• 한국해양공학회지
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• 제18권6호
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• pp.58-69
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• 2004

In order to investigate the characteristics of the lateral earth pressure at rest, under hysteretic $K_o-loading/unloading$ conditions, seven types of multi-cyclic models have been studied, using dry sand. For this study, the new type of $K_o-oedometer$ apparatus was developed, and the horizontal pressure was accurately measured. The multi-cyclic models consist of primarily 3 cases: (i) $K_o-test$ under the same loading / unloading condition, (ii) multi-cyclic loading / unloading $K_o-test$ exceeding the maximum pre-vertical stress, and (iii) multi-cyclic loading / unloading $K_o-test$ within the maximum pre-vertical stress. Results fromthe multi-cyclic model indicated that a single-cyclic model could be extended if the exponents for the unloading condition $(\alpha\;and\;\alpha^*)$ and the reloading coefficients $(m_r,\;and\;m_r^{\ast})$ were primarily dependent upon the type of model, number of cycles, and the relative density.

• 한국지반공학회지:지반
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• 제11권1호
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• pp.23-40
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• 1995

다주기 Ko-재하/제하 시에 수평응력의 변화특성을 관찰하기 위하여 7종류의 시험모형을 선 정하였고, Ko조건을 크게 만족할 수 있도록 특별히 고안한압밀링 형태의 Ko-시험기를 제작하여 실내 건조된 모래에 대하여 실험을 수행하였다. 시험모형은 동일한 재하/제하 응력의 반복, 최대선행응력을 초과하는 반복 재하/제하, 그리고 최대선행 연직응력 내의 반복 재하/제하 Ko시험으로 구분된다. 실험결과에서 다주기 이력모형도 역시 기존의 단주기 이력모형을 확대하여 사용할 수 있음을 보였다. 여기서, 제하시의 지수 (a 및 a*)와 재재하 시의 계수(mr 및 mr*)는 응력이력의 형태, 반복회수 및 상대밀도에 따라 주로 지배되었다.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2011년도 춘계학술대회 논문집
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• pp.238-243
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• 2011

This study compared Kd, loss factor and thickness of floor impact isolator by loading/unloading heat treatment with results by continuous loading treatment and checked problem and improvement method of heat treatment condition for the long-term stability evaluation of the floor impact isolation. As the results, it is required the change of heat treatment condition unloading now to loading as actual weigh on the floor impact isolator.

• 대한용접접합학회:학술대회논문집
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• 대한용접접합학회 2002년도 Proceedings of the International Welding/Joining Conference-Korea
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• pp.378-383
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• 2002

In previous study, the decrease and recovery of total stiffness in welded structure was discussed on the basis of experimental examination through tensile loading and unloading test of welded specimen. The recovery of structure stiffness was caused by the release of welding residual stress through mechanical loading. In this study, analysis model that is indispensable for the effective application of MSR method was established on the basis of test and measurement result. Thermal elasto-plastic analysis for welding process was performed by non-coupled analysis. Analysis results of welding process were transfer to elasto-plastic model for tensile loading & unloading by restart technique. In elasto-plastic analysis model for mechanical loading & unloading, hardening appearance of weld metal was considered by rezoning technique and tying technique was used for JIG condition of test machine.

• International Journal of Korean Welding Society
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• 제2권1호
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• pp.29-32
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• 2002

In previous study, the decrease and recovery of total stiffness in welded structure was discussed on the basis of experimental examination through tensile loading and unloading test of welded specimen. The recovery of structure stiffness was caused by the release of welding residual stress through mechanical loading. In this study, analysis model that is indispensable for the effective application of MSR method was established on the basis of test and measurement result. Thermal elasto-plastic analysis for welding process was performed by non- coupled analysis. Analysis results of welding process were transfer to elasto-plastic model for tensile loading & unloading by restart technique. In elasto-plastic analysis model for mechanical loading & unloading, hardening appearance of weld metal was considered by rezoning technique and tying technique was used for JIG condition of test machine.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2004년도 추계 학술대회논문집
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• pp.33-36
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• 2004

The ballast tank of a ship is a system that realizes the required shipping condition and controls the draft of a ship. The loading/unloading of the ballast tank is frequently operated during navigation and the accurate prediction of the loading/unloading time is very important. A numerical algorithm that predicts the loading/unloading time of the ballast tank has been developed and applied to the prediction of the loading/unloading time of the ballast tank with various piping systems. This algorithm can be useful in optimizing the ballast tank system in early design stage.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2010년도 추계 학술발표회
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• pp.1156-1167
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• 2010

The constant rate of strain (CRS) consolidation test has been widely used to evaluate consolidation characteristics of soils instead of the standard Incremental Loading Test. In practical problems, after the ground improvement, the condition of the soil is over-consolidated. Therefore, it is important to determine the recompression indices and the coefficient of consolidation(or the coefficient of swelling) of unloading-reloading cycle to predict the settlement behavior. However, since standard testing procedures or studies related with strain rate are insufficient especially in unloading-reloading cycle, it is difficult to predict the settlement field behavior accurately from the CRS consolidation test results in spite of its lots of strengths. The several CRS consolidation tests were performed changing the unloading strain rate from 0.2%/hr to 20%/hr with vertical drainage condition using the reconstituted kaolinite sample. For the reconstituted kaolinite sample in CRS consolidation test, the recompression indices are insensitive to the strain rate. It is revealed that the coefficient of consolidation of reloading is affected by the developed pore pressure during unloading. Additionally, the test should be conducted in the positive pore pressure ratio range (3~15%) to obtain the reasonable coefficient of consolidation in the whole range(loading, unloading and reloading).

