Abstract
The paper presents an analysis of mixed-mode fatigue crack growth in bridge steel after 100-years operating time. Experiments were carried out under mode I + II configuration on Compact Tension Shear (CTS) specimens and mode I + III on rectangular specimens with lateral stress concentrator under bending and torsion loading type. Due to the lack of accurate Stress Intensity Factor (SIF) solutions, the crack path was modelled with the finite element method according to its experimental observation. As a result, the Kinetic Fatigue Fracture Diagrams (KFFD) were constructed. Due to the change in the tendency of higher fatigue crack growth rates from KI towards KIII dominance for the samples subjected to bending and torsion, it was decided to analyze this phenomenon in detail using electron-scanning microscopy. The fractographic analysis was carried out for specimens subjected to I + III crack loading mode. The mechanism of crack growth in old bridge steel at complex loads was determined and analyzed.
Highlights
Fatigue fracture is one of the most frequent failure reasons for bridge structures
Compact Tension Shear (CTS) specimens used in this study presented an initial notch with dimensions: Length, l = 20 mm
The following conclusions from the testamplitude results for of fatigue growth in the longinitiation operatedofbridge fatigue crack growth in the specimens begins from stress concentrators in the middle of their steel under mixed-mode (I + II, I + III) loading conditions can be drawn: thickness due to KI type stress effect
Summary
It is worth noting that the research guidelines [1] for old bridge structures are conservative as regard fatigue, namely as concerns the sub-critical period of fatigue crack growth. This is motivated by the absence of reliable data from old bridge materials, especially original data. Many papers have been devoted to the puddle iron [2,3,4,5,6] in the field of material characterization, including fatigue testing. Papers [7,8,9] of the authors’ team devoted to the mixed-mode (I + II) fatigue fracture of puddle iron, show significant discrepancies in the expected
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