Macro-micro Performances of Granular Materials Considering the Influences of Density and Stress Path under True Triaxial Conditions: A DEM Investigation

Hailin Wang,Hong Sun,Xiurun Ge,Fujun Niu 대한토목학회 2023 KSCE Journal of Civil Engineering Vol.27 No.10

The mechanical behaviors of granular materials are dominated by internal structure, which are related to fabric evolution during loading. This study investigated the fabric evolution of granular materials with different densities and stress paths under true triaxial conditions. A series of discrete element numerical simulations with different intermediate principal stress coefficient b were carried out along the constant mean stress p and the constant minor principal stress σ3 stress paths for both loose and dense specimens. The results indicated that the constant-p stress path produced a faster increase in stress ratio than the constant-σ3 stress path at the same b. The effects of specimen density on the peak friction angle are greater than that of stress path. The microscopic analyses revealed that the constant-p stress path facilitates a much more preferential distribution of normal contact force network along the major principal direction. The discrepancies in the peak stress ratio under two stress paths were thus interpreted. The dense specimen will rapidly form a higher anisotropic distribution of the normal contact force network upon shearing, and its anisotropic intensity was almost twice that of the loose specimen at the peak stress state. In addition, a unique relationship between the strong deviatoric fabric ratio and stress ratio was presented. The ratio of the two was approximately 1.0 regardless of stress path, density and b value. Finally, an underlying relationship between the stress components and the whole fabric components at the critical state was confirmed by introducing a new stress tensor. The three principal components (F1, F2 and F3) of the whole fabric tensor can be quantitatively represented with the imposed three principal stress components (σ1, σ2 and σ3) by employing a relationship of F1:F2:F3 = σ10.27:σ20.27:σ30.27. It provides a more comprehensive perspective to analyze the macro-micro performances of granular materials at the critical state.

암반 응력조건에 따른 원형수직구 굴착시의 응력경로 및 응력모드 분석

박상찬,문현구 한국자원공학회 2014 한국자원공학회지 Vol.51 No.6

수직구는 심도에 따른 초기응력 조건이 계속 변화하는 특징을 갖는다. 암반내 다양한 초기응력 조건을측압계수와 수평응력비를 이용한 초기주응력모드로 분류하고 초기주응력비가 갖는 응력상태의 특징을 분석하였다. 굴착으로 재형성되는 수직구 벽면의 2차주응력을 크기와 방향에 따라 2차주응력모드로 분류하고, 원형공동에 대한 이론해와 3차원 수치해석법을 이용하여 다양한 초기응력 조건에서의 원형수직구 굴착에 따른 응력경로와 응력모드 분석을 수행하였다. 주응력 평면에서의 응력경로 분석을 통하여 초기주응력모드와 2차주응력모드와의 상관성을 평가하였다. 또한, 암반조건과 보강조건이 수직구 굴착시의 응력경로와 응력모드에 미치는영향을 분석하였다. In-situ stresses change continuously as the depth of the shaft increases. Various in-situ stress conditions are classified using In-situ principal stress mode defined by the ratio of horizontal to vertical stress and the ratio of horizontal stresses. And the characteristics of in-situ principal stress ratio relating to stress condition are analysed. Secondary principal stress mode is used to classify the principal stresses states acting on the shaft wall after excavation according to the magnitude and direction of the principal stresses. And stress-path and stress-mode analyses are performed by using analytic solution and 3-dimensional numerical method for a circular-shaped shaft excavation with various in-situ stress conditions. With analysis of stress-path, correlation between In-situ principal stress mode and Secondary principal stress mode is estimated. Also, the effects of rock mass condition and support state on the stress-path and stress-mode during the shaft excavation are analysed.

