%Co/low carbon steel MMC has a excellent wear resistance by exiting Fe6w6c and WC-12%Co grit. The consequence was that region of overlay with Fe$_{6}$W$_{6}$C phase has been showed a model of adhesive wear, but region of overlay with WC-12%Co grit was restrained as a result of mechanism that wear of WC-12%Co grit is not adhesive but fracture.racture.
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WC-12%Co/저탄소강 MMC 용접 오버레이의 마모거동
임희식,김태형,박경채 대한용접접합학회 2003 대한용접·접합학회지 Vol.21 No.2
The protection of steel surfaces against wear is a practical problem far agricultural, mining and manufacturing industries. Commercial processes are available in which a hard tungsten carbides rich steel layer is formed on the surface of carbon steel digging, drilling and gouging tools to improve their wear resistance. The nature of the interaction of the tungsten carbide with the steel matrix is important in determining the wear and corrosion properties of the resulting metal matrix composites(MMC). In the study, WC-12%Co/low carbon steel MMC overlays have been prepared by gas metal arc welding(GMAW) according to size of WC-12%Co grits. The characteristics wear resistance and wear mechanism have been investigated in relation to the experiment conditions each other. After MMC overlay had been tested by rubber wheel abrasion test, it was known that MMC overlay has a excellent wear resistance. Fe$_{6}$W$_{6}$C carbides of matrix in overlays were not important to restrain rubber wheal abrasion wear. Wear loss is proportioned to a applied load according to time. On the case of low load, wear occurred severely in the matrix of overlay more than WC-12%Co grit, on the contrary it is reverse on the case of high load because of fracture of WC-12%Co grits.its.
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이현재,최병재,김순주,손흥규,임희식 大韓小兒齒科學會 1988 大韓小兒齒科學會誌 Vol.15 No.1
The most important condition associated with dens evaginatus is the loss of vitality of the affected tooth. this can be caused by fracture of the tubercle during mastication or attrition or attrition, which can eventually lead to pupal disease. Though it is not uncommon for dental patients of the Mongoloid group of races to present with dens evaginatus, there is no absolute prophylactic treatment to prevent several complications associated with this anomaly. The purpose of this article is to review various aspets of dens evaginatus and introduce some methods of prophylactic treatment such as mechanical grinding, direct or indirect capping and use of sealant with clinical cases.
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고주파전류를 이용한 치수절단술에 따른 성견 치수의 병리조직학적 연구
임희식,이종갑 大韓小兒齒科學會 1989 大韓小兒齒科學會誌 Vol.16 No.1
The purpose of this study was to contrast histopathologically the pulp response to formocresol with electrosurgical pulpotomy. Upper and lower teeth in three dogs, aged about 1 year, were subjected to mechanical pulp amputations and were divided into two groups, pulpotomized with formocresol and momentary electrosurgical exposure. The experimental animals were sacrificed at 3 days, 2 weeks postoperatively, section were obtained and observed with light microscope. The results were as follows. 1. In the formocresol groups, pulp tissue responses showed inflammation and atrophy of odontoblast confined to subjacent to amputation site and reparative dentin was formed in 6-week group. 2. In the electrosurgical groups, inflammatory zone was decreased with time elapsed and reparative dentin was formed in 6-week group. 3. Electrosurgical pulpotomy exibited no significant difference with formocresol histopathologically and almost typical morphology of pulp tissue for the time studied.
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김희진,임희식,최병재,오현주,박형우 大韓小兒齒科學會 1998 大韓小兒齒科學會誌 Vol.25 No.2
Tooth development is usually described in four stages such as bud stage, cap stage, bell stage and crown stage. Exact time of appearance of tooth primordia is different among reports, and up to now there is no timetable regarding initial tooth development. To understand the congenital malformations and other disorders of the orofacial region, there is need to establish a standard timetable of early tooth development. Till now, studies on the tooth development were mainly on later fetuses, and only few reports on early stage. Also, there were no reports on the time when bud stage turns to cap stage, and cap stage to bell stage. In this study, external morphology of face and the early development of the tooth, and transition of bud stage to cap stage, cap stage to bell stage were studied using 27 staged human embryos and 9 serially sectioned human fetuses. the results are as follows : 1. Mandibular region was formed by union of both mandibular arch at stage 15, and maxillary region by union of maxillary arch, medial nasal prominence, and intermaxillary segment at stage 19. 2. Ectodermal thickening which represents the primordia of tooth appeared in mandibular region at stage 13, and maxillary region at stage 15. 3. Bud stage began from mandibular primary central incisor at stage 17, and maxillary primary central incisor at stage 18. And the sequence of appearance was in the mandibular primary lateral incisor at stage 19, maxillary primary lateral incisor at stage 20, mandibular primary canine at stage 22, maxillary primary canine and primary first molar at stage 23, madibular primary first molar and maxillary primary second molar at 9th week, and mandibular primary second molar at 10th week of development. 4. cap stage began from the primary anterior teeth at 9th week, and primary second molar still had the characteristics of cap stage at 12th week of development. 5. Transition to bell stage started from the primary anterior teeth at 12th week, and primary second molar started at 16th week of development. 6. Trnasition to crown stage started from primary anterior teeth at 16th week, and primary second molar at 26th week of development.
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