• 소성∙가공
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• 제17권6호
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• pp.420-428
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• 2008

The effect of loading path changes on the strain and mechanical properties of a commercial pure aluminum was studied using flat rolling and groove rolling. Material during flat rolling undergoes a continuous monotonic compressive loading, while one during groove rolling experiences a series of cross compressive loading. Four-pass flat rolling and groove rolling experiment are designed such that the aluminum undergoes the same amount of the strain at each pass. The rolling experiment was performed at room temperatures. Specimens for tensile test are fabricated from the plate and bar rolled. In addition, the strain distribution for the plate and bar cold rolled specimens is also calculated by finite element method. The results reveal that differences of loading path attributed by monotonic loading(flat rolling) and cross loading(groove rolling) significantly influence the mechanical properties such as yield stress, ultimate tensile stress, strain hardening and elongation. It is clear that the different loading path can give raise to change the deformation history, although it is deformed with same amount of strain for same material.

• 사회복지연구
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• 제44권2호
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• pp.113-140
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• 2013

본 연구는 미혼모의 스트레스와 대처, 적응의 모형과 그 변인과의 관계를 Lazarus and Folkman(1984)의 '스트레스-대처-적응(stress-coping-adaptation)' 의 이론적 모델에 입각해 검증하고 분석하여 미혼모의 스트레스를 경감하고 적응을 도모할 수 있는 사회복지 정책적, 실천적 함의를 제공하고자 하였다. 연구의 목적을 달성하기 위해 전국 423명의 미혼모를 대상으로 조사를 실시한 결과, Lazarus and Folkman(1984)의 '스트레스-대처-적응' 의 이론적 모델을 기초로 구성한 미혼모의 '스트레스-대처-적응' 모형의 실증적 자료는 적합성이 확인되었고 미혼모의 사회적 지지 자원과 스트레스, 대처, 적응의 관계가 통계적으로 유의한 것으로 나타나 '사회적 지지 추구' 의 조절효과를 제외한 연구의 가설들이 지지되었다. 본 연구는 미혼모의 스트레스를 경감하고 적응을 향상시킬 수 있는 사회복지정책을 수립하고 사회복지서비스를 제공하는 데 필요한 이론적인 토대를 마련하고 기초적인 자료를 제공하였다는 학문적·실천적 함의를 갖는다.

• 한국공작기계학회:학술대회논문집
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• 한국공작기계학회 1998년도 추계학술대회 논문집
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• pp.248-253
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• 1998

Recently, the uses of Ceramic/metal bonded joints, resin/metal joints, adhesive joints, composite materials which are composed of dissimiliar materials have increased in various industry fields. Since the ceramic/metal bonded joints material is made at a high temperature, residual stress distributions due to differences in material properties were investigated by varying material parameters. The two dimensional finite element analysis was performed to study residual stress distribution in Si3N4/SM45C bonded joint with a copper interlayer between the silicon nitride(Si3N4) and the structural carbon steel(SM45C) and 4-point bending tests were carried out under room temperature. Fracture surface and crack propagation path were observed using scanning electron microscope and characteristics of its fracture was discussed.

• 한국지반신소재학회논문집
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• 제10권3호
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• pp.25-32
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• 2011

본 연구에서는 자동 흙-함수특성곡선 시험장치를 이용하여 새만금지역에서 채취한 준설토의 모관흡수력과 체적함수비를 측정하였다. 측정결과를 토대로 Van Genuchten(1980)의 방법을 이용하여 흙-함수특성곡선(SWCC)을 산정하였다. 동일한 유효포화도에서 건조과정의 모관흡수력은 습윤과정의 모관흡수력보다 크게 나타났다. Lu and Likos(2006)의 방법을 이용하여 모관흡수력에 따른 흡입응력을 산정하고, 흙-함수특성곡선(SWCC)의 불포화 관련계수를 토대로 흡입응력특성곡선(SSCC)을 예측하였다. 건조과정의 흡입응력은 유효포화도가 증가함에 따라 증가하다가 감소하지만 습윤과정의 흡입응력은 유효포화도가 증가함에 따라 지속적으로 감소한다. 또한 동일한 유효포화도에서 건조과정의 흡입응력은 습윤과정의 흡입응력보다 크게 나타났다. 한편 van Genuchten(1980)의 방법을 이용하여 투수계수함수(HCF)를 예측하였다. 체적함수비가 증가함에 따라 불포화 투수계수는 증가하며, 동일한 모관흡수력에서 건조과정의 투수계수가 습윤과정의 투수계수보다 크게 나타났다. 흙-함수특성곡선(SWCC)과 흡입응력특성곡선(SSCC)의 산정결과에 의하면 건조 및 습윤과정에서 흡입응력 혹은 모관흡수력에 대한 이력현상이 발생되었다. 이러한 이력현상은 흙입자 사이의 간극수로 인한 잉크병 효과에 의한 것이다.

• 한국기계가공학회지
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• 제6권1호
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• pp.20-26
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• 2007

In this study, fatigue strength of load-carrying cruciform fillet welded joints were evaluated using a new method proposed by Yamada, for geometric or structural stress in welded joint, that is, one-millimeter stress below the surface in the direction corresponding to the expected crack path. Validity of the method is verified by analyzing fatigue test results for load-carrying cruciform welded specimens has different size of weld toe radius, leg length and plate thickness reported in literature. Structural stress concentration factor for 1mm below the surface was calculated by finite element analysis for each specimen respectively. When compared to the basic fatigue resistance curve offered by BS7608, the one-millimeter stress method shows conservative evaluation for load-carrying cruciform fillet welded joints.

