• 한국해양공학회:학술대회논문집
• /
• 한국해양공학회 2002년도 춘계학술대회 논문집
• /
• pp.134-139
• /
• 2002

Fracture behaviors of pipes with local wall thinning are very important for the integrity of nuclear power plant. However, effects of local wall thinning on strength and fracture behaviors of piping system were not well studied. Acoustic emission(AE) has been widely used in various fields because of its extreme sensitivity, dynamic detection ability and location of growing defects. In this study, we investigated failure modes of locally wall thinned pipes and AE signals by bending test. From test results, we could be divided four types of failure modes of ovalization, crack initiation after ovalization, local buckling and crack initiation after local buckling. And fracture behaviors such as elastic region, yielding range, plastic deformation range and crack progress could be evaluated by AE counts, accumulative counts and time-frequency analysis during bending test. It is expected to be basic data that can protect a risk according to local wall thinning of pipes, as a real time test of AE.

• 터널과지하공간
• /
• 제14권4호
• /
• pp.295-303
• /
• 2004

연약층과 견고한 암반층이 습곡형태로 혼재된 지질조건의 지하 심부 채굴 현장을 대상으로, 심부 급경사 연약층의 단계적 굴착 진행에 따른 갱도 및 주변 암반의 거동 양상을 전산해석과 현장계측을 통하여 비교 분석하였다. 전산해석에서는 Hoek ＆ Brown의 경험적 파괴기준 및 변형률연화모델을 적용한 탄소성 해석 기법을 이용하였다. 현장계측에서는 유압캡슐, 지중변위계, 내공변위계를 갱도 및 주변 암반에 설치하여 응력과 변위를 계측하였다. 경험적 파괴조건 및 변형률연화모델을 이용한 탄소성 해석은, 현장 지질조건 및 채굴과정의 복잡함에도 불구하고 현장계측결과와 유사한 양상을 보여주어 타당성을 검증할 수 있었다. 이러한 전산해석 및 현장계측의 비교를 통해 지하 굴착 갱도의 변형 거동 과정을 예측하고 이후의 굴착 및 지보보강 설계의 지침을 제공할 수 있을 것이다.

• Nuclear Engineering and Technology
• /
• 제53권4호
• /
• pp.1236-1249
• /
• 2021

Although there are still controversial opinions and uncertainty on application of SiC_f/SiC composite cladding as next-generation cladding material for its great oxidation resistance in high temperature steam environment and other outstanding advantages, it cannot deny that SiC_f/SiC cladding is a potential accident tolerant fuel (ATF) cladding with high research priority and still in the engineering design stage for now. However, considering its disadvantages, such as low irradiated thermal conductivity, ductility that barely not exist, further evaluations of its in-pile behaviors are still necessary. Based on the self-developed code we recently updated, relevant thermohydraulic and mechanical models in FROBA-ATF were applied to simulate the cladding behaviors under normal and accident conditions in this paper. Even through steady-state performance analysis revealed that this kind of cladding material could greatly reduce the oxidation thickness, the thermal performance of UO₂-SiC was poor due to its low inpile thermal conductivity and creep rate. Besides, the risk of failure exists when reactor power decreased. With geometry optimization and dopant addition in pellets, the steady-state performance of UO₂-SiC was enhanced and the failure risk was reduced. The thermal and mechanical performance of the improved UO₂-SiC was further evaluated under Loss of coolant accident (LOCA) and Reactivity Initiated Accident (RIA) conditions. Transient results showed that the optimized ATF had better thermal performance, lower cladding hoop stress, and could provide more coping time under accident conditions.

• 한국지진공학회논문집
• /
• 제6권5호
• /
• pp.19-27
• /
• 2002

본 연구에서는 지진하중을 받는 교량구조물의 동적거동을 보다 실제적으로 예측하기 위하여 받침의 손상여부는 물론 다양한 영향요소를 고려할 수 있는 이상화된 다자유도 교량해석모형을 개발하였으며, 이를 바탕으로 받침의 손상이 교량구조물의 지진응답에 미치는 영향을 분석하였다. 받침의 손상은 마찰요소를 이용한 단순화된 모형으로 고려하였으며, 발생가능한 받침의 손상조건에 따른 영향을 분석하기 위하여 다양한 마찰계수의 적용에 따른 교량구조물의 응답분포특성을 구하였다. 모의분석 결과로부터 받침손상의 고려여부 및 적용된 마찰계수에 따라 최대응답의 크기 및 발생위치가 서로 다르게 평가되었으며, 특히 교량구조물에서 낙교의 발생가능성이 큰 위치에서의 최대상대거리는 받침의 손상여부에 따라 상당한 영을 받는 것으로 나타났다. 그러나 최대응답의 증가량은 크지 않은 것으로 분석되었다. 그러므로 다경간 단순형 교량구조물에 있어서 받침의 손상에 따른 낙교의 발생가능성을 감소시키기 위한 부가적인 받침보강은 필요시 선택적으로 적용될 수 있을 것으로 판단된다.

