Influence of microstructure and residual stresses on the fatigue behaviour of ribbed rebar rods

• Applicants: Professor Dr.-Ing. Christoph Gehlen; Professor Dr. Ewald Werner
• Subject Area: Construction Material Sciences, Chemistry, Building Physics
• Term: from 2019 to 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 410264412

The introduction of modern surface geometry for steel rebar has affected its fatigue behaviour. In comparison with smooth reinforcing steel, fatigue strength has decreased while the scatter of the results of fatigue tests has increased. A holistic consideration of the relationships between the manufacturing process, microstructure, residual stress, surface form and the resulting properties has not been made up to now. This research project aims to close this gap in knowledge.Reinforcing steel (rebar or ring material) with inadequate or strongly scattering fatigue behaviour severely restricts the service life of the concrete structure. A specific adaption of the reinforcing steel during the manufacturing process could significantly improve the current low level and large scatter of the fatigue strength of the reinforcing steel. To achieve this, the manufacturing process should be comprehensively analysed, the methods for determining residual stress matched to the complicated surface geometry of the reinforcing steel, the formation of residual stresses described by numerical simulations, detailed surface models of reinforcing steel created, the relevant microstructural parts of multi-phase reinforcing steel quantified with regard to dynamic and static properties, and the structural/mechanical behaviour of concrete reinforcement steel with all quantified effects thereon and the corresponding geometry numerically simulated. This should make it possible to close the considerable gaps in knowledge that currently exist for reinforcing steel with regard to the relationship between manufacturing, microstructure and properties, and to develop reliable tools for the prediction of fatigue behaviour and, based on this, to develop specifically tailored rebar.

• DFG Programme: Research Grants