• Title, Summary, Keyword: failure mechanism

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Study of Life Prediction and Failure Mechanisms of Cramic Heater for Home Appliance (가전 제품용 세라믹 히터의 수명 및 고장 원인에 대한 연구)

  • Choi, Hyoungseuk
    • Journal of Applied Reliability
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    • v.17 no.4
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    • pp.355-361
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    • 2017
  • Purpose: The purpose of this research is to establish the life test method for ceramic heater and identify the failure mechanisms. Methods: We do accelerated life test in the condition of thermal shock and failure analysis for failed samples. Conclusion: The main failure mechanisms of ceramic heater are identified as overstress failure mechanisms as results of failure analysis and the shape parameters of weibull distribution by accelerated life test are identified as 0.8, 1.2 and 0.4 each at $400^{\circ}C$, $600^{\circ}C$ and $900^{\circ}C$. At $900^{\circ}C$, the shape parameter 0.4 means that It is exactly initial failure caused that the stress exceeds the strength of ceramic heater highly and the shape parameters 0.8, 1.2 at $400^{\circ}C$, $600^{\circ}C$ means that the shape parameters are around 1.0 so that the main failure mechanism is overstress failure which is same result as failure analysis. It means that the appropriate life test method for ceramic heater is reliability qualification test method rather than accelerated life test.

Finite Element Analysis of the Direct Shear Test (직접 전단시험의 유한 요소 해석)

  • 이장덕
    • Geotechnical Engineering
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    • v.12 no.6
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    • pp.21-36
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    • 1996
  • The stress transfer mechanism between soil and grid reinforcements involves two basic mechanism : frictional soil resistance and passive soil resistance. However the mechanism of the passive soil resistance is very complex to understand. To study the failure mechanism of ribbed reinforcement, the direct shear tests which are dominated by passive soil resistance are analyzed by using the finite element method. The finite element method is used to examine the effects of ribs on this passive soil resistance development and the met hanism of failure. The calculated behavior of the ribbed reinforcement is compared with the measured behavi or. Comparisons between the measured and the simulated strain pat terns, failure modes and load displacement relationship are presented. The behavior of the ribbed reinforcements in a cohesive soil is predicted on the basis of a good agreement between the measured and the Predicted behavior of the Ottawa sand.

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Failure Mechanism of NATM tunneling using Computational Methods and Geology Investigation (수치해석수법과 지질공학적 분석을 통한 NATM터널의 붕괴메커니즘에 관한 연구)

  • Lee, Jae-Ho;Kim, Young-Su;Choi, Hea-Jun;Jeong, Yun-Young;Jin, Guang-Ri;Rim, Hong-Rae
    • Proceedings of the Korean Geotechical Society Conference
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    • pp.742-753
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    • 2008
  • Currently an increasing number of urban tunnels with small overburden are excavated according to the principle of the New Austrian Tunneling Method (NATM). Therefore, a possibility of a tunnel collapse during excavation is getting higher in a proportionate manner. This paper will analyze causes the failure mechanism of a shallow NATM tunnel for different geological conditions, ground-water and invert solutions by investigation typical collapse site during tunnel construction. In this paper, this analysis performed two phase, firstly, the field investigation considering displacement measurement, ground-water level, geological characteristic, secondly, the numerical simulation considering the exist of invert construction and the effect of ground-water. It has been found that environmental factors such as state of underground water or construction sequences could influence failure mechanism of a shallow tunnel.

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Energy-based design base shear for RC frames considering global failure mechanism and reduced hysteretic behavior

  • Merter, Onur;Ucar, Taner
    • Structural Engineering and Mechanics
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    • v.63 no.1
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    • pp.23-35
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    • 2017
  • A nonlinear static procedure considering work-energy principle and global failure mechanism to estimate base shears of reinforced concrete (RC) frame-type structures is presented. The relative energy equation comprising of elastic vibrational energy, plastic strain energy and seismic input energy is obtained. The input energy is modified with a factor depending on damping ratio and ductility, and the energy that contributes to damage is obtained. The plastic energy is decreased with a factor to consider the reduced hysteretic behavior of RC members. Given the pre-selected failure mechanism, the modified energy balance equality is written using various approximations for modification factors of input energy and plastic energy in scientific literature. External work done by the design lateral forces distributed to story levels in accordance with Turkish Seismic Design Code is calculated considering the target plastic drift. Equating the plastic energy obtained from energy balance to external work done by the equivalent inertia forces considering, a total of 16 energy-based base shears for each frame are derived considering different combinations of modification factors. Ductility related parameters of modification factors are determined from pushover analysis. Relative input energy of multi degree of freedom (MDOF) system is approximated by using the modal-energy-decomposition approach. Energy-based design base shears are compared with those obtained from nonlinear time history (NLTH) analysis using recorded accelerograms. It is found that some of the energy-based base shears are in reasonable agreement with the mean base shear obtained from NLTH analysis.

