• 한국음향학회지
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• 제42권5호
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• pp.403-411
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• 2023

탄성 영상과 미세 혈류 도플러 영상과 같은 기능성 초음파 영상은 조직의 기계적, 기능적 정보를 제공함으로써 진단 성능을 향상시킨다. 그러나 기능성 초음파 영상의 구현은 데이터 획득 및 처리 시 대용량 데이터 저장과 같은 한계를 야기한다. 본 논문에서는 효율적인 횡탄성 영상 기법을 위해 데이터 획득 양을 절감시키는 서브 나이퀴스트 접근법을 제안한다. 제안하는 방법은 기존 나이퀴스트 샘플링 속도보다 1/3배 낮은 샘플링 속도로 데이터를 획득하고, 주파수 스펙트럼의 주기성을 이용하여 대역 통과 필터링 기반의 보간을 통해 재구성된 Radio Frequency(RF) 신호를 사용하여 횡파 신호를 추적한다. 이때 RF 신호는 67 % 미만의 비대역폭으로 제한된다. 제안하는 접근법을 검증하기 위해 기존 샘플링 속도로 획득한 횡파 추적 데이터를 이용하여 서브 나이퀴스트 샘플링된 RF 신호를 재현하고, 기존 접근법과 횡파 속도 영상을 재구성한다. 정량적 평가를 위해 재구성한 횡파 속도 영상의 군속도, 대조도 잡음 비, 그리고 구조적 유사성 지수를 비교하였다. 우리는 서브 나이퀴스트 샘플링 기반 횡탄성 영상의 가능성을 정성적, 정량적으로 입증하였고, 향후 실시간 3차원 횡탄성 영상 기술에 유용하게 적용 가능할 것으로 기대된다.

• 대한금속재료학회지
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• 제46권8호
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• pp.524-537
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• 2008

Zr-based amorphous alloy matrix composites reinforced with metallic continuous fibers were fabricated by liquid pressing process, and their fracture properties were investigated by directly observing microfracture process using an in situ loading stage installed inside a scanning electron microscope chamber. About 60 vol.% of metallic fibers were homogeneously distributed inside the amorphous matrix. Apparent fracture toughness of the stainless-steel- and tungsten-fiber-reinforced composites was lower than that of monolithic amorphous alloy, while that of the Ta-fiber-reinforced composite was higher. According to the microfracture observation, shear bands or cracks were initiated at the amorphous matrix, and the propagation of the initiated shear bands or cracks was effectively blocked by fibers, thereby resulting in stable crack growth which could be confirmed by the fracture resistance curve (R-curve) behavior. This increase in fracture resistance with increasing crack length improved fracture properties of the fiber-reinforced composites, and could be explained by mechanisms of formation of multiple shear bands or multiple cracks at the amorphous matrix and blocking of crack or shear band propagation and multiple necking at metallic fibers.

• Geomechanics and Engineering
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• 제38권3호
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• pp.307-317
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• 2024

To get a better understanding of the effect of drying-wetting cycles (DWC) on the mechanical behaviors of silty clay hiving different initial moisture content (IMC), the direct shear tests were performed on sliding band soil taken from a reservoirinduced landslide at the Three Gorges Reservoir area. The results indicated that, as the increasing number of DWC, the shear stress-displacement curves type changed from strain-hardening to strain-softening, and both the soil peak strengths and strength parameters reduced first and then nearly remain unchanged after a certain number of DWC. The effects of DWC on the cohesion were predominated that on the internal friction angle. The IMC of 17% is regarding as the critical moisture content, and the evolution laws of both peak shear strength and strength parameters presented a reversed 'U' type with the rising of the IMC. Based on it, a strength deterioration evolution model incorporating the influence of IMC and DWC was developed to describe the total degradation degree and degradation rate of strength parameters, and the degradation of strength parameters caused by DWC could be counterbalanced to some extent as the soil IMC close to critical moisture content. The microscopic mechanism for the soil strength caused by the IMC and DWC were discussed separately. The research results are of great significance for further understanding the water-weakening mechanicals of the silty clay subjected to the water absorption/desorption.

