• Geomechanics and Engineering
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• 제22권5호
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• pp.385-396
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• 2020

A uniaxial compression test was performed to analyse the mechanical properties and macroscale and mesoscale failure mechanisms of sandstone with pyrite concretions. The effect of the pyrite concretions on the evolution of macroscale cracks in the sandstone was further investigated through numerical simulations with Particle Flow Code in 2D (PFC2D). The results revealed that pyrite concretions substantially influence the mechanical properties and macroscale and mesoscale failure characteristics of sandstone. During the initial loading stage, significant stress concentrations occurred around the edges of the pyrite concretion accompanied by the preferential generation of cracks. Meanwhile, the events and cumulative energy counts of the acoustic emission (AE) signal increased rapidly because of friction sliding between the concretion and sandstone matrix. As the axial stress increased, the degree of the stress concentration remained relatively unchanged around the edges of the concretions. The cracks continued growing rapidly around the edges of the concretions and gradually expanded toward the centre of the sample. During this stage, the AE events and cumulative energy counts increased quite slowly. As the axial stress approached the peak strength of the sandstone, the cracks that developed around the edges of the concretion started to merge with cracks that propagated at the top-left and bottom-right corners of the sample. This crack evolution ultimately resulted in the shear failure of the sandstone sample around the edges of the pyrite concretions.

• 폴리머
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• 제35권6호
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• pp.574-579
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• 2011

자동차 선도장 강판을 위한 핵심 응용기술로서 3-롤코팅 공정을 연구하였다. 본 연구를 위한 3-롤코팅은 저장조로부터 코팅액을 끌어 올리는 pick-up롤, 적절한 코팅 두께로 계량시키기 위한 계량롤, 강판에 직접 코팅시키기 위한 applicator 롤로 구성되어 있다. 전단담화의 유변물성을 갖는 고분자 도료의 코팅 유동 특성과 코팅 운전 영역을 pickup 롤과 계량롤 사이의 속도비와 간격 등의 공정조건과의 상관관계를 통해 고찰하였다. 안정한 코팅 영역에서, 간격이 크거나 속도비가 작을수록 코팅 두께는 증가하였다. 또한, ribbing과 cascade라는 불안정성은 각각 속도비가 낮고 높을 때 관찰되었다. 특히, 속도비가 낮을때, ribbing의 파장과 심각도가 증가함을 확인하였다.

• Structural Engineering and Mechanics
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• 제55권6호
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• pp.1139-1155
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• 2015

In this study, a new retrofitting method for improving the seismic performance of reinforced concrete column was presented, in which prestressed steel strips were utilized as retrofitting stuff to confine the reinforced concrete column transversely. In order to figure out the seismic performance of concrete column specimen retrofitted by such prestressed steel strips methods, a series of quasi-static tests of five retrofitted specimens and two unconfined column specimen which acted as control specimens were conducted. Based on the test results, the seismic performance including the failure modes, hysteresis performance, ductility performance, energy dissipation and stiffness degradation of all these specimens were fully investigated and analyzed. And furthermore the influences of some key parameters such as the axial force ratios, shear span ratios and steel strips spacing on seismic performance of those retrofitted reinforced concrete column specimens were also studied. It was shown that the prestressed steel strips provided large transverse confining effect on reinforced concrete column specimens, which resulted in improving the shearing bearing capacity, ductility performance, deformation capacity and energy dissipation performance of retrofitted specimens effectively. In comparison to the specimen which was retrofitted by the carbon fiber reinforced plastics (CFRP) strips method, the seismic performance of the specimens retrofitted by the prestressed steel strips was a bit better, and with much less cost both in material and labor. From this research results, it can be concluded that this new retrofitting method is really useful and has significant advantages both in saving money and time over some other retrofitting methods.

