• Steel and Composite Structures
• /
• v.26 no.5
• /
• pp.533-547
• /
• 2018

In this paper the time-dependent creep analysis of a thick-walled FG cylinder with finite length subjected to axisymmetric mechanical and thermal loads are presented. First order shear deformation theory (FSDT) is used for description of displacement components. Inner and outer temperatures and outer pressure are considered as thermo-mechanical loadings. Both thermal and mechanical loadings are assumed variable along the axial direction using the sinusoidal distribution. To find temperature distribution, two dimensional heat transfer equation is solved using the required boundary conditions. The energy method and Euler equations are employed to reach final governing equations of the cylinder. After determination of elastic stresses and strains, the creep analysis can be performed based on the Yang method. The results of this research indicate that the boundaries have important effects on the responses of the cylinder. The effect of important parameters of this analysis such as variable loading, non-homogeneous index of functionally graded materials and time of creep is studied on the behaviors of the cylinder.

• Journal of the Korean Society for Precision Engineering
• /
• v.26 no.12
• /
• pp.110-116
• /
• 2009

Thick-walled cylinders, such as a cannon or nuclear reactor, are autofrettaged to induce advantageous residual stresses into pressure vessels and to increase operating pressure and the fatigue lifetimes. As the autofrettage level increases, the magnitude of compressive residual stress at the bore also increases. However, the Bauschinger effect reduces the compressive residual stresses as a result of prior tensile plastic strain, and decreases the beneficial autofrettage effect. The purpose of the present paper is to predict the accurate residual stress of SNCM8 high strength steel using the Kendall model which was adopted by ASME Code. The uniaxial Bauschinger effect test was performed to decide BEF, then this constant was used in calculation. There were some differences between theoretical solution and modified solution.

• Asian-Australasian Journal of Animal Sciences
• /
• v.9 no.5
• /
• pp.519-524
• /
• 1996

An investigation was carried out to study the microbial colonization and degradation of five crop residues, viz., sago waste, rice straw, oil palm trunk shavings, untreated palm press fibre and palm press fibre teated with 3% ammonium hydroxide in the rumen of goats. Colonisation by rumen bacteria and fungi was already established on all the five crop residues 8 h after incubation. However, the extent of colonization varied among the crop residues. Microbial colonization was poor on palm press fibre (treated and untreated) but more extensive on sago waste, oil palm trunk shavings and rice straw. By 24 h, most of the soft-walled tissues in sago waste, rice straw and oil palm trunk shavings were degraded leaving the thick-walled tissues extensively colonized by bacteria and fungi. Degradation on palm press fibre was still limited. At 48 h, the thick-walled tissues of sago waste, oil palm trunk shavings and rice straw showed various degrees of degradation - from small erosion zones to large digested areas. Bacterial growth was similar to that at 24 h but fungal growth was less. On palm press fibre, microbial colonization was more extensive than at 24 h but degradation of the fibres was still limited. Degradation of all the five crop residues at 72 h was somewhat similar to that at 48 h. Overall, microbial colonization and degradation were the most extensive on sago waste, followed by rice straw and oil palm trunk shavings, and the least on palm press fibre (treated and untreated). Dry matter loss of the five crop residues at the various incubation periods also showed the same order of degradation.

• Structural Engineering and Mechanics
• /
• v.43 no.1
• /
• pp.105-126
• /
• 2012

Based on the first-order shear deformation theory (FSDT), and the virtual work principle, an elastic analysis for axisymmetric clamped-clamped Pressurized thick truncated conical shells made of functionally graded materials have been performed. The governing equations are a system of nonhomogeneous ordinary differential equations with variable coefficients. Using the matched asymptotic method (MAM) of the perturbation theory, these equations could be converted into a system of algebraic equations with variable coefficients and two systems of differential equations with constant coefficients. For different FGM conical angles, displacements and stresses along the radius and length have been calculated and plotted.

• Composites Research
• /
• v.24 no.2
• /
• pp.22-29
• /
• 2011

To increase the performance of thick-walled cylinders recently their length is continually enlarged. For that reason it is important to reduce weight of the thick-walled cylinders. In this paper the FE models to predict and estimate effects on the composite tapes were created with MSC.Nastran/Patran v.2005. First of all a autofrettage method was applied to the 2D model of the AISI4340 cylinder reduced the thick. And then the comparison of the numerical results with analysis results showed and verified by using T300/5208, IM7/PETI5, IM7/8552 tapes. Those are predicted to the effects of the angle of the composite tapes and elastic modulus according to the composite properties.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
• /
• v.22 no.12
• /
• pp.1089-1094
• /
• 2009

