• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2001.10a
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• pp.228-232
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• 2001

Fatigue strength, electrical conductivity and stress-corrosion-cracking resistance are considered as important factors at aircraft Al alloys, therefore Al7050 alloy has been developed to improve such properties. However, hammer-forged Al7050 parts showed the undesirable structures such as severe local grain coarsening and inhomogeneous material flow, resulted in the degraded mechanical properties. In this paper, process conditions are investigated for elimination of the grain coarsening and improved material flow during forging process by both of experiments and FEM analysis. Particular interest has been given to understand role of preform shape on the grain coarsening behavior and magnitude of the hammer forging load The use of preform has been beneficial for reduction of the forging load and elimination of the grain coarsening. However, in the cases of as received bar and the round bar, which was machined to 2.5mm thickness in surface layer, some degree of local grain coarsening behavior has been observed. The optimized preform shape could be properly designed by applying the FEM simulation.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2005.06a
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• pp.1303-1306
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• 2005

The mechanical properties of bellows, such as the extensibility and the strength can be changed depending on the shape. For the shipbuilding material, it is favorable that the fatigue life is long due to the elastic property and the reduction of thermal stress in piping system. Nowadays, the domestic production and design of bellows are based on the E.J.M.A Code. Therefore, the design standard is in need because of much errors and lack of detailed analysis. In this study, it is attempted to find out the optimal shape of U-type bellows using the finite element method. The effective factors, mountain height, length, thickness, and number of mountains and the length of joint are considered and the proper values are chosen for the simulation. The results shows that if the number of mountains are reduced, the volume decreases while the stress increases. However, the number of mountains are increased, the volume increases above the standard volume and the stress obviously increases. In addition, the effect of the thickness of bellows on the stress is very large. Both of the volume and stress are decreasing at a certain lower value region.

• Geomechanics and Engineering
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• v.14 no.5
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• pp.453-458
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• 2018

Geomechanical parameters are important factors for engineering projects during design, construction and support stages of tunnel and dam projects. Geostatistical estimation methods are known as one of the most significant approach at estimation of Geomechanical parameters. In this study, Azad dam headrace tunnel is chosen to estimate Geomechanical parameters such as Rock Quality Designation (RQD) and uniaxial compressive strength (UCS) by ordinary kriging as a geostatistical method. Also Rock Mass Rating (RMR) distribution is presented along the tunnel. Main aim in employment of geostatistical methods is estimation of points that unsampled by sampled points.To estimation of parameters, initially data are transformed to Gaussian distribution, next structural data analysis is completed, and then ordinary kriging is applied. At end, specified distribution maps for each parameter are presented. Results from the geostatistical estimation method and actual data have been compared. Results show that, the estimated parameters with this method are very close to the actual parameters. Regarding to the reduction of costs and time consuming, this method can use to geomechanical estimation.

• Geomechanics and Engineering
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• v.22 no.1
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• pp.35-48
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• 2020

This paper provides methods for the deterministic and reliability-based design of the support pressures necessary to prevent tunnel face collapse. The deterministic method is developed by extending the use of the unique load multiplier, which is embedded within OptumG2/G3 with the intention of determining the maximum load that can be supported by a system. Both two-dimensional and three-dimensional examples are presented to illustrate the applications. The obtained solutions are validated according to those derived from the existing methods. The reliability-based method is developed by incorporating the Response Surface Method and the advanced first-order second-moment reliability method into the bisection algorithm, which continuously updates the support pressure within previously determined brackets until the difference between the computed reliability index and the user-defined value is less than a specified tolerance. Two-dimensional reliability-based support pressure is compared and validated via Monte Carlo simulations, whereas the three-dimensional solution is compared with the relationship between the support pressure and the resulting reliability index provided in the existing literature. Finally, a parametric study is carried out to investigate the influences of factors on the required support pressure.

