Abstract
In order to study the effect of initial defects on fatigue crack propagation law, a test method to identify fatigue crack propagation rate and path based on load waveform variation was presented, and a new test device was designed to apply fatigue pulsation loads to multiple wires for bridge cables simultaneously in this paper. To simplify the corrosion defect formation process, a machine-cut notch was used to describe the initial defect on the steel wire surface. Firstly, fatigue crack propagation tests were conducted on the surface notched steel wire specimens. By using crack front marking technique, the “beach-like patterns” visible to the naked eyes on the cross sections of the steel wires were formed, and the process of fatigue crack propagation can be tracked and reproduced. Then Autodesk Computer Aided Design (AutoCAD) software was used to describe the morphology of “beach-like patterns” and accurately measure the depth and width of cracks. Finally, the influence of initial defect morphology on fatigue crack propagation rate was investigated according to the relationship between fatigue cracks depth and cyclic loading numbers. The results show that the test device designed in this paper can effectively realize the synchronous fatigue crack propagation test of multiple wires, and significantly shorten the fatigue test period. By observing and analyzing the change of load waveform, the moment of fatigue crack propagation can be directly and accurately determined. The larger the depth, the smaller the width and the sharper the morphology of initial defect, the faster the crack propagation rate and the shorter the life of notched wire specimens under the combined action of fatigue loads and corrosive medium.
Highlights
Due to the coupling effect of corrosive medium and fatigue load during bridge service, corrosion defects tend to appear on the surface of high-strength steel wire used in bridge cables
The results show that there is an obvious relationship between the crack propagation morphology and the initial prefabricated crack depth under uniaxial cyclic tensile load, and the influence of the initial crack depth on the crack morphology gradually weakens with the cracks gradually extending
Investigate the influencenotches of depth of machine-cut notches on the for fatigue crack propagation of steel semi-ellipsoidal with different depths are used the test in paper
Summary
Due to the coupling effect of corrosive medium and fatigue load during bridge service, corrosion defects tend to appear on the surface of high-strength steel wire used in bridge cables. Scholars at home and abroad have begun to analyze the fatigue crack propagation of steel by using the crack front marking technique [15,16], which can reproduce the whole process of fatigue crack propagation by artificially creating “beach-like pattern”, providing a powerful tool for in-depth study of crack propagation rate in depth direction This technique can make up for the limitations of the commonly used test methods, such as acoustic emission method, potential method, flaw detection method and thermal radiation method, etc. In this paper the fatigue crack propagation tests of defective high-strength steel wire used in bridge cables were carried out to study the influence of initial defects on the fatigue crack propagation rate and path. Based on the relationship between fatigue crack depth and cyclic loading numbers, the effects of initial defect depth, width and shape on fatigue crack propagation rate of defective steel wire specimen were quantitatively analyzed
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