Papers by Keyword: Multi-Scale

Abstract: Aluminum die casting components are widely used in vehicle constructions because they satisfy the conflicting requirements between weight reduction and mechanical property improvement. However, the analysis of deformation and damage behavior of aluminum cast components is very complex, since local mechanical properties in the components are inhomogeneous as a consequence of spatial distribution of microstructure. For crash simulation it is necessary to well predict the damage behavior which is strongly influenced by micro-defects especially by cast pores. The conventional continuum mechanics approaches often fail due to the statistical character of cast pores. In this work the Markov random field model (Ising) is used to describe the pore morphology. Markov random field classes are defined by porosity (macroscopic property) and equivalent pore size (microscopic property) and determined by micro computer tomography (CT) analysis.A multi scale approach was applied to map the results of the stochastic model to the FE models, which results in a distribution of porosity. A porosity dependent continuum model was developed based on results of representative volume elements with variation of porosity. It was shown that the continuum model with porosity distributions from the Ising model as initial conditions captures well the spatial material properties (i.e. fracture strain) and their variations in the bridging scale.

Abstract: At present, the discussion about pores/ voids in large ingots is still actual. Researchers investigated the closing behavior during the open die forging process. Mostly, the approaches take the account into void closure with artificial pores. But artificial pores do not reflect the real closing behavior. This is caused in the surface/ structure of inner voids. During drilling and heating, the voids got a smooth surface and have contact to the atmosphere. Therefore, the material oxidizes on surface and the closing behavior is not similar to the real process. Real pores show a fractal surface with dendrites. And the inner of voids contains a vaccum. In the framework of a new approach, for void closure cast ingots with pores were generated and the structure and the closing behavior were investigated.The final goal is to find out a global closing function “Z”. This closing function should improve the understanding of void behavior and in the future the industrial process. The function depends on different parameters, like yield strength of material (P_kf), the pore size (A_Eq), the pore structure (P_struct) and process parameters (P_proc), such as tool geometry or bite ratio. Finally, there is a parameter P_disturb. This parameter works against the final closure and is important for the understanding of the process, because it represents the influence of dendrites. Furthermore the closing behavior is not comprehensible without the consideration of recrystallization.

Abstract: Deterioration of reinforced concrete infrastructure such as bridges, tunnels, and buildings represents one of the major challenges currently facing developed countries. While engineering tools and methods for structural modelling and design of new reinforced concrete infrastructure are mature, methods and tools for modelling decades-long deterioration and maintenance are much less developed. In this paper, a multi-physics and multi-scale modelling approach for structural deterioration of reinforced concrete components due to reinforcement corrosion is presented. The multi-disciplinary modelling approach includes physical, chemical, electrochemical, and fracture mechanical processes at the material and meso-scale, which are further coupled with mechanical deterioration processes at the structural scale.

Abstract: A micro-cell size dependent damage law is proposed by the multi-scale damage representation to remedy the mesh sensitivities involving in the numerical simulations. The homogenization based multi-scale damage representation is firstly introduced in obtaining the macro-damage evolution from micro-cell analysis. Then, the micro-cells with different sizes are generated and the corresponding simulations are given. Based on the simulation results, we define the micro-cell size dependent damage law. Finally, the accuracy and efficiency of the proposed damage law are verified by the notched beam simulation results.

Abstract: Multi-scale grid is an essential deformation carrier in optical methods for multi-scale deformation measurement. In this study, several new-type multi-scale grids were designed and fabricated by electron beam lithography. Each pattern includes several periodically distributed dots with the same spacing but different sizes. As a consequence, the grayscale of the whole grid pattern periodically changes. The peak parts of the grayscale generate a secondary grid, i.e., the large-scale grid. The ratio of the large-scale grid pitch to the small-scale grid pitch can be easily adjusted according to the requirement. The natural integration between the small-scale grid and the large-scale grid works well in eliminating the mutual disturbance between the different-scale grids. Besides, this type of grid has a very high success rate in fabrication owing to the small differences in size between the big dots and the small dots. The proposed multi-scale grid pattern is expected to serve as the deformation carrier in moiré methods and geometric phase analysis for multi-scale deformation measurement.

Abstract: The island survey is important in economic and strategic field, and in recent years the use of remote sensing technology becomes the mainstream in island investigation. As an effective way for improving the efficiency and accuracy of island survey, the automatic segmentation and recognition algorithm has greater significance. For the difficulty in application of deformed model to high-resolution remote sensing images, the segmentation framework of global initial segmentation and local extractive segmentation based on narrow band deformable model is proposed. Based on the sea and land extraction the island initial segmentation is accomplished, and then the narrow band deformable model is used to increase the accuracy of segmentation. Finally the double rings feature of island is used to improve the quality of the segmentation.

Abstract: In recent years, saliency detection has been gaining increasing attention since it could significantly boost many content-based multimedia applications. In this paper, we propose a visual saliency detection algorithm based on multi-scale superpixel and dictionary learning . Firstly, in each scale space, we extract the boundaries as the training samples to learn a dictionary through sparse coding and dictionary learning methods. Then, according to reconstruction error of each superpixel, the saliency map is generated for each scale of superpixel. Finally, some saliency maps from different scale spaces are fused together to generate the final saliency map. The experimental results show that the proposed algorithm can highlight the salient regions uniformly and performs better compared with the other five methods.

Abstract: In order to study the damage problem caused by the transmission tower fatigue cracks and bolt pretightening force loss ,this paper proposes a transmission tower damage identification method based on concurrent multi-scale model, namely establish solid model on nodes of fatigue crack and bolt looseness based on large scale model., subdividing elements size. Take a practical engineering 500kV transmission towers as an example to establish a concurrent multi-scale models. This paper simulates 8 kinds of conditions including bolt pretightening force loss and angle steel crack, research shows that the sum of wavelet packet energy curvature difference can effectively identify minute damage, and then get the function relation between damage level and damage index with no noise interference, also this provides a theoretical basis for it as actual damage monitoring indicators index.

Abstract: In order to study the residual fatigue life of 500 kv transmission tower under load conditions, a multi-scale finite element model of transmission tower is established. By simulating time course of wind load, using Miner fatigue cumulative damage theory and linear S-N curve, the calculation method of transmission towers fatigue life is established. The research shows that the multi-scale model can better simulate the stress and strain state of the transmission tower, and can predict the remaining service life of the transmission tower .The research has important significance and application value for the safe operation of the transmission lines.

Abstract: Hierarchically structured LDHs are being actively investigated due to their potential applications in bioseparation and catalysis which result from their special surface structures and positively charged nanosheets. This work presents an effective method of fabricating hierarchical LDHs based materials with high surface-to-volume ratios. To do this, the microscaled Al₂O₃ fibers are fabricated via a simple biotemplate method employing paper fibers as templates and in the second step the nanoscaled Ni-Al LDH platelets are fabricated into hierarchical architectures based on crystal growth on surface of Al₂O₃ fibers. In order to obtain the multi-component and multi-scale structure LDHs based materials, the ZnO/LDHs composites are obtained by controlling crystal growth process. The developed facile route is highly valuable and feasible for hierarchical porous LDHs based materials for applications in research and industrial fields.