Public defence in civil engineering, Rui Hao, M.Sc.

Evaluation of fatigue behavior of notched details under cyclic loading

In bridge engineering, the fatigue cracks caused by cyclic vehicle loads always impose great threats to the safety of in-service bridges. To provide some references to the solution of tackling this damage type, this study is targeted to investigate the fatigue behavior of cutout details that frequently employed in the orthotropic steel deck bridges and to evaluate the possibility of fatigue crack initiation. 

To achieve the primary goal, the work is further divided into three sub-goals: to detect the fatigue crack initiation in its early stage, to find a reliable theoretical method that is consistent with the civil engineering practice for predicting their fatigue lives, and to numerically predict their fatigue lives. To achieve these subgoals, laboratory fatigue tests on notched specimens with notch radii that used in real bridges were first conducted, and for some specimens, the surface roughness parameters were also measured during the fatigue test. The surface roughness evolutions during the fatigue load were obtained, and effective crack detection parameters were also found. The prediction of fatigue life using theory of critical distance was conducted, and a new formulation of critical distance-fatigue life was proposed and validated with experimental data. Besides, a new SWT-model-based algorithm for the fatigue crack initiation life prediction of notched details in the high-cycle-fatigue regime was proposed by considering the cycle-by-cycle fatigue damage accumulation, and a good agreement between the predicted fatigue initiation life and experimental results was confirmed. 

The aforementioned key findings can serve as a foundation for evaluating fatigue damage in cutout details and make significant contributions to the bridge engineering. In addition, the research outcomes can also be referred to the research in the field of Mechanical Engineering.

Opponent: Associate professor John Leander, KTH Royal Institute of Technology, Sweden

Custos: Associate professor Weiwei Lin,  Aalto University School of Engineering, Department of Civil Engineering

Contact information of the doctoral student: Rui Hao, rui.hao@aalto.fi, tel. +358504088675

The public defence will be organised on campus (auditorium M1, Otakaari 1).

The thesis is publicly displayed 10 days before the defence in the publication archive Aaltodoc of Aalto University.

Electronic thesis