• 한국자동차공학회논문집
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• 제4권2호
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• pp.69-79
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• 1996

Dynamic stress intensity factors are derives when the crack is propagating with constant velocity under longitudinal shear stress in orthotropic disk plate. General stress fields of crack tip propagating with constant velocity and least square method are used to obtain the dynamic stress intensity factor. The dynamic stress intensity factors of GLV/GTV=1(=isotropic material or transversely isotropic material) which is obtained in out study nearly coincides with Chiang's results when mode Ⅲ stress is applied to boundary of isotropic disk. The D.S.I.F. of mode Ⅲ stress is greater when α(=angle of crack propagation direction with fiber direction) is 90° than that when α is 0°. In case of a/D(a:crack length, D:disk diameter)<0. 58, the faster crack propagation velocity, the less D.S.I.F. but when crack propagation velocity arrive on ghear stress wave velocity, the D.S.I.F. but when crack propagation velocity arrive on shear stress wave velocity, the D.S.I.F. unexpectedly increases and decreases to zero.

• 한국강구조학회 논문집
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• 제24권2호
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• pp.137-147
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• 2012

본 연구는 L형, I형 실험체에 강판 콘크리트 구조와 철근콘크리트 구조를 적용하여 이질접합부를 만들고, 실험체에 반복하중을 파괴 시 까지 가력하여 면외 휨 내력 및 면내 전단 내력을 평가하고 구조특성을 검토하기 위해서 실험연구를 수행하였다.본 연구에서 면외 휨 성능실험은 접합부에서 정착부 수직철근이 인발되면서 파괴되었고, 면내 전단성능실험은 기초부에서의 휨 균열이 발생하여 파괴되었으며, 이론식과의 비교결과 최대 내력이 실험값/이론값의 결과가 면외 휨성능실험은 96%, 면내 전단성능실험은 82%의 값을 나타내었다.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2005년도 추계 학술발표회 제17권2호
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• pp.57-60
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• 2005

The objective of this paper is to investigate and analyze the behaviour of prestressed I section structural members constructed with ultra high perfomance steel fiber reinforced cementitious concrete (SFR-UHPC). This material is known as reactive powder concrete (RPC) mixed with domestic materials and its compressive strength is over 150MP. The parameters of test specimens were span to depth ratio, prestressing force, prestressing wire placement and web width. Most influential parameter to determine the failure mode between shear and flexural action was proved to be shear span ratio. The characteristics of ultra high-strength concrete is basically brittle, but due to the steel fiber reinforcement behaviour of this structure member became ductile after the peak load. As a result of the test, the stress block of compressive zone should be redefined. The proposed analytical calculation of internal force capacity based by plastic analysis gave a good prediction for the shear and flexural strength of specimens. The numerical verification of the finite element model which constitutive law developed for Mode I fracture of fiber reinforced concrete correctly captured the overall behaviour of the specimens tested.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2008년도 학술대회
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• pp.297-301
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• 2008

The flight vehicles have cavities such as wheel wells and bomb bays. The flow around a cavity is characterized as unsteady flow because of the formation and dissipation of vortices due to the interaction between the freestream shear layer and cavity internal flow, the generation of shock and expansion waves. Resonance phenomena can damage the structures around the cavity and negatively affect aerodynamic performance and stability. The flow field is observed to oscillate in the "shear layer mode" with low aspect ratio. In the present study, numerical analysis was performed for cavity flows by the unsteady compressible three dimensional Reynolds-Averaged Navier-Stokes (RANS) equations with Wilcox's $\kappa$-$\omega$ turbulence model. The flow field is observed to oscillate in the shear layer mode" with large aspect ratio. Based on the SPL(Sound Pressure Level) analysis of the pressure variation at the cavity trailing edge, the dominant frequency was analyzed and compared with the results of Rossiter's formul. The aero-acoustic wave analyzed with CPD(Correlation of Pressure Distribution).

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2008년 추계학술대회논문집
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• pp.297-301
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• 2008

The flight vehicles have cavities such as wheel wells and bomb bays. The flow around a cavity is characterized as unsteady flow because of the formation and dissipation of vortices due to the interaction between the freestream shear layer and cavity internal flow, the generation of shock and expansion waves. Resonance phenomena can damage the structures around the cavity and negatively affect aerodynamic performance and stability. The flow field is observed to oscillate in the "shear layer mode" with low aspect ratio. In the present study, numerical analysis was performed for cavity flows by the unsteady compressible three dimensional Reynolds-Averaged Navier-Stokes (RANS) equations with Wilcox's ${\kappa}-{\varepsilon}$ turbulence model. The flow field is observed to oscillate in the "shear layer mode" with large aspect ratio. Based on the SPL(Sound Pressure Level) analysis of the pressure variation at the cavity trailing edge, the dominant frequency was analyzed and compared with the results of Rossiter's formul. The aero-acoustic wave analyzed with CPD(Correlation of Pressure Distribution).

