• Composites Research
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• v.22 no.3
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• pp.29-34
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• 2009

In this paper, finite element analyses were used to estimate the strain distribution at the fracture site of a tibia bone. A stainless steel bone plate and various composite bone plates were considered to find out the best conditions for callus generation while bone fracture was cured for 16 weeks. Through this research, the appropriate load condition which makes the strains between the appropriate range($2{\sim}10%$) was sought. From this analysis, it was found that lower level of external load is needed for the appropriate strain for the case of composite bone plate application and it was also found that the composite bone plate had potential advantages for effective bone fracture healing relieved stress shielding effect.

• Journal of Korean Society of Steel Construction
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• v.19 no.3
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• pp.291-301
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• 2007

The overlay model is a certain kinds of numerical analysis method to present the material non-lineariy which is represented the baushinger effect and the strain hardening. This model simulates the complex behavior of material by controlling the properties of the layers which like the hardening ratio, the section area and the yield stress. In this paper, the constitutive equation and plastic flow rule of each layer which are laid in the plane stress field are obtained by using the thermodynamics. Two numerical examples were tested for the validity of proposed method in uniaxial stress and plane stress field with comparable experimental results. The only parameter for the test is the yield stress distribution of each layers.

• Transactions of the Korean Society of Mechanical Engineers
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• v.15 no.3
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• pp.751-756
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• 1991

본 연구에서는 Ashwell이 제시한 변형률요소를 전단효과를 고려한 두꺼운 곡 선보 요소에 적용 하였다. 막 변형률, 곡률, 전단변형률 각각에 독립된 변형률 함수 를 가정하여 미분 방정식의 일반해를 구하면 정확한 강체변위의 표현은 물론, 강성과 잉현상을 피할 수 있고 얇은 곡선보에서 두꺼운 곡선보에 이르기까지 보의 해석에 있 어서, 2절점으로 구성되는 적은 자유도수에서 높은 정확도를 보여주는 간편하고도 효 율적인 요소를 개발하고자 하였다.

• Journal of the Korean Geotechnical Society
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• v.28 no.12
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• pp.17-25
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• 2012

FEM requires the stress-strain relationship equations for numerical analyses. However, most formulations for the stress-strain relationship published up to the present are not satisfactory enough to properly express all the levels from the small strain to the peak. Tatsuoka and Shibuya (1991) suggested a new single formulation applicable not only to a wide range of geo-materials from soft clay to soft rock, but also to a wide range of strain levels from $10^{-6}$ to $10^{-2}$. The plain strain compression test is carried out to seven samples of research standard sand specimens and two samples of glass beads, which have been used at world-renowned research institutes. In this study, strains of the maximum principal stress (${\sigma}_1$) and the minimum principal stress (${\sigma}_3$) were thoroughly measured from $10^{-6}$ to $10^{-2}$, and the result, applied to Tatsuoka and Shibuya's new formulation, coincided closely with the measured data of the stress-strain relationship from the small strain to the peak.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.13 no.4
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• pp.449-459
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• 2000

The original Mindlin-type degenerated shell element perform reasonably well for moderately thick shell structures. However, when full integration for analysis of thin shell is used to evaluate the stiffness matrix, the stiffness of shell element is often over-estimated due to shear or membrane locking phenomena. To correct this problem, the formulation of the new degenerated shell element is derived by the combination of two different techniques. The first type of elements(TypeⅠ) has used assumed shear strains in the natural coordinate system to overcome the shear locking problem, the reduced integration technique in in-plane strains(membrane strains) to avoid membrane locking behaviour. Another element(TypeⅡ) has applied the assumed strains to both of membrane strain and transverse shear strains. The improved degenerated shell element has been tested by several numerical problems of shell structures. Numerical results indicate that this shell element shows fast convergence and reliable solutions.

• Journal of the Korean Society for Nondestructive Testing
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• v.31 no.4
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• pp.335-342
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• 2011

Application of FBG (Fiber Bragg Grating) sensors to measure strain of steel roof trusses has been performed. This is to check and confirm the structural integrity of an unusually shaped, reverse shell structure made of reinforced concrete. The issue was to place sensors at proper location and compare the measured values to the results from structural analysis. It has been learned that a deliberate measurement scheme is needed in order to monitor a complex structure during construction. In this study, the measured values were within allowable range of strain, thus confirming the safety of the structure during measurement and construction.

• Journal of the Korean Society for Railway
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• v.19 no.6
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• pp.755-764
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• 2016

In this paper, to verify the field application of a displacement estimation technique based on the relationship between displacement and strain, static and dynamic field load test are performed on three-span continuous real bridge structures. The superstructure types of the test bridges are IPC girder highway bridge and steel box girder AGT bridge. LVDTs and strain gauges are attached to them; then, the responses due to test vehicle are measured. To obtain the displacement-strain relationship of the test bridges, the bridges are modeled as grillage system with 6 DOFs for the purpose of structural analyses. Static and dynamic displacements, which are estimated using both the calculated displacement-strain relationship and the measured strain signal, agree well with the values measured by LVDT. This study demonstrates that the displacement estimation technique using the strain signal can be effectively applied to the displacement measurement of bridge structures that cross rivers/roads/railways or have high clearance.

• Journal of the Korean Geotechnical Society
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• v.15 no.6
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• pp.17-28
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• 1999

In order to analyze effects of strain rate on consolidation of natural clay, this paper presents a nonlinear elasto viscoplastic model in which viscoplastic behavior is modeled by a unique effective stress-strain-strain rate relationship (equation omitted). The predicted values using numerical analysis are compared with measured ones in several laboratory tests such as creep test, multistage load test, and relaxation test for Berthierville clay. It is possible to estimate consolidation behavior of natural clay with reasonable accuracy using the proposed nonlinear viscoplastic model.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.23 no.3
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• pp.315-323
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• 2010

Five concrete compressive stress-strain models have been analyzed to check the validity of the strength method for determining the nominal moment of strengthened members using commercially available computer language. The results show that the concrete stress-strain models do not influence on the flexural analysis. The moment of a strengthened member obtained from the flexural analysis at concrete compressive strain reaching 0.003 is well agreed with nominal moment using the strength method. The flexural analysis results show that when the steel reinforcement, FRP ratio, FRP failure strain, and concrete failure compressive strain are relatively lower, the strength method overestimates the flexural capacity of the strengthened members.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.35 no.9
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• pp.1041-1050
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• 2011

An elasto-plastic finite element method using the theory of strain gradient plasticity is proposed to evaluate the size dependency of structural plasticity that occurs when the configuration size decreases to micron scale. For this method, we suggest a low-order plane and three-dimensional displacement-based elements, eliminating the need for a high order, many degrees of freedom, a mixed element, or super elements, which have been considered necessary in previous researches. The proposed method can be performed in the framework of nonlinear incremental analysis in which plastic strains are calculated and averaged at nodes. These strains are then interpolated and differentiated for gradient calculation. We adopted a strain-gradient-hardening constitutive equation from the Taylor dislocation model, which requires the plastic strain gradient. The developed finite elements are tested numerically on the basis of typical size-effect problems such as micro-bending, micro-torsion, and micro-voids. With respect to the strain gradient plasticity, i.e., the size effects, the results obtained by using the proposed method, which are simple in their calculation, are in good agreement with the experimental results cited in previously published papers.