Papers by Keyword: Failure

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Authors: T.V. Zaporozhets, I.V. Sobchenko, Andriy Gusak
Abstract: The 3D Monte Carlo scheme is proposed for simulation of simultaneous self-consistent current redistribution, surface diffusion, drift and void migration and coalescence at the interface metal/dielectric. Results of simulation as well as simple phenomenological model demonstrate a possibility of trapping at and migration along the grainboundaries (GBs). Critical size of “detrapping” after coalescence has been estimated.
Authors: Ying Jun Wu, Ying Bei Yao, Bei Cao
Abstract: A distribution network reconfiguration method with the considerations of time-varying weather conditions is proposed. The aim of distribution network reconfiguration is to minimize the outage risk. The effects of weather condition in evaluating the outage risk are considered. Finally, simulations on the 33-node test system validate the proposed method.
Authors: M.Rizwan Malik, Tie Lin Shi, Zi Rong Tang, Shi Yuan Liu, M. Haseeb
Abstract: Engineering medical applications are enriched by the fabrication potential of the growing technology of Micro-Electro-Mechanical Systems (MEMS). Within this technological expansion, device manufacturing costs, failure and long-term performance reliability are critical issues that have to be resolved using basic probabilistic design methodologies which are yet largely unexploited by industrial and service companies at the mature innovation level. Modeling and testing of high-performance MEMS is a promising route, based upon these methodologies, to enhancing reliability and preventing surface failure. In this paper, we focus on the modeling of the mechanical properties of MEMS, as exemplified by a capacitive accelerometer, using probabilistic techniques. The accuracy of these techniques is also evaluated for the accelerometer with regard to those parameters that affect mainly reliability and failure. The simulated analysis of the mechanical properties is performed with easy-to-use probabilistic software known as “NESSUS”. It is concluded that probabilistic design methodologies are very effective and balanced for making design decisions that can, with both reliability and ease, ensure component or system efficiency.
Authors: Yan Wang, Rui Gao, Hong Wu Zhang, Ling Qiang Yang
Abstract: Based on more than 30 Km field survey, many samples has been got from sluice pier which is collapsed due to sulfate attack. The microstructure of sample and mineral component of separated material was analysis by X-ray diffraction (XRD) and scanning electron microscope-energy dispersion X-ray analysis (SEM-EDAX). The test shows the failure mechanism is contact dissolution associating sulfate attack. The contact dissolution gave chance to sulfate attack. The concrete expand due to sulfate attack accelerate contact dissolution. So concrete can be failure quickly.
Authors: Gang Liu, Fang Li
Abstract: To solve the difficulty of equipment testability verification experiment sample selection, a sample selection method of testability verification experiment was presented. The failure-test dependency matrix and its extended matrix, failure modes function equivalence set and failure modes test equivalence set were analyzed, on the basis, failure modes sample equivalence set was proposed. Meanwhile, importance characteristic was analyzed and maximum entropy was solved, and the sample selection method was presented, its process was obtained. Moreover, the method was comparatively analyzed with actual methods in the experiment. The results show that application the method in paper, can reduce sample number, save test expenses, and meet the test requirement of adequacy, so the method in paper is proved effective and feasible.
