• Journal of the Korean Society of Safety
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• v.13 no.4
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• pp.131-136
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• 1998

The creep behavior and failure mechanism of the 30 vol% hot-pressed $SiC_t/Si_3N_4$ ceramic composite was experimentally investigated at $1200^{\circ}C$ and at various stress levels in air. The creep threshold stress for zero creep rate after 100 hr was found to be approximately 60 MPa. The stress exponent was estimated to be n~1, which suggests that fiber-reinforcement reduced the stress sensitivity of the HPSN matrix with the stress exponent of 2. The tertiary stage leading to creep rupture was found at 250 MPa but was very short. The microstructure of the crept specimen showed random fiber fracture and no matrix cracking. Interfacial debonding was absent.

• Journal of the Korean Society for Railway
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• v.7 no.2
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• pp.125-129
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• 2004

This study investigates the fatigue lift estimation of butt weld specimen for the railway vehicle by examining butt weld bead profiles. The butt weld beads, which are welded by semi-robot method, have non-uniform bead profiles described by $\theta$, p and h. The stress concentration factors, K$\_$t/, are changed by different $\theta$, p and h from 1.395 to 2.863. Hence, the sensitivity of K$\_$k/ is changed by each $\theta$, p and h. As $\theta$ becomes lower and p and h become higher, K$\_$t/ increases. The fatigue life can be estimated very closely for the AAY specimens without residual stress using only butt weld bead profiles. But, for the AAN specimens with residual stress, the fatigue life must be estimated by considering both the weld bead profiles and the residual stress data.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.09a
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• pp.623-624
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• 2006

The behavior of hardmetals under cyclic loads is investigated. Unnotched specimens were employed to obtain practical information regarding fatigue in hardmetals. All the tested hardmetals exhibit an increase in the number of cycles until failure with a decrease in the maximum stress, i.e., the hardmetals exhibit a high fatigue sensitivity. The fatigue strength increases with the cobalt content. Although distinct fatigue limits, as observed in metals, cannot be observed, the calculated fatigue limit stress at $10^7$ cycles is found to be approximately 70% of the flexural strength, and the stress value exhibits a linear relationship with the flexural stress.

• Journal of Korean Foot and Ankle Society
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• v.25 no.1
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• pp.1-5
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• 2021

Physical examination and surgical findings and symptoms are often inconsistent with magnetic resonance imaging (MRI) findings when diagnosing chronic ankle lateral ligament instability, and confirmed surgical findings are used as the gold standard in most clinical studies. Anterior drawer testing is considered unreliable because normal findings are highly variable, and its accuracy ranges from 50% to 100%. Furthermore, radiographic stress imaging, such as in anterior drawer stress view, is performed under manual stress or using a stress device, and its findings also vary widely and confuse when interpreting stress views. The average accuracy of MRI findings is around 85% (range, 66%~91.7%), and thus, cannot be used as a primary indicator for surgery. For patients with suspected lateral ankle ligament instability, based on symptoms and physical examination findings, MRI may be useful for identifying lesions in ankle joints and for differentiating them from other conditions.

• Steel and Composite Structures
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• v.41 no.6
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• pp.851-860
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• 2021

In this paper, a new approach of interface stress analysis in steel beam strengthened by porous FGM (Functionally Graded Materials) is presented to calculate the shear stress in the hybrid steel beam and loaded by a uniformly distributed load. The results show that there exists a high concentration of shear stress at the ends of the imperfect FGM, which might result in premature failure of the strengthening scheme at these locations. A parametric study has been conducted to investigate the sensitivity of interface behavior to parameters such as the rigidity of FGM plate (degree of homogeneity), the porosity index of FGM and the thickness of adhesive all were found to have a marked effect on the magnitude of maximum shear stress in the FGM member. we can conclude that the new approach is general in nature and may be applicable to all kinds of materials.

• Journal of the Earthquake Engineering Society of Korea
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• v.17 no.5
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• pp.219-225
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• 2013

This work examines the feasibility for estimating existing tensile stress on a stressed wire using the permeability of magnetic flux. A closed magnetic circuit has been constructed to induce magnetic flux inside a steel wire. With different tension stress levels on a wire, the permeability of magnetic flux on the wire has been measured. Two different experimental case studies have been conducted for the examination of sensitivity of permeability of magnetic flux on the stressed wire. One is a varying-length stress test, and the other is a fixed-length stress test. The results show that the permeability of magnetic flux in the varying-length stress test is inversely proportional to the applied stress, while the permeability in the fixed-length stress test is linearly proportional to the applied stress on the stressed wire. It is thus expected that the permeability of magnetic flux on a wire can be a promising indicator for the inspection of its tensile stress.