• Advances in Automotive Engineering
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• v.1 no.1
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• pp.41-59
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• 2018

In the study, investigation of fiber- reinforced composite materials that can be an alternative to conventional steel was performed by finite element analysis with the help of software. Steel and composite materials have been studied on a four axle truck chassis model. Three-dimensional finite element model was created with software, and then analyzes were performed. The analyses were performed for static and dynamic/fatigue cases. Fatigue cases are formed with the help of design spectra model and fatigue analyses were performed as static analyses with this design spectra. First, analyses were performed for steel and after that optimization analyses were made for the AS4-PEEK carbon fiber composite and Eglass-Epoxy fiber composite materials. Optimization of composite material analyzes include determining the total laminate thickness, thickness of each ply, orientation of each ply and ply stacking sequence. Analyzes were made according to macro mechanical properties of composite, micromechanics case has not been considered. Improvements in weight reduction up to %50 provided at the end of the composite optimization analyzes with satisfying stiffness performance of chassis. Fatigue strength of the composite structure depends on various factors such as, fiber orientation, ply thickness, ply stack sequence, fiber ductility, ductility of the matrix, loading angle. Therefore, the accuracy of theoretical calculations and analyzes should be correlated by testing.

• Tunnel and Underground Space
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• v.24 no.1
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• pp.89-96
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• 2014

Rock joint surface roughness, which is known to be one of the most important factors for defining shear strength of rock mass, has been researched in various methods. However, approaches to separate a roughness into two groups (primary and secondary) for evaluating the roughness have been rarely performed. In this study, elements of secondary roughness were eliminated through direct shear testing with tensile joint specimen and they were quantified with joint parameters. It is revealed that roughness parameters decrease with increasing the normal stress and sampling intervals, except for the case in which the normal stress is larger than 1.5 MPa. Also it is analyzed that ratio of area reduction in the opposite direction of shearing decreases with increasing the roughness parameter.

• Geomechanics and Engineering
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• v.31 no.1
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• pp.71-86
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• 2022

In Taiwan, an efficient approach for enhancing the stability of colluvium slopes is the drilled shaft method. For slopes with drilled shafts, the soil arching effect is one of the primary factors influencing slope stability and intertwines to the failure mechanism of the pile-soil system. In this study, the contribution of soil arching effect to slope stability is evaluated using the FEM software (Plaxis 3D) with the built-in strength reduction technique. The result indicates the depth of the failure surface is influenced by the S/D ratio (the distance to the diameter of piles), which can reflect the contribution of the soil arching effect to soil stability. When α (rock inclination angles)=β (slope angles) is considered and the S/D ratio=4, the failure surface of the slope is not significantly influenced by the piles. Overall, the soil arching effect is more significant on α=β, especially for the steep slopes. Additionally, the soil arching effect has been included in the proposed stability charts. The proposed charts were validated through two case studies, including that of the well-known Woo-Wan-Chai field in Taiwan. The differences in safety factor (FoS) values between the referenced literature and this study was approximately 4.9%.

• Journal of Korean Society of Steel Construction
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• v.10 no.3 s.36
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• pp.423-435
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• 1998

In this paper fatigue strength reduction of butt weld with penetration defect, which can be seen frequently in the steel bridge, was assessed quantitatively. S-N curves were derived and investigated through the constant amplitude fatigue test of fully or partially penetrated welded specimen made of SWS490 steel. The fracture mechanical method was applied in order to calculate the remaining fatigue life of the partially penetrated butt welds. The fatigue limit of the fully penetrated butt welds was higher than that of category A in AASHTO's fatigue design curves, and the slope of S-N curves with 5.57 was stiffer than that of other result for welded part generally accepted as 3. The fatigue strength of the partially Penetrated butt weld was strongly influenced by the size of lack of penetration, D. It decreased drastically with increasing D from 3.9 to 14.7mm. Fracture behaviour of the partially penetrated butt weld is able to be explained obviously from the beach mark test that a semi-elliptical surface crack with small a/c ratio initiates at a internal weld root and propagates through the weld metal. To estimate the fatigue life of the partially penetrated butt weld with fracture mechanics, stress intensity factors K of 3-dimensional semi-elliptical crack were calculated by appling finite elements method and fracture mechanics parameters such as C and m were derived through the fatigue test of CT-specimen. As a result, the fatigue lives obtained by using the fracture mechanical method agreed well with the experimental results. The results were applied to Sung-Su bridge collapsed due to penetration defects in butt weld of vertical member.

