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A Phenomenological discrete Brittle Damage-Mechanics Model for Fatigue of MEMS Devices With Application to LIGA Ni

JOURNAL OF MICROELECTROMECHANICAL SYSTEMS 2009年第1期18卷 119-128页

作者： Slack, Trevor S. Sadeghi, Farshid Peroulis, Dimitrios Purdue Univ Sch Mech Engn W Lafayette IN 47906 USA Purdue Univ Sch Elect & Comp Engn W Lafayette IN 47906 USA

Fatigue initiation and failure of various microelectro-mechanical systems (MEMS) is of significant importance as they gain widespread acceptance in sensors and electronics. This paper presents an approach for utilizing available experimental fatigue data to evaluate the fatigue lives of MEMS components. The approach is based on a phenomenological discrete material representation in which a domain is represented by a collection of rigid elements that interacts via springs along their boundaries. The principles of continuum damage mechanics are used to degrade the spring stiffnesses as brittle damage occurs when the domain is subjected to fatigue loading. The model utilizes experimental stress-life data for LIGA Ni to identify the material properties used in the model. The proposed model captures the statistical distribution of material properties and geometrical randomness of the microstructure commonly observed in a wide variety of MEMS. Consequently, simulations that account for the variability in fatigue life can be readily performed. The model is applied to a dog-bone-shaped specimen to evaluate the influence of material heterogeneity and material flaws on fatigue crack initiation life and scatter. The ability of the model to predict the fatigue life of different types of MEMS devices and loading conditions is also demonstrated by simulating the fatigue stress-life behavior of a MEMS resonator support beam. [2008-0087]

关键词： Damage mechanics discrete-element method fatigue microelectromechanical systems (MEMS)

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Potential application of particle based simulations in reservoir security management

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Journal of Southeast University(English Edition) 2008年第S1期24卷 120-125页

作者： Yang, Ping Tang, Xinming Shi, Shaoyu Wu, Xiaoliang School of Resources and Environmental Science Wuhan University Wuhan 430079 China Chinese Academy of Surveying and Mapping Beijing 100039 China CSIRO Mathematical and Information Sciences Wembley WA 6913 Australia

In order to model the movement progress in case of risks such as dam collapse and coastal inundation, particle-based simulation methods, including the discrete-element method and smoothed particle hydrodynamics, which have specific advantages in modeling complex three-dimensional environmental fluid and particulate flows, are adopted as an effective way to illustrate environmental applications possibly happening in the real world. The theory of these methods and their relative advantages compared with traditional methods are discussed. Examples of 3-D flows on realistic topography including the flooding of a river valley as a result of a dam collapse and coastal inundation by a tsunami are introduced. Issues related to validation and quality data availability are also discussed. The results show that the simulations provide a valuable insight in a given situation for the security management of reservoir dams. Validation can only be performed where both the initial and final states can be very well characterized.

关键词： geophysical simulations particle based simulation methods discrete-element method smoothed particle hydrodynamics dam-breaks

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Semi-automated discrete-element modelling of arch structures incorporating SfM photogrammetry

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PROCEEDINGS OF THE INSTITUTION OF CIVIL ENGINEERS-ENGINEERING HISTORY AND HERITAGE 2023年第1期176卷 3-17页

作者： Kassotakis, Nicko Sarhosis, Vasilis Peppa, Maria-Valasia Mills, Jon P. Imetrum Bristol Avon England Univ Exeter Coll Engn Math & Phys Sci Penryn Cornwall England Univ Leeds Sch Civil Engn Leeds W Yorkshire England Newcastle Univ Sch Engn Newcastle Upon Tyne Tyne & Wear England

This paper presents Image2DEM, a framework for the semi-automated structural analysis of arches. Numerical models of arch specimens were semi-automatically developed from structure-from-motion (SfM) photogrammetry, by employing image-processing techniques, to bypass laborious computer-aided design (Cad)-based processes. Then, the numerical models of the proposed framework were assessed by comparison with a conventional Cad-based framework in terms of (a) geometrical agreement (i.e. joint and block properties) and (b) structural capacity agreement (i.e. stiffness, load multipliers and normal forces between joints at each hinge formation). The results firstly demonstrated SfM photogrammetry as an effective avenue of structural surveying for numerical modelling. Afterwards, the numerical models developed from the proposed and conventional frameworks were demonstrated to have good agreement in terms of geometry. Furthermore, good agreement was also found in the predicted structural capacity, with differences in structural capacity of less than 7%. Although only the potential to capture both the geometry and structural capacity of small-scale arch structures was demonstrated here, this study lays the foundation for automated geometry acquisition for arches for their structural analysis.

