• KSCE Journal of Civil and Environmental Engineering Research
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• v.29 no.6C
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• pp.321-329
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• 2009

Laboratory compressive test was conducted on 6 different types of rock in order to investigate the characteristic of critical strain under uniaxial and triaxial stress condition. The results of uniaxial compressive test mostly ranged within 1~100MPa, the critical strain was also located between 0.1~1.0%. Therefore the results distributed within the upper and lower boundary proposed by Sakurai (1982). And the failure/critical strain ratio (${\varepsilon}_f/{\varepsilon}_0$) showed between 1.0~1.8 value depending on the uniaxial compressive strength. The results of critical strain by triaxial compressive test showed below 0.8% value for all test, the M value calculated from uniaxial and triaxial compressive test results ranged 1.0~8.0 for most of rock specimens. It is concluded that failure strain (${\varepsilon}_{f3}$) of rock mass, which is in triaxial stress condition is larger than the results of uniaxial stress condition (${\varepsilon}_{f1}$) by 1.0~8.0 times and value showed 1.0~1.8 larger value than critical strain (${\varepsilon}_{01}$). Therefore it is a conservative way for rock tunnel to use critical strain (${\varepsilon}_{01}$) calculated from a uniaxial compressive strength on tunnel displacement monitoring.

• Journal of Korean Society of Steel Construction
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• v.17 no.1 s.74
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• pp.103-113
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• 2005

In the present study, the Direct Inelastic Design (DID) for steel structures developed in the previous study was improved to expand it applicability. The proposed design method can perform inelastic designs that address the design characteristics of steel structures: Group member design, discrete member sizes, variation of moment-carrying capacity according to axial force, connection types, and multiple design criteria and load conditions. The design procedure for the proposed method was established, and a computer program incorporating the design procedure was developed. The design results from the conventional elastic method and the DID were compared and verified by the existing computer program for nonlinear analysis. Compared with the conventional elastic design, the DID addressing the inelastic behavior reduced the total weight of steel members and enhanced the deformability of the structure. The proposed design method is convenient because it can directly perform inelastic design by using linear analysis for secant stiffness. Also, it can achieve structural safety and economical design by controlling deformations of the plastic hinges.

• Journal of the Korean Geotechnical Society
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• v.15 no.3
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• pp.71-81
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• 1999

A study on the undrained behavior of isotropically consolidated clay-sand mixtures was carried out using the automated triaxial testing apparatus. Overconsolidated ratio, effective mean pressure and clay content( up to 20% bentonite) were the factors varied in the experimental investigation. Undrained behavior(strength and pore water pressure generation during shear in triaxial loading) depends upon overconsolidation ratio, confining pressure and clay content. Significant changes in undrained compression characteristics occurred at around 20% of clay contents in the sand. The test results were analyzed and their behaviors were interpreted within the framework of plasticity constitutive model for clay-sand mixtures. Possible physical bases for the proposed forms are discussed. Validation of the applied model using the laboratory results is also given.

• Aerospace Engineering and Technology
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• v.9 no.2
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• pp.73-79
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• 2010

In this study, the equivalent elastic modulus of flexible textile composites was predicted by nonlinear finite element analysis. The analysis was carried out considering the material nonlinearity of fiber tows and the geometrical nonlinearity during large deformation using commercial analysis software, ABAQUS. To account for the geometrical nonlinearity due to the large shear deformation of fiber tows, a user defined material algorithm was developed and inserted in ABAQUS. In results, nonlinear stress-strain curve for the flexible textile composites under uni-axial tension was predicted from which effective elastic modulus was obtained and compared to the test result. The effective elastic moduli were calculated for the various finite element models with different waviness ratio of fiber tow.

• Composites Research
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• v.18 no.2
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• pp.30-37
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• 2005

In this paper, geometrically non-linear finite element analyses were performed to study the mechanical behavior of the material system of the envelope of stratospheric airships. The microstructure of the load-bearing plain weave layer was identified and modeled. The Updated Lagrangian formulation was employed to consider the geometric non-linearity as well as the induced structural non-linearity for the fiber tows. The stress-strain behavior was predicted and the effective elastic modulus was calculated by numerical experiments. It was found the non-linear stress-strain curves were largely different from those by linear analysis. And non-linear elastic moduli were much higher than linear elastic moduli. The difference was more distinguishable when the tow waviness ratio was smaller.

