• 대한기계학회논문집A
• /
• 제25권7호
• /
• pp.1082-1088
• /
• 2001

Nowadays study on recycling disused plastics for automobiles was lively progressed. Rubber and talcum powder was added to retrieve degradation of physical properties caused by recycling disused polypropylene. The effect of the temperature, the fatigue load and the loading speed on DEN(double edged notch) specimen which was made by the pp-rubber composites during fracture was studied by. DEN specimen was made on PP-rubber composites through the injection molding. With increasing temperature the fracture strength was linearly decreased and the fracture energy was increased by $0^{\circ}C$ and after that decreased. In the same temperature the fracture strength during increasing the notch radius was hardly increased. The fracture behaviour at low and high loading speed was different entirely. At high loading speed plastic region was small and fracture behaviour was seen to brittle fracture tendency. With increasing fatigue load fracture energy was first rapidly decreased and subsequently steady when radius of notch tip was 2mm, but Maximum load during fracture scarcely varied. The deformation mechanism of polypropylene-rubber composites during fracture was studied by SEM fractography. A strong plastic deformation of the matrix ahead of the notch/crack occurred. The deformation seem to be enhanced by a thermal blunting of the notch/crack.

• Steel and Composite Structures
• /
• 제25권6호
• /
• pp.685-692
• /
• 2017

In this study, the effect of various adhesively bonded composite patches on mechanical properties of notched Al-Mg alloy plates was analyzed. For this purpose firstly, the un-notched and notched specimens were fabricated from 5086 Al-Mg alloys which have been used in armor-plated military vehicles. The surface notches as a flaw were machined with circular cutting tool to form notch aspect ratio a/c=0.15 and notch-to-thickness ratios a/t=0.5 in the radial direction on the test specimens. Then, various composite patches which reinforced by glass, carbon and Kevlar fibers were bonded adhesively at elliptically surface notches. Finally, experimental measurements conducted by applying tensile static loading. The experimental results showed that repairing with composite patches with order of carbon, glass and Kevlar fibers have remarkable effect on tensile strength of the notched plate. Also the finite element models were developed using Abaqus/Explicit code to predict the tensile strength and elongation of unrepaired notched specimen and specimen repaired by carbon fiber composite patch. The comparison between numerical and experimental results showed good agreement between them and proved the accuracy of numerical modeling.

• 한국해양공학회지
• /
• 제2권2호
• /
• pp.112-121
• /
• 1988

A study on friction welding of carbon steel bar (SM45C) to chrome molybedenum steel bar(SCM4) is examined experimentally through tensile test, hardness test, microstructure test and fatigue test. so, this paper deals with optimizing the welding concitions and analyzing various mechanical properties about friction welds of SM45C to SCM4 steel bars. The results obtained are summarized as follows; 1) For friction welded joints of SM45C to SCM4 steel bars, the total upset(U)increases linearly with an increase of heating time ($t_{1}$) till 6s. 2) The determined optimum welding conditions are heating time ($t_{1}$)2s, upsetting time($t_{2}$), 3s, heating pressure($p_{1}$), 4kgf/$mm^{2}$(39.2MPa), upsetting pressure($p_{2}$, 8kgf/mm$^{2}$(78.4MPa) and rotating speed(N), 2, 000rpm when the total upset(U) is 3.4mm, resulting in a computed relationship between the joint tensile strength .sigma.$_{t}$ (kgf/mm$^{2}$and the total upset U(mm); .sigma.$_{t}$ =$0.21U^{3}$ - $3.38U^{2}$ +17.03U + 66.00 3) As the elongation is increased more and more, the fracture position becomes away from weld interface and the fractures are similar to those of SM45C. Fracture is taken place on SM45C side. 4) The weld interface of two dissimilar materials is mixed strongly, and the heat affected zone is about 2.0mm at SM45C while about 2.7 mm at SCM4 side. Therefore, the welded zone and heat affected zone are very narrow, comparing with those of the joints welded by the other welding methods. 5) The fatigue strengths at N=10$^{6}$ cycles of SM45C, SCM4 and friction welded joints are 23kgf/$mm^{2}$, 33kgf/$mm^{2}$(220.5 MPa), and 22.5kgf/$mm^{2}$(220.5MPa) respectively, and fracture at friction welded joint takes place at the side of SM45C. 6) The hardness of the friction weld interface is 3 times higher than that of base metal. 7) Fatigue strength of friction welded joint is higher than that of base metal. 8) Notch sensitivity factor of friction welded joint is lower than that of base metal.

• 전기학회논문지
• /
• 제62권3호
• /
• pp.431-436
• /
• 2013

A neutral section is installed around feeding substation(SS) and sectioning post(SP) that M phase and T phase are isolated in AC feeding system. Electric Train under "Notch-OFF" is operated by inertia within the neutral section. It causes disturbing the operation of electric trains for speed drop and driver's mistakes. A automatic changeover system with thyristor recently have taken under development. In the paper, it is introduced the configuration of train detection system and performance testing on automatic changeover system..

• 선박안전
• /
• 통권25호
• /
• pp.64-76
• /
• 2008

This paper describes the failure mechanism and Charpy impact test of Fiber glass Reinforced Plastic composites which it was actually used for side plate of vessel. There are two examinations. The examination I, the specimens which it given temperature range $-25^{\circ}C$-$50^{\circ}C$ and with different initial notch length did impact test and then it compared impact energy(Uc) and impact fracture toughness(GIC). The examination II, the specimens which it putted into fresh water and sea water for scheduled hours did impact test and it compared impact energy(Uc) and impact fracture toughness(GIC). From examination I, it showed that impact energy(Uc) and impact fracture toughness(GIC) were peak at ambient temperature and decrease as temperature reduced. Fracture toughness(GIC) showed increase as initial notch length reduced. From examination II, impact energy(Uc) and impact fracture toughness(GIC) tended to increase which specimens putted in fresh water compared with sea water and maximum tolerance rate tend to decrease as permeation hours will be long.

