• 비파괴검사학회지
• /
• 제30권2호
• /
• pp.126-131
• /
• 2010

본 연구에서는 유도초음파를 이용하여 다양한 온도에서 사용되어지는 항공기 복합재료의 건전성에 대하여 평가하였다. 항공기가 지상과 비행고도에서 운행할 때의 온도편차나, 반복되어지는 열주기 횟수와 같이, 항공기가 운행되어지는 온도와 관련하여 복합재료의 건전성에 결정적인 영향을 미치는 요소에 관한 연구는 항공기 안전에 있어서 매우 중요한 요소가 되고 있다. 본 연구에서는 유도초음파를 이용하여 항공기의 운행환경과 유사한 환경 하에서 열피로가 가해진 항공기의 복합재료 시편을 평가하였다. 유도초음파의 분산선도 곡선은 서로 다른 열피로가 가해진 시편에 대한 민감성을 나타내기 위해 최적의 모드를 선택하는데 사용되었다. 현재 제시된 접근법 또한 항공기의 건전성을 평가하는데 있어서 하나의 도구로 구현될 수 있다.

• 한국안전학회지
• /
• 제34권2호
• /
• pp.40-47
• /
• 2019

The Half-depth precast deck is a structural system that utilizes pre-cast panels pre-built at the factory as formwork at the construction stage and as a major structural member at the same time after completion. These systems have joints between segments, and the detail and performance of the joints are factors that have a very large impact on the quality, such as the constructability and durability of the bridge decks. In this study, strength performance evaluation was performed for improved joints using connecting rebar by experimental method. Static loading tests were conducted on the test specimen with improved joint, those with existing joint and those without joint. The test results of the specimens were compared to each other, and the flexural strength required by the design was compared. The flexural strength required in the design was presented by finite element analysis. It has been shown that the flexural strength of the specimens with joints were more than twice that required by the design. But the flexural strength of the specimen with existing joint was about 84% of that without joint. The flexural strength of the specimen with improved joints was a nearly similar degree of that compared to the specimen without joint. And a comparison of the moment-deflection relationship curves of the two specimens also shows a very similar flexural behavior. It is confirmed that improved joint has sufficient flexural strength. In addition to strength, the bridge decks require serviceability, such as deflection and cracking, and in particular, fatigue resistance due to repetitive live loads is an important performance factor. Therefore, further verification studies are required.

• Safety and Health at Work
• /
• 제11권4호
• /
• pp.543-549
• /
• 2020

Background: The working conditions of bus drivers are difficult; they lead to occupational diseases and require careful study, particularly in Ukraine. The objective of the article is the description of occupational health risks of passenger bus drivers that lead to deteriorating health. Methods: The risk assessment was performed using a modified Risk Score method, which allowed determining the generalized level of danger to the driver's health. The hygienic hazards level was assessed as based on Stevenson's law, which was generalized later. Results: Based on the modification of the Risk Score method, it was possible to depart from expert assessments method of the risk level and calculate the general indicator based on the degree of dependence of the impact on the human body on its intensity, proposed by V. Minko. This allows objective determining of the impact of hygiene hazards on the health of the driver and to predict the occurrence of occupational diseases associated with the cardiovascular system, musculoskeletal system, and partial or complete disability due to the accumulation of emotional fatigue. The hazard assessment was carried out for three brands of passenger buses common in Ukraine, in which the driver is exposed to the dangers of fever, vibration, noise, harmful impurities in the bus cabin, and emotional load. Conclusion: The health of drivers in the cabins of passenger buses is most affected by hygiene hazards: fever, vibration, and emotional stress. The generalized level of risk is calculated by the modified method of Risk Score is 0.83; -0.99, -0.92 respectively.