Stress-strain Behaviour and Shear Strength of Municipal Solid Waste (MSW)

Xiulei Li,Jianyong Shi 대한토목학회 2016 KSCE JOURNAL OF CIVIL ENGINEERING Vol.20 No.5

An understanding of the stress-strain behaviour of Municipal Solid Waste (MSW) is important in landfill design and stability analysis of landfill slopes. A series of triaxial compression tests were carried out on reconstituted MSW specimens. The effect of stress path on the drained stress-strain response and shear strength of MSW were investigated. For the compression stress paths of Δσ3 ≥0, a straight-lined increase section and an upward curvature are observed in the stress-strain curves of MSW; the upward curvature results from the fibrous constituents (primarily plastic and paper) reinforcing the waste matrix; the hardening points defined in stress-strain curves are used as failure criterion to calculate the strength parameters of MSW. For the compression stress paths of Δσ3 < 0, the stress-strain responses of MSW exhibit a rapidly increasing section towards a slowly increasing section without upward curvature; the development of fibrous reinforcement is not enough due to the reduction of confining stress σ3; the failure points defined in stress-strain curves are also used as failure criterion to calculate the strength parameters of MSW. A new method to estimate MSW strength parameters is proposed in this study. The differences of MSW friction angle are very small for different stress path tests. However, the cohesions obtained in compression stress path tests of Δσ3 < 0 are much smaller than that in conventional triaxial compression tests.

임상간호사의 직무스트레스, 직무만족도 및 이직충동

안혜경,강인순 한국자료분석학회 2008 Journal of the Korean Data Analysis Society Vol.10 No.1

This study was designed to figure out the relationships between job stress and coping type of clinical nurses so as to apply appropriate stress management and intervention programs to groups in each stage of stress in order to help them overcome stress, and provide basic data required to improve work motivation and efficiency. The subject of this study were 254 nurses who worked at "C" hospital in Busan. In order to measure the stress of clinical nurses, this study used the measures of stress experienced by nurses during work that had been developed by Gu and Kim(1985). For the measurement of copying types of nurses, the tool developed by Lazarus & Folkman(1984) and translated, revised and completed by Han and Oh(1990) was used. The data for this study was gathered from September 3 to 7, 2007 and analyzed through SPSS/Win 12.0 program for frequency, percentile, t-test, ANOVA and AMOS 4.0. The result of this study are summarized below: The average job stress was 2.44 points(highest score:5), which was relatively low. By items, job circumstances 2.66 points, the hospital administration and ward management 2.53 points, personal relations 2.53, and nursing job 2.26 points. Age, shift, position, satisfaction of the job, satisfaction of amount of the job were related with an elements of stress(p<.05). In conclusion, the extent of the job stress of clinical nurses was relatively high, and they received heaviest stress from job circumstances. The factor of the job stress of the nurse is correlated with one another and influenced to the degree of the job stress directly and indirectly. The factor that affected the degree of the job stress directly was the job satisfaction and the personal values. As shown this result, it is important that the factor of the job stress. 본 연구는 임상 간호사의 직무스트레스, 직무만족도 및 이직충동간의 경로를 분석하기 위한 조사연구이다. 연구대상자는 부산시에 소재한 2차 병원에 근무하는 간호사 254명이며, 연구도구는 직무스트레스를 측정하기 위하여 구미옥, 김매자(1985)가 개발한 간호사가 근무 중에 경험하는 직무스트레스 척도를 수정·보완한 것을 사용하였으며, 직무만족도는 한정석, 오가설(1990)이 개발한 것, 간호직에 대한 이직충동여부를 조사하기 위하여 본 연구자가 작성한 문항을 사용하였다. 수집된 자료는 SPSS/Win 12.0과 AMOS 4.0 통계프로그램을 이용하여 빈도, 백분율, t-test, ANOVA 및 구조방정식모형으로 분석하였다. 본 연구의 주요 결과로써 임상간호사는 직무환경에서 느끼는 직무스트레스가 높게 나타났다. 임상간호사의 직무스트레스는 직무만족도와 서로 연관성을 가지고 있고 이직충동에 직 간접적으로 영향을 미치고 있으며 이 중 직무만족도와 직무스트레스는 이직충동에 직접적으로 영향을 미치는 요인임을 알 수 있었다.

