• 제목/요약/키워드: Stress reduction coefficient

검색결과 84건 처리시간 0.026초

원공이 있는 복합적층판의 파괴특성 연구 (Study on Failure Characteristics of Laminate with a Hole)

  • 송관형;이재욱
    • 대한조선학회지
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    • 제26권4호
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    • pp.67-80
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    • 1989
  • 복합적층 구조물의 체결특성을 연구하기에 앞서 구조물 제작시 필연적으로 대두되는 원공이 있는 적층판의 기 제시된 몇 가지 파괴해석 모델을 고찰하고, 파괴특성을 알아 보았다. 또한, 원공이 있는 단일방향 복합재료와 $[{\pm}45^{\circ}]2s,\;[0^{\circ}/90^{\circ}]2s,\;[{\pm}45^{\circ}/0^{\circ}/90^{\circ}]s$ 적층판의 시편실험 결과를 이용, 특성길이를 계산하여 파손강도를 예측하고자 했다. AE(Acoustic Emission) 실험평가는 주로 손상의 발생과 거동을 추적하여 파손과정을 평가하는 방법으로 사용했고 Ultrasonic 시험법은 초기 손상검출, 손상 영역의 크기를 규명하고자 했다.

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부재의 길이가 폴리머 콘크리트의 휨압축 강도에 미치는 영향 (Effects of Specimen Length on Flexural Compressive Strength of Polymer Concrete)

  • 연규석;김남길;주명기;유근우;권윤환
    • 한국콘크리트학회:학술대회논문집
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    • 한국콘크리트학회 2002년도 봄 학술발표회 논문집
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    • pp.99-104
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    • 2002
  • In this paper the influence or specimen length on flexural compressive strength and parameter or equivalent rectangular stress block of polymer concrete was evaluated. For this purpose, a series of C-shaped specimens subjected to eccentric compression were tested using four different length-to-depth ratios(from 1.0, 2.0, 3.0 and 4.0) of specimens with compressive strength of 1,020kgf/cm$^2$. Results indicate that for the region of h/c$\leq$3.0 the reduction in equivalent rectangular stress block depth and flexural compressive strength with increase of length-to-depth ratios was apparent but for the region of h/c$\geq$3.0 they were nearly constant. It means that for the region of h/c$\geq$3.0 effect of specimen length on equivalent rectangular stress block depth and flexural compressive strength was negligible. It was also founded that the effect of specimen length on v, a coefficient of strength, that was from 0.84 to 0.86 regardless of h/c was petty. Finally, predictive equation is, suggested by using modified law of effect of specimen length and results.

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Elasto-plastic thermal stress analysis of functionally graded hyperbolic discs

  • Demir, Ersin;Callioglu, Hasan;Sayer, Metin
    • Structural Engineering and Mechanics
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    • 제62권5호
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    • pp.587-593
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    • 2017
  • The objective of this analytical study is to calculate the elasto-plastic stresses of Functionally Graded (FG) hyperbolic disc subjected to uniform temperature. The material properties (elastic modulus, thermal expansion coefficient and yield strength) and the geometry (thickness) of the disc are assumed to vary radially with a power law function, but Poisson's ratio does not vary. FG disc material is assumed to be non-work hardening. Radial and tangential stresses are obtained for various thickness profile, temperature and material properties. The results indicate that thickness profile and volume fractions of constituent materials play very important role on the thermal stresses of the FG hyperbolic discs. It is seen that thermal stresses in a disc with variable thickness are lower than those with constant thickness at the same temperature. As a result of this, variations in the thickness profile increase the operation temperature. Moreover, thickness variation in the discs provides a significant weight reduction. A disc with lower rigidity at the inner surface according to the outer surface should be selected to obtain almost homogenous stress distribution and to increase resistance to temperature. So, discs, which have more rigid region at the outer surface, are more useful in terms of resistance to temperature.

