Study of structural behavior and damage mechanisms appearing in composite materials with the use of numerical simulations
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Tsivolas, Eleftherios
Τσιβόλας, Ελευθέριος
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Πανεπιστήμιο Ιωαννίνων. Πολυτεχνική Σχολή. Τμήμα Μηχανικών Επιστήμης Υλικών
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Μελέτη δομικής συμπεριφοράς και μηχανισμών αστοχίας σύνθετων υλικών με χρήση
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Over the years, the design of sophisticated structural materials has become an importantengineering task. The developmnent of composite materials partially solves this growing need because their behavior is tailor made for the desired application. For that reason,efforts in materials science and engineering has been focused in the design and manufacturing of new materials by changing their composition at multiple scales. This need for new materials has lead to the developement of the continuum micromechanics field, which is a subdomain ofthe mechanics of solids. This field introduces new concepts for the prediction of the macroscopic properties of a composite material knowing the properties of its individual constituents. Concepts like Representative Volume Element (RVE), micromechanics and mean-field material homogenization are vital for the separation of scales in the process of material characterization.Furthermore, the rapid increase of computer power is followed by the increasing need for simulation of complicated systems and materials. The study of heterogeneous materials necessitates a detailed description of the microstructure to accurately capture changes in micro or nano scales. The increase of computational memory and processor speed has not only permitted the simulation of large structures but also to perform analyses in multiple scales in order to predict complex material behaviors.This work focuses on the numerical simulation of structures consisted by heterogeneous materials, and in the prediction of progressive damage and failure under mechanical loading using multiscale methodologies. Special attention was given in the comprehension and implementation of the state of the art homogenization methods, prior to their modification in order to capture more complex phenomena. In the context of this research, several methods have been developed to predict the structural response in both macro and microscales and all these methods are integrated under an in-house multidisciplinary software for multiscale analysis.Mean-field homogenization strategies, which are widely used in this thesis, provide an efficient way to simulate the behavior of non homogeneous materials. In this category be long several homogenization solutions with varying accuracy and complexity. Generally, they are analytical or semi analytical solutions of the boundary value problem defined in the microstructure of the heterogeneous material and can be very accurate in predicting the mean response of the RVE. The most of the aforementioned homogenization strategies are based on Eshelby’s single inclusion solution, and initially designed for the prediction of the elastic behavior of composites. Some approaches extend their applicability to nonlinear regimes such as elasto-plasticity and rate dependent plasticity. Since these methods are semi-analytical, the comparison with finite element approaches allows not only the validation of such methods, but also assists the discovery of limitations that can be overcome by future research and development.In this thesis the theoretical aspects and concepts of mechanics of composite materials along with their novel numerical simulation campaigns are presented. In the first chapter, the state of the art of the multiscale methods is presented. In the second chapter, a comparison between numerical and mean-field homogenization methods is conducted regarding linear isotropic, transversely isotropic and orthotropic composite materials to understand the impact of the assumptions and simplifications that are made in the mean-field methods. In the sequel, this comparison is extended for nonlinear composite materials. In the third chapter, the aim is to predict the transverse cracking of a cross-ply composite material loaded in uniaxial tension. The properties of each ply were predicted by performing visco-elastic mean-field homogenization using a modified Mori-Tanaka homogenization scheme. The transverse cracking was predicted using the cohesive zone modelling technique. Finally, a cross ply microstructure was generated for the simulation of the cracking propagation in microscale with the eXtended Finite Element Method(XFEM) and the correlation of the stress concentration between the micro and macro scale. In the fourth chapter, the mean-field homogenization scheme was extended to take into account nonlinear effects such as microplasticity and progressive damage with failure criteria in both the homogeneous and constituent levels to control the element deletion. This multiscale method produced results closer to the available experimental measurements. It is also capable to predict successfully the matrix softening and the total failure of the composite specimen. Finally, in the fifth chapter, the aforementioned mean-field methodology is extended once more to take into account healing effects in a self healing mechanism coupled with damage. Based on this phenomenon, the increasing damage rate can be reduced, resulting either in partial damage restoration or in full retrieval of the material’s structural integrity. Furthermore, a methodology in microscale is proposed to predict the healing efficiency of a composite material embedded with healing microcapsules.
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Finite element analysis, Multiscale modeling, Composite materials
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Επιστήμη των υλικών
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en
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Πανεπιστήμιο Ιωαννίνων. Πολυτεχνική Σχολή. Τμήμα Μηχανικών Επιστήμης Υλικών
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Γεργίδης, Λεωνίδας
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Παϊπέτης, Αλκιβιάδης
Χαραλαμπόπουλος, Αντώνιος
Φωτιάδης, Δημήτριος
Μπάρκουλα, Νεκταρία-Μαριάνθη
Ματίκας, Θεόδωρος
Λέκκα, Χριστίνα
Χαραλαμπόπουλος, Αντώνιος
Φωτιάδης, Δημήτριος
Μπάρκουλα, Νεκταρία-Μαριάνθη
Ματίκας, Θεόδωρος
Λέκκα, Χριστίνα
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Πανεπιστήμιο Ιωαννίνων. Πολυτεχνική Σχολή. Τμήμα Μηχανικών Επιστήμης Υλικών
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213
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Except where otherwised noted, this item's license is described as CC0 1.0 Universal