• 제목/요약/키워드: stress-relaxation

검색결과 708건 처리시간 0.026초

304 스테인리스강의 점소성 특성에 관한 연구 (The Rate Dependent Deformation Behavior of AISI Type 304 Stainless Steel at Room Temperature)

  • 호광수
    • 소성∙가공
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    • 제16권2호
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    • pp.101-106
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    • 2007
  • Uniaxial displacement controlled tests were performed on annealed Type 304 stainless steel at room temperature. A servo-controlled testing machine and strain measurement on the gage length were employed to measure the response to a given input. The test results exhibit that the flow stress increases nonlinearly with the strain rate and the relaxed stress at the end of the relaxation periods depends strongly on the strain rate preceding the relaxation test. The rate-dependent inelastic deformation behavior is simulated using a new unified viscoplasticity model that has the rate-dependent format of nonlinear kinematic hardening rule, which plays a key role in modeling the rate dependence of relaxation behavior. The model does not employ yield or loading/unloading criteria and consists of a flow law and the evolution laws of two tensor and one scalar-valued state variables.

천연고무 용융체의 점탄성적 거동에 대한 카본블랙의 영향 (Effects of Carbon Blacks on Viscoelastic Behavior of Natural Rubber Melt)

  • 신수;최창남;나창운;강신영
    • Elastomers and Composites
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    • 제34권3호
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    • pp.262-268
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    • 1999
  • 미가교 천연고무의 응력완화와 탄성복원에 대한 카본블랙의 영향을 조사하였다. 카본블랙의 형태가 보다 작고 높은 구조의 특징을 가질 때 응력완화는 더 지연되었고 탄성복원은 더 활발하였다. 이 결과는 결합고무의 크기, 즉 천연고무와 카본블랙의 상호작용의 크기에 기인하였다.

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과실(果實)의 리올러지 선형화(線型化) 모델(模型) (Linearized Rheological Models of Fruits)

  • 박종민;김만수
    • Journal of Biosystems Engineering
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    • 제19권2호
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    • pp.138-147
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    • 1994
  • The stress relaxation and creep characteristics of fruits have usually been fit to an exponential expression based on a generalized Maxwell model and Burger's model. It is known that two to three terms in the expansion of those models are necessary to obtain a satisfactory fit to the rheological characteristics of fruits. Since four to six constants appear in the models, it is very difficult to determine their physical meaning according to the experimental conditions and levels. Therefore in order to ease the comparison of data, this study was conducted to develop the linearized rheological model of the fruit from the previous studies of stress relaxation and creep characteristics of fruits. Stress relaxation and creep characteristics were able to normalize and presented in the linear form of $t/S(t)=K_1+k_2t$ and $t/C(t)={K_1}^{\prime}+{K_2}^{\prime}t$, respectively. It was possible to compare the effects of experimental conditions and levels much easier from the linearized models developed in this study than from the generalized Maxwell model and Burger's model.

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자유 체적이론을 고려한 급냉 폴리스티렌판에 발생하는 잔류응력과 복굴절 형성에 관한 연구 (A Study on the Prediction of Thermally-Induced Residual Stress and Birefringence in Quenched Polystyrene Plate Including Free Volume Theory)

  • 김종선;윤경환
    • 대한기계학회논문집A
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    • 제27권1호
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    • pp.77-87
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    • 2003
  • The residual stress and birefringence in injection-molded plastic parts can be divided into the flow-induced residual stress and birefringence produced in flowing stage, the thermally-induced residual stress and birefringence produced in cooling stage. However, the physics involved in the generation of the thermally-induced residual stress and birefringence still remains to be understood. Because polymer experiences viscoelastic history near the glass-transition temperature it is hard to model the entire process. Volume relaxation phenomenon was included to predict the final thermally-induced residual stress and birefringence in quenched plastic parts more accurately. The present study focused on comparing the predicted values far thermally-induced residual stress and birefringence with and without volume relaxation behavior (or free volume theory) under free and constrained quenching conditions. As a result, tile residual stress remained as a tensile stress at the center and as a compressible stress near the surface for the free quenching cases. In contract the residual stress remained as a compressible stress at the center and as a tensile stress near the surface fur the constrained quenching cases. The residual birefringence remained as minus values at the center and as plus values near the surface for the free quenching cases. Interestingly the residual birefringence showed minus values in entire zone for the constrained quenching cases. In the prediction of birefringence only the case including free volume theory showed the correct result for the distribution of birefringence in thickness direction.

