• 한국콘크리트학회:학술대회논문집
• /
• 한국콘크리트학회 2001년도 가을 학술발표회 논문집
• /
• pp.641-646
• /
• 2001

In early-age concrete, volumetric deformations due to thermal expansion and moisture transfer are restrained by various boundary conditions, and then restraint stresses occur in proportion to developed stiffness. With increase of the age, these stresses are gradually relieved by significant relaxation behavior of early-age concrete. Therefore, it is necessary to consider the stress relaxation in order to analyze the behavior of early-age concrete more accurately. In this paper, we propose a unified algorithm which combines a relaxation model with hydration model, heat conduction model, micropore structure formation model, moisture diffusion model and mechanical properties development model and develop a finite element program based on the algorithm. The program is applied to evaluate stress development if a temperature-stress test machine (TSTM) specimen and a massive concrete structure, and then validity of the program is discussed and evaluated.

• 대한기계학회:학술대회논문집
• /
• 대한기계학회 2003년도 춘계학술대회
• /
• pp.43-48
• /
• 2003

The problem of welding stresses and fatigue behavior is the main concerns of welding research fields. The residual stresses and distortion of structures by welding is exert negative effect on the safety of mechanical structures. That is, expansion of material by high temperature and distortion by cooling during welding process is caused of tensile and compressive residual stresses on welding material, and this residual stresses reduce fracture and fatigue strength of welding structures. The accurate prediction of residual stress and relaxation due to loading and post weld heat treatment of weld zone is very important to improve the quality of weldment. In this study, a finite element modeling technique is developed to simulate the relaxation of residual stresses due to loading and post weld heat treatment of weld zone. The accuracy of finite element models is evaluated based on experimental results and the results of the analytical solution.

• Elastomers and Composites
• /
• 제47권3호
• /
• pp.223-230
• /
• 2012

응력완화 실험 곡선을 Eyring-Halsey 비뉴톤 모델의 이론식에 적용하여 poly(methyl acrylate)-poly(acrylonitrile) 공중합체의 유변학적 파라메타를 얻었다. 응력완화 실험은 용매기를 부착한 인장 시험기를 사용하였다. 유동 파라메타를 컴퓨터 프로그램을 이용하여 계산하였다. 이들 시료의 유동 파라메타는 유동 단위의 자체확산, 유동점성, 유동 활성화 에너지와 직접적인 연관을 갖는 것으로 규명되었다.

• 대한물리치료과학회지
• /
• 제22권2호
• /
• pp.37-42
• /
• 2015

Background : The purpose of this study is to identify how the relaxation music listening during exercise influences body flexibility and stress. Methods : Twenty healthy adults 20s and 30s who lack of body flexibility were recruited and each subjects performed exercise during the relaxation music listening or no listening. Bach, aria of linear G was used as the relaxation music. The experiment was conducted for 4 weeks. In this study, PASW ver 18.0 was utilized to perform non-parametric tests for comparisons. Result : The result with respect to the dependent variables are as follows: When non-parametric tests were conducted to compare body flexibility at the test of the right ear touch behind head by left hand and the stretching hands test between the two groups after exercise, they showed significant differences in statistical terms (p<.05). Conclusion : From the above results of the study it was found that the application of the relaxation music during the exercise is effective, it improved the body flexibility of the right ear touch behind head by left hand and the stretching hands more than the exercise without the relaxation music did. The outcome of the experiment may provide basic data for developing an effective way to increase body flexibility.

• 대한조선학회논문집
• /
• 제41권6호
• /
• pp.84-90
• /
• 2004

For the precise assessment of the effect of welding residual stresses on structural strength and fatigue crack growth behavior, new FE analysis algorithms for the estimation of residual stress relaxation due to external load and redistribution due to fatigue crack propagation were proposed in this paper. Initial welding residual stress field was obtained by thermal elasto-plastic analysis considering temperature dependent material properties, and the amount of residual stress relaxation and redistribution were assessed by subsequent elasto-plastic analysis In the analysis of fatigue crack propagation, the applied SIF(Stress Intensity Factor) range was evaluated by $\frac{1}{4}$-point displacement extrapolation method, and the effect of welding residual stresses on crack propagation was considered by introducing the effective SIF concept. The test results of crack propagations were compared with the predicted data obtained by the analysis.

• 한국식품조리과학회지
• /
• 제5권1호
• /
• pp.49-52
• /
• 1989

도토리 조전분겔과 정제전분겔에 대하여, 변형의 정도를 달리한 응력완화시험을 실시하였다. 그 결과 초기응력($\sigma$$_{o}$ )은 변형정도에 무관하게 항상 정제전분겔이 큰값을 나타내었고, 평형응력($\sigma$$_{e}$)은 조전분겔이 더 큰 값을 보여주었다. 그러나 초기응력에 대한 평형응력의 비($\sigma$$_{e}$/$\sigma$$_{o}$ )는 60%변형의 경우에 최소값을 나타내었다. 응력완화곡선의 물성론적 모형 분석은 축차잔차법을 사용하였다. 60%변형의 경우, 조전분겔은 7-element 정제전분겔 은 5-element generalized Maxwell model로 분석되었고, 45%변형의 경우에는 조전분겔은 5-element, 정제전분겔은 3-element model로 표현할 수 있었다. 즉 조전분겔에 비해 타 성분들이 좀 더 제거된 정제전분겔이 보다 더 단순한 모형으로 분석되었다.

