• Transactions of the Korean Society of Mechanical Engineers A
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• v.24 no.4 s.175
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• pp.1055-1064
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• 2000

First, various specimen geometries, namely, coupon type, waisted type and dog-bone type, were examined to determine appropriate fatigue specimen of thermoplastic composite material AS4/PEEK and the n, fatigue strength of smooth and notched specimens of AS4/PEEK [-45/0/+45/90]2s was investigated. Fatigue tests were performed under load controlled condition at a stress ratio of 0. 1 at a frequency of 5Hz. Stiffness degradation of specimens with fatigue cycling was monitored using an automated unloading compliance technique. The waisted type specimen is found appropriate for smooth fatigue specimen geometry of AS4/PEEK. As for the effect of stress concentration, it is found that fatigue strength is higher for a 2mm-diameter hole notched specimen than a 5mm-diameter one. Fatigue notch factor decreases with the increase of fatigue life. These results are far different from the trend of fatigue strength of metallic materials. The stiffness variation of smooth specimen was only 4% at maximum until final fracture. On the other hand, the stiffness of hole notched specimen was reduced by 45% at maximum. Notched fatigue strength was compared between thermoplastic composite AS4/PEEK and thermosetting composite Graphite/Epoxy. In long-life fatigue (>104), the AS4/PEEK composite shows superior fatigue strength, but in short-life fatigue, the fatigue strength of the Graphite/Epoxy composite is nearly equal or somewhat higher than that of the AS4/PEEK composite.

• Journal of Energy Engineering
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• v.29 no.3
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• pp.91-96
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• 2020

For the anchor bolts and brackets that fix the stone wall, which is an external finishing material, it is necessary to maintain the performance required for the mechanical structure from the initial design stage and secure high durability. For this, the design and safety evaluation in consideration of the load conditions are necessary, so the structural analysis applying the finite element analysis technique was performed as a method to verify durability. As a result of structural analysis for various shapes for optimal design, a reinforcing structure was added to alleviate the maximum stress generated at the rear part of the bracket in contact with the bolt. In addition, a reinforcing plate was additionally attached to the bracket to relieve the stress concentration of the L-shaped bracket to make the stress distribution uniform, so that the safety factor satisfies the standard conditions. In addition, the fatigue life analysis by cyclic load was performed, and the fatigue safety factor was analyzed. As a result, the durability was obtained.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.20 no.7
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• pp.2097-2107
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• 1996

The dynamic photoelastic technique had been utilized to investigate the possibillity of relieving the large local singular stresses induced at the corner of a right- angle- indenter. The indenter compressed a semi-infinite body dynamically with an impact load applied on the top of the indenter. The effects of the geometric changes of the indenter in terms of the diameter (d) and the location (1) of the stress relieving notch on the behavior of the dynamic contact stresses were investigated. The influence of stress relieving notches positioned along the edge of the semi-infinite body on the dynamic contact stresses were also studied by changing the diameter (D) and the location (L) of the notch. A multi-speak-high speed camera with twelve sparks were used to take photographs of full field dynamic isochromatic fringe patterns. The contact singular stresses were found to be released significantly by the stress relief notches both along the indenter and the edge of the semi-infinite body. The optimal position and geometry of the stress relieving notches were obtained with the aid of limited experimental results.

• Geomechanics and Engineering
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• v.27 no.5
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• pp.497-509
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• 2021

A large deformation FEM (Finite Element Method) based numerical analysis has been performed to study the behaviour of the bell-shaped anchor embedded in undrained saturated (cohesive) soil with the help of finite element based software ABAQUS. A typical model anchor with bell-diameter of 0.125 m, embedded in undrained saturated soil with varying cohesive strength (from 5 kN/m² to 200 kN/m²) has been chosen for studying the characteristic behaviour of the bell-shaped anchor installed in cohesive soil. Breakout factors have been evaluated for each case and verified with the results of experimental model tests for three different types of soil samples. The maximum value of breakout factor was found as about 8.5 within a range of critical embedment ratio of 2.5 to 3. An explicit model has been developed to estimate the breakout factor (F_c) for uplift capacity of bell-shaped anchor within clay mass in terms of H/D ratio (embedment ratio). It was also found that, the ultimate uplift capacity of the anchor increases with the increase of the value of cohesive strength of the soil and H/D ratio. The empirical equation developed in the present investigation is usable within the range of cohesion value and H/D ratio from 5 kN/m² to 200 kN /m² and 0.5 to 3.0 respectively. The proposed model has been validated against data obtained from a series of model tests carried out in the present investigation. From the stress-profile analysis of the soil mass surrounding the anchor, occurrence of stress concentration is found to be generated at the joint of anchor shaft and bell. It was also found that the vertical and horizontal stresses surrounding the anchor diminish at about a distance of 0.3 m and 0.15 m respectively.

