Numerical framework for modeling of cementitious composites at the meso-scale

Jerábek, Jakub; Meskouris, Konstantin (Thesis advisor)

Aachen : Publikationsserver der RWTH Aachen University (2011)
Dissertation / PhD Thesis

Abstract

The application of composite materials as a building material has been constantly growing in popularity during the last decades. Composite materials combine several material components to allow for an optimal utilization of their favorable properties. The focus of this work is the modeling of the cementitious composites at the extit{meso-scale}. In particular, the motivation of the thesis is to model textile reinforced concrete, a new composite material combining a high-strength textile reinforcement with a fine grained concrete matrix. The existing models for concrete and composites are not directly applicable for textile reinforced concrete. This is due to the fact, that in comparison to other composite materials, except the cementitious matrix, the scales of heterogeneity of textile reinforced concrete include additionally the yarn cross-section, the scale of the bond imperfections as a result of the irregular penetration of the matrix into the yarn and the scale of the textile fabric mesh. As consequence, the damage localization process of textile reinforced concrete exhibits interactions between elementary failure mechanisms in the matrix, in the reinforcement and in the bond. The objective of this thesis is to provide the simulation environment for an easy implementation of the advanced applications of the finite element method required in the modeling of cementitious composites. This includes particularly the modeling of the crack development at meso-scale. The considered failure mechanisms on the meso-scale include debonding of the yarn from the matrix, the brittle cracking of the matrix, and yarn failure. The used models require effective bond laws for yarns with irregular bond to the concrete matrix reflected in appropriate non-linear material models. The simulation of the crack development is focused on zones with complex stress states, like shear zones or construction details characterized by dominant, interacting cracks bridged by the tensile reinforcement. In such situations, the state of the crack bridge in terms of its opening and sliding is crucial for the assessment of the ultimate structural strength. An explicit representation of the matrix crack is therefore inevitable and is effectively introduced using the extit{extended finite element method} (XFEM). The mentioned numerical techniques are setting requirements on the numerical framework in terms of flexibility and extensibility. Therefore, special attention in the thesis is given to the design of the framework, which has to take into account not only the requirements of the simulation but also the demands defined by its application as a scientific development tool in the fields of material science and numerical methods. In this context, the application of modern approaches like the object-oriented design and the utilization of scripting languages are emphasized.

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