• Earthquakes and Structures
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• 제14권6호
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• pp.589-598
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• 2018

An attempt is conducted to explore the relationship between the macroscopic global damage and the local damage of shear-type RC frames. A story damage index, which can be expressed as multi-variate functions of modal parameters, is deduced based on the tridiagonal matrix of the shear-type frame. The global damage model is also originated from structural modal parameters. Due to the connection of modal damage indexes, the relationship between the macroscopic global damage and the local story damage is reasonably established. In order to validate the derivation, a case study is carried out via an 8-story shear-type frame. The sensitivities of modal damage indexes to the location and severity of local story damages are studied. The evolution of the global damage is investigated as well. Results show that the global damage is sensitive to the degree of story damage, but it's not sensitive to its location. As the number of the damaged stories increases, more and more modes will be involved. Meanwhile, the global damage evolution curve changes from the concave shape to the S-type and then finally transforms into the convex shape. Through the proposed story damage, modal damage and global damage model, a multi-level damage assessment method is established.

• Structural Engineering and Mechanics
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• 제42권4호
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• pp.551-570
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• 2012

An experimental program was carried out to investigate the influence of fibre reinforcement on the mechanical behaviour of high strength reinforced concrete beams. Eighteen beams, loaded in four-point bending tests, were examined by applying monotonically increasing controlled displacements and recording the response in terms of load-deflection curves up to failure. The major test variables were the volume fraction of steel fibres and the transverse steel amount for two different values of shear span. The contribution of the stirrups to the shear strength was derived from the deformations of their vertical legs, measured by means of strain gauges. The structural response of the tested beams was analyzed to evaluate strength, stiffness, energy absorption capacity and failure mode. The experimental results and observed behaviour are in good agreement with those obtained by other authors, confirming that an adequate amount of steel fibres in the concrete can be an alternative solution for minimizing the density of transverse reinforcement. However, the paper shows that the use of different theoretical or semi-empirical models, available in literature, leads to different predictions of the ultimate load in the case of dominant shear failure mode.

• 전기학회논문지
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• 제60권3호
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• pp.594-599
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• 2011

A SAW strain sensor based on Shear Horizontal wave with an 92 MHz central frequency was developed. It consists of SAW sensor, PCB substrate and bonding material (Loctite 401). External force applied to PCB substrate bonded to a piezoelectric substrate induces strain at the substrate surface, which causes changes in the elastic constant and density of the substrate and hence the propagation velocity of the SAW. The change in the velocity of the SAW result in a frequency shift of the sensor and by measuring a frequency shift, we can extract the strain induced by the external force. The $41^{\circ}$ YX $LiNbO_3$ was used because it has a Leaky shear horizontal(SH) wave propagation mode and a high electromechanical coupling coefficient ($K^2$=17.2%). And to compare with Rayleigh wave mode, $128^{\circ}$ YX $LiNbO_3$ was used. And to make a stable and low insert loss, Split IDT structure was used. The obtained sensitivity and linearity of the SAW strain sensor in the case of Split IDT were measured to be 17.2 kHz / % and 0.99, respectively.

• Journal of Welding and Joining
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• 제31권6호
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• pp.77-83
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• 2013

3D packaging technology using TSV (Through Silicon Via)has been studied in the recent years to achieve higher performance, lower power consumption and smaller package size because electrical line is shorter electrical resistivity than any other packaging technology. To stack TSV chips vertically, reliable and robust bonding technology is required because mechanical stress and thermal stress cause fracture during the bonding process. Cu pillar/solder ${\mu}$-bump bonding process is usually to interconnect TSV chips vertically although it has weak shape to mechanical stress and thermal stress. In this study, we suggest Insert-Bump (ISB) bonding process newly to stack TSV chips. Through experiments, we tried to find optimal bonding conditions such as bonding temperature and bonding pressure. After ISB bonding, we observed microstructure of bump joint by SEM and then evaluated properties of bump joint by die shear test.

• Earthquakes and Structures
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• 제16권5호
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• pp.533-546
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• 2019

This study presents an experimental investigation on six beam-column joint specimens under the lateral cyclic loading. The aim was to explore the effectiveness of steel fiber-reinforced concrete (SFRC) in reducing the transverse shear stirrups in beam-column joints of the reinforced concrete (RC) frames with strong-columns and weak-beams. Two RC and four SFRC specimens with different types of reinforcement detailing and steel fibers of volume fraction in the range of 0.75-1.5% were tested under gradually increasing cyclic displacements. The main parameters investigated were lateral load-resisting capacity, hysteresis response, energy dissipation capacity, stiffness degradation, viscous damping variation, and mode of failure. Test results showed that the diagonally bent configuration of beam longitudinal bars in the beam-column joints resulted in the shear failure at the joint region against the flexural failure of beams having straight bar configurations. However, all SFRC specimens exhibited similar lateral strength, energy dissipation potential and mode of failure even in the absence of transverse steel in the beam-column joints. Finally, a methodology has been proposed to compute the shear strength of SFRC beam-column joints under the lateral loading condition.