• Journal of muscle and joint health
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• v.10 no.1
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• pp.62-76
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• 2003

This study was a quasi-experimental study of non-equivalent control group pretest and posttest design. The purpose of this study was to determine the effect of Tai Chi exercise program on physical functions, psychological functions, and fall among the fall-prone elderly. The data were collected from September 19, 2001 to January 31, 2002. The study, conducted at two facilities located in Kwang-ju, was targeted to the ambulatory aged 60 years or older who had at least one of the key fall risk factors. Experimental group participated in Tai Chi exercise for 40 minutes per one time and three times a week for 12weeks at an auditorium. Fifty nine fall-prone elderly were assigned to 12-week Tai Chi exercise program (n=29) and control group (n=30). They underwent tests of lower muscle strength, time for chair stand, balance, flexibility, depression, falls efficacy, fear of falling, and numbers of fall at the baseline and at the 12th week. Numbers of fall and fall injuries were monitored for 16 weeks(12-weeks intervention plus 4-week follow-up periods) using fall calendar. Each participant was given a calendar to record the numbers of fall per day for a month. The calendars were collected at the last week of each month. 1. Tai Chi exercisers showed significant improvement in the strength of knee flexors, and ankle dorsiflexors and plantarflexors compared to the control group. The experimental group had improvement in the strength of knee extensors while the control group did not, with no statistical significance. 2. Tai Chi exercisers reported positive change in the average time of chair stand as compared to the control group. 3. Tai Chi exercisers had significant improvement in flexibility as compared to the control group. 4. There was no significant difference in the depression between the two groups, even though the Tai Chi exercisers maintained depression score in the same level while the others were increased. 5. Tai Chi exercisers showed significant improvements in the falls efficacy as compared to the control group. The falls efficacy was significantly improved among the experimental group while the opposite was identified among the control group. 6. The experimental group reported the significant reduction of the fear of fall, whereas control group reported the opposite. 7. Of the 59 subjects for 16weeks(12weeks intervention period and 4weeks follow up), 9 (31.0%) of the 29 in exercise group and 15 (50%) of the 30 in the control group fell (relative risk=0.62. 95% CI 0.32-1.19), even with no statistical difference. The results suggest that the Tai Chi exercise program can improve the strength of knee flexors, ankle dorsiflexors and plantarflexors, chair stand. flexibility, falls efficacy, and fear of falling for the fall-prone elderly.

• Culinary science and hospitality research
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• v.23 no.1
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• pp.66-78
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• 2017

"Sarcopenia", sarcopenia is an old age syndrome, and used to describe the reduction of skeletal muscle. Initially, it was thought that sarcopenia was only a senile disease characterized by degeneration of muscle tissue. However, its cause is widely regarded as multifactorial, with neurological decline, hormonal changes, inflammatory pathway activation, declines in activity, chronic illness, fatty infiltration, and poor nutrition, all shown to be contributing factors. Skeletal muscle mass can be measured by a variety of methods, currently, the commonly used methods are dual-energy X-ray scanning (DXA), computer tomography (CT), magnetic resonance imaging (MRI), etc. Muscular skeletal disorders can also be assessed by measuring appendicular skeletal muscle (ASM), particularly muscle tissue content. At the same time, sarcopenia refers to skeletal muscle cell denervation, mitochondrial dysfunction, inflammation, hormone synthesis and secretion changes and a series of consequences caused by the above process and is a progressive loss of skeletal muscle syndrome, which can lead to the decrease of muscle strength, physical and functional disorders, and increase the risk of death. Sarcopenia is mainly associated with the aging process, but also related to other causes such as severe malnutrition, neurodegenerative diseases, and disuse and endocrine diseases associated with muscular dystrophy, and it is the comprehensive results of multi-factors, so it is difficult to define that sarcopenia is caused by a specific disease. With the aging problem of the population, the incidence of this disease is increasingly common, and seriously affects the quality of the life of the elderly. This paper reviews the etiology and pathogenesis of myopathy, screening methods and diagnosis, the influence of eating habits, etc, and hopes to provide reference for the diagnosis and treatment of this disease. At present, adequate nutrition and targeted exercise remain the gold standard for the therapy of sarcopenia.