• Journal of the Korean Society for Heat Treatment
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• v.10 no.4
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• pp.266-277
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• 1997

Near-threshold fatigue crack growth characteristics was investigated on the Ni-Cr-Mo-V low alloy steel, which has the different microstructure obtained by tempering at various temperature. The specimens were austenized at $950^{\circ}C$ and then followed by tempering at $200^{\circ}C$, $530^{\circ}C$ and $600^{\circ}C$. Strain rate was obtained from strain gauge attached on the crack tip and crack opening point was observed through load-strain curve. Threshold stress intensity range(${\Delta}K_{th}$) was increased with increasing tempering tempuerature, but the effective threshold stress intensity rage (${\Delta}K_{eff,\;th}$) was not affected with the increasing temperature. Grain size increased with increasing tempering temperature.

• Transactions of the Korean Society of Automotive Engineers
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• v.11 no.5
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• pp.89-94
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• 2003

Rolling stock structures such as bogie frame and car body play an important role for the support of vehicle leading. In general, more than 25 years' durability is needed for them. A lot of study has been carried out for the prediction of the fatigue life of the bogie frame and car body in experimental and theoretical domains. One of the new methods is a probabilistic fatigue lift evaluation. The objective of this paper is to estimate the fatigue lift of the bogie frame of an electric car, which was developed by the Korea Railroad Research Institute (KRRI). We used two approaches. In the first approach probabilistic distribution of S-N curve and limit state function of the equivalent stress of the measured stress spectra are used. In the second approach, limit state function is also used. And load spectra measured by strain gauges are approximated by the two-parameter Weibull distribution. Other probabilistic variables are represented by log-normal and normal distributions. Finally, reliability index and structural integrity of the bogie frame are estimated.

• Journal of the Society of Naval Architects of Korea
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• v.33 no.2
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• pp.96-110
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• 1996

Aging ships can suffer structural damage due to corrosion, fatigue crack etc., and possibility of catastrophic failure of seriously damaged ships is very high. To reduce the risk of loss of ships due to hull collapse, it is essential to evaluate ultimate hull strength of aging ships taking into account various uncertainties associated with structural damages. In this paper, ultimate strength-based reliability analysis of ship structures considering wear of structural members due to corrosion is described. A corrosion rate estimate model for structural members is introduced. An ultimate limit state function of a ship hull is formulated taking into account corrosion effects. The model is applied to an existing oil tanker, and reliability index associated with hull collapse is calculated by using the second-order reliability method (SORM). Discussions on structure safety of corroded ships are made.

• Journal of Dental Rehabilitation and Applied Science
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• v.24 no.3
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• pp.269-281
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• 2008

Fatigue or overload can result in mechanical problems of implant components. The mechanical strength in the implant system is dependent on several factors, such as screw and fixture diameters, material, and design of the fixture-abutment connection and abutment. In these factors, the last rules the strength and stability of the fixture-abutment assembly. There have been some previous reports on the mechanical strength of the fixture-abutment assembly with the compressive bending test or short-term cyclic loading test. However, it is restrictive to predict the long-term stability of the implant system with them. The purpose of this study was to evaluate the influence of the design of the fixture-abutment connection and abutment on the mechanical strength and failure mode by conducting the endurance limit test as well as the compressive bending strength test. Tests were performed according to a specified test(ISO/FDIS 14801) in 4 fixture-abutment assemblies of the Osstem implant system: an external butt joint with Cemented abutment (group BJT), an external butt joint with Safe abutment (group BJS), an internal conical joint with Solid abutment (group CJO), and an internal conical joint with ComOcta abutment (group CJT). The following conclusions were drawn within the limitation of this study. Compressive bending strengths were decreased in order of group BJS(1392.0N), group CJO(1261.8N), group BJT(1153.2N), and group CJT(1110.2N). There were no significant differences in compressive bending strengths between group BJT and group CJT(P>.05). Endurance limits were decreased in order of group CJO(600N), group CJT(453N), group BJS(360N), and group BJT(300N). 3. Compressive bending strengths were influenced by the connection and abutment design of the implant system, however endurance limits were affected more considerably by the connection design.