• 한국지반환경공학회 논문집
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• 제14권10호
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• pp.17-27
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• 2013

This paper explores stress release induced by unloading in dry sand. A series of model tests were carried out to measure stresses developed in testing sand during loading and those released during unloading for different boundary conditions. It was found that stress in the sand increased linearly with applied load. At the onset of unloading, almost no stress release was observed. Significant stress release took place when the shear stress in the sand induced by unloading exceeded the frictional resistance and caused movement of sand particles. The initiation and the magnitude of stress release depend on the stress condition prior to unloading, the decrease of external load, and also the frictional resistance in sand. A new conceptual stress-release model was next developed based on the model test results by considering the fundamental frictional behavior of granular materials.

• 대한치과교정학회지
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• 제30권6호
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• pp.731-738
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• 2000

본 연구의 목적은 재생된 니켈-티타늄 호선의 3점 굴곡물성의 변화를 조사하여, 임상적으로 니켈-티타늄 호선을 재생하여 사용하는 것이 타당한지를 알아보는 것이다. 4종의 니켈-티타늄 호선(Align, NiTi, Optimallo, Sentalloy)을 처리전(T0: 대조군)과 인공타액에 4주간 처리한 군(T1), 그리고 인공타액 처리 후 가압증기 멸균소독한 군(T2)으로 구분하여 3점 굴곡실험을 하였다. 3mm 변형시의 loading force, unloading force, hysteresis와 1mm 변형시의 loading, unloading force, stress hysteresis의 변화를 관찰하여 다음과 같은 결과를 얻었다. 1. Align은 재생 (T2)후에 3mm 변형시의 loading force, unloding force가 통계적으로 유의성 있게 증가하였다(loading force: p,0.05, unloading force:p<0.01). NiTi, Optimmalloy, Sentalloy에서는 통계적으로 유의성 있는 차이가 보이지 않았다. 2. Align은 재생(T2)후에 hysteresis가 통계적으로 유의성 있게 감소하였다(p<0.01). NiTi, Optimmalloy, Sentalloy에서는 통계적으로 유의성있는 차이가 보이지 않았다. 3. 모든 호선에서 1mm 변형시의 loading force는 재생(T2)후에 통계적으로 유의성있는 차이를 보이지 않았다. 4. Align은 재생(T2)후에 1mm 변형시의 unloading force가 통계적으로 유의성있게 증가하였다(p<0.05). NiTi, Optimmalloy, Sentalloy에서는 통계적으로 유의성있는 차이가 보이지 않았다. 5. Align의 loading force와 unloading force는 T1과 T0는 통계적으로 유의한 차이가 없었으며, T2와 T0사이에 유의성 있는 차이가 있었다(각각 p<0.05, p<0.01). 6. Align은 T1에서 pseudoelasticity가 감소하고, T2에서는 pseudoplasticity와 pseudoelasticity가 감소하였다.

• Structural Engineering and Mechanics
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• 제22권5호
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• pp.563-574
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• 2006

This paper studies mechanical behavior of the superelastic shape memory alloy (SMA) rods in terms of local deformations and time via tensile loading-unloading cycles for both ends fixed end constraints. Besides the unique stress induced martensitic transformation (SIMT), SMA's time dependent behavior when it is in mixed-phase condition upon loading and unloading, also need careful attention with a view of investigating the local deformation of the structural elements made of the same material. With this perspective, the so-called stress-relaxation tests have been performed to demonstrate and investigate the local strains-total strains relationships with time, particularly, during the forward SIMT. Some remarkable phenomena have been observed pertaining to SIMT, which are absent in traditional materials and those unique phenomena have been explained qualitatively. For example, at the stopped loading conditions the two ends (fixed end and moving end of the tensile testing machine) were in fixed positions. So that there was no axial overall deformation of the specimen but some notable increase in the axial local deformation was shown by the extensometer placed at the middle of the SMA specimen. It should be noted that this peculiar behavior termed as 'inertia driven SIMT' occurs only when the loading was stopped at mixed phase condition. Besides this relaxation test for the SMA specimens, the same is performed for the mild steel (MS) specimens under similar test conditions. The MS specimens, however, show no unusual increase of local strains during the stress relaxation tests.