간호대학생의 생활스트레스와 우울의 관계에서 마음챙김의 매개효과 (Mediating Effect of Mindfulness between Stressful Life Events and Depression in Nursing Students)

  • 송영숙
    • 한국보건간호학회지
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    • 제31권3호
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    • pp.518-527
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    • 2017
  • Purpose: This study examined the relationship among stressful life events, mindfulness and depression, and explored the mediating role of mindfulness between stressful life events and depression in nursing students. Methods: A cross-sectional survey was undertaken. A sample of 120 nursing students participated in the study. The self-reported measures of stressful life events (revised life stress scale), depression (DASS-D) and mindfulness (MAAS) were adopted in April, 2017. The data were analyzed using descriptive statistics, frequency, Pearson correlation coefficient and multiple regression. Mediation analysis was performed using the Baron & Kenny method and Sobel test. Results: The mean scores of stressful life events, mindfulness and depression were 39.50, 77.03, and 8.18, respectively. Higher levels of stressful life events were associated with lower mindfulness (r = -46, p < .001) and higher depression (r = -44, p < .001), and mindfulness was negatively associated with depression (r = -72, p < .001). Mindfulness showed full mediation in the relationship between stressful life events and depression. Conclusion: Stressful life events influenced the nursing students' depression via the full mediating effect of mindfulness. Promoting mindfulness plays an important role in reducing depression in nursing students. Therefore, it is important to develop a mindfulness program or use a mindfulness-based stress reduction program (MBSR) for nursing students.

니들 롤러 베어링의 피로 수명 향상에 대한 연구 (Improvement in Fatigue Life of Needle Roller Bearing)

  • 다리스렝 스르멩닥와;아마노프 아웨즈한;편영식
    • Tribology and Lubricants
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    • 제35권4호
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    • pp.237-243
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    • 2019
  • Through this study, we investigate the effects of ultrasonic nanocrystal surface modification (UNSM) technology on the fatigue life of needle roller bearings. The fatigue life of untreated and UNSM-treated needle roller bearings is evaluated using a roller fatigue tester at various contact stress levels under oil-lubricated conditions. We can ascertain that the fatigue life of an UNSM-treated needle roller bearing was extended by approximately 34.3% in comparison with an untreated one, where the effectiveness of UNSM technology diminishes with increasing contact stress. The surface roughness and surface hardness of needle roller bearings before and after being treated by UNSM technology are compared and discussed to understand the role of UNSM technology in improving the fatigue life of needle roller bearings. In addition, a fractograph of the damaged bearings is observed using a scanning electron microscopy to shed light on the fracture mechanisms of bearings under different contact stress levels. We can therefore conclude that the application of UNSM technology to the needle roller bearings improves the fatigue life by reducing the friction coefficient and increasing the wear resistance; this may be attributed to a reduction in surface roughness from 0.5 to $0.149{\mu}m$ and an increase in surface hardness from 58 to 62 HRc.

Effects of freezing and thawing on retaining wall with changes in groundwater level

  • Kim, Garam;Kim, Incheol;Yun, Tae Sup;Lee, Junhwan
    • Geomechanics and Engineering
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    • 제24권6호
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    • pp.531-543
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    • 2021
  • Freezing and thawing of pore water within backfill can affect the stability of retaining wall as the phase change of pore water causes changes in the mechanical characteristics of backfill material. In this study, the effects of freezing and thawing on the mechanical performance of retaining wall with granular backfill were investigated for various temperature and groundwater level (GWL) conditions. The thermal and mechanical finite element analyses were performed by assigning the coefficient of lateral earth pressure according to phase change of soil for at-rest, active and passive stress states. For the at-rest condition, the mobilized lateral stress and overturning moment changed markedly during freezing and thawing. Active-state displacements for the thawed condition were larger than for the unfrozen condition whereas the effect of freezing and thawing was small for the passive condition. GWL affected significantly the lateral force and overturning moment (Mo) acting on the wall during freezing and thawing, indicating that the reduction of safety margin and wall collapse due to freezing and thawing can occur in sudden, unexpected patterns. The beneficial effect of an insulation layer between the retaining wall and the backfill in reducing the heat conduction from the wall face was also investigated and presented.