• 한국구조물진단유지관리공학회 논문집
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• 제23권4호
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• pp.131-136
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• 2019

굳지 않은 콘크리트의 적층성은 콘크리트 3D 프린팅의 핵심 요소로써 필라멘트의 변형 및 붕괴 없이 일정한 높이로 적층하는 성능이다. 적층성은 항복응력과 밀접한 관련이 있으며, 항복응력이 높을수록 우수하다. 또한, 굳지 않은 콘크리트는 압출된 후 시간경과에 따라 경화되면서 전단응력이 증가하기 때문에 적층성이 높아지게 된다. 따라서, 콘크리트 3D 프린팅 시 굳지 않은 콘크리트의 적층성 확보를 위해서는 출력되는 레이어 사이의 적절한 시간 간격(Printing Time Gap, 이하 PTG)이 필요하다. PTG가 증가함에 따라 적층성은 증가하지만, PTG가 과다하게 커지면 출력된 레이어 간의 부착성능이 감소하며, 출력시간이 길어짐에 따라서 압출성능이 저하될 수 있다. 이 연구에서는 100 MPa급 고강도 콘크리트 배합에 적합한 적층성을 확보하기 위하여 PTG를 변수로 한 3D 프린팅 실험을 수행하였으며, 이와 더불어 콘크리트 3D 프린팅 방법을 유사하게 모사할 수 있는 모의 적층실험 방법의 유효성을 검토하기 위하여 모의 적층실험을 수행하였다.

• Computers and Concrete
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• 제23권1호
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• pp.61-68
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• 2019

This paper presents a computational rational model to predict the ultimate and optimized load capacity of reinforced concrete (RC) beams strengthened by a combination of longitudinal and transverse fiber reinforced polymer (FRP) composite plates/sheets (flexure and shear strengthening system). Several experimental and analytical studies on the confinement effect and failure mechanisms of fiber reinforced polymer (FRP) wrapped columns have been conducted over recent years. Although typical axial members are large-scale square/rectangular reinforced concrete (RC) columns in practice, the majority of such studies have concentrated on the behavior of small-scale circular concrete specimens. A high performance concrete, known as polymer concrete, made up of natural aggregates and an orthophthalic polyester binder, reinforced with non-metallic bars (glass reinforced polymer) has been studied. The material is described at micro and macro level, presenting the key physical and mechanical properties using different experimental techniques. Furthermore, a full description of non-metallic bars is presented to evaluate its structural expectancies, embedded in the polymer concrete matrix. In this paper, the mechanism of mechanical interaction of smooth and lugged FRP rods with concrete is presented. A general modeling and application of various elements are demonstrated. The contact parameters are defined and the procedures of calculation and evaluation of contact parameters are introduced. The method of calibration of the calculated parameters is presented. Finally, the numerical results are obtained for different bond parameters which show a good agreement with experimental results reported in literature.

• 국제강구조저널
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• 제18권4호
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• pp.1440-1463
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• 2018

The Wagner coefficient is a key parameter used to describe the inelastic lateral-torsional buckling (LTB) behaviour of the I-beam, since even for a doubly-symmetric I-section with residual stress, it becomes a monosymmetric I-section due to the characteristics of the non-symmetrical distribution of plastic regions. However, so far no theoretical derivation on the energy equation and Wagner's coefficient have been presented due to the limitation of Vlasov's buckling theory. In order to simplify the nonlinear analysis and calculation, this paper presents a simplified mechanical model and an analytical solution for doubly-symmetric I-beams under pure bending, in which residual stresses and yielding are taken into account. According to the plate-beam theory proposed by the lead author, the energy equation for the inelastic LTB of an I-beam is derived in detail, using only the Euler-Bernoulli beam model and the Kirchhoff-plate model. In this derivation, the concept of the instantaneous shear centre is used and its position can be determined naturally by the condition that the coefficient of the cross-term in the strain energy should be zero; formulae for both the critical moment and the corresponding critical beam length are proposed based upon the analytical buckling equation. An analytical formula of the Wagner coefficient is obtained and the validity of Wagner hypothesis is reconfirmed. Finally, the accuracy of the analytical solution is verified by a FEM solution based upon a bi-modulus model of I-beams. It is found that the critical moments given by the analytical solution almost is identical to those given by Trahair's formulae, and hence the analytical solution can be used as a benchmark to verify the results obtained by other numerical algorithms for inelastic LTB behaviour.