• Restorative Dentistry and Endodontics
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• v.34 no.1
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• pp.69-79
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• 2009

The purpose of this study was to evaluate the influence of elastic modulus of restorative materials and the number of interfaces of post and core systems on the stress distribution of three differently restored endodontically treated maxillary second premolars using 3D FE analysis. Model 1, 2 was restored with a stainless steel or glass fiber post and direct composite resin. A PFG or a sintered alumina crown was considered. Model 3 was restored by EndoCrown. An oblique 500 N was applied on the buccal (Load A) and palatal (Load B) cusp. The von Mises stresses in the coronal and root structure of each model were analyzed using ANSYS. The elastic modulus of the definitive restorations rather than the type of post and core system was the primary factor that influenced the stress distribution of endodontically treated maxillary premolars. The stress concentration at the coronal structure could be lowered through the use of definitive restoration of high elastic modulus. The stress concentration at the root structure could be lowered through the use of definitive restoration of low elastic modulus.

• Composites Research
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• v.24 no.4
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• pp.29-35
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• 2011

The characteristic length method used to determine a laminate's strength generally requires the test for un-notched and notched laminates and finite element analysis together. In this paper, the methods used to predict the stress distribution and tensile characteristic length of open-hole laminates using the stress concentration factor and equivalent material properties are proposed. These methods do not require data on the failure load of open-hole laminates or finite element analysis. Once the stress and characteristic length have been determined, the failure load of the open-hole laminate can be calculated. The proposed method considers the effect of the material properties as a parameter and therefore can be applied to a variety of materials. The stress distribution is verified by comparing with a finite element analysis and test results. The predicted failure load shows a maximum deviation of 8% from the test results.

• Journal of Welding and Joining
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• v.33 no.6
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• pp.6-12
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• 2015

Thermal fatigue life of the automobile exhaust manifold is directly affected by the restraint force according to the structure of exhaust system and bead shape of the welded joints. In the present study, the microstructural changes and precipitation behavior during thermal fatigue cycle of the 18wt% Cr ferritic stainless steel weld heat affected zone (HAZ) considering restraint stress were investigated. The simulation of weld HAZ and thermal fatigue test were carried out using a metal thermal cycle simulator under complete constraint force in the static jig. The change of the restraint stress on the weld HAZ was simulated by changing the shape of notch in the specimen considering the stress concentration factor. Thermal fatigue properties of the weld HAZ were deteriorated during cyclic heating and cooling in the temperature range of $200^{\circ}C$ to $900^{\circ}C$ due to the decrease of Nb content in solid solution and coarsening of MX type precipitates, laves phase, $M_6C$ with coarsening of grain and softening of the matrix. As the restraint stress on the specimen increased, the thermal fatigue life was decreased by dynamic precipitation and rapid coarsening of the precipitates.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.14 no.1
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• pp.57-62
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• 2013

Because there is no suspension and differential devices at cart body, the deformation of the frame happened during kart driving affects the driving performance caused by the elastic deformation and the fatigue life of kart frame resulted from the permanent deformation. The dynamic behavior of kart caused by the torsional deformation during circular driving is the important factor of these two kinds of deformations. In order to analyze the dynamic behavior of kart at this curved section, GPS is used to trace the track of kart and the torsional stress at kart-frame has been measured with real time. The mechanical properties of kart-frames for leisure and racing are investigated through material property analysis and tensile test. Torsional stress concentration and frame distortion are investigated through stress analysis on frame on the basis of study result. The real karts for leisure and racing kart are also tested in each driving condition by using the driving analysis equipment. The driving behavior of kart at the curved section are investigated through this test. As the phenomenon of load movement due to centrifugal force at car is happened during circular driving, the torsional stress occurs at cart steel frame.