Premature failure Criteria of RC Beams Strengthened with FRP II (FRP보강 RC보의 조기파괴기준 II)

  • Kim, Tae-Woo
    • Proceedings of the Korea Concrete Institute Conference
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    • pp.141-144
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    • 2005
  • Rip-off failure and Debonding failure were commonly reported premature failure modes. The main reasons of premature failure in RC beams bonded with FRP were strengthening length and the reinforcement ratio. in this study, On the basis of premature failure mechanism in RC beams bonded with FRP, premature failure criteria were proposed. Also It was verified that Rip-off failure and Debonding failure occured according to premature failure criteria

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No Collapse Design for Typical Bridges (일반교량의 붕괴방지설계)

  • Kook, Seung-Kyu
    • Journal of the Computational Structural Engineering Institute of Korea
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    • v.27 no.3
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    • pp.163-172
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    • 2014
  • The purpose of earthquake resistant design for typical bridges is the No Collapse Design and the Earthquake Resistant Design Part of Roadway Bridge Design Code provides a design process to construct the Ductile Failure Mechanism for the bridge structure. However, if it is not practical to provide the Ductile Failure Mechanism due to structure types or site conditions, the Brittle Failure Mechanism is an alternative way to get the No Collapse Design. As well as the existing design process constructing the Ductile Failure Mechanism, the Earthquake Resistant Design Part provides a ductility-based design process as an appendix, which is prepared for bridges with reinforced concrete piers. According to the new design process, designer determines a required response modification factor for substructure and transverse reinforcement for confinement therefrom. In this study, a typical bridge with steel bearing connections and reinforced concrete piers is selected for which the existing as well as the ductility-based design processes are applied and different results from the two design processes are identified. Based on the results, an earthquake resistant design procedure is proposed in which designers should consider the two design processes.

Computational methodology to determine the strength of reinforced concrete joint

  • Sasmal, Saptarshi;Vishnu Pradeesh, L.;Devi, A. Kanchana;Ramanjaneyulu, K.
    • Advances in Computational Design
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    • v.1 no.1
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    • pp.61-77
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    • 2016
  • Seismic performance of structures depends on the force flow mechanism inside the structure. Discontinuity regions, like beam-column joints, are often affected during earthquake event due to the complex and discontinuous load paths. The evaluation of shear strength and identification of failure mode of the joint region are helpful to (i) define the strength hierarchy of the beam-column sub-assemblage, (ii) quantify the influence of different parameters on the behaviour of beam-column joint and, (iii) develop suitable and adequate strengthening scheme for the joints, if required, to obtain the desired strength hierarchy. In view of this, it is very important to estimate the joint shear strength and identify the failure modes of the joint region as it is the most critical part in any beam-column sub-assemblage. One of the most effective models is softened strut and tie model which was developed by incorporating force equilibrium, strain compatibility and constitutive laws of cracked reinforced concrete. In this study, softened strut and tie model, which incorporates force equilibrium equations, compatibility conditions and material constitutive relation of the cracked concrete, are used to simulate the shear strength behaviour and to identify failure mechanisms of the beam-column joints. The observations of the present study will be helpful to arrive at the design strategy of the joints to ensure the desired failure mechanism and strength hierarchy to achieve sustainability of structural systems under seismic loading.

Failure Mechanism Analysis of SAW Device under RF High Power Stress (RF 고전력 스트레스에 의한 SAW Device의 고장메카니즘 분석)

  • Kim, Young-Goo;Kim, Tae-Hong
    • The Journal of The Institute of Internet, Broadcasting and Communication
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    • v.14 no.5
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    • pp.215-221
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    • 2014
  • In this paper, the improved power durability test system and method for an reliability analysis of SAW device is proposed and the failure mechanism through failure analysis is analyzed. As a result of the failure analysis using microscope, SEM and EDX, the failure mechanism of the SAW device is electromigration due to joule heating under high current density and high temperature condition. The electromigration makes voids and hillocks in the IDT electrode and the voids and hillocks can lead to short circuit and open circuit faults, respectively, increasing the insertion loss of an SAW filter. The accelerated life testing of the SAW filter for 450MHz CDMA application using the proposed power durability test system and method is carried out. $B_{10}$ lifetime of the SAW filter using Eyring model and Weibull distribution is estimated as about 98,500 hours.

A Study on Reliability Compliance Test based on Thermal Fatigue Accelerated Test for CVVL BLDC Motor (CVVL BLDC 모터의 열피로 가속시험을 통한 수명보증시험 설계)

  • Lee, San-Hoon;Park, Sang-Wook;Kim, Min-Geiun;Seon, Han-Geol;Hong, Sung Ryeul;Han, Man-Seung
    • Journal of Applied Reliability
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    • v.15 no.4
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    • pp.241-247
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    • 2015
  • Purpose : The demand for higher fuel economy vehicles has helped develop fuel-efficient vehicles such as a CVVL called continuous variable valve lift. Existing CVVL has been applying DC type motor to control intake valve, but recently some car parts manufacturers have been developing a BLDC type CVVL motor for improvements of endurance performance. The purpose of this study is to find the potential failure mechanism of the CVVL BLDC moto in early stage of development based on the design properties and design the accelerated life test model. Methods : CVVL BLDC is consist of brushs, coil, magnetic, PCB, bearing and so on. Each component has a latent failure mechanism caused by temperature, humidity, vibration. By analysis result of the failure mechanism, thermal fatigue is the most important factor of a durability of CVVL BLDC motor. So, we designed a new accelerated life test model for guarantee of the CVVL BLDC motor. Results : A crack occurred on via hole in test using the conditions we designed, so we did change the design to avoid this failure. The via hole dimension is changed a little larger, as a result we achieve improvements in reliability of the CVVL BLDC motor. By applying various kinds and extreme level of stresses, we can find the operating limits of products. Conclusion : In thesis, We analyzed the failure mechanism of CVVL BLDC and designed an accelerated life test method to give a guarantee for reliability. Based on the test results, we could improve the reliability of developments by change of design.