• 한국진공학회지
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• 제5권3호
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• pp.229-238
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• 1996

The electromigration phenomena and the characterizations of the conductor lifetime (Time-To-Failure, TTF) in Al-1%Si thin film interconnections under D.C. and Pulsed D.C. conditions were investigated . Meander type test patterns were fabricated with the dimensions of 21080$mu \textrm{m}$ length, 3$\mu\textrm{m}$ width, 0.7$\mu\textrm{m}$ thickness and the 0.1$\mu\textrm{m}$/0.8$\mu\textrm{m}$($SiO_2$/PSG)dielectric overlayer. The current densities of $2 \times10^6 A/\textrm{cm}^2$ and $1 \times10^7 A/\textrm{cm}^2$ were stressed in Al-1%Si thin film interconnection s under a D.C. condition. The peak current densities of $2 \times10^6 A/\textrm{cm}^2$ and $1 \times10^7 A/\textrm{cm}^2$ were also applied under a Pulsed D.C. condition at frequencies of 200KHz, 800KHz, 1MHz, and 4MHz with the duty factor of 0.5. THe time-to-failure under a Pulsed D.C.($TTF_{pulsed D.C}$) was appeared to be larger than that under a D.C. condition. It was found that the TTF under both a D.C. and a Pulsed D.C. condition. It was found that the TTF under both a D.C. and a Pulsed D.C. condition largely depends upon the appiled current densities respectively . This can be explained by a relaxation mechanism view due to a duty cycle under a Pulsed D.C. related to the wave on off. The relaxation phenomena during the pulsed off period result in the decayof excess vacancies generated in the Al-1%Si thin film interconnections because of the electrical and mechanical stress gradient . Hillocks and voids formed by an electromigration were observed by using a SEM (Scanning Electron Microscopy).

• 한국복합재료학회:학술대회논문집
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• 한국복합재료학회 2000년도 추계학술발표대회 논문집
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• pp.102-105
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• 2000

Recently, applications of integrated large composite structures have been attempted to many structures of vehicles. To improve the cost performance and reliability of the integrated composite structures, it is necessary to judge structural integrity of the composite structures. For the judgement, we need fracture simulation techniques for composite structures. Many researches oil the fracture simulation method using FEM have been reported by now. Most of the researches carried out simulations considering only matrix cracking and fiber breaking as fracture modes, and did not consider delamination. Several papers have reported the delamination simulation, but all these reports require three-dimensional elements or quasi three- dimensional elements for FEM analysis. Among fracture mechanisms of composite laminates, delamination is the most important factor because it causes stiffness degradation in composite structures. It is known that onset and propagation of delamination are dominated by the strain energy release rate and interfacial moment. In this study, laminated composite has been described by using 3 dimensional finite elements. Then impact behavior of the laminated composite is simulated using FEM(ABAQUS/Explicit) with progressive failure mechanism. These results are compared with experimental results.

• Geomechanics and Engineering
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• 제11권3호
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• pp.345-359
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• 2016

In order to investigate the influence of the interfacial angel on failure characteristics and mechanism of combined coal-rock mass, 35 uniaxial/biaxial compressive simulation tests with 5 different interfacial angels of combined coal-rock samples were conducted by PFC2D software. The following conclusions are drawn: (1) The compressive strength and cohesion decrease with the increase of interfacial angle, which is defined as the angle between structure plane and the exterior normal of maximum principal plane, while the changes of elastic modulus and internal friction angle are not obvious; (2) The impact energy index $K_E$ decreases with the increase of interfacial angle, and the slip failure of the interface can be predicted based on whether the number of acoustic emission (AE) hits has multiple peaks or not; (3) There are four typical failure patterns for combined coal-rock samples including I (V-shaped shear failure of coal), II (single-fracture shear failure of coal), III (shear failure of rock and coal), and IV (slip rupture of interface); and (4) A positive correlation between interfacial angle and interface effect is shown obviously, and the interfacial angle can be divided into weak-influencing scope ($0-15^{\circ}$), moderate-influencing scope ($15-45^{\circ}$), and strong-influencing scope (> $45^{\circ}$), respectively. However, the confining pressure has a certain constraint effect on the interface effect.

• Structural Engineering and Mechanics
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• 제38권6호
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• pp.803-823
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• 2011

In this paper, the three dimensional Parallel Realistic Failure Process Analysis ($RFPA^{3D}$-Parallel) code based on micromechanical model is employed to investigate the bonding behavior in FRP sheet bonded to concrete in single shear test. In the model, the heterogeneity of brittle disordered material at a meso-scale was taken into consideration in order to realistically demonstrate the mechanical characteristics of FRP-to-concrete. Modified Mohr-coulomb strength criterion with tension cut-off, where a stressed element can damage in shear or in tension, was adopted and a stiffness degradation approach was used to simulate the initiation, propagation and growth of microcracks in the model. In addition, a Master-Slave parallel operation control technique was adopted to implement the parallel computation of a large numerical model. Parallel computational results of debonding of FRP-concrete visually reproduce the spatial and temporal debonding failure progression of microcracks in FRP sheet bonded to concrete, which agrees well with the existing testing results in laboratory. The numerical approach in this study provides a useful tool for enhancing our understanding of cracking and debonding failure process and mechanism of FRP-concrete and our ability to predict mechanical performance and reliability of these FRP sheet bonded to concrete structures.