합성단면의 콘크리트 크리프 해석을 위한 이완계수법 (Stress Relaxation Coefficient Method for Concrete Creep Analysis of Composite Sections)

  • 연정흠;경태현;김다나
    • 콘크리트학회논문집
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    • 제23권1호
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    • pp.77-86
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    • 2011
  • 복합구조의 합성단면에서 콘크리트 크리프변형은 합성단면에 추가 변형을 발생시키며, 장기변형의 일부 구속에 의한 응력이완은 콘크리트단면에 도입된 선압축응력의 심각한 손실을 초래할 수 있다. 이 논문에서는 복잡한 합성단면의 콘크리트 크리프변형에 대해 공학적인 목적에서 단순 해석이 가능한 이완계수법을 유도하고, 이완계수법에 요구되는 응력이완계수 식을 제안하였다. 이완계수법은 크리프계수와 합성단면의 환산단면특성 및 하중특성을 매개변수로 사용하는 균등 크리프계수 단계별계산법(CC-SSM)과 같은 방법으로 유도되었다. 제안된 이완계수 식에 의한 응력이완계법의 오차는 CC-SSM으로부터 평가된 이완계수법의 평균 응력이완계수에 의한 오차보다 향상되었으며, 자유상태에서 크리프변형에 대한 제안식에 의한 이완계수법 반응의 평균오차율은 3보다 크지 않은 크리프계수에 대해 1.2%보다 작으며, 99% 신뢰도에서 최대 3.3%이었다. 제안된 응력이완계수 식은 크리프변형에 대한 합성단면의 내부구속 정도를 반영하며, 외부구속 효과를 분석하기 위한 전산구조해석에서 응력이완계수가 적용된 유효탄성계수는 합성단면의 요소에 대한 강성 계산에 효율적으로 적용될 수 있다.

저장중의 두부에 WLF식을 이용한 물성 변화 예측에 관하여 (Prediction of the Rhelolgical of Soybean Curd during Storage by using WLF equation)

  • 장원영;김병용;김명환
    • 한국식품과학회지
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    • 제27권2호
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    • pp.193-198
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    • 1995
  • 여러 저장온도($5{\sim}25^{\circ}C$)에서 저장하는 동안의 두부의 물성 변화는 응력완화현상을 이용하여 시간-온도 중첩 이론을 통해 계산하고 분석하였으며 WLF(Williams-Landel-Ferry)식을 이용해서 품질변화를 예측할 수 있는 적용식을 제시하였다. 저장온도가 낮을수록 저장시 두부 조직의 초기응력 및 평형응력(equilibrium stress)이 강하게 나타났고, $15^{\circ}C$ 온도를 기준으로 이동인자를 이용하여 좌우 수평으로 이동시 하나의 중첩곡선(master curve)을 구하였다. 이동인자와 중첩곡선을 이용하여 WLF식에 적용해서 활성화 에너지를 계산하였고 임의 온도에서 저장 시간을 예측하였으며, 실제 두부 조직의 저장성을 논하였다.

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용매 환경에서의 폴리아미드 고분자 재료의 자체확산과 유변학적인 특성 (Self Diffusions and Rheological Properties of Polyamide Polymer Materials in Various Solvents)

  • 김남정
    • 한국응용과학기술학회지
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    • 제36권4호
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    • pp.1050-1059
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    • 2019
  • 비결정성 영역에서의 유동단위의 고찰을 위하여 유동 파라메타와 결정크기로부터 폴리아미드 섬유고분자 물질의 자체확산, 홀 부피, 유동 열역학 파라메타 등을 계산하였다. 폴리아미드 섬유의 응력완화 실험은 용매기를 부착한 인장 시험기를 사용하여 여러 온도의 공기, 증류수, 산, 염기 용액에서 실행하였다. REM 모델의 이론적인 응력완화 식에 응력완화 실험 결과를 적용하여 여러 가지 유동 파라메타를 계산하였다. 이들 시료의 유동 파라메타는 완화 스펙트럼, 자체확산, 점도 및 유동 활성화 에너지와 직접적인 연관을 갖는 것으로 규명되었다.