• Steel and Composite Structures
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• 제19권1호
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• pp.209-221
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• 2015

Results from an experimental study on the seismic response of six composite reinforced concrete column-to-steel beam interior joints are presented. The primary variable investigated is the details in the joint. For the basic specimen, the main subassemblies of the beam and column are both continuous, and the steel beam flanges extended to the joint are partly cut off. Transverse beam, steel band plates, cove plates, X shape reinforcement bars and end plates are used in the other five specimens, respectively. After the joint steel panel yielded, two failure modes were observed during the test: local failure in Specimens 1, 2 and 4, shear failure in Specimens 3, 5 and 6. Specimens 6, 3, 5 and 4 have a better strength and deformation capacity than the other two specimens for the effectiveness of their subassemblies. For Specimens 2 and 4, though the performance of strength degradation and stiffness degradation are not as good as the other four specimens, they all have excellent energy dissipation capacity comparing to the RC joint, or the Steel Reinforced Concrete (SRC) joint. Based on the test result, some suggestions are presented for the design of composite RCS joint.

• 한국지반공학회지:지반
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• 제13권3호
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• pp.21-32
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• 1997

본 연구에서는 암반의 국부파괴 현상을 현실적으로 모형 화하기 위하여 혼합체기법을 적용한 새로운 유한요소를 제안하였다. 이를 위하여 각 유한요소의 적분점에서 재료의 안정성을 검토하고 필요시 국부파괴 요소와 인접한 암반 물성을 이용한 혼합체 물성을 도출하였으며 국부파괴 후의 재료 거동을 추적하였다. 제시한 모형을 사용하면 변형율 연화 모형을 사용하더라도 유한요소망의 객관성을 유지할 수 있으며 국부파괴 이후 재료의 거동을 현실적으로 모형화 할 수 있다. 또한 유한요소 갯수가 비교적 작더라도 수치해석 결과와 실험 결과가 잘 일치하고 있음을 알 수 있다.

• 열처리공학회지
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• 제9권3호
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• pp.212-218
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• 1996

To clarify the influence of precipitation microstructure and inclusion on the monotonic tensile fracture behaviors in 2090 alloy aged at $180^{\circ}C$, the detailed measurement of hardness, tensile strength, elongation and the observation of scanning electron micrography, transmision electron micrography have been carried out. The transgranular shear ductile fracture has been observed in specimen quenched after solution treatment at $500^{\circ}C$ for 45min. While the under-aged specimen was fractured in both transgranular shear ductile and intergranular fracture mode, the fracture mode of peak-aged and over-aged alloy was predominantly intergranular fracture. The fracture behavior of each ageing condition was influenced by the change of precipitation microstructural features. In the case of peak-aged and over-aged alloys, the coarse and heterogeneous slip band caused by both shearable nature of the ${\delta}^{\prime}(Al_3Li)$ precipitates and PFZ along the high angle grain boundary aid the localization of deformation, resulting in low energy intergranular fracture. It was also estimated that the fractured T-type intermetallic phases (inclusion) and the equilibrium ${\delta}$(AlLi) phases which were formed at grain boundaries palyed an important role in promoting intergranular fracture mode.

• 폴리머
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• 제35권3호
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• pp.272-276
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• 2011

선택 반사를 보여주는 콜레스테릭 액정의(cholesteric liquid crystal; CLC) planar 배열이 유도되는 메카니즘을 CLC 셀의 선택 반사율과 FTIR $C{\equiv}N$ 피크 세기를 측정하여 조사하였다. 배향막을 사용한 경우보다는 planar 배열 유도가 완전하지는 않았지만 shear force를 이용하거나 또는 고분자 기판을 연신하여 배향막을 사용하지 않은 상태에서 planar 배열을 유도하였다. CLC의 planar 배열이 유도되는 메카니즘은 기판 표면에 접촉하는 액정분자들이 한 방향으로 늘어서면, 그 액정분자 위에 CLC의 나선 구조들이 기판에 수직으로 형성되며 planar 배열이 유도되는 것이다.