• 대한기계학회논문집A
• /
• 제25권12호
• /
• pp.2056-2061
• /
• 2001

Non-proportional loading tests of Nylon 66 at room temperature exhibit path dependent behavior and plasticity-relaxation interactions. The uniaxial formulation of the viscoplasticity theory based on overstress (VBO), which has been used to reproduce the nonlinear strain rate sensitivity, relaxation, significant recovery and cyclic softening behaviors of Nylon 66, is extended to three-dimensions to predict the response in strain-controlled, comer-path tests. VBO consists of a flow law that is easily written for either the stress or the strain as the independent variable. The flow law depends on the overstress, the difference between the stress and the equilibrium stress that is a state variable in VBO. The evolution law of the equilibrium stress in turn contains two additional state variables, the kinematic stress and the isotropic stress. The simulations show that the constitutive model is competent at modeling the deformation behavior of Nylon 66 and other solid polymers.

• 대한기계학회논문집A
• /
• 제24권10호
• /
• pp.2552-2559
• /
• 2000

Most of ferrous b.c.c weld materials have martensitic transformation during rapid cooling after welding. It is well known that volume expansion due to the phase transformation could influence on the relaxation of welding residual stress. To apply this effect practically, it is necessary to establish a numerical model which is able to estimate the effect of phase transformation on residual stress relaxation quantitatively. For this purpose, the analysis is carried out in two regions, i.e., heating and cooling, because the variation of material properties following a phase transformation in cooling is different in comparison with the case in heating, even at the same temperature. The variation of material properties following phase transformation is considered by the adjustment of specific heat and thermal expansion coefficient, and the distribution of residual stress in analysis is compared with that of experiment by previous study. In this study, simplified numerical procedures considering phase transformation, which based on a commercial finite element package was established through comparing with the experimental data of residual stress distribution by other researcher. To consider the phase transformation effect on residual stress relaxation, the transition of mechanical and thermal property such as thermal expansion coefficient and specific heat capacity was found by try and error method in this analysis. In addition to, since the transformation temperature changes by the kind and control of alloying elements, the steel with many kinds of transformation temperature were selected and the effect of transformation on stress releasement was investigated by the numerical procedures considering phase transformation.

• 한국전문물리치료학회지
• /
• 제28권1호
• /
• pp.72-76
• /
• 2021

Background: A pressure ulcer is common in soft tissue over the greater trochanter (GT) in side-lying position, and sustained tissue deformation induced by the prolonged external force is a primary cause, which can be discussed with soft tissues' viscoelastic properties (i.e., stress relaxation, creep response). Objects: Using an automated hand-held indentation device, we measured the viscoelastic properties of soft tissue over the hip area, in order to examine how the properties are affected by site with respect to the GT. Methods: Twenty participants (15 males and 5 females) who aged from 21 to 32 were participated. An automated hand-held indentation device was used to measure the stress relaxation time and creep response. Trials were acquired for three different locations with respect to the GT (i.e., right over the GT, 6 cm anterior or posterior to the GT). For each location, five trials were acquired and averaged for data analyses. Results: Soft tissues' stress relaxation time and creep response were associated with site (F = 23.98, p < 0.005; F = 24.09, p < 0.005; respectively). The stress relaxation time was greatest at posterior gluteal region (19.22 ± 2.49 ms), and followed by anterior region (15.39 ± 2.47 ms) and right over the GT (14.40 ± 3.18 ms). Similarly, creep response was greatest at posterior gluteal region (1.16 ± 0.14), and followed by anterior region (0.95 ± 0.14) and right over the GT (0.89 ± 0.18). Conclusion: Our results showed that the stress relaxation and creep were greatest at the posterior gluteal region and least at right over the GT, indicating that the gluteal soft tissue is more protective to the prolonged external force, when compared to the trochanteric soft tissue. The results suggest that a risk of pressure ulcer over the GT may decrease with slightly posteriorly rotated side-lying position.

• 폴리머
• /
• 제35권3호
• /
• pp.232-237
• /
• 2011

Polyacrylonitrile-poly (vinyl chloride) 공중합체의 완화스펙트럼을 이론적인 완화스펙트럼 식에 실험적인 응력완화 곡선을 대입하여 계산하였다. 이론적인 완화스펙트럼 식은 Ree-Eyring and Maxwell 모델로부터 유도하였다. 응력완화 실험은 용매기를 부착한 인장 시험기를 사용하였다. 완화스펙트럼의 계산은 컴퓨터 프로그램을 이용하였으며, 완화스펙트럼으로부터 고체 고분자의 미세구조, 점탄성적인 성실, 홀 부피가 연구되었다. 또한 이들 시료의 완화스펙트럼은 유동단위의 분자량과 자체확산 분포와 밀접한 관계가 있음을 알 수 있었다.