Mechanism for Reducing Stress Concentrations in Bolt- Nut Connectors

Chae-Ho Lee,한석영,김범준 한국정밀공학회 2014 International Journal of Precision Engineering and Vol. No.

As the structural systems become more and more complicated, bolt-nut connectors play an increasingly important role in the safetyand reliability of structures. If the strength of bolt-nut connectors is insufficient, fatigue failure can initiate at the point of maximumprincipal stress. In this study, reduction mechanism of the stress concentration in bolt-nut connectors was investigated by performingshape optimization using finite element method (FEM) implementing progressive quadratic response surface modeling (PQRSM) andthe growth-strain method (GSM). The best reduction mechanism of stress concentration was achieved by stress control of GSM. Itwas also found that stress concentration can significantly be reduced by uniformly distributing stresses over the entire threads as faras possible.

경찰공무원의 외상후 성장 영향요인

Seung Woo Han,Hee Sook Kim 위기관리 이론과 실천 2015 Crisisonomy Vol.11 No.3

본 연구는 경찰공무원의 외상후 성장에 미치는 외상사건 경험, 자존감 ,스트레스대처 능력과 스트레스 반응의 영향력을 파악하기 위한 서술적 조사연구로 경찰공무원들의 외상후 성장을 증가시키기 위해 다양한 정보제공과 함께 의사소통을 증진하는 간호중재 프로그램을 개발하는데 기초적인 자료를 제공하고자 실시되었다. 연구대상은 본 연구에 자발적으로 참여할 것을 서면 동의한 경찰공무원 171명이었다. 외상후 성장, 외상사건 경험, 자존감 ,스트레스 대처, 스트레스 반응 척도를 사용하여 2014년 8월 18일 부터 8월 31일까지 자료를 수집하였다. 자료분석은 SPSS Win 12.0을 이용하여 단계별 다중회귀로 분석하였다. 연구결과는 대상자의 일반적 특성에 따른 외상후 성장은 성별에서 여성, 종교 유무에서는 종교를 가지고 있는 집단에서 유의하게 높게 나타났다. 대상자의 외상후 성장은 평균 57.7(±14.88)점, 자존감은 36.0(±4.55)점, 스트레스 대처에서 문제중심적 스트레스대처는 평균 18.2(±2.70)점이었으며, 정서중심적 스트레스대처는 26.1(±3.23)점, 스트레스 반응에서 신체화 반응 12.4(±7.06)점, 우울8.9(±6.06)점, 분노반응은 7.4(±4.54)점이었다. 외상후 성장과 자존감, 문제중심대처, 정서중심대처는 유의한 정상관으로 나타났고(p<.001), 외상후 성장에 영향을 미치는 요인은 정서중심 대처가 가장높게 나타났고(ß=.35, p<.001), 성별(여자)(ß=.24, p<.001) 및 자존감 이였으며(ß=.23, p=.002), 이들 변수의 외상후 성장에 대한 설명력은 24%였다. 따라서 경찰공무원들이 스트레스에 대해 정서중심적 대처 및 자존감이 높고 성별이 여성일수록 외상후 성장 정도가 높음으로 평상시 스트레스에 정서중심적 대처방법과 효율적인 의사소통 전략을 익히도록 훈련할 필요가 있으며 자존감을 증진하기 위한 프로그램개발, 그리고 성별 및 인구학적 특성에 따른 체계적인 연구가 뒷받침 되어야 할 것이다. Purpose: This study was conducted to investigate the factors influencing Post-traumatic growth with police officer. Methods: The variables were collected from August 18 to 31, 2014 from 171 the police officers of section in charge of violent crime and detective in ten different police offices in seoul. The variables were assessed by research tool of post-traumatic growth, traumatic event experience, self-esteem, stress coping method, stress response. The data analysis were performed using mean, standard deviation, t-test, one-way ANOVA and post-test were analyzed using Pearson's correlation Coefficient. Stepwise multiple regression analyzed with the SPSS 12.0 program. Result: Post-traumatic growth shows significant difference according to female police officer and having a religion among general characteristics. There were positive correlation between self-esteem, emotion and problem focused coping. Factors affecting post-traumatic growth were emotion focused coping, female police officer and self-esteem, accounting for 24% of the varience in the outcome. Conclusion: Based on the findings of this study, it is necessary to develop self-esteem improvement programs and improve stress coping method. Furthermore, further research. will have to be supported by the systematic method according to general characteristics.

