• The Journal of Engineering Geology
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• v.26 no.4
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• pp.583-591
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• 2016

Vibrating wire (VW) strain gauges are widely used for the evaluation of pipeline safety in extreme cold region. The development of VW strain gauges for the low temperature environment is necessary because of the high cost of gauges sold in developed countries. Thermistors embedded in the regular VW strain gauges and PT 100 sensors embedded in the gauges specially manufactured for this study have gone through credibility tests for temperature measurements. The use of PT 100 is recommended at low temperature environments because thermistors have low credibility at temperatures below $-15^{\circ}C$. Strain measurements using regular VW strain gauges also show low accuracies as temperature goes down. VW strain gauges manufactured using inconel give high credibility of strain measurements at low temperatures. More reliable VW strain gauges for the low temperature environment will be developed in the near future.

• Journal of the Korean Institute of Gas
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• v.9 no.3 s.28
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• pp.27-31
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• 2005

The membrane to be applied inside of the LNG storage tank is provided with corrugations to absorb thermal contraction and expansion caused by LNG temperature and pressure changes. It is very important to measure their thermal strains under LNG temperature by analytical and experimental stress analysis of the membrane. We have developed a stress measurement system using strain gages and measured the strain during cooldown and storing the LNG. We also analyzed the measured data by comparison with the FEM data.

• Journal of the Korean Institute of Gas
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• v.7 no.3 s.20
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• pp.13-17
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• 2003

A membrane unit for Liquefied Natural Gas (LNG) storage tank is a structural member which is designed specifically for preventing undesirable LNG leakage. Membrane units have to endure gas and liquid pressures by LNG and thermal stresses by the contact with cryogenic liquid of $-162^{\circ}C$. It is of importance to assure the strengths of membrane by experimental stress analysis under the temperature of LNG. In this paper, we proposed measurement system using commercial electrical strain gage and mechanical extension meter designed for this study.

• Proceedings of the KWS Conference
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• 2010.05a
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• pp.79-79
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• 2010

저온용 무연 솔더의 대표 조성으로 고려되고 있는 Sn-58Bi(융점: $138^{\circ}C$) 공정(eutectic) 조성은 우수한 강도에도 불구하고 연성(ductility) 측면에서의 문제점이 지속적으로 보고되고 있다. 따라서 이 합금계의 연성을 최대로 개선시킬 수 있으면서도 실제 상용화가 가능한 합금 조성의 개발 연구가 요청된다. 본 연구에서는 Sn-Bi 2원계 조성에서 최대의 연성을 나타내는 것으로 보고된 Sn-40Bi 조성에 미량의 합금원소를 첨가함으로써 최대의 연성을 확보하는 한편, 그 연성 특성이 변형속도에 어느 정도 민감한지를 인장 실험을 통해 결정하고자 하였다. 합금원소로는 0.1~0.5 wt%의 Ag, Mn, In, Cu를 선택하였으며, 인장 시편을 제조하여 $10^{-2}$, $10^{-3}$, $10^{-4}\;s^{-1}$의 3종류로 변형속도를 변형시켜가며 응력-변형 곡선(stress-strain curve)을 측정하였고, 조성별, 변형속도별로 최대인장강도(ultimate tensile stress, UTS) 및 연신율 결과들을 정리하였다. 합금원소를 첨가한 조성의 경우는 모든 시험 조건에서 Sn-40Bi보다 우수한 연신률을 나타내는 것으로 측정되었으나, $10^{-2}\;s^{-1}$의 빠른 변형속도에서는 그 향상 정도가 상대적으로 감소하는 경향이 관찰되었다. 특히 Sn-40Bi-0.5Ag 조성의 경우 느린 변형속도에서 특히 눈에 띄는 연신률 값을 나타내며, 모든 변형속도 조건에서 가장 우수한 연성을 나타내었다. 한편 Sn-40Bi-0.1Cu 조성의 경우 변형속도에 따른 연신률의 변화 정도, 즉, 변형속도에 따른 연신률의 민감도가 매우 커 $10^{-4}\;s^{-1}$ 속도에서는 Sn-40Bi-0.5Ag에 버금가는 연신률 값이 측정되었으나, $10^{-2}\;s^{-1}$ 속도에서는 가장 나쁜 연신률 특성을 보여주었다. Sn-40Bi-0.2Mn 조성은 최고의 연신률 향상 특성을 나타내지는 않았으나, In을 첨가한 경우보다는 대체적으로 우수한 연성을 나타내었다. 이상의 각 합금별 연성 특성은 인장시험 전의 미세조직 관찰 결과와 인장시험 후 파면부의 조직변화 관찰 결과로부터 해석되었다. 그 결과 석출상의 형성 여부, 인장 시험 중 재결정 조직의 형성 여부, 라멜라(lamellar) 조직의 분율과 라멜라 간격(lamellar spacing)의 정도 또는 $\beta$-Sn과 라멜라 조직 사이의 결정립계와 라멜라 조직 내 결정립계에서의 슬라이딩 모드(sliding mode) 변형 정도, 석출상의 크기와 분포 정도 등이 연신률 및 변형속도 민감도와 같은 연성 특성에 가장 큰 영향을 미치는 인자인 것으로 분석되었다.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.40 no.1
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• pp.23-31
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• 2016

