• Elastomers and Composites
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• 제25권2호
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• pp.97-102
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• 1990

국내에서 생산, 혹은 수입 시판되고 있는 11종류의 EPDM과 1종의 EPM고무에 대한 선형점탄성적 성질을 RDS로 측정하였다. 측정은 $210^{\circ}C$에서 등온적으로 행하였으며. 이들 고무의 복합점도, 저장탄성계수, 손실탄성계수, 손실 tangent 및 완화스팩트럼 data는 고무 블렌딩이나, 복합화과정에서 중요한 자료로 이용될 것으로 믿는다.

• Steel and Composite Structures
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• 제42권5호
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• pp.671-683
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• 2022

To investigate and predict the long-term time-dependent behavior, such as creep, shrinkage, and relaxation of PS strands, and prestress loss in prestressed steel-concrete composite beams, named Precom, full-scale tests were conducted and the collected data were compared with those obtained from the two proposed analytical models. The combined effective modulus method (EMM)-empirical model proposed with a flowchart considered the creep effect to determine the prestress loss. Conversely, the age-adjusted effective modulus method (AEMM) with CEB-FIP equation was developed to account for the concrete aging. The results indicated that the AEMM with CEB-FIP model predicts the long-term behavior of Precom effectively.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 1989년도 가을 학술발표회 논문집
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• pp.73-76
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• 1989

A numerical procedure is developed to analyze the time-dependent behavior of prestressed concrete bridges constructed by the segmental cantilever method. The developed computer program accounts for the time-dependent properties of prestressed concrete materials due to the varing modulus of elasticity, creep and shrinkage of concrete and the stress relaxation of prestressing steel. It also accounts for the stiffness increase due to the presence of the steel reinforcements and the effects of the shear deformation of the prestressed concrete bridge girders. The program is applied to a multi-span continuous segmental prestressed concrete bridge to demonstrate its capabilities.

• 한국식품과학회지
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• 제24권3호
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• pp.294-299
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• 1992

본 연구에서는 분리대두단백질에 단백질 가수분해효소를 처리하여 대두단백질에 가수분해적 변성을 야기하여 그 기능성을 변화 고찰하고 실제 식품에의 이용방법으로 효소처리된 두유로 두부를 만들어 물성실험과 관능평가를 실시하였다. 장엽에서 SPI를 제조한 후 15분간 bromelain으로 처리하여 2.7% 가수분해된 MSPI를 만들어 기능특성을 측정 비교하였다. MSPI는 전 pH범위에서 용해도가 증가하였고, 특히 등전점에서 15% 정도 증가하였다. 유화형성력과 기포팽창력은 증가하였으나 이들의 안정성은 감소하였는데, 특히 기포안정성은 알칼리쪽에서 급격히 감소하였고, 등전점에서는 가장 큰 것으로 나타났다. 표준두유와 변형두유를 혼합하여 제조한 두부로 물성실험과 관능평가를 실시하였을 때 압착실험에서는 변형두부I이 연하고 탄력성 있는 두부를 형성하는 것으로 나타났다. 각 두부의 물성모형은 spring 한개와 Maxwell 모형 세개를 가진 7요소모형으로 동일한 물성모형을 나타내었다. 관능평가에서는 표준두유와 변형두유를 3 : 1의 비율로 혼합하여 제조한 두부의 품질이 가장 우수한 것으로 평가되었다.

• 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.

• Structural Engineering and Mechanics
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• 제11권6호
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• pp.637-650
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• 2001

A structural analysis of cracked R.C. members under instantaneous or sustained loads and imposed displacements is presented. In the first part of the paper the problem of deriving feasible moment-curvature diagrams for a long term analysis of R.C. sections is approached in an exact way by using the Reduced Relaxation Function Method in state I uncracked and the method suggested by CEB in state II cracked. In both states the analysis of the main parameters governing the problem has shown that it is possible to describe the concrete creep behaviour in an approximate way by using the algebraic formulation connected to the Effective Modulus Method. In this way the calculations become quite simple and can be applied in design practice without introducing significant errors. Referring to continuous beams, the structural analysis is then approached in a general way, applying the Force Method and the Principle of Virtual Works. Finally, considering single members, the structural analysis is performed by means of a graphical procedure based on the application of feasible moment-rotation diagrams which allow to easily solve various structural problems and to point out the most interesting aspects of the long term behaviour of cracked R.C. members with rigid or elastically deformable redundant restraints.