탄성 선형 경화 재료로 구성된 복합 구조물의 자유 경계면에서 나타나는 응력특이도

정철섭 한국전산구조공학회 1997 한국전산구조공학회논문집 Vol.10 No.3

탄성 선형 경화 재료로 구성된 복합 구조물의 자유 경계면에서 나타나는 응력 특이도를 평면 변형률 상태에서 계산하였다. 자유 표면력 경계조건과 계면 연속조건을 만족해야하는 지배 탄성 방정식은 2점 경계치문제로 정의되며, 일반 고유치 문제의 해인 고유치가 응력 특이도가 될 것이다. 자유경계면 근처에서 응력 성분을 rs-1에 비례한다고 가정하여 특정한 s(고유치)를 구하는 고유치 문제를 뉴톤향상법과 사격법을 사용하여 수치적으로 해를 구하였다. The order of the stress singularity that occurs at the termination of an interface between materials exhibiting bilinear stress-strain response under plane strain conditions has been calculated, The governing equation of elasticity together with traction-free boundary condition and interface continuity condition defines a two-point boundary value problem. The stress components near the free edge are assumed to be proportional to rs-1, with solutions existing only for certain values of s. Finding these values entails the solution of an eigenvalue problem. Because it has been impossible to integrate the differential equations analytically, the integration has been performed numerically with a shooting method coupled with a Newton improvement scheme.

탄성 선형 경화 재료로 구성된 복합 구조물의 자유 경계면에서 나타나는 응력특이도

정철섭 한국전산구조공학회 1997 전산구조공학 Vol.10 No.3

탄성 선형 경화 재료로 구성된 복합 구조물의 자유 경계면에서 나타나는 응력 특이도를 평면 변형률 상태에서 계산하였다. 자유 표면력 경계조건과 계면 연속조건을 만족해야하는 지배 탄성 방정식은 2점 경계치문제로 정의되며, 일반 고유치 문제의 해인 고유치가 응력 특이도가 될 것이다. 자유경계면 근처에서 응력 성분을 r/sup s-1/에 비례한다고 가정하여 특정한 s(고유치)를 구하는 고유치 문제를 뉴톤향상법과 사격법을 사용하여 수치적으로 해를 구하였다. The order of the stress singularity that occurs at the termination of an interface between materials exhibiting bilinear stress-strain response under plane strain conditions has been calculated, The governing equation of elasticity together with traction-free boundary condition and interface continuity condition defines a two-point boundary value problem. The stress components near the free edge are assumed to be proportional to r/sup s-1/, with solutions existing only for certain values of s. Finding these values entails the solution of an eigenvalue problem. Because it has been impossible to integrate the differential equations analytically, the integration has been performed numerically with a shooting method coupled with a Newton improvement scheme.

Rapid <i>in vivo</i> screening system for anti-oxidant activity using bacterial redox sensor strains

Park, S-J.,Chung, H.Y.,Lee, J-H. Blackwell Publishing Ltd 2010 Journal of Applied Microbiology Vol.108 No.4

<P>Abstract</P><P>Aim: </P><P>To develop a faster and easier <I>in vivo</I> method to screen compounds for anti-oxidant activity using a microbial system.</P><P>Methods and Results: </P><P>Bacterial redox sensor-based assay systems were applied. The activities of SoxR and OxyR, the bacterial redox sensors, were monitored to probe the intracellular redox status through two reporter strains, <I>Escherichia coli soxS</I><SUB>p</SUB>-<I>lacZ</I> and <I>oxyS</I><SUB>p</SUB>-<I>lacZ</I> fusions, which specifically respond to paraquat, a superoxide generator, and H<SUB>2</SUB>O<SUB>2</SUB>, respectively, with practically no cross reactivity. For the test screening, 27 natural compounds including phenolics and flavonoids that are putatively considered anti-oxidant nutritional supplements were collected and assayed for their capability to alleviate oxidative stress in these bacterial systems. Among them, rutin, kaempferol and quercetin had significant anti-H<SUB>2</SUB>O<SUB>2</SUB> activity, and betaine, glycyrrhizic acid and baicalin had weak anti-superoxide activity. While rutin, kaempferol and quercetin significantly reduced the H<SUB>2</SUB>O<SUB>2</SUB> stress at low concentrations, betaine, glycyrrhizic acid and baicalin required higher concentration for their anti-superoxide effects. <I>In vitro</I>, only quercetin protected DNA in a metal-catalysed oxidation system, suggesting that the other compounds might indirectly exert their anti-oxidant activities through other biological functions. Finally, quercetin, rutin and kaempferol significantly restored the viability of a superoxide dismutase mutant that has limited viability because of defective defence against oxidative stress.</P><P>Conclusion: </P><P>These bacterial systems could provide a more efficient method for measuring the activity of compounds affecting cellular oxidative stress and viability.</P><P>Significance and Impact of the Study: </P><P>The demand for anti-oxidant and anti-ageing activities is increasing in one of the fastest growing segments of the functional food market, but the screening for these activities is currently very laborious, expensive and time consuming. This study suggests a basis for a high throughput screening method for these activities.</P>