• 한국지반공학회논문집
• /
• 제23권3호
• /
• pp.41-50
• /
• 2007

본 논문에서는 실트 함유율이 높은 모래에 대한 정규압밀 등방배수 및 비배수 삼축압축시험(NCIU 및 NCID) 결과를 나타내었다. 유효구속응력 $100\sim400kpa$하에서 실트 함유율이 63%인 낙동강 모래 시료를 사용하여 실험을 실시하였다. 실험결과, 모래질 실트는 초기에는 압축이 되지만 전체적인 응력-변형률 곡선에서 최종적으로 체적팽창반응을 보였다. 모래질 실트의 거동은 낮은 소성 특성으로 인하여 점토와 모래보다 비하여 그 특성을 묘사하기가 어려웠다. 특히, 시료는 파괴 후 전단과정에서 팽창현상을 보였다. 모래질 실트의 전단거동과 전단강도정수는 응력-변형률 거동과 Mohr-Coulomb 파괴규준에 의하여 결정되는데, 전단거동은 파괴 후 변형률 연화 경향과 같이 체적변화가 증가하는 것으로 관찰되었다. 본 논문에서 모래질 실트의 전단과정 동안에 발생되는 팽창거동은 모래 함유율 뿐만 아니라 저점착력을 가진 세립자의 함유율에 의해서도 달라졌다.

• 한국소성가공학회:학술대회논문집
• /
• 한국소성가공학회 2007년도 춘계학술대회 논문집
• /
• pp.258-261
• /
• 2007

Failure phenomena in uni-axial tension test were experimentally and numerically investigated for AA6111-T4, AA5083-H18 and DP-Steel, which were friction-stir welded with the same and different thicknesses. Forming limit diagram(FLD) was measured using hemispherical dome stretching tests for base materials and also predicted by Hill's bifurcation and M-K theories for welded areas. Finite element simulations well predicted hardening behaviors, failure locations as well as failure patterns for the uni-axial tension tests especially utilizing very fine meshes and FLD along with stress softening.

• 한국구조물진단유지관리공학회 논문집
• /
• 제10권5호
• /
• pp.121-129
• /
• 2006

본 연구는 균열이 발생한 R/C보를 탄소섬유시트(Carbon fiber sheet)로 보수했을 경우 시트의 박락과 균열의 확대 및 성장 메커니즘을 조사한 것이다. 실험변수는 하중형식, 재하속도, 사전균열 유무 등이다. 실험에서, 보의 파괴는 전단력 급변에 의한 재하점 직하부의 단차박리의 발전과 전파로 시작됨이 확인되었지만, 파괴기구는 하중형식, 재하속도, 사전균열 유무 등에 영향을 받지 않았다. 특히, 사전균열을 갖는 보의 경우, 균열의 성장은 재하점 직하의 특정한 균열에 집중되고, 이 균열의 확장에 의한 탈착이 보의 파괴를 이끌었다.

• Computers and Concrete
• /
• 제26권3호
• /
• pp.239-255
• /
• 2020

Experimental and discrete element method were used to investigate the effects of joint number and its angularities on the shear behaviour of joint's bridge area. A new shear test condition was used to model the gypsum cracks under shear loading. Gypsum samples with dimension of 120 mm×100 mm×50 mm were prepared. the length of joints was 2cm. in experimental tests, the joint number is 1, 2 and 3 and its angularities change from 0° to 90° with increment of 45°. Assuming a plane strain condition, special rectangular models are prepared with dimension of 120 mm×100 mm. similar to joints configuration in experimental test, 9 models with different joint number and joint angularities were prepared. This testing show that the failure process is mostly governed by the joint number and joint angularities. The shear strengths of the specimens are related to the fracture pattern and failure mechanism of the discontinuities. The shear behaviour of discontinuities is related to the number of induced tensile cracks which are increased by increasing the rock bridge length. The strength of samples decreases by increasing the joint number and joint angularities. Failure pattern and failure strength are similar in both of the experimental test and numerical simulation.

• Wind and Structures
• /
• 제26권1호
• /
• pp.45-56
• /
• 2018

Wind damage of urban trees arises to be a serious issue especially in the typhoon-prone areas. As a family of tree species widely-planted in Southeast China, the structural behaviors of Plane tree is investigated. In order to accommodate the complexities of tree morphology, a fractal theory based finite element modeling method is proposed. On-site measurement of Plane trees is performed for physical definition of structural parameters. It is revealed that modal frequencies of Plane trees distribute in a manner of grouped dense-frequencies; bending is the main mode of structural failure. In conjunction with the probability density evolution method, the fragility assessment of urban trees subjected to wind excitations is then proceeded. Numerical results indicate that small-size segments such as secondary branches feature a relatively higher failure risk in a low wind level, and a relatively lower failure risk in a high wind level owing to windward shrinks. Besides, the trunk of Plane tree is the segment most likely to be damaged than other segments in case of high winds. The failure position tends to occur at the connection between trunk and primary branches, where the logical protections and reinforcement measures can be implemented for mitigating the wind damage.

• 한국정밀공학회:학술대회논문집
• /
• 한국정밀공학회 2000년도 추계학술대회 논문집
• /
• pp.527-532
• /
• 2000

The armor composite material targets such as aramid FRMLs with different type and ply number of face material and different type of back-up material, were studied to determine ballistic impact resistance and dynamic failure behavior during ballistic impact. Ballistic impact resistance is determined by $\textrm{V}_{50}$ ballistic limit, a statical velocity with 50% probability for complete penetration, test method. Also dynamic failure behaviors are respectfully observed that result from $\textrm{V}_{50}$ tests. $\textrm{V}_{50}$ tests with $0^{\circ}$ obliquity at room temperature were conducted with projectiles that were able to achieve near or complete penetration during high velocity impact tests. As a result, ballistic impact resistance of anodized Al 5052-H34 alloy(2 ply) is better than that of anodized Al 5052-H34 alloy(1 ply), but Titanium alloy showed the similar ballistic impact resistance. In the face material, ballistic impact resistance of titanium alloy is better than that of anodized Al 5052-H34 alloy. In the back-up material, ballistic impact resistance of T750 type aramid fiber is better than that of CT709 type aramid fiber.