• 한국치위생학회지
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• 제12권3호
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• pp.471-483
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• 2012

Objectives : This study looked at the relationship between occupational stress and the Oral Health Impact Profile (OHIP), to evaluate the effect of occupational stress-related factors. Methods : Data was obtained from a cross-sectional survey of 260 local officials in Gangwondo. The research comprised three questions relating to subjective oral symptoms, an occupational stress measurement tool and an oral health impact factor which was composed of questions. The data was analysed using t-test, one-way ANOVA, Pearson correlation and path analysis in Amos. Results : Occupational stress had a positive correlation to drinking frequency, Oral symptoms had a negative correlation. And drinking frequency, smoking amount and occupational stress had a positive correlation to oral symptoms. It denoted that drinking frequency, occupational stress and oral symptoms had a negative correlation to OHIP. The path model had an excellent goodness of fit (p=0.07, namely p>0.05). Five 'goodness-of-fit indices' of the model were all above 0.9: GFI=0.987, AGFI=0.952, NFI=0.902, IFI=0.939, CFI=0.934), and its RMSEA was 0.045. Occupational stress and oral symptoms had a firsthand impact on OHIP. In addition, it affected OHIP through the parameters of oral symptoms. Occupational stress exercised a firsthand influence on drinking frequency, drinking frequency exercised a firsthand influence on smoking amount. Smoking amount had a firsthand impact on oral symptoms. Conclusions: Oral health education programs for the development of an improved oral hygiene environment through reduction in drinking and smoking also need to focus on relieving stress by improving workplace culture. In addition, due to good communication is required to reduce occupational stress caused by interpersonal conflict.

• Geomechanics and Engineering
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• 제5권6호
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• pp.499-517
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• 2013

In order to investigate shear behavior of granular materials due to excavation and associated unloading actions, load-controlled plane strain compression tests under decreasing confining pressure were performed under drained conditions and the results were compared with the conventional plane strain compression tests. Four types of granular material consisting of two quartz sands and two glass beads were used to investigate particle shape effects. It is clarified that macro stress-strain behavior is more easily influenced by stress level and stress path in sands than in glass beads. Development of localized deformation was analyzed using photogrammetry method. It was found that shear bands are generated before peak strength and shear band patterns vary during the whole shearing process. Under the same test condition, shear band thickness in the two sands was smaller than that in one type of glass beads even if the materials have almost the same mean particle size. Shear band thickness also decreased with increase of confining pressure regardless of particle shape or size. Local maximum shear strain inside shear band grew approximately linearly with global axial strain from onset of shear band to the end of softening. The growth rate is found related to shear band thickness. The wider shear band, the relatively lower the growth rate. Finally, observed shear band inclination angles were compared with classical Coulomb and Roscoe solutions and different results were found for sands and glass beads.

• 한국지반공학회지:지반
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• 제10권3호
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• pp.41-54
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• 1994

본 문은 입방체 삼축시험기에 의한 점토지반의 특성을 연구하기 위하여 Lade형의 삼축시험기를 시험제작하여 그 특성을 논하고 이 시험기를 이용하여 점성토에 대해서 압밀 비배수 시험과 평면변형률의 실험결과를 바탕으로 입방체 시료와 평면변형률 상태의 시료에 대해서 축차응력, 간극수압, 응력경로 등에 대해서 상호 비교한 것이다.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2008년도 추계학술대회A
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• pp.390-395
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• 2008

This study is performed to understand three dimensional characteristics of weld residual stress for the surface weld on the stainless steel plate. AISI 304 plate with one path weld on the surface was used as a test specimen. Finite element analysis was done to analyze thermal transient and residual stress due to weld. The result of finite element analysis was validated by previous paper and measurement data. Among various techniques for residual stress measurement, instrumented ball indentation method was applied. The calculated residual stresses by finite element analysis showed good agreement with the measured results.

• 한국농공학회지
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• 제30권4호
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• pp.134-153
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• 1988

This paper was carried out to investigate the existence of a unique stress- strain behavior by obtaining some factors influencing the time dependent stress- strain behavior of clay. The results obtained from this study were summarized as follows ; 1. The relationship between stress ratro and strain in normally consolidated clay was in- dependent on pre-shear consolidation pressure. Therefore, shear strain could be expressed as a function with stress ratio. 2. The constitutive equation of shear strain on Modified Carn Clay Model coincided better with the observed value than Cam Clay Model. 3. The relationships between deviator stress and shear strain, between pore water pressure and shear strain were unified by the mean equivalent pressure. 4. The shear strain contour in norrnally consolidated clay was increased linearly through origin, but that in overconsolidated clay was not in accordance with the result of the former. 5. Because the effective stress path of normally consolidated clay was unified by the mean equivalent pressure, state boundary surface in (e,p,q) space was transformed into two dimensional surface. But it was considered to be suitable that the unified stress- strain in overconsolidated clay be expressed by a function with overconsolidation ratio. 6. The deviator for constant strain was increased linearly with increment of strain rate ($\varepsilon$) on semi-log scale, but pore water pressure was decreased. 7. The behavior of stress relaxation was transformed from linear to curvilinear with inc - rement of strain rate before stress relaxation test, and pore water pressure was increased in total range. 8. The strain of creep was increased linearly with increment of time on semi-log scale. The greater the strain rate before creep test became, the greater the increment of strain of creep became. And the pore water pressure during creep test was increased generally with increment of time on semi-log scale.