발달지체 영유아와 어머니에 대한 RT중재 적용효과

김정미 한국유아특수교육학회 2010 유아특수교육연구 Vol.10 No.2

This study examined the effectiveness of the Responsive Teaching intervention based on family-centered approach on mothers and young children with developmental disabilities. Participants consisted of eleven mother and child dyads, in range of 15 to 76 months. They were intervened RT intervention once a week during three months. To collect the data, Korean Maternal Behavior Rating Scales(K-MBRS) and Korean Child Behavior Rating Scales(K-CBRS) were used to assess mother-child interaction; the parenting Stress Inventory (PSI) and Beck Depression Inventory(BDI) were completed to assess the parenting stress and maternal depression; and the Korean Child Development Inventory(K-CDI) was administered to diagnose the child developmental functioning. The data were analyzed with Wilcoxon signed rank test, Mann-whitney test and regression as the nonparametric statistical method. The results indicated that the maternal responsive behavior have an influence on promoting the children's pivotal developmental behaviors. Also the RT intervention declined significantly on the parenting stress and maternal depression. In this study, it was suggested that children's pivotal developmental behaviors should be recognized as an objective behavior in the early childhood curricula and intervention service with special needs based on family-centered approach. 본 연구에서는 발달지체 영유아와 어머니를 대상으로 가족-중심적 접근에 근거한 RT중재를 적용하고 그 효과를 검증하였다. 연구 대상은 유아특수학교와 치료기관에서 발달진단 평가를 받은 후 조기중재 서비스를 희망하는 15개월에서 76개월 사이의 영유아와 어머니 11쌍이다. 영유아와 어머니 쌍은 약 3개월 동안 주 1회씩 총 12~13회기의 RT중재를 받았다. 영유아와 어머니의 상호작용 행동 특성, 어머니의 심리적 건강, 그리고 영유아의 발달 수준을 평가하기 위하여 중재 전-후에 걸쳐 한국판 어머니행동 평가척도(K-MBRS), 한국판 아동행동 평가척도(K-CBRS), 부모양육스트레스 척도(PSI), Beck우울척도(BDI), 그리고 한국판 아동발달검사(K-CDI)를 실시하였다. 수집된 자료는 비모수통계방법인 Wilcoxon signed test, Mann-whitney test 그리고 단순회귀분석을 통하여 분석되었다. 연구 결과, RT중재는 어머니의 반응적 행동과 효율적 행동을 긍정적으로 변화시켰으며 영유아의 중심축 발달행동을 효과적으로 증가시켰다. 또한 RT중재는 어머니의 양육스트레스와 우울을 효과적으로 감소시켰다. 본 연구는 발달지체 영유아를 대상으로 부모를 매개로하는 가족-중심적 접근 중재의 효과를 검증하고 장애영유아를 위한 교육과정 및 중재서비스의 목표로서 중심축 발달행동의 인식에 대한 중요성을 제언하였다는데 의의가 있다.

Numerical and Experimental Study on Strain Rate Effect of Ordinary Concrete under Low Strain Rate

Xiao Chen,Chong Shi,Yu-Long Zhang,Jun-Xiong Yang 대한토목학회 2021 KSCE JOURNAL OF CIVIL ENGINEERING Vol.25 No.5

The strain rate effect of ordinary concrete is researched through the particle discrete element method. A random construction method of three-dimensional aggregate is used, and the numerical sample consistent with the experimental specimen is constructed using particle flow code. Moreover, the simulation method that can properly reflect the strain rate effect with the parallel bond model is proposed. The meso-parameters are calibrated by triaxial compression test. Based on the proposed simulation method and calibrated meso-parameters, the numerical tests of direct tension, uniaxial compression, and cyclic loading under strain rates from 10−5 s−1 to 10−1 s−1 are carried out. The results show that the strain rate effect of concrete can be simulated with particle flow code by assuming that the micromechanical properties of materials vary with the strain rate, and the strength and failure characteristics of numerical samples under different strain rates are described well by the proposed method. In addition, the different mechanical responses of the samples to the strain rate in the compression test and the tensile test are obtained, and the changes of mechanical parameters and damage degree with strain rates in the cyclic loading test are also successfully simulated. This study can provide a feasible numerical method for the follow-up research of dynamic mechanical behavior of concrete and offer theoretical guidance for the stability assessment of concrete engineering.