수복재와 이장재에 따른 응력과 온도 분포의 유한 요소 분석 (FINITE ELEMENT ANALYSIS OF STRESS AND TEMPERATURE DISTRIBUTION AFFECTED BY VARIOUS RESTORATIVE AND BASE MATERIAL)

  • 이재영;오태석;임성삼
    • Restorative Dentistry and Endodontics
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    • 제25권3호
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    • pp.321-337
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    • 2000
  • Dental caries, one of the most frequent dental disease, become larger because it can be thought as a simple disease. Further more, it can progress to unexpected root canal therapy with fabrication of crown that needs reduction of tooth structure. Base is required in a large caries and ZOE, ZPC, glass ionomer are used frequently as base material. They, with restorative material, can affect the longevity of the restoration. In this study, we assume that the mandibular 1st molar has deep class I cavity. So, installing the 3 base material, 3 kinds of fillings were restored over the base as follows; 1) amalgam only, 2) amalgam with ZPC, 3) amalgam with ZOE, 4) amalgam with GI cement, 5) gold inlay with ZPC, 6) gold inlay with GI cement, 7) composite resin only, 8) composite resin with GI cement. After develop the 3-dimensional model for finite element analysis, we observe the distribution of stress and temperature with force of 500N to apical direction at 3 point on occlusal surface and temperature of 55 degree, 15 degree on entire surface. The analyzed results were as follow : 1. Principal stress produced at the interface of base, dentin, cavity wall was smallest in case of using GI cement as base material under the amalgam. 2. Principal stress produced at the interface of base, dentin, cavity wall was smaller in case of using GI cement as a base material than ZPC under gold inlay. 3. Composite resin-filled tooth showed stress distributed over entire tooth structure. In other words, there was little concentration of stress. 4. ZOE was the most effective base material against hot stimuli under the amalgam and GI cement was the next. In case of gold inlay, GI cement was more effective than ZPC. 5. Composite resin has the small coefficient of thermal conductivity. So, composite resin filling is the most effective insulating material.

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대학생의 생활사건, 대인감정, 심리적 강인성, 자기통제력이 대학차원스트레스에 미치는 영향 (The Effects of College Students' Life Events, Interpersonal Emotion, Psychological Hardiness, and Self-Control on College-Based Stress)

  • 박미라;제남주
    • 디지털융복합연구
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    • 제18권9호
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    • pp.285-295
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    • 2020
  • 본 연구는 대학생의 대학차원스트레스의 영향요인을 파악하여 대학차원스트레스 감소를 위한 교육프로그램을 마련하고자 시도되었다. G도 대학생 169명을 대상으로 2020년 6월 15일부터 7월 15일까지 자료수집하였다. IBM SPSS 21.0으로 빈도와 백분율, 평균, 표준편차, t-test, ANOVA, Pearson correlation coefficient, Multiple regression로 분석하였다. 대학차원스트레스는 생활사건발생, 생활사건중요도, 대인감정, 자기통제력과 양의 상관관계가 있었다. 대상자의 대학차원스트레스에 가장 영향을 미치는 요인은 심리적강인성(β=-.323, p<.001)이었고, 그 다음으로 동아리활동(β=.237, p<.001), 대인갈등(β=.215, p=.001), 학년-2(β=-.203, p=.001), 학과적응(β=.161, p=.010), 연령-21세(β=-.149, p=.024)순이었다. 모형에 대한 설명력은 44.4%이었다(F=42.43, p<.001). 본 연구의 결과가 대학차원에서 스트레스 감소를 위한 교육프로그램 개발에 기초자료로 활용되어 질 것으로 기대한다. 또한 대학차원스트레스 감소를 위해서는 심리적강인성과 학과적응을 도모할 수 있는 교육프로그램 마련이 필요하며, 연령과 학년을 고려하고, 지지체계인 동아리활동을 활용한 맞춤형 교육이 요구된다.

