65 research outputs found
Simulation of uniaxial tensile behavior of quasi-brittle materials using softening contact models in DEM
No full textInternational audienceThis study proposes new contact models to be incorporated into discrete element method (DEM) to more accurately simulate the tensile softening in quasi-brittle materials, such as plain concrete and masonry with emphasis on fracture mechanism and post-peak response. For this purpose, a plain concrete specimen (double notched) and stack bonded masonry prism under direct tensile test are modeled. Furthermore, mixed mode crack propagation is investigated in concrete and brickwork assemblages. Two modeling approaches are proposed, the simplified and detailed meso modeling, both based on DEM. In the simplified meso-model, a smooth contact surface is considered between two separate blocks, whereas the internal structure of the material is explicitly represented as a tessellation into random polyhe-dral blocks in the detailed meso-model. Furthermore, recently developed tensile softening contact constitu-tive models implemented into a commercial discrete element code (3DEC) are used to simulate the softening behavior of concrete and masonry. As an important novel contribution, it is indicated that the proposed R. Quey Mines Saint-Etienne, CNRS, Saint-Étienne, France computational models successfully capture the complete (pre-and post-peak) material behavior and realistically replicate the cracking mechanism. Additionally , a sensitivity analysis demonstrates the influence of the various micro-contact parameters on the overall response of the examined materials
[[alternative]]A Maintaining Strategy on the Quality of Item Bank in Computerized Adaptive Testing
No full text[[abstract]]The purpose of this study is to apply item response theory(IRT), computerized adaptive testing (CAT) theory and the techniques of quality management to develop aprocedure and proffer some useful strategies to screen useless items and maintain the IRT-based item banks. The results of the research will provide a planning ,designing ,developing, implementing and maintaining guideline of dynamic item bankfor computerized adaptive testing and even networking adaptive testing. The methodology of the study consists of three stages. First, according to the result of paper review plan and design the procedure of maintaining IRT-based item banks.Base on the technology of quality management, adopting three conditions (Urry's,Baker's and MicroCAT's suggestions) and three degrees (loose ,medium and strict) ofquality control to elaborate nine strategies. Second, the quality evaluating system was designed and implemented. Then, some simulation experimentations were proceeded.At the last, evaluate the effect of the procedure and nine quality control strategies. According to the analytical results of the simulation experimentations, Baker-loosestrategy is better than the others in screening the items with lower item informationfrom IRT-Based item banks. When adopting Urry-strict , Baker-strict and MicroCAT-strictstrategies to maintain item banks, some useful items misjudged. Because the criterionis too strict. Similarly, the similar result appears when the medium strategies were applied.Moreover, to modify the upper bound of a-parameter from 2.0 to 3.0 in Baker's suggestionsand the lower bound of c-parameter form 0.05 to 0 in MicroCAT's suggestions, it will makebetter efficiency in maintaining work of real item banks. Adjusting the weight of a-parameterin the item-defect formula will increase the utility of quality control strategy in virtual item banks. The research proposes a new maintaining procedure and some simple , economic , and useful quality control strategies. The results of the research present the availability of quality control strategies in IRT-Based item banks. In other words, the qualitycontrol strategy could screen useless items , increase the usage of space , upraise theefficiency of item selections and keep the quality of IRT-Based item banks. It will bevery useful for computerized adaptive testing and even networking adaptive testing.
