• Structural Engineering and Mechanics
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• v.55 no.6
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• pp.1087-1097
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• 2015

In this paper, the effect of functionally graded material (FGM) coatings on the fracture behavior of semi-elliptical cracks in cylinders is assessed. The objective is to calculate the stress intensity factor (SIF) of a longitudinal semi-elliptical crack on the wall of an aluminum cylinder with FGM coating. A three-dimensional finite element method (FEM) is used for constructing the mechanical models and analyzing the SIFs of cracks. The effect of many geometrical parameters such as relative depth, crack aspect ratio, FG coating thickness to liner thickness as well as the mechanical properties of the FG coating on the SIF of the cracks is discussed. For a special case, the validity of the FE model is examined. The results indicated that there is a particular crack aspect ratio in which the maximum value of SIFs changes from the deepest point to the surface point of the crack. Moreover, it was found that the SIFs decrease by increasing the thickness ratio of the cylinder. But, the cylinder length has no effect on the crack SIFs.

• Journal of Surface Science and Engineering
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• v.32 no.2
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• pp.144-156
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• 1999

Thermal Barrier Coating with Functional Gradient Materials (FGM-TBC) can play an important role to protect the parts from harmful environments in high temperatures such as oxidation, corrosion, and wear and to improve the efficiency of aircraft engine by lowering the surface temperature on turbine blade. FGM-TBC can increase the life spans of product and improve the operating properties. Therfore, in this study the evaluations of mechanical and thermal properties of FGM-TBC such as fatigue, oxidation and wear-resistance at high temperatures have been conducted. The samples of both the TBC with 2, 3, 5 layers (YSZ/NiCrAlY) to be produced by Air Plasma Spray method (APS) and the bulk TBC with 6 layers to be produced by Plasma Assisted Sintering method (PAS) were used. Furthermore, residual stress, bond strength, and thermal conductivity were evaluated. The average thickness of the APS was 500$\mu\textrm{m}$ to 600$\mu\textrm{m}$ and the average thickness of the PAS was 3mm. The hardness number of the top layer of APS was 750 Hv to 810Hv and that of PAS was 950 Hv to 1440Hv. The $ZrO_2$ coating layer of APS was composed of tetragonal structure after spraying as the result of XRD analysis. As shown in the results of the high temperature wear test, the 3 layer coating of APS had the best wear resistance at $800^{\circ}C$ and the 5 layer coating of APS had the best wear resistance at $600^{\circ}C$. But, these coatings had the tendency of the low-temperature softening at $300^{\circ}C$. The main mechanism of wear was the adhesive wear and the friction coefficient of coatings was increased as increasing the test temperatures. A s results of thermal conductivity test, the ${\Delta}T$ of the APS coating was increased as number of layer and the range of thermal conductivity of the PAS was $800^{\circ}C$ to $1000^{\circ}C$.

• Corrosion Science and Technology
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• v.23 no.3
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• pp.179-194
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• 2024

A layer-by-layer coating was produced using electrophoretic deposition for a HA/Al₂O₃ coating layer and a bioglass coating layer on Co-Cr-Mo alloy with a roughness of 0.5 ㎛ (400 emery paper SiC). The corrosion behaviour was analyzed by assessing the coating layers' exceptional corrosion resistance, which outperformed the substrate. Cr ion release test using AAS was carried out, indicating that factional graded coating inhibited ion release from the uncoated substrate to coated sample. The porosity was expressed as a percentage, representing the extent of imperfections on the surface of all coatings. These imperfections fell within an acceptable range of 1% to 3%. The roughness of the coated surface was measured using atomic force microscopy, which revealed an excellent roughness value of 3.32 nm. Tape test technique for adhesion revealed that the removal area of the substrate coating layer varied by 11.92%. X-ray diffraction analysis confirmed the presence of all coating material peaks and verified phases of the deposited coating layers. These findings provided evidence that the coating composition remains unaffected by the electrophoretic deposition process. The bioactivity was assessed by immersion in a simulated bodily fluid, which revealed the formation of HCA during a period of 5 days.

• Journal of Oral Medicine and Pain
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• v.46 no.4
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• pp.117-124
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• 2021

Purpose: Salivation is considered to be an important factor in the control of halitosis, and the amount of salivation has been shown to be closely related to the level of hydration. The purpose of our study was to evaluate the relationship between dehydration and halitosis. Methods: Twenty healthy young females with no dental problems were recruited. All participants were induced to become dehydrated and then over-hydrated. After inducing each hydration state, the severity of hydration and halitosis factor (organoleptic scores, amounts of resting and functional saliva, gas examinations, and tongue coatings) were measured. Hydration statuses were graded as dehydration, normal, or over-hydration according to urine osmolality. This was a cross sectional study with a cross over design. Results: The dehydrated status was associated with higher organoleptic scores than the normal or over-hydrated status (1.75±0.75 vs. 0.87±0.63, and 0.65±0.53, respectively. p<0.05). Mean values of CH₃SH, (CH₃)₂S in portable gas chromatography for the dehydrated, normal, and over-hydrated status were 11.70±37.00, 6.75±13.50, and 2.80±5.87 nmol/mol, 10.50±15.59, 7.25±10.87, and 1.50±2.55 nmol/mol, respectively. p>0.05). (CH₃)₂S (r=0.410, p=0.009) showed a moderate positive correlation with dehydration status. The resting salivation rates were relatively lower for the dehydrated status than for the normal or overhydrated status (p>0.05), and tongue coating results were also higher for the dehydrated status (p>0.05). Conclusions: Dehydration status appears to be positively correlated with a low resting salivation rate and high portable gas chromatography results. This shows that dehydration might be an etiologic factor of halitosis.

• Composites Research
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• v.33 no.5
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• pp.235-240
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• 2020

In this study, in order to improve the impact resistance of the B₄C tile-inserted B₄C_p/Al7075 hybrid composite, a control method of the B₄C/Al7075 interface was developed and the characteristics of the controlled interface were analyzed. B₂O₃, Ni, and Si were coated on the B₄C tile surface using additional thermal oxidation, electroless plating, and plasma spraying. The coated B₄C tile is inserted into the B₄C_p/Al7075 composite material using the liquid pressurization method. Interfacial energy, bonding strength, and impact resistance were measured to analyze the effect of the coating. All coatings enhanced interfacial energy, bonding strength, and impact resistance, and in particular, it was confirmed that the impact resistance increased by 86.8% when B₂O₃ coating was used. This study is significant in developing and analyzing a core surface treatment method that improves the performance of B₄C/Al series composites, which are attracting attention as next-generation lightweight amour and bulletproof materials.