B2/GRK 2250: Modeling of the reinforcement-matrix bond
Table of contents
Project data
| Titel | Title TP B2: Modellierung des Bewehrung-Matrix-Verbundes und des mechanischen Verhaltens von Verstärkungskompositen bei kurzzeitdynamischen Einwirkungen als Teilprojekt des GRK 2250 | TP B2: Modeling of the bond between reinforcement and of the mechanical behavior of reinforcement composites during shortterm dynamic loading as part of the GRK 2250 Förderer | Funding Deutsche Forschungsgemeinschaft (DFG) / GRK 2250 – Impaktsicherheit von Baukonstruktionen durch mineralisch gebundene Komposite | Mineral-bonded composites for enhanced structural impact safety Zeitraum | Period 05/2017 – 04/2020 Leiter | 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 GRK 2250 |
Report in the annual report 2018
2D-SIMULATIONS NEED THIN SPECIMENS
Dünner hantelförmiger SHCC-Probekörper mit Kerbung
This project is a part of the larger project DFG-GRK 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 subproject aims to establish a model based on bonding characteristics between fibre and concrete ingredients capable of simulating the behaviour of fibre 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 behaviour of high strength SHCCs (strain-hardening cement-based composites) reinforced with high-performance polymer fibres under quasi-
static tensile loading. High-density polyethylene fibres are modelled explicitly and distributed randomly in a two-dimensional model. Single fibre 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 fibres due to brittle failure of the specimen with a low volume ratio of fibres 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 fibre 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 fibre embedded in a drop of the matrix
This project is part of the larger project DFGGRK 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 subproject aims to establish a model capable of simulating the behaviour of a fibre reinforced concrete structure under impact load based on bonding characteristics between fibre 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 behaviour, 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 fibres besides the interfacial zones between mortar and aggregate and between mortar and fibre 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 behaviour of all components was assumed to have a linear behaviour, however nonlinear behaviour of structural elements should be considered in further steps to make the model behave more realistically. We started to introduce a nonlinear material behaviour to represent the bond-law between fibres 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 fibre pull-out tests which have been performed in Leibniz Institute and modeled with DIANA software.