• Nutrition Research and Practice
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• v.14 no.4
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• pp.334-351
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• 2020

BACKGROUND/OBJECTIVES: This study was designed to investigate the improvement effect of white ginseng extract (GS-KG9) on D-galactosamine (Ga1N)-induced oxidative stress and liver injury. SUBJECTS/METHODS: Sixty Sprague-Dawley rats were divided into 6 groups. Rats were orally administrated with GS-KG9 (300, 500, or 700 mg/kg) or silymarin (25 mg/kg) for 2 weeks. The rats of the GS-KG9- and silymarin-treated groups and a control group were then intraperitoneally injected Ga1N at a concentration of 650 mg/kg for 4 days. To investigate the protective effect of GS-KG9 against GalN-induced liver injury, blood liver function indicators, anti-oxidative stress indicators, and histopathological features were analyzed. RESULTS: Serum biochemical analysis indicated that GS-KG9 ameliorated the elevation of aspartate aminotransferase (AST), alanine aminotransferase (ALT), alkaline phosphatase (ALP), and lactate dehydrogenase (LDH) in GalN-treated rats. The hepatoprotective effects of GS-KG9 involved enhancing components of the hepatic antioxidant defense system, including glutathione, glutathione peroxidase (GPx), superoxide dismutase (SOD), and catalase (CAT). In addition, GS-KG9 treatment inhibited reactive oxygen species (ROS) production induced by GalN treatment in hepatocytes and significantly increased the expression levels of nuclear factor erythroid-2-related factor 2 (Nrf2) and heme oxygenase-1 (HO-1) proteins, which are antioxidant proteins. In particular, by histological analyses bases on hematoxylin and eosin, Masson's trichrome, α-smooth muscle actin, and transforming growth factor-β1 staining, we determined that the administration of 500 mg/kg GS-KG9 inhibited hepatic inflammation and fibrosis due to the excessive accumulation of collagen. CONCLUSIONS: These findings demonstrate that GS-KG9 improves GalN-induced liver inflammation, necrosis, and fibrosis by attenuating oxidative stress. Therefore, GS-KG9 may be considered a useful candidate in the development of a natural preventive agent against liver injury.

• Animal Bioscience
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• v.34 no.7
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• pp.1169-1180
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• 2021

Objective: This research aimed to study the effects of Artemisia argyi flavonoids (AAF) supplemented in diets on the growth performance and immune function of broiler chickens challenged with lipopolysaccharide (LPS). Methods: A total of one hundred and ninety-two 1-d-old broiler chicks were assigned into 4 treatment groups, which were, respectively, fed a basal diet (control), fed a diet with 750 mg/kg AAF, fed a basal diet, and challenged with LPS, fed a diet with 750 mg/kg AAF, and challenged with LPS. Each treatment had six pens with 8 chicks per pen. On days 14, 16, 18, 20 (stress phase I) and 28, 30, 32, 34 (stress phase II), broilers were injected with LPS (500 ㎍/kg body weight) or an equivalent amount of saline. Results: The results demonstrated that dietary AAF significantly improved the body weight (d 21) and alleviated the decrease of average daily gain in broilers challenged with LPS on d 21 and d 35 (p<0.05). Dietary AAF increased bursa fabricius index, and dramatically attenuated the elevation of spleen index caused by LPS on d 35 (p<0.05). Furthermore, serum interleukin-6 (IL-6) concentration decreased with AAF supplementation on d 21 (p<0.05). Diet treatment and LPS challenge exhibited a significant interaction for the concentration of IL-1β (d 21) and IL-6 (d 35) in serum (p<0.05). Additionally, AAF supplementation mitigated the increase of IL-1β, IL-6 in liver and spleen induced by LPS on d 21 and 35 (p<0.05). This study also showed that AAF supplementation significantly reduced the expression of IL-1β (d 21) and nuclear transcription factor kappa-B p65 (d 21 and 35) in liver (p<0.05), and dietary AAF and LPS treatment exhibited significant interaction for the gene expression of IL-6 (d 21), toll like receptor 4 (d 35) and myeloid differentiation factor 88 (d 35) in spleen (p<0.05). Conclusion: In conclusion, AAF could be used as a potential natural immunomodulator to improve growth performance and alleviate immune stress in broilers challenged with LPS.