• Structural Engineering and Mechanics
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• 제82권6호
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• pp.713-724
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• 2022

Effects of coal tensile strength and plow configuration on the coal fragmentation process was modeled by two-dimensional particles flow code (PFC2D). Three tensile strength values, 0.5, 1,5 and 3.5 MPa were considered in this numerical study. The cutters of plow penetrated in the coal for 4 mm at a rate of 0.016 m/s. According to the PFC manual, the local damping factor was 0.7. Three failure mechanism of coal during the fragmentation process by plow were modelled. The coal material beneath the cutters showed the elastic, plastic and fracturing behaviors in this analysis. In all the models, the plastic zone was fractured and some micro-cracks were induced but the elastic zone remained undamaged. It was observed that the tensile strength affected the failure mechanism of coal significantly and as it increased the extent of the fractured zone underneath the plow cutter decreased during the fragmentation process.

• Structural Engineering and Mechanics
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• 제85권5호
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• pp.693-707
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• 2023

In order to deeply reveal the working mechanism of ultra-high performance concrete (UHPC) filled steel tubular columns (UHPCFSTs) under cyclic loading, a three-dimension (3D) macro-mesoscale finite element (FE) model was established considering the randomness of steel fibers and the damage of UHPC. Model correctness and reliability were verified based on the experimental results. Next, the whole failure process of UHPC reinforced with steel fibers, passive confinement effect and internal force distribution laws were comprehensively analyzed and discussed. Finally, a simplified and practical method was proposed for predicting the ultimate bending strengths of UHPCFSTs. It was found that the non-uniform confinement effect of steel tube occurred when the drift ratio exceeded 0.5%, while the confining stress increased then decreased afterwards. There was preferable synergy between the steel tube and UHPC until failure. Compared with experimental results, the ultimate bending strengths of UHPCFSTs were undervalued by the current code provisions such as AISC360-10, EC4 and GB50936 with computed mean values (MVs) of 0.855, 0.880 and 0.836, respectively. The proposed practical method was highly accurate, as evidenced by a mean value of 1.058.

• 한국해양공학회지
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• 제16권4호
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• pp.7-12
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• 2002

This study is aimed to find the scouring mechanism at the toe of rubble mound structures. To investigate the characteristics of scouring in front of the structure, experiments were performed with regular waves in a 2-D flume. The results of this study are as follows. 1) It can be said the characteristics of incident wave causes rolling and sliding of armour block. The difference of wave pressure on the slope, internal flow as well as settlement of armour block due to the weight cause scouring. 2) It is observed that scouring depth at the toe increased when wave height or period increased. The location of ultimate scouring and deposition depth moved seaward when wave period increased. 3) The failure of rubble mound structure was caused by waves or scouring. Failure by erosion increased with high waves and long waves. 4) Using surf-similarity parameter including characteristics of incident waves and structure, scouring and deposition pattern were found and their limit was formulated.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 1994년도 연약지반처리위원회 봄 학술발표회 논문집 연약지반처리
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• pp.3-12
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• 1994

Based on the shear failure mechanism, hydraulic fracturing criteria are extended to three dimensional stress state. According to the situation of the directions of borehole and major principal stress axes, three equations can be derived for three dimensional hydraulic fracturing problems. By comparing these equations, a single criterion is selected for hydraulic fracturing pressure in cohesive soils. The criterion is a function of maximum principal stress, minimum principal stress and soil parameters in UU conditions. The equation indicates that with any increase in maximim principal stress, hydraulic fracturing pressure decreases. In order to prove the integrity of the criteria, laboratory tests are performed on compacted cubical specimens using true a triaxial apparatus. The shape and direction of fractures are determined by injecting colored water after fracture initiation. It is found that the direction of fractures are perpendicular to the o1 plane.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2000년도 추계학술대회논문집
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• pp.737-741
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• 2000

Portable communication devices such as laptop computers suffer impact-induced failure in their usage. Drop/impact performance of these products is one of important concerns of product design. Because of the small size of this kind of electronics products, it is very expensive, time-consuming and difficult to conduct drop tests to directly detect the failure mechanism and identify their drop behaviors. Finite element analysis provides a vital, powerful vehicle to solve the problems. The models are created with HYPERMESH, and the analysis is carried out with LS-DYNA3D. The analysis is focused on HDD impact behavior in acceleration peak values.

• 대한기계학회논문집A
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• 제36권12호
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• pp.1577-1583
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• 2012

횡방향 관통 효율 강화 탄체(PELE)는 기폭장치가 없는 새로운 개념의 발사체이다. PELE 는 배면이 닫혀있는 고밀도 피복과 저밀도 충전재로 구성되어있다. PELE 의 폭발 특성을 연구하기 위해 AUTODYN-3D code 를 이용하여 발사체와 표적체의 모델을 구축하였다. PELE 의 의해 알루미늄-2024 합금 표적체를 천공하는 과정을 시뮬레이션으로 구현하였으며 또한 다양한 내부 충전재에 의해 분산되는 표적체의 파편 특성도 연구하였다. PELE 파편의 유한요소해석은 AUTODYN-3D code 의 추계학적 파괴기준을 사용하여 구현되었다. 내부 충전재의 팽창으로 인해 파편은 속도를 얻으며 횡방향으로 분산된다. 따라서 손상영역의 범위가 증강한다. 관통 및 횡방향 분산 과정에서 생성되는 파편은 내부 충전재의 충격 압력에 따라 그 양과 형태가 다른 것으로 나타났다.