[[alternative]]CASE Toolkit for Computer Software and Hardware Specifications
No full text[[abstract]]電腦科技產品的種類繁多且技術日新月異，再加上軟硬體規格資訊的
複雜與知識的獲取不易，使得規格選擇(selection)與設定(
constitution)的工作變得繁瑣費時且難以完成。為解決前述問題及提高
知識的再利用(reuse)，本研究先蒐集並編纂整理(codify)現行電腦軟硬
體設備的知識與資訊；繼而提出現代電腦設備功能分類模式與規格描述方
式的骨架(framework)；然後再為傳播及貢獻再利用知識而製作通則性的
規格表參考規範；最後，以自動化知識及軟體工程手冊的設計理念和目標
，實作一電腦輔助軟體工程(Computer Aided Software Engineering,
CASE)工具，稱為電腦軟硬體規格選擇與文件編輯工具(Software/
HardWare Specifications Selector & Editor toolkit,簡稱 SHWSSE工
具)，用以幫助系統發展者利用自動化工具及既有所編纂的知識資訊，迅
速完成軟硬體規格的選擇與設定，以及規格文件製作的工作。
Owing to the variety and complexity of computer products and
state of the art, the selection and constitution of software/
hardware environment for information system has become more and
more time-consuming and unconquerable. This study is conducted
in an effort to solve the problems mentioned by enhancing and
automating the usage of the knowledge. We collect and codify
knowledge and information of the current computer products
first; then propose a framework for computer specifications
description; thirdly, we create reusable table paradigms for
describing each computer component's specification; finally, we
develop a Computer Aided Software Engineering (CASE) toolkit,
called Software/HardWare Specifications Selector & Editor
(SHWSSE), to automate the using of existing knowledge for
specifying and constituting software/hardware environments in
systems development.
Owing to the variety and complexity of computer products and
PATRICE ET MARIO CHANTENT..... / PATRICE ET MARIO, avec accompagnement d'orchestre
No full textComprend : VIENS (When) / A. SALVET, G. BERTRET, P. EVANS, J. REARDON - JE T'AIMERAI, T'AIMERAI / G. COULANGES, PEDRO LIBERAL - COME PRIMA (tu me donnes) / J. LARUE, M. PANZERI, S. TACCANI ; DI PAOLA - GARDE CA POUR TOI / M. VIDALIN, P. VANCE, LEE POCKRISS - TU M'ETAIS DESTINEE / J. PLANTE, P. ANKA - TROIS JOLIES FILLES / G. QUEY, R. DENONCIN, J.P. MOTTIER - CARNAVAL DES ROSES / P. DELANOE, R. DESBOIS, PIA DEL MORO - JE PARS (Alone) / F. BONIFAY, MORTON CRAFT - LA FETE DES PECHEURS / M. RIVGAUCHE, LAVAGNINO - PAN AMORE E FANTASIA (en italien) / NISA, CINIBnF-Partenariats, Collection sonore - BelieveContient une table des matière
A resource-based analysis of organizational turnaround: The contingency role of organizational life stages
No full textAbstractDrawing on the resource-based view (RBV) of the firm, this study proposes two levels of resource action: shedding resources and adding resources as the main two turnaround approaches. Since firms differ in the way they manage their resources over stages of organizational development, this study further analyzes the link between the RBV and organizational life-cycle model to investigate the contingency role of life stages in the turnaround context. The study sample consists of 72 Taiwan firms had ever experienced a successful turnaround. The results indicate that cost-cutting and investment in training and R&D, which represent respectively a shedding and an adding resource action, enable firms to turn around their deteriorating performance. The results also show that R&D investment is more effective for early-stage firms, while cost-cutting is more useful to firms in the late-stage.</jats:p
Microtexture tracking of sub-boundary evolution during hot deformation of aluminium
No full textInternational audienceThe microstructure and microtexture evolution of the same 3 grains around a triple point has been followed during hot plane strain compression by electron backscattered diffraction (EBSD) up to a strain of 1.2. A large grained model alloy of Al-0.1 wt% Mn was deformed in the form of a split sample in channel die compression at 400 degrees C by 3 repeated cycles, each involving EBSD grain orientation mapping, hot deformation and quenching. Detailed substructure maps of 3 grains on an inner surface demonstrates that their dislocation substructure develops up to a strain of about 0.5 then stabilises at approximately constant size, disorientation distribution and boundary alignment. The results are consistent with the repolygonisation model of steady state sub-boundary creation and dissolution during hot deformation
A numerical modelling of 3D polycrystal-to-polycrystal diffusive phase transformations involving crystal plasticity
No full textInternational audienceA FE modelling of the elastoplastic interactions occurring within a 3D polycrystal subjected to diffusive phase transformation is proposed. The parent polycrystal is represented by a Voronoi tessellation, where grains differ in shape, size and crystallographic orientation. Grains of the new phase nucleate at favourable sites of the parent polycrystal then grow isotropically, following specific kinetics. This process can result in various product polycrystal morphologies where grains are distinguished by their morphologies and their crystallographic orientations, and have crystalline properties different from those of the parent grains. Application is performed on the austenite-to-ferrite transformation of a low carbon steel, by analysing different basic cases of transformation history with different constitutive modellings. Microplasticity and its related internal stresses are shown to develop during the phase transformations and to affect significantly the elastoplasticity of the product medium
