• Proceedings of the Korean Society for Technology of Plasticity Conference
• /
• 2009.05a
• /
• pp.353-354
• /
• 2009

Tensile deformation behavior with different strain rate was investigated. $Zr_{56.2}Ti_{13.8}Nb_{5.0}Cu_{6.9}Ni_{5.6}Be_{12.5}$ (bulk metallic glass alloy possessed crystal phase which was called $\beta$-phase of dendrite shape, mean size of $20{\sim}30{\mu}m$ and occupied 25% of the total volume) was used in this study. Maximum tensile strength was obtained as 1.74Gpa at strain rate of $10^2/s$ and minimum strength was found to be 1.6GPa at $10^{-1}/s$. And then, maximum plastic deformation occurred at the strain rate of $5{\times}10^{-2}/s$ and represented 1.75%, though minimum plastic deformation showed 0%. In the specific range of strain rate, relatively higher plastic deformation and lower ultimate tensile strength were found with lots of shear bands. The fractographical observation after tensile test indicated that vein like pattern on the fracture surface was well developed especially in the above range of strain rate.

• Korean Journal of Materials Research
• /
• v.7 no.11
• /
• pp.1007-1011
• /
• 1997

영활화혁발전소 보일러헤다 재질인 1Cr0.5Mo강의 파형에 따른 저주기 피로특성을 규명하고자 상온(298K) 및 고온(177K)의 삼각파와 사인파형 저주기 피로시험을 수행하였고 소성에너지법을 이용하여 파형에 따른 소성변형에너지와 피로수명과의 +관계를 분석하였다. 저주기 피로시 재료내부의 소성변형에너지를 히스테리시스루프의 면적으로 계산하여 구하였으며 이를통해 저주기 피로수명을 예측하였고 Coffin-Manson법 및 변형률분할법을 이용한 저주기 피로수명 결과와 서로 잘 일치하였다. 또한 상온 및 고온에서 피로반복수의 증가와 함께 재료가 반봅연화됨을 알 수 있었다.

• Proceedings of the KSME Conference
• /
• 2000.11a
• /
• pp.185-192
• /
• 2000

A novel indentation theory is proposed by examining the data from the incremental plasticity theory based finite element analyses. First the optimal data acquisition location is selected, where the strain gradient is the least and the effect of friction is negligible. This data acquisition point increases the strain range by a factor of five. Numerical regressions of obtained data exhibit that strain hardening exponent and yield strain are the two main parameters which govern the subindenter deformation characteristics. The new indentation theory successfully provides the stress-strain curve with an average error less than 3%.

• Geotechnical Engineering
• /
• v.11 no.3
• /
• pp.113-122
• /
• 1995

The purposes of this study are to investigate the mechanical prospeities of the inter mediate soils through consolidation tests and triaxial compression shear tests. The intermediate soils used in this study are artificial soils which are composed of sea clay, sand and it's crushed component. The relationship between plastic index and mechanical prosperties (permeability and compressibility) is investigated through series of consoli dation tests. Strain hardening phenomenon under shearing is explored based on several overconsideration ratios and strain rates in undrained shear tests. To make a comparative study difference of drain condition and strain rate, drain shear tests are performed with overconsolidation ratio.

• Journal of the Korean Geotechnical Society
• /
• v.29 no.1
• /
• pp.171-181
• /
• 2013

The radial mapping rule in bounding surface model was experimentally investigated by analyzing the drained stress probe tests on Chicago clays. The experimental data obtained from 10 drained stress probe paths were analyzed to calculate the directions of the plastic strain increments. The anisotropic bounding surface model was adopted to represent a bounding yield surface which resides in the pre-consolidation yield stress of undisturbed clays. The projection origins were estimated by finding the interceptions of the straight lines passing through the current stress point and the imaginary yield stress point on the bounding surface. The results show that the projection origin is not fixed at a point but moves toward the direction of the stress probe path after it is established around the initial stress point.

