• 한국정밀공학회지
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• 제22권2호
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• pp.79-88
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• 2005

Evaluating the effective properties of materials containing various types of in-homogeneities is an important issue in the analysis of structures composed of those materials. A simple and effective method for the purpose is to impose the periodic displacement boundary conditions on the finite element model of a unit cell. Their theoretical background is explained based on the purely kinematical relations in the regularly spaced in-homogeneity problems, and the strategies to implement them into the analysis and to evaluate the homogenized material constants are introduced. The creep behavior of a thin sheet with square arrayed rectangular voids is characterized, where the orthotropy is induced by the presence of the voids. The homogenization method is validated through the comparison of the analysis of detailed model with that of the simplified one with the effective parameters.

• 동력기계공학회지
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• 제6권2호
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• pp.40-47
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• 2002

In this paper, friction welding optimization for 1Cr0.5Mo-STS304 (${\phi}14\;mm$), AE applications for the weld quality evaluation and the applications of various life prediction methods such as LMP (Larson-Miller Parameter) and ISM (initial strain method) were investigated : The creep behaviors of those steels and the friction welded joints under static load were examined by ISM combined with LMP at 400, 500, 550 and $600^{\circ}C$, and the relationship between these two kinds of phenomena was studied. The real-time predicting equations of elevated-temperature creep life (rupture time) under any creep stress at any elevated-temperature could be developed by LMP and LMP-ISM. It was confirmed that the life prediction equations by LMP and LMP-ISM are effective only up to 102 h and can not be used for long times of 103-106 h, but by ISM it can be used for long times creep prediction of more than 104 h with most reliability.

• 한국해양공학회:학술대회논문집
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• 한국해양공학회 2001년도 춘계학술대회 논문집
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• pp.307-313
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• 2001

In this Paper, friction welding optimization for 1Cr0.5Mo-STS304($\Phi$14mm), AE applications for the weld quality evaluation and the applications of various life prediction methods such as LMP(Larson-Miller Parameter) and ISM(initial strain method) were investigated : the creep behaviors of those steels and the friction welded joints under static load were examined by ISM combined with LMP at 400, 500, 550 and $600^{\circ}C$, and the relationship between these two kinds of phenomena was studied. The real-time predicting equations of elevated-temperature creep life(fracture time) under any creep stress at any elevated- temperature could be developed by LMP and LMP-ISM, It was confirmed that the life prediction equations by LMP and LMP-ISM are effective only up to 10$^2$hrs and can not be used for long times of 10$^3$-10$^{6}$ hrs, but by ISM it can be used for long times creep prediction of more than 10$^4$hrs with most reliability.

• 한국해양공학회지
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• 제15권2호
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• pp.53-60
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• 2001

It was confirmed that the life predictive equation by LMP and LMP-ISM are effective only up to 10$^2$hours and can not be used for long times of $10^3~10^5$ hours, but that by ISM can be used for long times creep life prediction with more reliability. The predictive creep life equation of ISM has better reliability than those by LMP and LMP-ISM, and its realizably is getting better for long time creep prediction($10^3~10^5$ h).

• 한국해양공학회:학술대회논문집
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• 한국해양공학회 2000년도 추계학술대회 논문집
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• pp.26-32
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• 2000

It was confirmed that the life predictive equation by LMP-ISM are effective only up to 10$^2$hours and can not be used for long times of 10$^3$~10$^{5}$ hours, but that by ISM can be used for long times creep life prediction with more reliability. The predictive creep life equation of ISM has better reliability than those by LMP and LMP-ISM, and its realizably is getting better for long time creep prediction(10$^3$~10$^{5}$ H).

• 한국전산구조공학회논문집
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• 제13권4호
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• pp.461-473
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• 2000

이 논문은 콘크리트의 크리프와 건조수축 현상을 고려한 강재와 콘크리트의 부분 합성보의 거동의 해석을 위한 모델을 제안하고 있다. 부분합성 거동은 선형 부분전단 연결이론을 토대로 합성보를 일정한 수의 요소로 분할한 후 각 절점에서 평형조건과 적합조건을 기초로하여 구성 방정식을 구성하고 경계조건과 각 요소에 대한 구성 방정식을 순차적으로 적용하는 방법으로 해석모델이 구성되었다. 또한 콘크리트의 시간에 따른 현상인 크리프와 건조수축의 영향도 고려되었다. 제안된 해석모델은 다경간 연속 합성보의 슬립거동을 효과적으로 나타낼 수 있다. 제안된 해석 모델의 검증을 위해 기존 연구의 결과와 비교되었으며, 여러 조건에 대한 합성보의 해석을 통해 제안된 모델의 적용성을 입증하였다.

