Papers by Keyword: Heterogeneous Material

Abstract: The present work deals with the analytical resolution of the problem of viscoelastic coated inclusion embedded in a viscoelastic matrix.In a first step, we will study the problem of a linear viscoelastic inclusion, without coating, embedded in a linear viscoelastic matrix.Then, the problem of coated viscoelastic inclusion considering the coating as a thin layer whose viscoelastic properties are different from those of the inclusion and the matrix is performed.The resolution of this problem will be based simultaneously on the Green function technique as well as the interface operator. The analytical expression of the solution is obtained by assuming the isotropy of the matrix as well as the spherical shape of the coatedinclusion.These results are used to determine the effective properties of a heterogeneous medium from a self-consistent approach taking into accountthe interactions between coated inclusions and the equivalent homogeneous medium.

Abstract: The mechanical behaviour of heterogeneous specimens under uniaxial tensile test is studied using finite element analysis. The difference between mechanical properties of adjacent regions in the heterogeneous specimen creates constraints which alter the strain path relatively to pure tension. A methodology for determining the local stress-strain curves is proposed and successfully tested numerically on the heterogeneous specimen composed by two materials with dissimilar plastic properties. This methodology has recourse to the same type of variables which are usually obtained experimentally with the digital image correlation technique.

Abstract: For the Three Gorges granite, a finite difference software package FLAC was used to study failure process of heterogeneous rock material. Based on mineral components identification results of the granite and fuzzy clustering method, the actual image date was transformed into the finite difference grid by applying image processing techniques. A convenient and efficient two-dimensional numerical modeling method for heterogeneous geomaterials was presented. Then, failure process of the granite were simulated in uniaxial compression test based on experimental strain soft model, and the stress concentration phenomenon was analyzed. The results show that the numerical modeling method based on digital image processing can be used to calculate the mechanical responses of geomaterials by taking their heterogeneities into considerations.

Abstract: The context of this work is the enhancement of the thermal conductivity of polymer by adding conductive particles. It will be shown how we can use effective thermal conductivity models to investigate effect of various factors such as the volume fraction of filler, matrix thermal conductivity, thermal contact resistance, and inner diameter for hollow particles. Analytical models for lower bounds and finite element models will be discussed. It is shown that one can get some insights from effective thermal conductivity models for the tailoring of conductive composite, therefore reducing the amount of experimental work.

Abstract: first of all, this paper intensive studies the hydraulic fracturing mechanism of heterogeneous material resultant from the seepage – damage coupling, based on which, the coupled seepage and damage effects during hydraulic fracturing is investigated, and the difficulties of hydraulic fracturing study are how to determine failure modes and breakdown pressure. By using numerically testing method, the mechanical mechanism of hydraulic fracturing under asymmetric distribution of pore pressure with three holes, including fracture patterns, stress flied distribution, initial fracturing pressure and breakdown pressure, was studied by using the FSD model. According to the results of this research, crack extension direction of hydraulic fracturing is influenced not only by the local pore pressure around crack tip, but also by the gradient distribution of macro pore water pressure. The fracturing direction always propagates towards the regions of higher local pore pressure and breakdown pressure decreases with the increasing of local pore pressure. These results are well aggress with the results in the experiments. This research has important theoretical and engineering value. In engineering practice, we can use the porous asymmetric hydraulic fracturing technology to control the direction of crack propagation. Keywords: hydraulic fracturing; numerical simulation; heterogeneous material; asymmetrical

Abstract: A novel method for the design and fabrication of heterogeneous objects is presented, which combines the Three Dimensional Printing (3DP) and micro droplets dispensing technology. It provides a solution to the fabrication of assemblies with multi materials, which can not be fabricated by traditional processes. An integrated design and fabrication system for heterogeneous objects based on the new process is introduced. Its constructive representation scheme is described. To show the effectiveness of the working process of multi-materials, based on slice software of color STL model and developing prototyping system, an example is shown to illustrate the entire design-fabrication cycle for heterogeneous objects.

Abstract: Amethod for extracting accuratemicrostructural information fromheterogeneousmaterialsusing micro Computed Tomography ( CT) is presented. A highly porous fibrous structure is used asa case study. The proposed method includes a filtering step to increase the resolution of the gray-scaleslices, a local segmentation step to accurately separate the fibres from the background and a thinningprocedure to simplify the structure and extract quantitative statistics such as the number of fibre jointsper fibre, fibre orientation and segment length (sections between joints) distributions.

Abstract: This paper considers multi-scale modeling strategies for heterogeneous materials while also highlighting the problems of determining experimentally the micro-scale properties and validating such techniques. Multi-scale modeling techniques enable us to capture the influence of (evolving) heterogeneous material microstructures on the overall macroscopic behavior. This paper discusses computational multi-scale modeling techniques for problems both with and without poor scale separation. In developing these powerful multi-scale modeling techniques, the obvious challenge of validating both the material behavior at multiple scales and the associated scale transition methodologies, using advances in material characterization and experimental mechanics, comes into sharp focus and this will be briefly explored here.

Abstract: The section of steel column under axial compression presents heterogeneous material and its load condition changes after experiencing fire damage of one side. Taking H-section steel column under axial compression commonly used in engineering for study object in this thesis in order to study post-fire residual load bearing capacity, the post-fire eccentric effect of steel column under axial compression exposure to one-side fire is analyzed using the method of equivalent section which considering the change of the material strength after high temperature, the influence of non-uniform temperature field on material properties and the stiffness degradation of member section. Calculation methods of the eccentricity and additional moment are proposed and further given a formula of residual load bearing capacity.

Abstract: A novel numerical model for simulating fracturing process of the heterogeneous materials such as rock or rocklike material has been developed and implemented in the FLAC, which is the numerical code for the engineering mechanics analysis. A constitutive model that captures an essential component of brittle material failure, that is, cohesion weakening and frictional strengthening (CWFS) is improved by taking accounting the elastic modulus of element may degrade when the element failure. Furthermore, a new energy index, Local Energy Release Rate (LERR), is put forward to simulate energy release during failure process by tracking the peak and trough values of elastic strain energy intensity before and after brittle failure. The numerical model has applied to simulate the initiation, propagation and coalescence of cracks in the failure processes of brittle material. Using this numerical model, we studied the failure processes of simulated rock specimens with different heterogeneity. The results suggest that the model is a powerful approach to the study of macroscopic fracturing behaviour of heterogeneous material.