关键词： discrete-element method geometric irregularity geometric model geometric uncertainty masonry SfM photogrammetry structural analysis

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discrete element modeling of the mass movement and loose material supplying the gully process of a debris avalanche in the Bayi Gully, Southwest China

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JOURNAL OF ASIAN EARTH SCIENCES 2015年 99卷 95-111页

作者： Zhou, Jia-wen Huang, Kang-xin Shi, Chong Hao, Ming-hui Guo, Chao-xu Sichuan Univ State Key Lab Hydraul & Mt River Engn Chengdu 610065 Peoples R China Sichuan Univ Coll Water Resources & Hydropower Chengdu 610065 Peoples R China Hohai Univ Key Lab Minist Educ Geomechan & Embankment Engn Nanjing 210098 Peoples R China Chinese Acad Sci Key Lab Mt Hazards & Earth Surface Processes Chengdu 610044 Peoples R China

The dynamic process of a debris avalanche in mountainous areas is influenced by the landslide volume, topographical conditions, mass-material composition, mechanical properties and other factors. A good understanding of the mass movement and loose material supplying the gully process is very important for understanding the dynamic properties of debris avalanches. Three-dimensional particle flow code (PFC3D) was used to simulate a debris avalanche in Quaternary deposits at the Bayi Gully, Southwest China. FORTRAN and AutoCAD were used for the secondary development to display the mass movement process and to quantitatively describe the mass movement and loose material supplying the gully process. The simulated results show that after the landslide is initiated, the gravitational potential energy is converted into kinetic energy with a variation velocity for the sliding masses. Two stages exist for the average-movement velocity: the acceleration stage and the slowdown stage, which are influenced by the topographical conditions. For the loose materials supplying the gully process, the cumulative volume of the sliding masses into the gully gradually increases over the time. When the landslide volume is not large enough, the increasing landslide volume does not obviously influence the movement process of the sliding masses. The travel distance and movement velocity increase with the decreasing numerical parameters, and the mass-movement process is finished more quickly using low-value parameters. The deposition area of the sliding masses decreases with the increasing numerical parameters and the corresponding deposition thickness increases. The mass movement of the debris avalanche is not only influenced by the mechanical parameters but is also controlled by the topographical conditions. (C) 2015 Elsevier Ltd. All rights reserved.

关键词： Wenchuan Earthquake Debris avalanche Mass movement Loose material supplying the gully process discrete-element method Dynamic process

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discrete-element numerical modeling of sub-salt structures in the Central Kelasu fold-thrust belt, Kuqa Depression, northwestern China

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JOURNAL OF GEODYNAMICS 2020年 134卷

作者： Zheng, Chunfang Sun, Xiongwei Hou, Guiting Peking Univ Sch Earth & Space Sci Key Lab Orogen Belts & Crustal Evolut Beijing 100871 Peoples R China SINOPEC Petr Explorat & Prod Res Inst Beijing 100083 Peoples R China Tarim Oilfield Inst Explorat & Dev Korla Peoples R China

Knowledge of the deformation history and dominant factors influencing the formation of sub-salt structures is necessary to understand the formation of sub-salt traps. In this study, the discrete-element method (DEM) is used to assess the deformation mechanism of sub-salt structures in the Central Kelasu fold-thrust belt of the Kuqa Depression. A series of DEM models of the Central Kelasu fold-thrust belt are constructed, the final deformation styles of the models are compared with the real structures in order to determine the fitting degree of each models, and the dominant factors influencing the formation of sub-salt structures are determined. A thin salt layer promotes the deformation in the sub-salt sequence. Salt sub-sags, basal uplifts, and pre-existing faults can also promote the deformation in the sub-salt sequence in the northern part of the models. Large deformations accumulate in pre-existing structures in the northern part of the models, and then subsequent deformations are also transmitted to the salt layer and supra-salt sequence;however, these deformations are hardly transmitted to the sub-salt sequence in the middle and southern parts of the models. Among the eight DEM models constructed in our research, the horizontal-stratum model without any initial structures showed the best fit to actual phenomena. Earlier simple structures of Mesozoic layers can be deformed into the current complex structures under compression effects in the late Himalayan period. By comparing with other regions and analyzing the deformation progress of the DEM model, the sub-salt structures in the Kuqa Depression are considered to be fold-accommodation fault structures.

关键词： Kuqa depression Fold-thrust belt Himalaya period Fold-accommodation fault structures discrete-element method

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Fabric evolution of granular soils under multidirectional cyclic loading

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ACTA GEOTECHNICA 2020年第9期15卷 2529-2543页

作者： Wei, Jiangtao Huang, Duruo Wang, Gang Southwest Jiaotong Univ Sch Civil Engn Dept Geotech Engn Chengdu Peoples R China Tsinghua Univ Dept Hydraul Engn Beijing Peoples R China Hong Kong Univ Sci & Technol Dept Civil & Environm Engn Clear Water Bay Hong Kong Peoples R China

Cyclic behavior of granular soils under multidirectional shaking is significantly different from that under unidirectional loading. In this study, a series of undrained simple shear simulations were conducted using a discrete-element method (DEM) under unidirectional and multidirectional loading conditions. Although the excess pore water pressure within a sample cannot reach the initial confining pressure, large shear strains of a similar amplitude still develop in samples under multidirectional loading. The simulation results further illustrate that granular soils have vastly different liquefaction resistance under different loading conditions. Evolution of soil fabric is also quantitatively studied in terms of inter-particle contacts and particle-void distribution. The same "stable state" of soil fabric will be reached under different multidirectional loading paths, which corresponds to that of a post-failure hardening state under unidirectional loading. The DEM study provides a new perspective in terms of microstructure evolution of granular soils under a variety of loading conditions.