• Korean Chemical Engineering Research
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• 제59권3호
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• pp.366-372
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• 2021

캐드헤린-카테닌 복합체는 세포의 부착 접합부에서 힘의 전달에 중요한 역할을 하는 것으로 생각된다. 그러나 기계적 힘 신호를 시각화 하고 감지하는 적절한 도구의 부재로, 캐드헤린-카테닌 복합체가 세포 간 접합에서 힘 전달을 조절하는 기본 메커니즘은 아직 파악하기가 어렵다. 본 연구에서는 형광공명에너지전이를 기반으로 설계된 알파카테닌 센서를 사용하여 캐드헤린에 의해 매개되는 힘 전달을 시각화 하였다. 이러한 결과는 알파카테닌이 세포-세포 접합부에서 캐드헤린 매개 기계적에너지변환(mechanotransduction) 경로의 핵심적인 힘 트랜스듀서(force transducer) 임을 보여준다. 본 연구는 향후 기계적 힘의 세포-세포 상호간의 의사소통에 미치는 영향과 생리학적/병리학적 현상과의 관계를 연구하는 데 중요한 이해를 제공할 것이라 본다.

• 마이크로전자및패키징학회지
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• 제28권2호
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• pp.59-64
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• 2021

차세대 반도체 기술은 이종소자 집적화(heterogeneous integration)를 이용한 시스템-인-패키징(system-inpackage, SIP) 기술로 발전하고 있고, 저온 Cu 본딩은 SIP 구조의 성능 향상과 미세 피치 배선을 위해서 매우 중요한 기술이라 하겠다. 본 연구에서는 porous한 Ag 나노막을 이용하여 Cu 표면의 산화 방지 효과와 저온 Cu 본딩의 가능성을 조사하였다. 100℃에서 200℃의 저온 영역에서 Ag가 Cu로 확산되는 것보다 Cu가 Ag로 확산되는 것이 빠르게 관찰되었고, 이는 저온에서 Ag를 이용한 Cu간의 고상 확산 본딩이 가능함을 나타내었다. 따라서 Ag 나노막을 이용한 Cu 본딩을 200℃에서 진행하였고, 본딩 계면의 전단 강도는 23.27 MPa로 측정되었다.

• Geomechanics and Engineering
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• 재33권6호
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• pp.553-565
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• 2023

As the structure of broken rock mass is complex, with obvious discontinuity and anisotropy, it is generally necessary to reinforce broken rock mass using grouting in underground construction. The purpose of this study is to experimentally investigate the mechanical properties of broken rock mass after grouting reinforcement with consideration of the characteristics of broken rock mass (i.e., degree of fragmentation and shape) and a range of reinforcement methods such as relative strength ratio between the broken rock mass and cement-based grout stone body (λ), and volumetric block proportion (VBP) representing the volumetric ratio of broken rock mass and the overall cement grout-broken rock mass mixture after the reinforcement. The experimental results show that the strength and deformation of the reinforced broken rock mass is largely determined by relative strength ratio (λ) and VBP. In addition, the enhancement in compressive strength by grouting is more obvious for broken rock mass with spherical shape under a relatively high strength ratio (e.g., λ=2.0), whereas the shape of rock mass has little influence when the strength ratio is low (e.g., λ=0.1). Importantly, the results indicate that columnar splitting failure and inclined shear failure are two typical failure modes of broken rock mass with grouting reinforcement.

• 대한토목학회논문집
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• 제29권5C호
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• pp.199-206
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• 2009

본 연구에서는 수평하중을 받는 강관합성 말뚝의 역학적 특성을 평가하기 위하여 서로 다른 단면 특성을 가진 모형 말뚝에 대하여 실내 모형 실험을 수행하였다. 지반 반력의 효율적인 모사를 위하여 스프링 장치를 이용한 지반 반력 시스템을 개발하였으며, 축하중 및 수평하중을 독립적으로 재하할 수 있는 하중 재하 시스템을 적용하여 사용하중 상태에서의 말뚝의 수평방향 거동 특성을 평가하였다. 강관합성 말뚝은 기존의 현장타설 말뚝에 비하여 증가된 수평저항 특성을 보여주며, 강관 합성 효과에 의하여 강관 및 철근 콘크리트의 수치합 보다 큰 수평 극한강도를 발휘하는 것을 확인하였다. 또한, 전단 연결재의 사용에 따른 강관-콘크리트의 일체화 거동을 검토하였으며, 고강도 콘크리트의 사용에 따른 강관합성 말뚝의 하중 지지성능을 평가하였다. 이와 함께, 강관합성 말뚝의 강관에 의한 내부 철근망의 대체 가능성 여부를 평가하였다.