치과위생사의 조직 커뮤니케이션 만족이 직무만족, 조직몰입, 이직의도에 미치는 영향: 대인관계 스트레스 매개효과를 중심으로 (Influence of organizational communication satisfaction on job satisfaction, organizational commitment, and turnover intention : Focused on the mediated effects of interpersonal stress)

  • 박영남;최용금;류다영
    • 한국치위생학회지
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    • 제15권5호
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    • pp.797-804
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    • 2015
  • Objectives: The purpose of the study was to investigate the influence of organizational communication satisfaction on the job satisfaction, organizational commitment, and turnover intention in the dental hygienists. Methods: A self-reported questionnaire was completed by 227 dental hygienists in Chungnam. The questionnaire consisted of 4 questions of general characteristics of the subjects, 8 questions of interpersonal stress, 12 questions of organizational communication satisfaction, 5 questions of job satisfaction, 5 questions of organizational commitment, and 5 questions of turnover intention. The four variables were measured by Likert 7 point scale. Data were analyzed using SPSS version 18.0 for frequency analysis, t test, one way ANOVA, Pearson's correlation coefficient, and stepwise regression analysis. Sobel test was used to verify the mediating effects. Results: The interpersonal stress was proportional to turnover intention and inversely proportional to the organizational communication satisfaction, job satisfaction, and organizational commitment(p<0.01). The organizational communication satisfaction was proportional to the job satisfaction and organizational commitment, and inversely proportional to turnover intention(p<0.01). The interpersonal stress had a meditating effect between organizational communication satisfaction, and job satisfaction. It also gave the mediating effect between organizational communication satisfaction and organizational commitment. Conclusions: The effective organization management system can enhance the job satisfaction, organizational commitment, and turnover intention reduction in the dental hygienists.

How Does Yoga Breathing Affect Prefrontal QEEG Quotients?

  • Kim, Eunmi
    • 감성과학
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    • 제16권1호
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    • pp.75-84
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    • 2013
  • The underlying changes in biological processes that are associated with reported changes in mental and physical health in response to yoga breathing ($pr{\bar{a}}n{\bar{a}}y{\bar{a}}ma$) have not been systematically explored yet. In this study, the effects of a yoga breathing program on prefrontal EEG were tested with middle-aged women. Participants were collected as volunteers and controlled into two groups. Two channel EEG was recorded in the prefrontal region (Fp1, Fp2) from the yoga breathing group (n=17) and control group (n=17). QEEG quotients were transformed from the EEGs and analyzed by the ANOVAs on gain scores. As a result, ${\alpha}/{\delta}$ (left, right) and CQ (correlation quotient) for yoga breathing participants were significantly decreased compared to control group (p<.05). ${\alpha}/{\beta}_H+{\alpha}/{\delta}$ (left, right) were increased significantly (p<.05). For those significantly changed QEEG quotients, the interaction effects of Group x prefrontal alpha (${\alpha}$) and beta (${\beta}$) asymmetry were tested. Only the ${\alpha}$ asymmetry showed main effect on the gain score of ${\alpha}/{\beta}_H+{\alpha}/{\delta}$ (right) with F (1, 34)=5.694 (p<.05). Pearson's correlation coefficient between ${\alpha}$ asymmetry and gain score of ${\alpha}/{\beta}_H+{\alpha}/{\delta}$ (right) was .374 (p<.05). The gain score of ${\alpha}/{\beta}_H+{\alpha}/{\delta}$ (right) was increased for the right ${\alpha}$ dominance of yoga breathing group. On the contrary it was decreased for the left ${\alpha}$ dominance of yoga breathing group as well as the control regardless of the dominance. The result of this study implies that yoga breathing increases stress resistance and is effective in the management of physical stress. Emotionally relaxed people may have greater instantaneous stress reduction after yoga breathing. Moreover, yoga breathing could be also beneficial for depressed who may be more vulnerable to stress.

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