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Ermüdungsinduzierte Schädigung von UHPC - Experimentelle Ergebnisse und BPM-Modellierung
Citation Link: https://doi.org/10.15480/882.13203
Publikationstyp
Doctoral Thesis
Date Issued
2024
Sprache
German
Author(s)
Advisor
Referee
Title Granting Institution
Technische Universität Hamburg
Place of Title Granting Institution
Hamburg
Examination Date
2023-10-20
Institute
TORE-DOI
Citation
Technische Universität Haburg (2024)
Due to the growing demand for more delicate, lighter and therefore more sustainable concrete structures, the need for UHPC is becoming more and more significant. Despite the impressive
mechanical properties, it must be noted that the tolerance to cyclic loads is significantly reduced compared to normal concrete. Until now, the description of fatigue resistance has been based on macroscopic relationships. However, an investigation of the mechanisms on smaller scales did not take place with regard to the fatigue problem. Consequently, this work pursues the goal of investigating fatigue-induced damage on the nano, micro, meso and macro scales using experimental (SEM, TEM) and numerical methods (Bonded-Particle-Model).
In the scope of mechanical characterisation of the UHPC, both static and cyclic tests were carried out. A specially developed rheological fatigue model made it possible to carry out fatigue simulations that reflect the essential fatigue characteristics of the material. The damaging influence of the aggregate, which leads to stress peaks in the microstructure and thus plays a key role in the mesoscale damage mechanisms, should be emphasised.
Furthermore, a cycle jump method was developed within the scope of this work in order to gain deeper insights during high-cycle loading. This method was combined with findings on the influence of the unhydrated cement on the fracture load cycles, showing possible explanations for the observed experimental scatter.
In addition, TEM investigations showed significant microstructural changes in the C-S-H structure and a formation of crack precursors during fatigue. Due to a higher concentration of sulphur and aluminium in the surrounding area of the crack precursors, it is suspected that the changes are associated with the presence and recrystallisation of ettringite.
The joint coupling of the applied experimental and numerical methods proved to be an effective tool for the investigations on nano, micro, meso and macro scales. As a result, essential insights were gained that decisively deepen the understanding of the fatigue process.
mechanical properties, it must be noted that the tolerance to cyclic loads is significantly reduced compared to normal concrete. Until now, the description of fatigue resistance has been based on macroscopic relationships. However, an investigation of the mechanisms on smaller scales did not take place with regard to the fatigue problem. Consequently, this work pursues the goal of investigating fatigue-induced damage on the nano, micro, meso and macro scales using experimental (SEM, TEM) and numerical methods (Bonded-Particle-Model).
In the scope of mechanical characterisation of the UHPC, both static and cyclic tests were carried out. A specially developed rheological fatigue model made it possible to carry out fatigue simulations that reflect the essential fatigue characteristics of the material. The damaging influence of the aggregate, which leads to stress peaks in the microstructure and thus plays a key role in the mesoscale damage mechanisms, should be emphasised.
Furthermore, a cycle jump method was developed within the scope of this work in order to gain deeper insights during high-cycle loading. This method was combined with findings on the influence of the unhydrated cement on the fracture load cycles, showing possible explanations for the observed experimental scatter.
In addition, TEM investigations showed significant microstructural changes in the C-S-H structure and a formation of crack precursors during fatigue. Due to a higher concentration of sulphur and aluminium in the surrounding area of the crack precursors, it is suspected that the changes are associated with the presence and recrystallisation of ettringite.
The joint coupling of the applied experimental and numerical methods proved to be an effective tool for the investigations on nano, micro, meso and macro scales. As a result, essential insights were gained that decisively deepen the understanding of the fatigue process.
Subjects
Betonermüdung
DEM
Ermüdungssimulation
REM
TEM
UHPC
DDC Class
620.1: Engineering Mechanics and Materials Science
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