• Journal of Korean Society of Rural Planning
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• v.24 no.2
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• pp.59-67
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• 2018

As high-rise buildings came in, the landscape of rural areas and natural landscapes often got damaged. Therefore, this study aims to prevent this, grasp the extent of the influence of the surrounding landscape, to grasp the range of height that can be permitted and present the direction of landscape management of agriculture and natural landscape. This study tried to grasp the range of height by using price sensitivity analysis method for two apartment and apartment complex which entered DangJin city and SeoSan city. First, in the case of a two apartment, the range of the height allowable section was from the 6th floor to the 11th floor in close range view, and it was a section from the 7th floor to the 12th floor in medium range view. In the case of the apartment complex, the range of the height allowable range was from the 10th floor to the 17th floor in close range view, the 9th floor to the 16th floor in medium range view. The stress index was found to be positive in a two apartment in close range view, and in the apartment complex case. therefore it was better to set it to a lower in the Range of Acceptable Height(RAH). Second, it showed no difference in the sensitivity of landscape to gender. Thirdly, the results of the landscape sensitivity analysis of major and non-major showed the difference in the medium range view picture of the apartment complex. Majors are lower than the point of minimum height(PMinH) than non-Majors. In the case of major, the stress index was 1.4. it turned out that it was better to make a decision closer to point of minimum height (PMinH). In the case of non-major, the stress index was -1.3. it was also able to accept decision close to the point of maximum height (PMaxH). Since the results of the above research gave changes only in the variable of the height of the landscape, we can not grasp the point of interaction with other variables, and future research is considered necessary.

• Journal of Korean Tunnelling and Underground Space Association
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• v.16 no.1
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• pp.91-104
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• 2014

An Excavation Damaged Zone (EDZ), in which rock properties are permanently changed due to blasting impact or stress redistribution, can influence the behavior and stability of structures. In this study, the mechanical stability of an underground opening was simulated by using FLAC, which is a two-dimensional modeling code, with a consideration of EDZ. A sensitivity analysis was also carried out with fractional factorial design. From the modeling, it was found that the behavior and the stability of an underground tunnel are strongly dependent on the existence of the EDZ. The sensitivity analysis showed that the key parameters affecting the factor of safety around the tunnel are in-situ stress ratio, depth, cohesion, reduction ratio, internal friction angle, and height and width of the tunnel. It is necessary to consider the EDZ, which can significantly affect mechanical stability in tunnel design.

• Polymer(Korea)
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• v.28 no.4
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• pp.285-290
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• 2004

Nondestructive damage sensitivity of carbon nanotube(CNT) and nanofiber (CNF)/epoxy composites with their adding contents was investigated using electro-micromechanical technique. Carbon black (CB) was used only for the comparison with CNT and CNF. The fracture of carbon fiber was detected by acoustic emission (AE), which was correlated to the change in electrical resistance, ΔR under double-matrix composites (DMC) test. Stress sensing on carbon nanocomposites was performed by electro-pullout test under uniform cyclic loading. At the same volume fraction, the damage sensitivity for fiber fracture, matrix deformation and stress sensing were highest for CNT/epoxy composite, whereas for CB/epoxy composite they were the lowest among three carbon nanomaterials (CNMs). Damage sensitivity was correlated with morphological observation of carbon nanocomposites. Homogeneous dispersion among CNMs could be keying parameters for better damage monitoring. In this study, damage sensing of carbon nanocomposites could be evaluated well nondestructively by the electrical resistance measurement with AE.

• Journal of the Korean Society of Industry Convergence
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• v.26 no.6_3
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• pp.1279-1288
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• 2023

Recently, domestic leisure boats have been actively researching eco-friendly product development to enter the global market. Since the hulls of existing leisure boats are mainly made of fiber reinforced plastic (FRP) or aluminum, design techniques for securing structural safety by applying related materials have been mainly studied. In this study, an initial structural design safety assessment of a trimaran pontoon leisure boat with a modular hull structure and eco-friendly high-density polyethylene (HDPE) material was conducted, and sensitivity evaluation and optimization analysis for lightweight design were performed. The initial structural design safety assessment was carried out by creating a finite element analysis model and applying the loading conditions specified in the ship classification regulation to check whether the specified allowable stresses are satisfied. For the sensitivity evaluation, the influence of stress and weight of each hull structural member was evaluated using the orthogonal array design of experiments method, and an approximate model based on the response surface method was generated using the results of the design of experiments. The optimization analysis set the thickness of the hull structural members as the design variable and considered the optimal design formulation to minimize the weight while satisfying the allowable stress. The algorithm of the optimization analysis applied the Gradient-population Based Optimizer (GBO) to improve the accuracy of the optimal solution convergence while reducing the numerical cost. Through this study, the optimal design of a newly developed eco-friendly trimaran pontoon leisure boat with a weight reduction of 10% was presented.