• Journal of Korean Society of Steel Construction
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• v.13 no.2
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• pp.143-152
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• 2001

This paper presents are monotonic and cyclic behavior of steel plates. The effects of design parameters, initial deflection and aspect ratio, width-thickness ratio are studied by using FEM analysis. The results obtained from the monotonic loadings show that the aspect ratio(a/b) on the strength is to be neglected in the range of $(a/b){\leq}1.0$. The major cause of the reduction in strength sbbjected to cyclic loadings are width-thickness ratio and displacement amplitude. Based on the results, this paper presents some new strength curve with considering the cyclic deteriorations. The results are also discussed about the deformation capacity accordance with the width-thickness ratio and displacement amplitude.

• Journal of the Korean Society for Nondestructive Testing
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• v.32 no.4
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• pp.388-392
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• 2012

This study proposes a fully non-contact measurement method to assess acoustic nonlinearity of narrowband surface waves generated by a line-arrayed laser beam by using a laser-ultrasonic detector in the way of two-wave mixing (TWM) method. This method was applied to figure out a relationship between plastic deformation and nonlinearity characteristics of a plastically deformed aluminum specimens. The experimental results showed that the acoustic nonlinearity of the laser-generated surface wave increased proportionally to the level of tensile deformation. This tendency is in good agreement with the result of measurement by contact method with PZT-transducer.

• Magazine of the Korea Concrete Institute
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• v.9 no.5
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• pp.115-125
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• 1997

콘크리트의 변형률국소화는 콘크리트의연화거동에 수반되어 변형이 국부적으로 집중되는 현상이다. 본 연구의 목적은 인장과 압축하중상태에서 콘크리트 부재에 발생하는 콘크리트 변형률 국소화 거동을 해석적으로 재현할 수 있는 통일된 모형을 제안하는 것이다. 본 논문에서는 인장과 압축에 대하여 변형률국소화가 일어나는 콘크리트 부재를 변형률 연화가 일어나는 국소화영역과 탄성제하가 발생하는 비국소화영역으로 구분하여 모델링하는 통일된 모형을 제안하였다. 또한 제안된 모형에서 미시역학적 평균화기법을 이용해 평균등가탄성계수와 수정된 평균등가탄성계수를 구하여 시편의 크기와 국소화영역의 크기에 따는 해석을 수행하였으며 기존의 실험값과 비교하였다. 연구결과, 본 연구에서의 변형률국소화모형이 크기효과를 포함한 콘크리트의 변형률국소화거동 해석에 타당하게 적용될 수 있음을 보여주었다.

• The Korean Journal of Rheology
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• v.1 no.1
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• pp.71-79
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• 1989

임계연신비로 특징지어지는 비등온 방사공정에서의 Draw Resonance 발생을, White 의 변형속도에 따라 변하는 물질의 이완시간 모델에 의한 convected Maxwell 유체의 방사 모형을 사용해서 연구했다. 임계연신비의 계산에는 다른 연구자들이 이용하는 통상의 복잡 한 수치계산인 eigenvalue 방법을 쓰지 않고 전파하는 동적 waves 에 근거한 간단한 Hyun 의 이론을 사용했다. 그 결과 Staton Number와 냉각 공기온도로서 나타내지는 방사공정의 냉각이 공정을 안정시킨다는 것이 밝혀졌다. 다시 말해서 연신점도가 변형후화인 유체이거 나 변형박화인 유체이거난 상관없이 항상 Stanton Number가 켜지거나 또는 냉각공기온도 가 낮아질수록(즉냉각효과가 커질 때) 임계연신비가 커지는 것이다(단변형박화 dvcp의 빌부 구간을 제외하고) 한편 Draw Resonacnce 에 미치는 냉각의 효과는 무차원 이완시간(a Weissenberg Number 혹은 a Deborah number)이 커질수록 작아진다는 것도 발견됐다. 이 것은 process Time 이 작아지면 열전달이 작아지기 때문이다. 이러한 내용들은 다른 연구 자들의 결과와도 잘 부합된다.

• Journal of the Korean Society for Railway
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• v.11 no.3
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• pp.311-316
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• 2008

Ratcheting is a cyclic accumulation of strain under a cyclic loading. It is a kind of mechanisms which generate cracks in rail steels. Though some experimental and numerical study has been performed, modeling of ratcheting is still a challenging problem. In this study, an elastic-plastic constitutive equation with non-linear kinematic hardening equation was applied. Contact stresses in wheel-rail were analyzed. Under the tangential stress of the contact stresses, a cyclic stress-strain relation was obtained by using the model. A constant ratcheting strain per cycle was accumulated.