• Journal of The Korean Society of Agricultural Engineers
• /
• v.55 no.5
• /
• pp.59-69
• /
• 2013

본 연구에서는 동적 점탄-점소성 구성식에 기초한 다층지반의 1차원 액상화 해석을 수행하였다. 일본 고베 포트아일랜드에서 발생한 1995 Hyogoken Nanbu 지진에 대하여 지반 모델링을 하였으며, 사질토 지반에는 탄소성 모델을, 점성토 지반에는 점탄-점소성 모델 및 탄-점소성 모델을 각각 적용하였다. 본 연구 결과, 모델 지반의 경우 지표 10 m 아래를 전후하여 액상화가 발생하였으며 액상화가 발생한 지반을 통과하는 지진파는 감쇠특성을 나타내고 이 때 전단변형률을 크게 증가시켰다. 또한, 대변형률 영역에서의 점성토의 동적거동 해석에서는 점소성 거동특성이 지배적이므로 점소성 모델의 적용이 중요함을 알 수 있었다. 한편 동적 점탄-점소성 구성모델은 대변형률 영역에서 점성토의 소성변형을 유발하는 대형 지진 발생시 점성토의 증폭 및 감쇠특성 분석에 적용 가능한 모델임을 확인하였다.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.34 no.7
• /
• pp.911-917
• /
• 2010

In this study, we performed structural and fatigue analyses of the engine exhaust manifold that was subjected to thermo-mechanical cyclic loading. The methodologies used in this study are based on an approach in which the techniques for modeling the exhaust system, the temperature-dependent properties of the material, and thermal cyclic loading are taken into consideration and a reliable strategy is adopted for failure prediction. An application example shows that at an elevated temperature, considerable compressive plastic deformation is observed and that at a low temperature, tensile stresses remain in those parts of the test exhaust manifold where failure is observed. In order to predict fatigue life, mechanical damage is determined on the basis of the stress.strain hysteresis loops by using the classical Coffin.Manson equation and by adopting a method in which the dissipated plastic energy is taken into consideration.

• KSCE Journal of Civil and Environmental Engineering Research
• /
• v.26 no.3A
• /
• pp.465-471
• /
• 2006

To describe hysteretic behavior of steel structures under dynamic loading such as earthquake, the dynamic cyclic plasticity model considering stress-strain relationship and characteristics of used steel materials under static-dynamic deforming is required. In this paper, mechanical characteristics and stress-strain relationship of SM490 was clarified by carrying out static-dynamic monotonic and cyclic loading test. A dynamic cyclic plasticity model of SM490 was proposed based on the test results and applied 3-dimensional finite element analysis using finite deformation theory. An analytical method developed by the authors was verified validity and accuracy by comparing both analysis and test results. The comparison result shows that the analytical method developed by the authors can predict static-dynamic hysteretic behavior of steel structures with accuracy.

• Proceedings of the Korea Concrete Institute Conference
• /
• 2008.04a
• /
• pp.193-196
• /
• 2008

This paper proposes a method to predict the ductility capacity of reinforced concrete beam-column joints failing in shear after the formations of plastic hinges at both ends of the adjacent beams. The current design code divides joints into two categories: Type 1 for structures in non seismically hazard area and Type 2 in seismically hazard area. While there are many researches related to joint shear strength in Type 1, those in regard to joint ductility capacity of Type 2 are scarce. This paper classified the ductility capacity of beam-column joints into column, joint panel, and beam deformability. Since a brittle failure such as shear or bond failure in the columns must be avoided, column deformability was calculated by elastic analysis. The plastic hinges of the adjacent beams affect joint deformability. Therefore, the prediction of joint deformability was calculated with consideration to the degradation of the diagonally compressed concrete due to the strain penetration.

• Transactions of Materials Processing
• /
• v.3 no.2
• /
• pp.215-228
• /
• 1994

The purpose of this paper is to pursue a general method to determine both the flow stress of a material and the friction factor by ring compression test. The materials are assumed to obey the expanded n-power hardening rule including the strain-rate effect. Ring compression is simulated by the rigid-plastic finite element method to obtain the database used in determining the flow stress and friction factor. The Simulation is conducted for various strain hardening exponent, strain-rate sensitivity, friction factor, and compressing speed, as variables. It is assumed that the friction factor is constant during the compression process. To evaluate the compatibility of the database, experiments are carried out at room and evaluated temperature using specimens of aluminum 6061-T6 under dry and grease lubrication condition. It is shown that the proposed test method is useful and easy to use in determining the flow stress and the friction factor.