3D random Voronoi grain-based models for simulation of brittle rock damage and fabric-guided micro-fracturing
No full textAbstractA grain-based distinct element model featuring three-dimensional (3D) Voronoi tessellations (random poly-crystals) is proposed for simulation of crack damage development in brittle rocks. The grain boundaries in poly-crystal structure produced by Voronoi tessellations can represent flaws in intact rock and allow for numerical replication of crack damage progression through initiation and propagation of micro-fractures along grain boundaries. The Voronoi modelling scheme has been used widely in the past for brittle fracture simulation of rock materials. However the difficulty of generating 3D Voronoi models has limited its application to two-dimensional (2D) codes. The proposed approach is implemented in Neper, an open-source engine for generation of 3D Voronoi grains, to generate block geometry files that can be read directly into 3DEC. A series of Unconfined Compressive Strength (UCS) tests are simulated in 3DEC to verify the proposed methodology for 3D simulation of brittle fractures and to investigate the relationship between each micro-parameter and the model's macro-response. The possibility of numerical replication of the classical U-shape strength curve for anisotropic rocks is also investigated in numerical UCS tests by using complex-shaped (elongated) grains that are cemented to one another along their adjoining sides. A micro-parameter calibration procedure is established for 3D Voronoi models for accurate replication of the mechanical behaviour of isotropic and anisotropic (containing a fabric) rocks
Grain orientation fragmentation in hot-deformed aluminium: Experiment and simulation
No full textInternational audienceGrain orientation fragmentation is studied in a set of 176 individual grains of an aluminium polycrystal deformed in plane strain compression at 400 degrees C to a strain of epsilon = 1.2. Experimental observations were made by EBSD at successive strains of 0, 0.42, 0.77 and 1.2 on the internal surface of a split sample. Statistics of the in-grain orientation spreads were computed based on approximately 3000 orientation measurements per grain. A high-resolution finite element simulation (about 1000 elements per grain) was carried out on a polycrystal whose grains were assigned the initial experimental crystal orientations. The experimental and simulation results were compared in terms of the fractions of grains that exhibit fragmentation and the lattice orientations of the fragmenting grains. The numbers of fragmented grains increase with strain, reaching values of 10% in the experiment (2-D characterization) and 20% in the simulation (3-D characterization) at epsilon = 1.2. For both experiment and simulation, fragmentation is more likely in grains whose lattice is symmetrically oriented with respect to the loading axes. Under plane strain compression, the orientations of the fragmented grains coincide with regions of orientation space in which the reorientation velocity field in the plane perpendicular to the reorientation velocity direction is unstable
Large-scale 3D random polycrystals for the finite element method: Generation, meshing and remeshing
No full textInternational audienceA methodology is presented for the generation and meshing of large-scale three-dimensional random polycrystals. Voronoi tessellations are used and are shown to include morphological properties that make them particularly challenging to mesh with high element quality. Original approaches are presented to solve these problems: (i) "geometry regularization", which consists in removing the geometrical details of the polycrystal morphology, (ii) "multimeshing" which consists in using simultaneously several meshing algorithms to optimize mesh quality, and (iii) remeshing, by which a new mesh is constructed over a deformed mesh and the state variables are transported, for large strain applications. Detailed statistical analyses are conducted on the polycrystal morphology and mesh quality. The results are mainly illustrated by the high-quality meshing of polycrystals with large number of grains (up to 105), and the finite element method simulation of a plane strain compression of ε = 1.4 of a 3000-grain polycrystal. The presented algorithms are implemented and distributed in a free (open-source) software package: Neper
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