고교생의 진로스트레스와 자살생각의 인과관계

김옥희 한국진로교육학회 2010 진로교육연구 Vol.23 No.2

The purpose of this study was to examine the impact of career stress on suicidal ideation. The data of Korean Education & Employment Penal of Korea Research Institute for Vocational Education and Training were utilized. The data were the fourth data provided by the penal about middle school students in the ninth grade. The subjects in this study were 2.976 high school seniors, and t-test, correlation analysis and path model were employed. As for the subvariables of career stress, personality and appearance were selected as the causes of personal stress, and academic performance and career concern were selected as the causes of stress about entrance into school of higher grade. Troubles with friends and lovers were selected as the causes of relational stress, and living standard and concern for family discord were selected as the causes of family stress. As a result of analyzing the influence of gender, gender made significant differences to suicidal ideation, personal stress, stress about entrance into school of higher grade and family stress, but that's not the case for relational stress. Concerning the influence of the grade of school, there were significant gaps in suicidal ideation and all the subvariables of career stress according to that. The path model turned out to be significantly good when the goodness of it was checked, and there was a correlation between stress about entrance into school of higher grade and relational stress. The stress about entrance into school of higher grade affected suicidal ideation through personal stress and family stress, and relational stress had an impact on suicidal ideation through personal stress and family stress as well. 본 연구의 목적은 진로스트레스의 하위변인들이 자살생각여부에 미치는 영향을 탐색하는 것이다. 연구자료는 한국직업능력개발원의 한국교육고용패널 4차 자료를 활용하였다. 연구대상은 고 3학생으로 2976명이다. 연구를 위해 t검증, 상관분석, 경로모형 검증을 실시하였다. 먼저, 진로스트레스를 성격과 외모의 개인스트레스, 성적과 진로의 진학스트레스, 친구와 애인의 관계스트레스, 가정환경과 가족 불화의 가정스트레스로 구분하였다. 연구결과에 의하면 성별에 따른 평균의 차이검증에서 자살생각여부, 개인스트레스, 진학스트레스 및 가정스트레스는 유의하게 나타났지만 관계스트레스는 차이가 없었다. 학교 급별에서는 자살생각여부와 진로스트레스의 하위변인이 모두 유의한 차이가 있었다. 경로모형의 적합도 검증에서는 유의하게 나타났다. 진학스트레스와 관계스트레스는 서로 상관이 있었다. 진학스트레스는 개인스트레스와 가정스트레스를 매개로 하여 자살생각여부에 영향을 미쳤고, 관계스트레스도 개인스트레스와 가정스트레스를 매개로 하여 자살생각여부에 영향을 미치는 것으로 나타났다.

Nano-Scale CMOSFET에서 Contact Etch Stop Layer의 Mechanical Film Stress에 대한 소자특성 분석

나민기(Min-Ki Na),한인식(In-Shik Han),최원호(Won-Ho Choi),권혁민(Hyuk-Min Kwon),지희환(Hee-Hwan Ji),박성형(Sung-Hyung Park),이가원(Ga-Won Lee),이희덕(Hi-Deok Lee) 대한전자공학회 2008 電子工學會論文誌-SD (Semiconductor and devices) Vol.45 No.4

본 논문에서는 Contact Etch Stop Layer (CESL)인 nitride film의 mechanical stress에 의해 인가되는 channel stress가 소자특성에 미치는 영향에 대해 분석하였다. 잘 알려진 바와 같이 NMOS는 tensile stress와 PMOS에서는 compressive stress가 인가되었을 경우 drain current가 증가하였으며 그 원인을 체계적으로 분석하였다. NMOS의 경우 tensile stress가 인가됨으로써 back scattering ratio (rsat)의 감소와 thermal injection velocity (Vinj)의 증가로 인해 mobility가 개선됨을 확인하였다. 또한 rsat 의 감소는 온도에 따른 mobility의 감소율이 작고, 그에 따른 mean free path ( λO)의 감소율이 작기 때문인 것으로 확인되었다. 한편 PMOS의 compressive stress 경우에는 tensile stress에 비해 온도에 따른 mobility의 감소율이 크기 때문에 channel back scattering 현상은 심해지지만 source에서의 Vinj가 큰 폭으로 증가함으로써 mobility가 개선됨을 확인 할 수 있었다. 따라서 CES-Layer에 의해 인가된 channel stress에 따른 소자 특성의 변화는 inversion layer에서의 channel back scattering 현상과 source에서의 thermal injection velocity에 매우 의존함을 알 수 있다. In this paper, the dependence of MOSFET performance on the channel stress is characterized in depth. The tensile and compressive stresses are applied to CMOSFET using a nitride film which is used for the contact etch stop layer (CESL). Drain current of NMOS and PMOS is increased by inducing tensile and compressive stress, respectively, due to the increased mobility as well known. In case of NMOS with tensile stress, both decrease of the back scattering ratio (rsat) and increase of the thermal injection velocity (Vinj) contribute the increase of mobility. It is also shown that the decrease of the rsat is due to the decrease of the mean free path (λ?). On the other hand, the mobility improvement of PMOS with compressive stress is analyzed to be only due to the so increased Vinj because the back scattering ratio is increased by the compressive stress. Therefore it was confirmed that the device performance has a strong dependency on the channel back scattering of the inversion layer and thermal injection velocity at the source side and NMOS and PMOS have different dependency on them.