• Journal of the Korea institute for structural maintenance and inspection
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• v.19 no.6
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• pp.46-54
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• 2015

Base on Korean design code, previous design code had not considered the effect of pavement on the orthotropic steel deck, however recent design code (Limit State Design Method, 2012) allowed to consider the effect of pavement on the orthotropic steel deck, and efforts to apply the stiffness of pavement to the deck continue. Meanwhile, research on the effect of ultra thin bridge deck overlay on the orthotropic steel deck is inadequate, previous study was limited in about fatigue stress and performance between pavement layer and the orthotropic steel deck. In this study, according to changing of pavement layer stiffness application, pavement materials, pavement thickness and steel deck thickness, analysis of deflection. In addition to base on this result, consider effectiveness of ultra-thin pavement stiffness application on the orthotropic steel deck.

• Korean Journal of Construction Engineering and Management
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• v.25 no.2
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• pp.36-44
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• 2024

This paper presents the application of Convolutional Neural Networks (CNNs) and Region of Interest (ROI) techniques for concrete crack analysis. Surfaces of concrete structures, such as beams, etc., are exposed to fatigue stress and cyclic loads, typically resulting in the initiation of cracks at a microscopic level on the structure's surface. Early detection enables preventative measures to mitigate potential damage and failures. Conventional manual inspections often yield subpar results, especially for large-scale infrastructure where access is challenging and detecting cracks can be difficult. This paper presents data collection, edge segmentation and ROI techniques application, and analysis of concrete cracks using Convolutional Neural Networks. This paper aims to achieve the following objectives: Firstly, achieving improved accuracy in crack detection using image-based technology compared to traditional manual inspection methods. Secondly, developing an algorithm that utilizes enhanced Sobel edge segmentation and ROI techniques. The algorithm provides automated crack detection capabilities for non-destructive testing.

• Journal of Korean Society of Steel Construction
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• v.23 no.4
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• pp.503-514
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• 2011

In this research, the seismic connection details for two concrete-filled U-shape steel beam-to-H columns were proposed and cyclically tested under a full-scale cruciform configuration. The key connecting components included the U-shape steel section (450 and 550 mm deep for specimens A and B, respectively), a concrete floor slab with a ribbed deck (165 mm deep for both specimens), welded couplers and rebars for negative moment transfer, and shear studs for full composite action and strengthening plates. Considering the unique constructional nature of the proposed connection, the critical limit states, such as the weld fracture, anchorage failure of the welded coupler, local buckling, concrete crushing, and rebar buckling, were carefully addressed in the specimen design. The test results showed that the connection details and design methods proposed in this study can well control the critical limit states mentioned above. Especially, the proposed connection according to the strengthening strategy successfully pushed the plastic hinge to the tip of the strengthened zone, as intended in the design, and was very effective in protecting the more vulnerable beam-to-column welded joint. The maximum story drift capacities of 6.0 and 6.8% radians were achieved in specimens A and B, respectively, thus far exceeding the minimumlimit of 4% radians required of special moment frames. Low-cycle fatigue fracture across the beam bottom flange at a 6% drift level was the final failure mode of specimen A. Specimen B failed through the fracture of the top splice plate of the bolted splice at a very high drift ratio of 8.0% radian.

• Journal of Hospice and Palliative Care
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• v.19 no.2
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• pp.163-169
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• 2016

Purpose: The unmet medical service needs of caregivers critically influence their caring for terminal cancer patients, but not much research has been done in this regard. Thus, the purpose of this study is to investigate the association between caregivers' characteristics and their unmet medical service needs. Methods: The survey was conducted with 109 family caregivers of terminal cancer patients admitted to four hospice units. The data were collected from March 2014 through December 2014 using a structured questionnaire. The unmet medical service needs were measured using 14 items which were adopted and modified by authors. Results: Seven areas of unmet medical service needs were shown to be significant. A well-educated group showed stronger needs for counsel about cancer screening and complementary-alternative medicine and health supplement food. A never-smoked group was identified with less need for sexual dysfunction counsel. Counsel about family and personal relations was more necessary for current drinkers and current workers, and less necessary for the married. Insurance counsel was more needed for a no-religion group. Occupation counsel was less necessary for healthy patients. Financial support was less necessary for the married group. Conclusion: Based on the results, it is highly recommended to further investigate the unmet medical service needs of family caregivers for terminal cancer patients and causes of the unmet needs.