응력한계상태를 이용한 해상풍력발전기 재킷구조물의 지진신뢰성해석

이기남(Gee-Nam Lee),김동현(Dong-Hyawn Kim) 한국해양공학회 2016 韓國海洋工學會誌 Vol.30 No.4

Considering the effect of dynamic response amplification, a reliability analysis of an offshore wind turbine support structure under an earthquake is presented. A reliability analysis based on the dynamic response requires a large amount of time when using not only a level 3 approach but also level 2 such as a first order reliability method (FORM). Moreover, if a limit state is defined by using the maximum stress at a structural joint where stress concentration occurs, a three-dimensional element should be used in the finite element analysis. This makes the computational load much heavier. To deal with this kind of problem, two techniques are suggested in this paper. One is the application of a quasi-static structural analysis that takes the dynamic amplification effect into account. The other is the use of a stress concentration factor to estimate the maximum local stress. The proposed reliability analysis is performed using a level 2 FORM and verified using a level 3 simulation approach.

Nonlinear Structural Safety Assessment under Dynamic Excitation Using SFEM

Huh, Jungwon 한국전산구조공학회 2000 한국전산구조공학회논문집 Vol.13 No.3

단기 동 하중(특히 지진하중)을 받는 비선형 강 프레임 구조물의 안전성을 평가하기 위하여 추계론적 유한요소 개념에 근거한 비선형 시간영역 신뢰성 해석 기법을 제안하였다. 제안된 알고리즘에서는 유한요소 공식화가 응답 표면법, 1차 신뢰성 방법, 그리고 반복 선형보간 기법의 개념들과 결합되어 지는데, 이것이 추계론적 유한요소 개념으로 귀결된다. 실제 지진하중의 시간이력이 구조물의 진동을 위해 사용되므로 사실적인 하중조건의 재현이 가능하다. 가상 응력에 기초한 유한요소 기법이 본 알고리즘의 효율성을 증대하기 위해 사용된다. 본 알고리즘은 지진하중 또는 임의의 단기 동적하중을 받는 유한요소 기법으로 표현되는 어떠한 선형 및 비선형 구조물과 관련된 위험도를 평가할 수 있는 잠재성을 가지고 있다. 수치예제를 통하여 알고리즘을 설명하였으며, 몬테카를로 시뮬레이션 기법을 사용하여 본 알고리즘을 검증하였다. To assess the safety of nonlinear steel frame structures subjected to short duration dynamic loadings, especially seismic loading, a nonlinear time domain reliability analysis procedure is proposed in the context of the stochastic finite element concept. In the proposed algorithm, the finite element formulation is combined with concepts of the response surface method, the first order reliability method, and the iterative linear interpolation scheme. This leads to the stochastic finite element concept. Actual earthquake loading time-histories are used to excite structures, enabling a realistic representation of the loading conditions. The assumed stress-based finite element formulation is used to increase its efficiency. The algorithm also has the potential to evaluate the risk associated with any linear or nonlinear structure that can be represented by a finite element algorithm subjected to seismic loading or any short duration dynamic loading. The algorithm is explained with help of an example and verified using the Monte Carlo simulation technique.

Enhancement of J estimation for typical nuclear pipes with a circumferential surface crack under tensile load

Cho, Doo-Ho,Woo, Seung-Wan,Chang, Yoon-Suk,Choi, Jae-Boong,Kim, Young-Jin,Jhung, Myung-Jo,Choi, Young-Hwan 대한기계학회 2010 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.24 No.3

This paper is to report enhancement of engineering J estimation for semi-elliptical surface cracks under tensile load. Firstly, limitation of the sole solution suggested by Zahoor is shown for reliable structural integrity assessment of thin-walled nuclear pipes. An improved solution is then developed based on extensive 3D FE analyses employing deformation plasticity theory for typical nuclear piping materials. It takes over the structure of the existing solution but provides new tabulated plastic influence functions to cover a wide range of pipe geometry and crack shape. Furthermore, to facilitate easy prediction of the plastic influence function, an alternative simple equation is also developed by using a statistical response surface method. The proposed $H_1$ values can be used for elastic-plastic fracture analyses of thin-walled pipes with a circumferential surface crack subjected to tensile loading.