간호대학생의 자아상태와 대응양상과의 관계 연구 (Study on the Ego states and Coping Style of Nursing Students)

  • 원정숙
    • 여성건강간호학회지
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    • 제8권4호
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    • pp.608-618
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    • 2002
  • The purpose of this study is to analyze the type of ego states and stress coping style on female college students who are in the course of nursing study. This study is performed in the view of Transactional Analysis and designed to scrutinize descriptive correlations between the type of ego states and stress coping style. The subject is consists of 144 freshmen and sophomore, 138 junior and senior students group, who are students of K nursing college located in Seoul. The sampling investigation period is on Sept. 14, 2002 to Oct. 26, 2002. The measuring instrument used for Transactional Analysis ego state is 50 items Ego-gram research paper devised by Dusay(1997). For studying coping style, Folkman & Lazarus's measurement(1984) was adopted, which is translated and modified by Han, and Oh,(1990). Statistic average and standard deviation were generated by using SPSS PC+, t-test and Pearson correlation. The results were as follows: 1) In the type of ego states on both groups(lower group : freshmen, sophomore upper group : junior, senior) indicated the arithmetic apex NP(maximum value), then the point A was high and the data made a down slope to point AC. In the comparison to type of ego states between two groups, only at point CP, the data value of upper year students represented higher than that of lower year ones by C(t=2.28, p=.023). In the psychological energy level of ego states, both groups indicated average level.2) Stress coping style of whole students were highly and affirmatively dedicated to research. Consecutive consequences follow like this(high to low) : the central point of problem, search for social support, hopeful aspect and indifference. Especially hopeful aspect(t=.67, p=.05), relaxation of tension(t=-2.16, p=.03) made significant difference each other in the view of arithmetic calculation 3) While verifying coping style in terms of ego states level between lower and upper students group, In type CP, high level ego states group indicated significant difference on stress coping style area than low leveled group and made such sequences as the central point of problem, hopeful aspect, search for social support, positive interest and relaxation of tension. In type NP, sequences such as the central point of problem, search for social support, positive interest and relaxation of tension were emerged with little differences. In type A, the central point of problem, positive interest and relaxation of tension. In type FC, hopeful aspect, search for social support, positive interest and relaxation of tension. In type AC, hopeful aspect and indifference were derived significantly different(p<.05). 4) In the aspect of relation between ego states and coping style, type CP presented the central point of problem and relaxation of tension, type NP presented positive interest, search for social support and the central point of problem, type A showed the central point of problem, positive interest and relaxation of tension, type FC showed relaxation of tension, positive interest, search for social support, indifference and the central point of problem, type AC showed hopeful aspect, indifference and the central point of problem. All the sequence shown above had high-to-low procedure and represented static relations each other(p<.05).

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시판 어묵 및 게맛살의 변형력완화 실험을 통한 유변학적 특성 (Determination of Rheological Properties of Surimi Gels and Imitation Crab-leg Products by Stress-Relaxation Test)

  • 최원석;이철호
    • 한국식품과학회지
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    • 제30권5호
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    • pp.1085-1091
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    • 1998
  • 본 실험에서는 변형력 완화시험을 통하여 고기풀을 주원료로 하는 시중 게맛살과 어묵의 물성학적 성질을 조사하였다. 또한 변형력완화시험과 T.P.A.값과의 상관관계를 조사하였다. 시료의 내부구조적 변화에 의한 영향을 가능한 한 피하기 위하여 인장율 20%에서, 또한 변형속도는 2.4 mm/sec의 조건에서 실험을 실시하였다. 어묵과 맛살의 변형력완화시험결과 초기변형력의 경우 2종류의 어묵(370.4 g)과 5종류의 맛살의 평균값(436.4 g)은 유사한 값을 나타내었으나, 변형력완화시간과 점성성분은 2종류 어묵의 평균값(17256.1 sec, $1.357{\times}10^{10}$ poise)이 5종류의 맛살의 평균값(6110 sec,$0.519^{\ast}10^{10}$ poise)보다 월등히 높은 값을 나타내었다. 변형력완화시험 결과와 T.P.A.결과를 비교시 지수항의 직선식에 대한 절편값은 T.P.A.실험에서의 경도 및 껌성, 씹힘성과 높은 상관관계(r=0.93, 0.93, 0.95, p

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외부하중에 의한 용접 체결부의 잔류응력 이완 특성 해석에 관한 연구 (Analysis of Residual Stress Relaxation in Welded Joints due to External Loads)

  • 장창두;송하철;조영천
    • 한국해양공학회:학술대회논문집
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    • 한국해양공학회 2003년도 추계학술대회 논문집
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    • pp.167-170
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    • 2003
  • Thermal elastic-plastic analysis was performed to assess the initial residual stress distribution of welded joints considering temperature dependent material properties. The test model was the idealized boxing fillet specimen, frequently appeared in the joints of longitudinal and transverse members of ship structure. Residual stress relaxations due to external loads were analyzed by subsequent elastic-plastic analysis considering loading and unloading steps, and the characteristics of residual stress relaxations were discussed with the levels of external loads. Additionally, to define the fatigue life of crack initiation and propagation, the S-N data for each crack length were appraised.

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