• 한국안전학회지
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• 제8권4호
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• pp.27-40
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• 1993

High temperature tensile tests, steady state creep tests, Internal stress tests and creep rupture tests using A17075 alloy( $T_{6}$ ) were performed over the temperature range of 9$0^{\circ}C$~50$0^{\circ}C$ (0.4 $T_{m}$ ~0.85 $T_{m}$ ) and stress range of 0.64~17.2(kgf/$\textrm{mm}^2$). The main results obtained in this paper were as follows. (1) The activation energies for yielding at the temperature of 0.4 $T_{m}$ ~0.75 $T_{m}$ were calculated to be 25.7~36.5kcal/mol, which were nearly equal to the activation energies for creep. (2) At around the temperature of 9$0^{\circ}C$~12$0^{\circ}C$ and under the stress level of 10~17.2(kgf/$\textrm{mm}^2$), and at around the temperature of 200~41$0^{\circ}C$ and under the stress level of 1.53~9.55(kgf/$\textrm{mm}^2$) and again at around the temperature of 470~50$0^{\circ}C$ and under the stress level of 0.62~l.02(kgf/$\textrm{mm}^2$), the applied stress dependence of steady state creep rate $n_{measu}$ measured were, respectively, 3.15, 6.62 and 1.1, which were in good agreement the calculated stress dependence $n_{ealeu}$ obtained by the difference of the applied stress dependence of the Internal stress and the ratio of the internal stress to the applied stress. (3) At the temperature range of 0.4~0.43 $T_{m}$ , and at the temperature range of 0.52~0.75 $T_{m}$ and again at the temperature range of 0.82~0.85 $T_{m}$ , the activation energies $Q_{measu}$ obtained by steady state creep rate, respective, 26. 16, 34.9, 36.2 and 36.1kcal/mol, which were in good agreement with those obtained with the activation energies under constant effective stress and the temperature dependence of Internal stress. (4) At the temperature range of the 0.52~0.73 $T_{m}$ and under the stress level of 1.53~9.55(kgf/$\textrm{mm}^2$), the stress dependence of rupture life(n’) measured was 6.3~6.6, which was in good agreement with the stress dependence of steady state creep rate(n). And at the same condition the activation energy for rupture( $Q_{f}$ ) measured was 32.0~36.9kca1/mol, which was also in good agreement with the activation energy obtained by steady state creep rate ( $Q_{c}$ ). (5) The rupture life( $t_{f}$ ) might be represented by athermal process attributed to the difference of the applied stress dependence of the internal stress and the ratio of the internal stress to the applied stress, and the thermal activated process attributied to the temperature dependence of the internal stress as $t_{f}$ = A'$\sigma$$_{a}$ ｛n(1-d $\sigma$$_{i}$ /d $\sigma$$_{a}$ )/(1-$\sigma$$_{i}$ / $\sigma$$_{a}$ )｝.exp[｛ $Q_{c}$ $^{*}$-( $n_{o}$ R $T^2$/ $E_{(T)}$) (d $E_{(T)}$/dT) - ( $n_{0}$ R $T^2$/ $\sigma$$_{a}$ - $\sigma$$_{i}$ ) (d $\sigma$$_{i}$ /dT)｝/RT]. (6) The relationship betwween Larson-Miller rupture parameter and logarithmic stress was linearly decreased, so creep rupture life of Al 7075 alloy seemed to be predicted exactly with Larson-Miller parameter.meter.