关键词： discrete-element method Fabric evolution Liquefaction Multidirectional loading

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Modeling notch-formation mechanisms in the URL mine-by test tunnel using bonded assemblies of circular particles

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International Journal of Rock Mechanics and Mining Sciences 1998年第4-5期35卷 510-511页

作者： Potyondy, D.O. Cundall, P.A. Itasca Consulting Group Inc. 708 South Third Street Minneapolis MN 55415 United States

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Grain Rotation-Based Analysis method for Shear Band

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JOURNAL OF ENGINEERING MECHANICS 2019年第10期145卷

作者： Zhu, Hua-Xiang Yin, Zhen-Yu Hong Kong Polytech Univ Dept Civil & Environm Engn Hung Hom Kowloon Hong Kong Peoples R China Ecole Ponts ParisTech Lab Navier F-77420 Paris France

The grain rotational field is significantly associated with the shear banding process and can be derived easily on the basis of individual grains, which could be an appropriate and convenient quantity in shear band analysis. In this paper, a novel method is proposed for directly analyzing the shear banding process in the granular assembly based on its grain rotational field. Numerical plain strain tests on a dense (S1) and an intermediate dense specimen (S2) are performed using the coupled discrete-element method (DEM) and finite-difference method (FDM). The grain rotational field is statistically characterized by the rotational distribution beta v(omega), a new index defined as the volumetric percentage of grains rotating to a greater degree than the rotation omega, in which the high rotation (HR) section basically indicates the grains inside the shear band. A measurement of beta v(omega)'s uniformity quantifies the degree of strain localization, and S2 is found to perform a more uniform rotational distribution than does S1. Taking the value of omega at which beta v(omega)'s curvature is higher than a threshold as the boundary of the HR section, HR grains are filtered out of the sample, based on which the inclination and thickness of the shear band, as well as two local quantities (average void ratio and coordination number) inside the shear band, are analyzed.

关键词： Granular materials discrete-element method Finite-difference method Shear band Grain rotation Biaxial test

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Hierarchical Modeling method for DEM Simulation and Its Application in Soil-Pile-Cap Interaction and Impact Case

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INTERNATIONAL JOURNAL OF GEOMECHANICS 2019年第7期19卷

作者： Zhao, Honghua Zhang, Jin Qiu, Peng Ji, Shunying Dalian Univ Technol Int Res Ctr Computat Mech Dept Engn Mech State Key Lab Struct Anal Ind Equipment Dalian 116023 Liaoning Peoples R China

By developing a hierarchical modeling method, using discrete element analysis software PFC3D, a discrete-element method (DEM) model can be built and solved more efficiently. In this method, smaller particles are used for the concerned part, medium-sized particles are used in the transition zone, and larger particles are used for the part that is close to the model boundary. By adjusting the micromechanical parameters of the particles through simulated triaxial tests, the macroscopic mechanical properties of the soils constituted by different-sized particles are kept consistent. This method can be applied to study the soil-structure interaction problems with the DEM method by saving computation cost. The proposed method is verified by a two-dimensional (2D) simulation of a laboratory pile load test. This method is then further applied to investigate the pile-soil-cap interaction problem focusing on the pile cap effects. A geohazard-related impact case is also analyzed using this method.

关键词： discrete-element method Pile foundation Hierarchical modeling Pile cap effects Impact

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Analysis on Railway Ballast-glue Micro-characteristics

Analysis on Railway Ballast-glue Micro-characteristics

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2nd International Conference on Applied Mechanics and Materials (ICAMM 2013)

作者： Wang, Zijie Jing, Guoqing Liu, Guixian Beijing Jiao Tong Univ Sch Civil Engn Beijing 100044 Peoples R China

ISBN: (纸本)9783037859841

Ballast-glue is a chemical material severed to adjust ballast stiffness and stabilize railway infrastructure, and its ballast-glue characteristics is less of microscopic research. The ballast-glue cubic sample compressed tests were carried, with curing time alteration, then a 3D discrete-element method (DEM) is used to investigate the glue bonding effects of the tests, where the ballast is made of real size irregular clumps, the ballast-glue is represented by bonds to simulate the tensile and shear strength, results show that ballast curing time is a key factor to govern the ballast-glue integrity and strength, ballast-glue increases the maximum compressed force up to 0.99Mpa, and the DEM bonding function is a potential tool for ballast-glue structure investigation.

关键词： discrete-element method Ballast-glue Compression test

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