Modeling of the reinforcement-matrix bond
Table of contents
Project data
| Titel | Title Promotionsprojekt B2/I: Modellierung des Bewehrung-Matrix-Verbundes und des mechanischen Verhaltens von Verstärkungskompositen bei kurzzeitdynamischen Einwirkungen als Teilprojekt des GRK 2250 | Doctoral poject B2/I: Modeling of the bond between reinforcement and of the mechanical behavior of reinforcement composites during shortterm dynamic loading as part of RTG 2250 Förderer | Funding Deutsche Forschungsgemeinschaft (DFG) / GRK 2250 Zeitraum | Period 05/2017 – 04/2020 (1. Kohorte | 1st cohort) Projektleiter | Project manager Prof. Dr.-Ing. habil. Ulrich Häußler-Combe Bearbeiterin | Contributor Alaleh Shehni, M.Sc. Co-Betreuung | Co-mentoring Leibniz-Institut für Polymerforschung Dresden (IPF) e.V. Homepage des GRK 2250 | Website of RTG 2250 |
Report in the annual report 2018
2D-SIMULATIONS NEED THIN SPECIMENS
Thin dumbbell-shaped SHCC specimen with notch
This doctoral project is a part of the DFG Research Training Group (RTG) 2250 “Mineral-bonded composites for enhanced structural impact safety,” involving 13 doctoral studies on different special topics at different institutes and faculties of TU Dresden. This doctoral project aims to establish a model based on bonding characteristics between fiber and concrete ingredients capable of simulating the behavior of fiber-reinforced concrete under impact load.
Previous studies have shown that 2D models yield reliable simulations of responses of concrete specimens under static and impact loads, while greatly simplify the modelling effort and reduce simulation time as compared to a 3D model. In this project, we have worked on modelling the behavior of high strength SHCCs (strain-hardening cement-based composites) reinforced with high-performance polymer fibers under quasi-
static tensile loading. High-density polyethylene fibers are modelled explicitly and distributed randomly in a two-dimensional model. Single fiber pull-out test results performed by the Institute of Construction Materials are used for micromechanical characterization of the bond strength.
Simulation in the area of the notch with crack pattern for notch model under quasi-static tensile load
Load test simulations are conducted with the in-house program CaeFem. However, we did not have experiment results for 2D specimens in hand to use as references for validation of our numerical simulations. To this aim, the Institute of Construction Materials as our experimental partner in the project performed several tests on very thin dumbbell specimens with and without a notch under quasi-static tensile loading. They faced several challenges with the thin specimens, such as limited minimum volume ratio of fibers due to brittle failure of the specimen with a low volume ratio of fibers which cause the cracks even before the test was started.
These experimental results will be compared with the simulation results. Several tests will be performed based on different fiber contents and notches located in the mid-height of a dumbbell specimen. The resultant mechanisms will be compared and verified versus obtained results from the commercial FEM program DIANA.
Report in the year book 2017
BOND MODEL FOR IMPACT LOADING
Single fiber embedded in a drop of the matrix
This doctoral project is a part of the DFG Research Training Group (RTG) 2250 “Mineral-bonded composites for enhanced structural impact safety,” involving 13 doctoral studies on different special topics at different institutes and faculties of TU Dresden. This doctoral project aims to establish a model capable of simulating the behavior of a fiber-reinforced concrete structure under impact load based on bonding characteristics between fiber and concrete ingredients.
The heterogeneous structure of concrete is described in terms of a multi-level system. To take different effects of crack propagation and crack arresting into consideration, different levels have been introduced. Since we are interested to know more about the bond-slip behavior, we need to focus on specific level of modelling. Mesoscopic level is one of these levels with a typical linear dimension of model in an order of magnitude of 10 mm. Moreover, in the mesoscale model, coarse aggregates, cementitious mortar, and fibers besides the interfacial zones between mortar and aggregate and between mortar and fiber are distinctively modelled with their material properties.
Previous studies have proven that 2D models with circular aggregates yield reliable simulations of responses of concrete specimens under static and impact loads, while greatly simplify the modeling effort and reduce simulation time as compared to a 3D model. To this aim, we start to simulate a 2D representative volume element with the mentioned components, while the coarse aggregates are assumed to have a circular shape with randomly distributed size and location. A static analysis using the in-house software “CaeFem” has been performed, and the results have been validated using the software DIANA. Meanwhile, several sensitivity analyses have been performed regarding different discretization methods, and results were in good agreement with each other, for both the regular mesh and irregular mesh method.
In the first phase of this project, the material behavior of all components was assumed to have a linear behavior, however nonlinear behavior of structural elements should be considered in further steps to make the model behave more realistically. We started to introduce a nonlinear material behavior to represent the bond-law between fibers and concrete. Subsequently, programs were further developed to solve the problems with new conditions. Input data for the bond material was derived from simulation of single glass fiber pull-out tests which have been performed in Leibniz Institute and modeled with DIANA software.