• The Korean Journal of Physiology and Pharmacology
• /
• 제23권4호
• /
• pp.251-261
• /
• 2019

Allergic asthma, is a common chronic inflammatory disease of the airway presenting with airway hyperresponsiveness and airway remodelling. T helper cells-derived cytokines are critically associated with asthma pathogenesis. Janus kinase-signal transduction and activation of transcription (JAK/STAT) signaling is found to be involved in asthma. Magnolol is a plant-derived bioactive compound with several pharmacological effects. The study aimed to assess the effects of magnolol in ovalbumin (OVA)-induced asthmatic model. BALB/c mice were sensitized and challenged with OVA. Magnolol (12.5, 25, or 50 mg/kg body weight) was administered to separate groups of animals. Dexamethasone was used as the positive control. Cellular infiltration into the bronchoalveolar lavage fluid (BALF) were reduced on magnolol treatment. The levels of Th2 and Th17 cytokines were reduced with noticeably raised levels of interferon gamma. Lung function was improved effectively along with restoration of bronchial tissue architecture. OVA-specific immunoglobulin E levels in serum and BALF were decreased by magnolol. Magnolol reduced Th17 cell population and effectively modulated the JAK-STAT and Notch 1 signaling. The results suggest the promising use of magnolol in therapy for allergic asthma.

• 대한기계학회논문집A
• /
• 제22권4호
• /
• pp.834-842
• /
• 1998

This paper examines the crack growth behavior of 7075-T651 and 5052-H32 aluminum alloy under high-low block loading condition. The cantilever beam type specimen with a chevron notch is used in this study. The crack growth and closure ae investigated by compliance method. The applied stress ratios are R=0.15, 0.0, -0.15 and R=-0.15, 0.0, 0.15. The crack growth rate was found to increase as the load amplitude increases. However,${\bigtriangleup}K_eff$ was almost independent on the stress ratio. The experimental constants of 7075-T651 and 5052-H32 in Paris law were c`=1-1.3${\times}{10^-7},m`=3~3.2 and c`=4~6{\times}{10^-9}, m`=4.3-4.8$, respectively. $K_op$ of 7075-T651 and 5052-H32 becomes smaller as the stress ratio decreases. It seems that the crack closure affects $K_op$.

• 대한기계학회논문집A
• /
• 제33권4호
• /
• pp.409-416
• /
• 2009

Standard procedures for a fracture toughness testing require very severe restrictions for the specimen geometry to eliminate a size effect on the measured properties. Therefore, the used standard fracture toughness data results in the integrity assessment being irrationally conservative. However, a realistic fracture in general structures, such as in nuclear power plants, may develop under the low constraint condition of a large scale yielding with a shallow surface crack. In this paper, cleavage fracture toughness tests have been made on side-grooved PCVN (precracked charpy V-notch) type specimens (10 by 10 by 55 mm) with various crack depths. The constraint effects on the crack depth ratios were evaluated quantitatively by the developed scaling method using the 3-D finite element method. After the fracture toughness correction from scaling model, the statistical size effects were also corrected according to the standard ASTM E 1921 procedure. The results were evaluated through a comparison with the $T_0$ of the standard CT specimen. The corrected $T_0$ for all of the PCVN specimens showed a good agreement to within $5.4^{\circ}C$ regardless of the crack depth, while the averaged PCVN $T_0$ was $13.4^{\circ}C$ higher than the real CT test results.

• Journal of Welding and Joining
• /
• 제11권4호
• /
• pp.57-69
• /
• 1993

In the present study, the microstructure and Charpy V notch toughness of multipass $CO_2$ FCA weldment in three different heat inputs(1-3KJ/mm)were investigated. The weldments using two different domestic FCAW wires(AWS E71T-1 and E71T-5 equivalent) in C-Mn steel were chemically analysed. The following conclusions can be inferred. 1. T-1 wire Showed a stable arc transfer, less spatter and harsh, a better bead spreading and easy slag removal, whereas T-5 wire suffered from the arc stability, which tended to increase spatter and produce a more convex bead. 2.The microsturctures of the top beads of the weldments in three different heat inputs consisted of coarse-grained boundary ferrite and Widmanstatten ferrite side plate with increasing heat inputs. The modest fraction of acicular ferrite in the two wire weldments was observed in the 2KJ/mm heat input. 3.The fine-grained reheated zones of both welds consisted of a duplex microstructure of polygonal ferrite and second phases. 4. The basic flux weldment of T-5wires showed a higher Charpy impact property than that of T-1 wires because of a higher fraction of acicular ferrite in the weld microstructure.

• 한국해양공학회지
• /
• 제6권2호
• /
• pp.71-75
• /
• 1992

기구나 구조물의 피로수명은 노치에서의 피로균열 방생수명에 의하여 지배되기때문에 노치로 인한 피로강도감소계수 $K_f$는 피로설계상 대단히 중요한 인자이다. 노치 선단(Notch root)에서의 피로균열발생명수 N$_c$를 기준으로하면 탄성응력집중계수 $K_t$가 10 정도까지 $K_f$와 $K_t$간에는 거의 직선적인 관계가 있음이 이다- 고에 의하여 명석해졌으나 이는 인장,압축의 축력이 작용하였을 때이며 따라서 기구나 구조부재는 축력외에도 굽힘 피로 하중이 작용하였을때도 많으므로 본 연구에서는 굽힘 피로 하중을 받았을때도 있다. -고의 결론이 적용되는지는 검시코져 본 연구를 실시하였다.