Authors: M.S. Niazi, V. Timo Meinders, H.H. Wisselink, C.H.L.J. ten Horn, Gerrit Klaseboer, A.H. van den Boogaard
Abstract: The global fuel crisis and increasing public safety concerns are driving the automotive industry to design high strength and low weight vehicles. The development of Dual Phase (DP) steels has been a big step forward in achieving this goal. DP steels are used in many automotive body-in-white structural components such as A and B pillar reinforcements, longitudinal members and crash structure parts. DP steels are also used in other industrial sectors such as precision tubes, train seats and Liquid Petroleum Gas (LPG) cylinders. Although the ductility of DP steel is higher than classical high strength steels, it is lower than that of classical deep drawing steels it has to replace. The low ductility of DP steels is attributed to damage development. Damage not only weakens the material but also reduces the ductility by formation of meso-cracks due to interacting micro defects. Damage in a material usually refers to presence of micro defects in the material. It is a known fact that plastic deformation induces damage in DP steels. Therefore damage development in these steels have to be included in the simulation of the forming process. In ductile metals, damage leads to crack initiation. A crack is anisotropic which makes damage anisotropic in nature. However, most researchers assume damage to be an isotropic phenomenon. For correct and accurate simulation results, damage shall be considered as anisotropic, especially if the results are used to determine the crack propagation direction. This paper presents an efficient plasticity induced anisotropic damage model to simulate complex failure mechanisms and accurately predict failure in macro-scale sheet forming processes. Anisotropy in damage can be categorized based on the cause which induces the anisotropy, i.e. the loading state and the material microstructure. According to the Load Induced Anisotropic Damage (LIAD) model, if the material is deformed in one direction then damage will be higher in this direction compared to the other two orthogonal directions, irrespective of the microstructure of the material. According to Material Induced Anisotropic Damage (MIAD) model, if there is an anisotropy in shape or distribution of the particles responsible for damage (hard second phase particles, inclusions or impurities) then the material will have different damage characteristics for different orientations in the sheet material. The LIAD part of the damage model is a modification of Lemaitre’s (ML) anisotropic damage model. Modifications are made for damage development under compression state and influence of strain rate on damage, and are presented in this paper. Viscoplastic regularization is used to avoid pathological mesh dependency. The MIAD part of the model is an extension of the LIAD model. Experimental evidence is given of the MIAD phenomenon in DP600 steel. The experimental analysis is carried out using tensile tests, optical strain measurement system (ARAMIS) and scanning electron microscopy. The extension to incorporate MIAD in the ML anisotropic damage model is presented in this paper as well. The paper concludes with a validation of the anisotropic damage model for different applications. The MIAD part of the model is validated by experimental cylindrical cup drawing wheras the LIAD part of the model is validated by the cross die drawing process.
Authors: Xiang Fen Wang, Gui Cui Fu, Cheng Gao, Jin Yong Yao
Abstract: A performance degradation assessment method is proposed based on probability statistic of common turn-on state of power MOSFET circuit in this paper. Threshold shift transient characteristics of MOSFET are studied and the performance degradation behavior of a bridge power MOSFET circuit is simulated. Threshold voltage degradation of a power MOSFET circuit caused by half bridge arm is observed and the probability of a period transient common turn-on state is calculated to evaluate the degree. The result can be used to evaluate the performance degradation trend and can also provide data support for predicting the degradation degree before circuit failed.
Authors: Ai Xin Feng, Yong Kang Zhang, H.K. Xie, Lan Cai
Abstract: The interfacial adhesion between thin film and substrate is often the predominant factor and chief target in determining the performance and reliability of thin film/substrate system. A new technique of laser scratch testing technique has been presented by the authors of the article to characterize the interfacial adhesion between film and substrate, which synthesizes the advantages of traditional scratching technique and laser measure technique. The failure procedure is studied detailedly in the article. On different failure step of the film/substrate system, there are different characteristic s of stress and strain, as well as the characteristic of thermal lensing effect, which can be used as the distinguishing rule of the bonding state of the film/substrate system.
Authors: Yu Yong Jiao, Quan Sheng Liu, Shu Cai Li
Abstract: This paper presents a three-dimensional numerical model for simulation of blocky rock structures based on static relaxation approach. The proposed method utilizes static equilibrium equations to calculate the displacements of blocks, compared to Newton’s second law applied by the traditional DEM. In order to obtain displacements simultaneously, the technique of global stiffness matrix is introduced in to form the global equilibrium equations. Because large displacements come from the accumulation of small displacement increments, an iteration procedure is adopted in the calculation. A C++ program is developed based on the proposed algorithm, and an illustrative example is computed for verification.
Authors: Hao Zhu, Yu Mei Hu, Yi Min Shao
Abstract: Involute helical gears, with advantages of large carrying capacity, smooth transmission and long life, etc., are widely used in automotive, mining, helicopters and other high-speed and heavy-load transmission system. Poor working conditions lead to fatigue crack and other faults of gear key parts such as tooth root and tooth face. To identify the root causes of gear faults, strain monitoring methods are often used to monitor the stress changes of gear key parts so as to work out individualized improvement plants. Good test results can be obtained using real-time wireless data collection technology when the gear is in low-speed and light loading condition, and we can get important data such as speed, torque and dynamic strain on tooth root, etc. However, involute helical gears tend to work in high-speed and heavy harsh conditions, especially when the gear speed reaches a large value (eg. 10000r/min above), gear strain measurement device will suffer big centrifugal force and the impact of shear force which may results partial bonded adhesive failure (cracks, erosion, etc.) and even whole peeling of strain gages, thus inaccurate and even error results will be obtained. Transient finite element analysis method is used in this paper to study the relationship between rotation velocity and test accuracy of strain gauge as well as the process of the bonded adhesive failure, which may provide effective guidance for the fault diagnoses of gear meshing.
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