비등방 압밀된 다짐화강풍화토의 응력-변형률 거동 예측

정진섭 ( Jeong Jin Seob ),양재혁 ( Yang Jae Hyouk ) 한국농공학회 2003 韓國農工學會誌 : 전원과 자원 Vol.45 No.2

During this study, constant stress ratio tests with previous compression anisotropic stress history are performed on compacted decomposed granite soil sampled at Iksan, Jeonbuk. Yielding points are determined from stress-strain curves. The shape and characteristics of compression anisotropic yield curves is examined. In addition, the measured value of yielding curve and stress-strain behavior is predicted by Yasufuku's anisotropic constitutive model based on non-associated flow rule. The main results are summarized as follows : 1) Shape of yielding curves shows almost ellipse but asymmetry with respect to stress path during previous consolidation stress. 2) Yasufuku's anisotropic constitutive model is suitable in evaluation of yielding curves on anisotropic consolidated decomposed granite soil. 3) The predicted stress-strain curve shows reasonable agreement to measured behaviours.

수치해석을 이용한 지하굴착에 의한 암반의 응력경로에 관한 연구

문현구,서용범 한국자원공학회 2010 한국자원공학회지 Vol.47 No.1

Rock mass shows various failure modes and deformation behavior types according to the stress state of rock mass. In the case of underground excavation such as a tunnel and cavern the prediction of the variation of stresses is difficult, when the stress-path from the initial state of stress to the current state is complex. This study presents the stress-path of the rock mass around a tunnel analyzed by a 3-D finite element. The traces of stress-paths in the principal stress plane from its initial state of stress to the completion of excavation are also presented in this study for some specific locations around the tunnel. To evaluate the stability of observation points, relationship between stress-path and Mohr-Coulomb failure envelope, and that between stress-path and Hoek-Brown failure envelope were analyzed, respectively. 암반에 작용하는 응력의 상태에 따라 암석의 역학적 거동은 취성 거동에서 연성 및 소성 거동에 이르기까지 다양한 파괴양상과 변형 거동을 보인다. 특히 터널, 캐번 등 지하공동 굴착시 초기응력 상태에서 현재의 응력 상태에 도달하기까지 암반이 겪은 응력경로가 복잡한 경우에는 쉽게 예측할 수 없다. 본 연구에서는 3차원 유한요소해석을 통해 지하굴착에 의한 암반의 응력경로를 분석하였다. 공동 주변의 필요한 특정 위치에서 초기응력 상태로부터 굴착작업 종료 시까지 응력성분들의 변화를 추적하여 주응력 평면에 응력경로를 도시하였다. 계측점의 안정성 평가를 위해 응력경로와 Mohr-Coulomb 파괴포락선 및 Hoek-Brown 파괴포락선과의 관계를 분석하였다.