• Fibers and Polymers
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• 제3권1호
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• pp.18-23
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• 2002

The structure development and dynamic properties of fibers produced by high-speed spinning of P(EN-ET) random copolymers were investigated. The as-spun fibers were found to remain amorphous up to the spinning speed of 1500 m/min, and subsequent increases in speed resulted in the crystalline domains containing primarily $\alpha$ crystalline modification of PEN. The f modification was not found up to spinning speeds of 4500 m/min. On the other hand, annealing of constrained fibers spun at the 2100 m/min at 180,200, and 240^{\circ}C$ exhibited $\beta$-form crystalline structure, while the annealed fibers spun in 600-1500 m/min range exhibited dominantly $\alpha$-form. However $\beta$-form crystals disappeared above the spinning speed of 3000 m/min. With increasing spinning speeds from 600 to 4500 m/min, the storage modulus of as-spun fibers increased continuously and reached a value of about 10.4 spa at room temperature. The tan $\delta$curves showed the $\alpha$-relaxation peak at about 155-165^{\circ}C$, which is considered to correspond to the glass transition. The $\alpha$-relaxation peaks became smaller and broader, and shift to higher temperatures as the spinning speed increases, meaning that molecular mobility in the amorphous region is restricted by increased crystalline domain.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2008년도 춘계학술대회 논문집
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• pp.273-276
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• 2008

Thermoplastic resin takes place stress relaxation and creep according to temperature and time. In room temperature, time dependent deformation (TDD) of polymer was carried out at previous study. In this study, it evaluates time dependent deformation to relate temperature. Nanoscale indents can be used as cells for molecular electronics and drug delivery, slots for integration into nanodevices, and defects for tailoring the structure and properties. Therefore, it is important to control pattern depth for change of indent depth by creep when using Nanoindenter. For evaluating TDD at high temperature, it is occurred thermal-nanoindentation test by changing hold time at maximum load. Temperature is putted at $90^{\circ}C$, hold time at maximum loads are putted at 1, 10, 50, 100, 200, 300 and 500s.

• 한국식품과학회지
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• 제26권2호
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• pp.103-109
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• 1994

응력완화 현상을 측정하여 생선단백질 겔의 선형적 점탄성과 열처리 공정에 따른 물성의 변화를 수식적 모델로 분석하였다. 생선단백질 겔은 정변형도 $0.105{\sim}0.693$, 압축속도 $50{\sim}250\;mm/min$의 범위에서 선형적 점탄성을 나타내었으며, generalized Maxwell 모형에 의해 분석한 결과, 압축변형도과 압축속도가 증가함에 따라 가열에 의해 형성된 내부조직 중 탄성 성분의 증가와 점성성분의 감소현상을 보였다. $4^{\circ}C$와 $40^{\circ}C$에서 전처리하여 $90^{\circ}C$에서 제조한 겔은 전처리 없이 $90^{\circ}C$에서 직접 열처리한 겔보다 탄성율(E) 및 평형탄성율$(E_e)$이 높았으나, 점성성분$({\eta})$은 적용된 모델에 따라서 그 값의 차이가 나타났다. 따라서 식품의 물성을 측정하는데 있어서 두 수학적 모델의 접근방법 및 정확도에 대하여 설명하였다.

• Korea-Australia Rheology Journal
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• 제18권2호
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• pp.67-81
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• 2006

Using a strain-controlled rheometer, the dynamic viscoelastic properties of aqueous xanthan gum solutions with different concentrations were measured over a wide range of strain amplitudes and then the linear viscoelastic behavior in small amplitude oscillatory shear flow fields was investigated over a broad range of angular frequencies. In this article, both the strain amplitude and concentration dependencies of dynamic viscoelastic behavior were reported at full length from the experimental data obtained from strain-sweep tests. In addition, the linear viscoelastic behavior was explained in detail and the effects of angular frequency and concentration on this behavior were discussed using the well-known power-law type equations. Finally, a fractional derivative model originally developed by Ma and Barbosa-Canovas (1996) was employed to make a quantitative description of a linear viscoelastic behavior and then the applicability of this model was examined with a brief comment on its limitations. Main findings obtained from this study can be summarized as follows: (1) At strain amplitude range larger than 10%, the storage modulus shows a nonlinear strain-thinning behavior, indicating a decrease in storage modulus as an increase in strain amplitude. (2) At strain amplitude range larger than 80%, the loss modulus exhibits an exceptional nonlinear strain-overshoot behavior, indicating that the loss modulus is first increased up to a certain strain amplitude(${\gamma}_0{\approx}150%$) beyond which followed by a decrease in loss modulus with an increase in strain amplitude. (3) At sufficiently large strain amplitude range (${\gamma}_0>200%$), a viscous behavior becomes superior to an elastic behavior. (4) An ability to flow without fracture at large strain amplitudes is one of the most important differences between typical strong gel systems and concentrated xanthan gum solutions. (5) The linear viscoelastic behavior of concentrated xanthan gum solutions is dominated by an elastic nature rather than a viscous nature and a gel-like structure is present in these systems. (6) As the polymer concentration is increased, xanthan gum solutions become more elastic and can be characterized by a slower relaxation mechanism. (7) Concentrated xanthan gum solutions do not form a chemically cross-linked stable (strong) gel but exhibit a weak gel-like behavior. (8) A fractional derivative model may be an attractive means for predicting a linear viscoelastic behavior of concentrated xanthan gum solutions but classified as a semi-empirical relationship because there exists no real physical meaning for the model parameters.