• 한국조경학회지
• /
• 제32권2호
• /
• pp.11-24
• /
• 2004

The purpose of this study is to present data on the human activities responding to the physical environment of ‘Ulsan’s Grand Parks by evaluating user behavior and activity, visiting motivations, and user satisfaction. This study was conducted using multi-methods such as interviews and questionnaires surveys. The main findings of this study can be summarized in six parts as follows: \circled1 Behavior patterns showed that the users visited the park left within 30 minutes and the frequency of visits was 1 or 2 times per week. They spent their time mostly on ‘walking’ and ‘picnicking’. The users visited regardless of the seasons or the day of the week. \circled2 The priorities for improvements were analyzed as follows: the users expressed their demands for ‘shadowing facilities’ like shelters and pergolas because they used these facilities frequently. Also, the users would like an ‘event program’, ‘sign system’ and ‘guide program’. \circled3 Analysis of the the user’s perception of the park showed that they perceive the park as ‘representative source of the landscape and open space in Ulsan and place for making contact with nature. \circled4 In examining the visiting motivations of the users of Ulsan Grand Park, it was revealed that people use the park for ‘time with family and friends’, ‘to escape from city life’, ‘to relieve fatigue. As a result of factor analysis, 4 factors were identified such as ‘physical motive(MF1)’, ‘exploratory motive(MF2)’, ‘social motive(MF3)’ and ‘emotional motive(MF4). \circled5 Park users’ evaluation for park facilities showed that people are satisfied with most of the facilities and especially, they have high level of satisfaction for ‘footpaths’, ‘squares’ and ‘picnicspace’. The evaluation of the park user’s of activity reveals that they are content with nearly all the variables. Especially, they have high level of satisfaction for the variables of ‘convenience for dynamic activities’, ‘making of a beautiful atmosphere, ‘accessibility from the outside’ and, ‘convenience in group activitie. Factor analysis of the park user’s of activity revealed 5 factors such as ‘convenience and interest factor (AF1)’, ‘park maintenance, management and use program(AF2)’, ‘visual beauty(AF3)’, ‘safety and accessibility(AF4)’ and ‘crowding(AF5)’. \circled6 Regression analysis was employed to get the predictor factors of overall satisfaction with a result of 60.0%($R^2$). The variance was explained as ‘quality of the picnic space’, ‘convenience and interest factor while using the park’, ‘park program for maintain and management in the park’, ‘visually beauty while using the park’, ‘safety and accessibility of the parks’, ‘quality of the pond’, ‘crowding’, ‘quality of the square’.

• Tribology and Lubricants
• /
• 제32권1호
• /
• pp.18-23
• /
• 2016

The effective case depth for case-hardened rolling bearing has been discussed. For this purpose, rolling contact fatigue tests for ball bearings built with inner race of various hardness values were conducted until L₁₀ calculating rating life using a bearing life test machine under radial loading. Then, the distribution of residual stress below the inner raceway, which depended on the hardness value, was measured by X-ray diffraction. As a result, the linear relationship was established between the hardness value of the inner race and the theoretical shear stress evaluated at the depth where the residual stress disappeared below the inner raceway. Based on the relationship, it could be found that the factor of safety in bearing manufacturer’s rules for the effective case depth of case hardened rolling bearings was set higher. However, it could be also found that the hardness values at the depth where the maximum shearing stress acted below the raceway surface in a tapered roller bearing hardened by the carburizing process, were not sufficient for preventing plastic deformation under the basic dynamic load rating. Consequently, further efforts were still required to reduce or to disperse the contact load on the material design of a rolling bearing in order to prolong its life.

• 대한조선학회지
• /
• 제4권1호
• /
• pp.59-65
• /
• 1967

Since the screw propellers were adopted as ship propulsion devices, the replacement of propeller shaft due to damage was mostly of fatigue failure due to the alternative stresses [1],[2]. To prevent such a failure, hence, it is suggested that careful attention should be paid to account of the alternative stresses on the design stage of the propeller shafts. In connection with this fact the Ship Classification Societies' Rules are regarded simply as guidance for preliminary determination of the shaft diameter. In this paper, limiting the topic to the small and medium-sized motor ships, an evaluation of the Rules formulae to a theoretical based on Soderberg's correlation [5] between the factor of safety and the resultant stresses obtained by application of the maximum shear theory is done. For this purpose eleven (11) ships built recently in Korea were taken as a species(refer to table 2. in text). In the end the following conclusions are made: (1) In general the Rules formulae give considerably larger size of the propeller shaft diameter than that derived from theoretical calculation, that is, about 7% more in AB and BV Rules, and about 20% more in LR and KR-NK Rules. (2) LR Rule gives the largest size of all, and AB Rule is mostly closed value to the theoretical. (3) The formular of the AB Rule is considered to be of the simplest in utilization and of the reasonable.