In this study, we modified the conventional tensile split Hopkinson bar(TSHB) apparatus typically used for the high strength steel to evaluate the tensile deformation behavior of soft metallic sheet materials under high strain rates. Stress-strain curves of high purity single and multi-crystalline materials were obtained using this experimental procedure. Grain morphology and initial crystallographic orientation were characterized by EBSD(Electron Backscattered Diffraction) method measured in a FE-SEM(Field emission-scanning electron microscopy). The fractured surfaces were observed by using optical microscopy. The relationship between plastic deformation of aluminum crystalline materials under high-strain rates and the initial microstructure and the crystallographic orientations has been addressed.

• Tunnel and Underground Space
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• v.10 no.1
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• pp.59-69
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• 2000

Acoustic emission is n burst of microseismic waves generated by microscopic failure due to deformation in materials. The study on the detection of initiation and propagation of microcracks from acoustic emission measurement is very important for the evaluation of the stability of underground rock structures by the nondestructive letting method. In this study, acoustic emission was measured under uniaxial stiffness loading test used to obtain the complete stress-strain curves of marble and concrete used as reinforced materials of rock structures. The analysis of acoustic emission parameters and source location were performed to discuss the characteristics of the deformation and failure behavior of rock and concrete. And acoustic emission was measured under cyclic loading test to verify the Kaiser effect associated with the damage of materials, in situ stress of rock, and stress history of concrete structure.

• Composites Research
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• v.24 no.3
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• pp.12-16
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• 2011

High strain rate tensile tests were performed to measure the strain rate sensitivity of fiber reinforced composite material. The composite material was developed for the light weight design of an automotive FEM(front end module) carrier. Standard specimens for quasi-static tests of fiber reinforced composites can be found in ASTM D3039. However, in case of high strain rate tests, it was hard to find standard specimen shapes. In this study, three kinds of tensile specimens designed based on ASTM D638 were investigated to determined the adequate gauge width of tensile specimen for fiber reinforced composite. A drop tower type of high speed tensile apparatus was developed for strain rates of about 15/s and 100/s. Gauge width of 6mm, 8mm and 10mm were investigated. Test results showed the specimen of 8mm width was adequate for the high strain rate tensile tests of fiber reinforced composite. It was found the strength of the composite material increased as the strain rate increased.

• Explosives and Blasting
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• v.35 no.3
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• pp.15-20
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• 2017

In order to obtain the dynamic response behavior of the rock subjected to blasting loading, a shock-proof high sensitivity impact sensor which can measure high frequency dynamic force and strain events should be adopted. Because the impact sensors which uses quartz and piezoelectric element are costly, generally the strain measurement-based impact (SMI) sensors are applied to high speed loading devices. In this study, dynamic Brazilian tension tests of granitic rocks was conducted using the Nonex Rock Cracker (NRC) reaction driven-high speed loading device which adopts SMI sensors. The dynamic response of the granite specimens were monitored and the intermediate strain rate dependency of Brazilian tensile strengths was discussed.

• Journal of the Korean Society of Hazard Mitigation
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• v.9 no.2
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• pp.1-9
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• 2009

Water binder ratio combine high-performance concrete shrinkage of less than 0.4 to determine the transformation to a total shrinkage of water to move outside and internal consumption of moisture due to drying shrinkage and autogenous shrinkage, and then, the relative humidity changes and strain to be approached by surface physics describe the relationship between self-desiccation and autogenous shrinkage was set. To verify the self-desiccation in the humidity shrinkage and humidity measurements performed, and the research model, Tazawa, CEB-FIP model than to let the measure and the most similar results in this study based on self-desiccation model, autogenous shrinkage didn't represent the linear shrinkage by the drying shrinkage of the external moving but exponential relationships, unlike with the nature and rapid in the early age properly describes the attributes in shrinkage could see. After this research to move moisture and to reflect the shrinkage model, temperature, moisture transfer, strain analysis by multi-physics model is very similar to the results of mock-up specimen measurements performed for this research, the value measured by the internal consumption of moisture, therefore self-desiccation and a multi-physics model considering autogenous shrinkage might be relevant.

• Journal of Korean Tunnelling and Underground Space Association
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• v.12 no.2
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• pp.177-192
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• 2010

The field measurements on the shotcrete lining are usually performed during the tunnel construction. However, the credibility of the measurements is not certain because of the non-stress related strains occurring in the shotcrete, the uncertainty of the deformation modulus of the shotcrete, and the intrinsic difficulties involved in the strain measurements in the shotcrete. The problem related to the field measurements on the shotcrete is investigated using the review of the previous studies and the field measurement performed for this study. A method for the correction of stress measurements at the shotcrete lining, considering the non-stress related strains, is suggested using the literature review and the actual measurements obtained from the non-stress shotcretes. The deformation modulus used for the calculation of the stress acting on the shotcrete is also suggested.