Multiscale multiphysics simulation in composite materials
The improvements in terms of computational power provides the capability to analyze with more detail the materials behavior. On one hand, going deeper in the materials to study an increasingly smaller dimension and capture micro- or nano- changes. On the other hand, the increasing computational memo...
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| Tipo de recurso: | tesis doctoral |
| Estado: | Versión publicada |
| Fecha de publicación: | 2019 |
| País: | España |
| Institución: | CBUC, CESCA |
| Repositorio: | TDR. Tesis Doctorales en Red |
| OAI Identifier: | oai:www.tdx.cat:10803/665129 |
| Acceso en línea: | http://hdl.handle.net/10803/665129 https://dx.doi.org/10.5821/dissertation-2117-127628 |
| Access Level: | acceso abierto |
| Palabra clave: | Àrees temàtiques de la UPC::Enginyeria civil 517 620 |
| Sumario: | The improvements in terms of computational power provides the capability to analyze with more detail the materials behavior. On one hand, going deeper in the materials to study an increasingly smaller dimension and capture micro- or nano- changes. On the other hand, the increasing computational memory allows to perform finite elements analysis with billions of nodes, that permits to obtain more accurate results. In this sense, the focus of this work is the numerical modeling of the microscale behavior of inhomogeneous materials, with special attention to composite materials under thermo-mechanical loading conditions. This work also proposes and implements optimization tools, at a constitutive law level, as well as the level of both, macro- and micro-structural algorithms. The thesis is proposed as compendium of articles written during the last years and all published in Q1 international journals. In the first publication, a novel damage-mechanics micro-model is presented, able to represent the mechanical behaviors of masonry constituents. The proposed micro-model is based on a tension-compression continuum damage model. The adoption of appropriate failure criteria enables controlling the dilatant behavior of the material, even though this aspect is not generally associated to continuum damage models as it is for plasticity models. The study proposes a simple solution to this issue, consisting in the appropriate definition of the failure surfaces under shear stress states, together with the formulation of proper evolution laws for damage variables. The model keeps the simple and efficient format of classical damage models, where the explicit evaluation of the internal variables avoids nested iterative procedures, thus increasing computational performance and robustness. Another purpose of this research is to carry out a critical comparison of the proposed continuous micro-model with other two well-known discrete micro-modeling strategies. The second publication presents a full thermo-mechanical multiscale methodology, covering the nano-, micro-, and macroscopic scales. In such methodology, direcly deriving from the Classical First-Order Multiscale Method, fundamental material properties are determined by means of molecular dynamics simulations. Afterwards, the material properties obtained are used at the microstructural level by means of finite element analyses. Finally, the macroscale problem is solved while considering the effect of the microstructure using a thermo-mechanical homogenization on a representative volume element (RVE). The publication that close this thesis presents two computationally efficient multiscale procedures able to predict the mechanical non-linear response of composite materials. This is achieved, using an RVE Data Base (DB) calculated a-priori. Through the definitions of an equivalent damage parameter ($d_{eq}$), function of the global stress at the microscale, a series of strain controlled virtual tests of the RVE are performed storing in the DB the homogenized stress and strain state reached at certain levels of d_eq. Afterwards, the solution of the macroscale structure can be solved using the interpolation of the stored data. The first proposed procedure, named Discrete Multiscale Threshold Surface definition (DMTS), stores in the database the tenso-deformational state in which damage starts. Once reaching this state, a non-linear analysis will require the construction of the RVE to analyze the material damage evolution. On the other hand, the second method proposed, named Discrete Multiscale Constitutive Model (DMCM), is completely based on offline data and uses only the stress information stored in the DB to obtain the failure threshold and the non-linear material performance. In the article, special attention has been paid on the construction and validation of the Data Base, as well as on the study of a complete composite structure comparing the speedup obtained with both methods. |
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