Carbon nanotubes (CNTs) have excellent electrical, chemical stability, mechanical and thermal properties. In this paper, networks of Multi-walled carbon nanotube (MWCNT) materials were investigated as resistive gas sensors for ethanol ($C_2H_5OH$) detection. Sensor films were fabricated by air spray method for the multi-walled CNTs solution on glass substrates. Sensors were characterized by resistance measurements in the sensing system, in order to find the optimum detection properties for the ethanol gas molecular. The film that was sprayed with the MWCNT dispersion for 60 see, was 300 nm thick. And the electric resistivity is $2{\times}10^{-2}\;{\Omega\cdot}cm$. Also, the sensitivity and the linearity of MWVNT sensor for ethanol gas are 0.389 %/sec and 17.541 %/FS, respectively. The MWCNT film was excellent in the response for the ethanol gas molecules and its reaction speed was very fast, which could be using as ethanol gas sensor. The conductance of the fabricated sensors decreases when the sensors are exposed to ethanol gas.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
• /
• v.23 no.4
• /
• pp.338-342
• /
• 2010

Carbon nanotubes (CNTs) have excellent electrical, chemical stability, mechanical and thermal properties. The MWCNT films were investigated as a transparent electrode for the solar cell, OLED, and field-emission display. MWCNT films were fabricated by air spray method, whose process is quite low-costed, using the multi-walled CNTs solution on glass substrates. Moreover, the most stable film was fabricated when the spraying time was 60 sec. The film that was sprayed with the MWCNT dispersion for 60 sec, has 300nm thick. And its electric resistivity, transmittance rate, mobility and carrier concentration are $6{\times}10^{-2}{\Omega}{\cdot}cm$, 50% at ${\lambda}=550mm$, $4.3{\times}10^{-2}cm^2/V{\cdot}s$ and $2.1{\times}10^{21}cm^{-3}$, respectively. Also, absorption energy of MWCNT films show from 3.9 eV to 4.6 eV. Furthermore, we can use MWCNT films fabricated by the spray method for the transparent electrode.

• Journal of Chest Surgery
• /
• v.12 no.2
• /
• pp.75-81
• /
• 1979

Eophagocardiomyotomy (modi/red Heller procedure) is a widely accepted operation for relief of dysphagia in patients with esophageal achalasia. But patients with advanced achalasia were more likely to get poorer results from a modified Ileller myotomy hecause of the dependent pouch that creates an angulation at the junction of thick-walled dilated esophagus with the thin walled aganglionic segment and hinders complete emptlllg. Thorhjarnarson(1975) prposcd the method including truncal vagectomy and pyloroplasty. Vagectomy and pyloroplasty should lesson the severity of acid-peptic esophagitis, if reflux should occur postoperatively. Here we presented 4 cases esophageal achalasia treated by modified Heller operation of 3 cases and one case of Thorbjarnarson method. All postoperative results are good.

• ALGAE
• /
• v.35 no.3
• /
• pp.253-262
• /
• 2020

Haematococcus pluvialis is a commercial microalga that can produce high quantities of astaxanthin. Under induced conditions, some important changes in the subcellular structures related to astaxanthin accumulation were observable. For example, a large number of astaxanthin granules, oil structures and starch granules appeared in the thick-walled cells; Astaxanthin granules gradually dissolved into the oil structures and spread throughout the entire cell with the fusion and diffusion process of oil structures during the middle and late stages of induction; The plastoglobules were closed to the newly formed structures, and some plastoglobules would abnormally increase in size under stress. Based on observations of cell damage, the degradation of membrane structures, such as chloroplasts, was found to be the primary form of damage during the early stage of induction. During the middle stage of induction, some transparent holes were exposed in the dissolving astaxanthin granules in the cytoplasm. In thick-walled cells, these transparent holes were covered by oil substances dissolving astaxanthin, thereby avoiding further damage to cells. Given the relatively few oil structures, in non-thick-walled cells, the transparent holes expanded to form multiple transparent areas, eventually resulting in the rupture and death of cells. These results suggested that the high level of synthesis and the wide range diffusion of oil explained the expansion of astaxanthin in H. pluvialis.

• Composites Research
• /
• v.23 no.2
• /
• pp.1-9
• /
• 2010

This study analyzes the apparent fracture toughness of a thick-walled cylinder with a functionally graded material (FGM) coating at the inner surface of the cylinder. The cylinder is assumed to have a single radial edge crack emanating from its inner surface. The crack surfaces and the inner surface of the cylinder are subjected to an internal pressure. The incompatible eigenstrain developed in the cylinder due to nonuniform coefficient of thermal expansion as a result of cooling from sintering temperature is taken into account. Based on a method of evaluating stress intensity factor introduced in our previous study, an approach is developed to calculate apparent fracture toughness. The approach is demonstrated for a cylinder with a TiC/$Al_{2}O_{3}$ FGM coating and some numerical results of apparent fracture toughness are presented graphically. The effects of material distribution profile, cylinder wall thickness, application temperature, and coating thickness on the apparent fracture toughness are investigated in details. It is found that all of these factors play an important role in controlling the apparent fracture toughness of the cylinder.