위기상황 스트레스 해소 교육 프로그램 제작을 위한 소방공무원의 외상 후 스트레스 장애 분석

최혜경,김지희 한국자료분석학회 2009 Journal of the Korean Data Analysis Society Vol.11 No.4

The purpose of this study was focused on the posttraumatic stress disorder analysis in Korea fire officers for the critical incident stress debriefing program development. In order to obtain the purpose, following variables were used; 3 independent variables(work burden, stress, stress response), 1 intermediating variable(on-scene stress), and 1 dependent variable (physical symptoms). The respondents were 970 fire officers in Korea from March to December in 2007 by using questionnaires developed by the researchers. Data was analyzed by SPSS 14.0 and AMOS 7.0 programs. Data cleaning was done for the exact data input. For the reliability and validity, exploratory factor analysis and Cronbach's alpha were analyzed. The general peculiarity of the respondents was shown by frequency analysis and descriptive analysis. In order to fulfill this study, the researchers proposed the hypothesis as follows : Work burden and stress will influence upon on-scene stress. Work burden, stress, on-scene stress and stress response will influence upon physical symptoms. Through the structured equation model analysis, the lower the level of work burden, stress and on-scene stress was, the lower the level of physical symptoms became. On the other hand, the higher the stress response was, the lower the level of physical symptoms became. 본 연구의 목적은 소방공무원이 현장에서 겪는 충격 스트레스로 발생하는 외상 후 스트레스장애 분석을 통해 위기상황 스트레스 해소 교육 프로그램 기초 자료를 제시하고자 하는 데 있다. 연구 목적을 달성하기 위하여 독립변인(업무부담감, 스트레스, 스트레스 대응) 3개, 매개변인(현장충격 스트레스) 1개, 종속변인(신체적 증상)으로 구성하여 영향력을 파악하였다. 본 연구 대상자는 전국 970명 소방공무원으로 2007년 3월부터 12월까지 구조화된 설문지를 이용하여 조사하였다. 자료분석은 SPSS 14.0과 AMOS 7.0 통계패키지를 사용하였으며, 정확한 코딩데이터의 입력확인을 위해 데이터클리닝(data cleaning) 작업을 실시하였다. 신뢰도와 타당도를 검정하기 위하여 탐색적 요인분석(exploratory factor analysis)과 Cronbach's 검증을 하였다. 연구대상의 일반적인 특성을 파악하기 위하여 빈도분석(frequency analysis)을 실시하였고, 각 요인에 대한 기술통계분석(descriptive analysis)을 실시하였다. 이 연구의 목적을 달성하기 위하여 설계한 연구가설은 선행 연구의 이론적 근거를 토대로 다음과 같이 설정하였다. 업무 부담감과 스트레스는 현장충격 스트레스에, 업무부담감, 스트레스, 현장충격스트레스, 스트레스대응은 신체적 증상에 영향을 줄 것이다. 가설검증을 위하여 구조방정식 모형분석을 실시한 결과, 업무부담감, 스트레스, 현장충격 스트레스가 낮고, 스트레스 대응이 높을 때 신체적 증상이 낮아지는 것으로 나타났다.

Ti-6Al-4V 판재에 Vanadium의 레이저 고에너지 적층 경로에 따른 잔류응력 특성

윤지홍,김성훈,김정한,이세환 한국기계가공학회 2022 한국기계가공학회지 Vol.21 No.11

Laser directed energy deposition (L-DED) has the advantages of complex shape production and easy stacking of dissimilar materials, but the reduction in residual stress owing to the rapid temperature change and difference in the thermal expansion behavior between materials should be considered. In this study, the residual stress characteristics according to the tool path in dissimilar materials of a Ti-6Al-4V plate and vanadium were compared and evaluated using finite element analysis. A vanadium layer was stacked on a Ti-6Al-4V plate using the L-DED method, and the simulation reliability was confirmed by comparing the temperatures under the same conditions. To compare the effect of the tool path on the residual stress, the zigzag path, spiral in-to-out (spiral IO), and spiral out-to-in (spiral OI) were simulated. Every path showed high residual stress in the outer area, and spiral IO had a low residual stress level and was uniform throughout the entire area. Therefore, the tool path when the outer area is stacked later similar to the spiral IO, was confirmed to be better for delamination and residual stress reduction. In the case of the zigzag path, the residual stress could be reduced on the final path, and the build-up speed was faster, but a high residual stress was generated on the starting path.