• 대한기계학회논문집A
• /
• 제25권4호
• /
• pp.703-713
• /
• 2001

Mechanical joints such as bolted or riveted joints are widely used in structural components and the reliable determination of the stress intensity factors for corner cracks in mechanical joints is needed to evaluate the safety and fatigue life. This paper analyzes the mixed-mode stress intensity factors of surface and deepest points for quarter elliptical corner cracks in mechanical joints by weight function method and the coefficients included in weight function are determined by finite element analyses for reference loadings. The extended form of the weight function method for two-dimensional mixed-mode to three-dimensional is presented and the number of terms in weight function is determined by comparing the results for the different number of terms. The amount of clearance is an important factor in evaluating the severity of elliptical corner cracks in mechanical joints and even horizontal crack normal to the applied load is under mixed-mode in the case that clearance exists.

• 한국군사과학기술학회지
• /
• 제13권6호
• /
• pp.1051-1057
• /
• 2010

Database for the damage reference by armor piercing bullet test was established for both tube and plate specimens having a range of thickness. As the inclined angles of hit are increasing, it has been found that penetration damage diameter tends to increases accordingly in both specimen of the tube and plate, and such penetration damage diameter on the rear side becomes bigger than those on the front side. The tube specimen showed that the damage becomes bigger when central areas rather than the peripheral were hit. Through the plate test, it also has been found that the penetration ballistic limit for Al alloy is about 25.4mm and that of stainless steel about 12.7mm. From the fatigue analysis results using the database for damage reference, it has been identified whether the safety requirements of military aircraft could be met.

• 대한의생명과학회지
• /
• 제30권1호
• /
• pp.1-9
• /
• 2024

Although there have been several attempts to use virtual reality (VR) in the treatment of depression, the results have been inconsistent and existing studies have mostly relied on subjective measures to assess the effectiveness of VR in improving depression. The aim of this study was to investigate the effect of nature experience-based VR intervention on depressive symptoms in a young population using both subjective and objective measurements. The study population included 15 participants who had more than 14 identifiers of the Korean Beck Depression Inventory (K-BDI)-II. Participants received three weeks (four times per week) of VR intervention. The effectiveness of VR was assessed through changes in K-BDI-II scores and depression-related blood biomarkers. Nature experience-based VR intervention led to an approximately 50% reduction of K-BDI-II score (before 25.7±7.7 vs. after 12.5±8.3 (P<0.001)). Of these, loss of pleasure and fatigue showed the largest amount of improvement. However, levels of cortisol, brain-derived neurotrophic factor, and interleukin-6 did not differ from those at baseline. The findings of our pilot study suggest that nature experience-based VR can be a useful adjunctive treatment method for improving depressive symptoms in individuals who have difficulty accessing the real outside natural environment.

• Advances in concrete construction
• /
• 제9권4호
• /
• pp.413-421
• /
• 2020

For steel-concrete girders made composite using shear studs, initial damage on studs induced by weld defect, unexpected overloading, fatigue and others might degrade the service performance and even threaten the structural safety. This paper conducted a numerical study to investigate the static behavior of damaged stud shear connectors that were embedded in ultra high performance concrete (UHPC). Parameters included damage degree and damage location. The material nonlinear behavior was characterized by multi-linear stress-strain relationship and damage plasticity model. The results indicated that the shear strength was not sensitive to the damage degree when the damage occurred at 2/3d (d is the stud diameter) from the stud root. An increased stud area would be engaged in resisting shear force as the distance of damage location from stud root increased and the failure section becomes inclined, resulting in a less reduction in the shear strength and shear stiffness. The reduction factor was proposed to consider the degradation of the shear strength of the damaged stud. The reduction factor can be calculated using two approaches: a linear relationship and a square relationship with the damage degree corresponding to the shear strength dominated by the section area and the nominal diameter of the damaged stud. It was found that the proposed method is preferred to predict the shear strength of a stud with initial damage.