• 한국지진공학회:학술대회논문집
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• 한국지진공학회 2005년도 학술발표회 논문집
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• pp.90-101
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• 2005

For the site characterization at two representative inland areas, Gyeongju and Hongsung, in Korea, in-situ seismic tests containing boring investigations and resonant column tests were performed and site-specific ground response analyses were conducted using equivalent linear as well as nonlinear scheme. The soil deposits in Korea were shallower and stiffer than those in the western US, from which the site classification system and site coefficients in Korea were derived. Most sites were categorized as site classes C and D based on the mean shear wave velocity to 30 m, Vs30 ranging between 250 and 650 m/s. Based on the acceleration response spectra determined from the site-specific analyses, the site coefficients specified in the Korean seismic design guide underestimate the ground motion in the short-period band and overestimate the ground motion in mid-period band. These differences can be explained by the differences in the bedrock depth and the soil stiffness profile between Korea and western US. The site coefficients were re-evaluated and the preliminary site classification system was introduced accounting for the local geologic conditions on the Korean peninsula.

• 한국지진공학회:학술대회논문집
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• 한국지진공학회 2006년도 학술발표회 논문집
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• pp.125-132
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• 2006

To estimate the local site effects at two town fortress areas where stone parapets were collapsed during historical earthquakes, site characteristics were evaluated using borehole drillings and seismic tests and equivalent-linear site response analyses were conducted based on the shear wave velocity (Vs) profiles determined from site investigations. The study sites are categorized as site classes C and B according to the mean Vs to 30 m ranging from 500 to 850 m/s, and their site periods are distributed in short period range of 0.06 to 0.16 sec. For site class C in the study areas, the short-period (0.1-0.5 sec) and mid-period (0.4-2.0 sec) site coefficients, $F_{\alpha}$ and $F_\nu$ specified in the Korean seismic design guide, underestimate the ground motion in short-period band and overestimate the ground motion in mid-period band, respectively, due to the characteristics showing high amplification in short period range, which can result in the collapse of stone parapets having the short natural period.

• Asian-Australasian Journal of Animal Sciences
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• 제20권6호
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• pp.994-1001
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• 2007

Changes in shear force value, transverse sections, myofibrils and intramuscular connective tissue of bovine skeletal muscle exposed to the combination of high-pressure up to 400 MPa and heat (30 and $60^{\circ}C$) were studied. The shear force value decreased by pressure-heat treatment up to 200 MPa at 30 and $60^{\circ}C$, and then slightly increased over 200 MPa at $30^{\circ}C$. Shear force values of treated muscles were lower than those of untreated ones. Gaps between muscle fibers in the untreated muscle were a little clear, and then they became very clear in the treated muscles up to 200 MPa at 30 and $60^{\circ}C$. However, the gaps reduced significantly over 200 MPa at $30^{\circ}C$. The remarkable rupture of I-band and loss of M-line materials progressed in the myofibrils with increasing pressure applied. However, degradation and loss of the Z-line in myofibrils observed in the muscle treated at $60^{\circ}C$ was not apparent in the muscle treated at $30^{\circ}C$. The length of the sarcomere initially contracted by pressure-heat treatment of 100 MPa at $30^{\circ}C$ seemed to have recovered with increase of the pressure up to 400 MPa. In the muscle treated at $60^{\circ}C$, the length of sarcomere gradually decreased with increase of the pressure up to 400 MPa. In the treated muscles, changes in the honeycomb-like structure of endomysium were observed and accelerated with increase of the pressure. A wavy appearance clearly observed at the inside surface of endomysium in the untreated muscles gradually decreased in the treated muscles with increase of the pressure. Tearing of the membrane was observed in the muscles treated over 150 MPa at $30^{\circ}C$, as observed in the sample pressurized at 100 MPa at $60^{\circ}C$. The roughening, disruption and fraying of the membrane were observed over 200 MPa at $60^{\circ}C$. From the results obtained, the combination of high-pressure and heat treatments seems to be effective to tenderize tough meat. The shear force value may have some relationship with deformation of intramuscular connective tissue and myofibrils.