• 콘크리트학회논문집
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• 제21권5호
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• pp.629-638
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• 2009

합성단면을 구성하는 콘크리트 단면에 크리프에 의한 장기변형이 발생되면 합성단면에는 추가의 변형이 발생되며 콘크리트 단면에는 장기변형의 일부구속으로 잔류응력이 발생한다. 이 논문에서는 복잡한 합성단면에서 콘크리트 단면의 장기변형에 대한 반응을 평가하는 기존의 단계별계산법을 보다 효율적으로 적용할 수 있도록 일반화 하였다. 장기변형이 발생하는 콘크리트 단면과 이 변형의 일부를 구속하는 구속단면의 단면특성과 재료특성으로부터 초기 합성단면의 환산단면특성이 유도되고, 각 단계의 크리프계수가 고려된 유효탄성계수가 적용된 환산 단면특성이 유도되었다. 합성단면의 일반화 반응에 대한 5개의 일반화 매개변수로 구성된 단계별계산법의 식이 유도되었다. 각 단계별 계산식에는 크리프계수의 증가가 일정하도록 하여 식의 단순화와 계산시간의 감축 및 균등한 단계별 계산오차가 가능한 균등 크리프 단계별계산법을 제안하였다. 콘크리트 단면의 초기 축방향 탄성 변형률에 대한 일반화 반응은 콘크리트 단면적의 비율에 가장 민감하고, 콘크리트 단면의 단면이차모멘트 비율보다는 구속단면의 단면이차모멘트 비율에 보다 민감하였다. 반면에 콘크리트 단면의 초기 탄성곡률에 대해서는 콘크리트 단면의 단면이차모멘트 비율에 가장 민감하였다.

• 대한기계학회논문집A
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• 제22권3호
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• pp.595-602
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• 1998

Specimens of 304 stainless steel were tested to failure at elevated temperatures under multiaxial stress states, uniaxial tension using smooth bar specimens, biaxial shearing using double shear bar specimens, and triaxial tension using notched bar specimens. Rupture times are compared for uniaxial, biaxial, and triaxial stress states with respect to the maximum principal stress, the von Mises effective stress, and the principal facet stress. The results indicate that the principal facet stress gives the best correlation for the material investigated, and this parameter can predict creep life data under multiaxial stress states with rupture data obtained with specimens under uniaxial stresses. The results also suggest that grain boundary cavitation, coupled with localized deformation processes such as grain boudary sliding, controls the lifetimes of the specimens.

• 한국체육학회지인문사회과학편
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• 제55권3호
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• pp.543-551
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• 2016

본 연구는 스마트 폰을 사용(≥ 60분/일)하는 건강한 20대 남성 50명을 대상으로 두부의 움직임에 직접 관여하는 경추부 근육(두판상근, 흉쇄유돌근, 상부승모근)에 연부조직 측정기 Myoton을 이용하여 스마트 폰 사용정도와 경추부 근육의 기계적 속성의 관련성을 규명하려는 목적으로 수행되었다. 스마트 폰 사용정도는 전용의 중독 척도설문지를 이용하였다. 경추부 근육의 기계적 속성은 Myoton을 이용하여 근 긴장도(frequency), 동강성(stiffness), 점탄성(decrement), 근변형률(creep) 및 회복시간(relaxation)의 반영지표를 각각 산출하였다. 스마트 폰 사용에 의한 중독 점수와 경추부 근육의 기계적 속성을 반영하는 각 지표와의 관련성을 평가하기 위해 상관분석을 실시하였다. 연구 결과 기계적 속성을 반영한 모든 parameters의 변동계수는 각각 2% 미만이었으며, 측정자 신뢰도인 급내상관계수 역시 높은 신뢰성이 도출되었다(ICC>.9, p<.01). 스마트 폰 중독점수는 상부승모근의 근 긴장도(r=.353, p<.05)와 동강성(r=.346, p<.05), 흉쇄유돌근의 점탄성(r=-.284, p<.05)과 근 변형률(r=.288, p<.05)과의 유의미한 상관이 나타났고, 특히 두부 통증과 관련된 두판상근의 근 긴장도(r=-.368, p<.01), 점탄성(r=-.405, p<.01), 동강성(r=-.424, p<.01)과의 높은 상관계수로 스마트 폰 과사용과 밀접한 관련성을 나타내었다. 결론적으로 젊은 남성들에 있어서 스마트 폰 과사용은 경추부 근 손상과 통증 및 두통에 유의미한 관련성이 있음을 간접적으로 시사하며, Myoton은 경추부 근육 성질을 예측 및 평가할 수 있는 유용한 기기임을 알 수 있었다.