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Damage analysis and lifetime prediction of steel strands

Abdeljalil Jikal

Steel wire ropes are widely used as the backbone of several civil engineering structures. During use, they are subject to various damage mechanisms, yet corrosion fatigue is the main mechanism causing their failure. To this end, experimental tensile tests were conducted on virgin steel strand samples and others damaged by corrosion at different times to assess the corrosion impact on their mechanical behavior. The test strands were taken from a 19*7 lifting wire rope. Moreover, based on damage models used in this study, the stages of the damage evolution and critical service life of the corroded steel strand were identified for predictive maintenance. The results show a significant loss of stiffness and a decrease in ultimate residual stress with increasing corrosion level. Therefore, through the evaluation of the ultimate stress of the wire rope damaged by corrosion during its service life, the engineers can assess the possibility to maintain the structure in service and define the time of its removal. They are composed of multi-wire strands twisted together to form a structure with enormous mechanical properties, combining high axial strength, rigidity and torsional flexibility. In most applications, wire ropes are exposed to different damage mechanisms. One of these mechanisms is corrosion, which can accelerate the damage to cable components and lead to brutal and unforeseen failure. In this regard, experimental tensile tests were carried out on several strand samples; one sample was virgin and the others were corroded by immersion of a well-defined number of strands in sulfuric acid solutions. The studied strands were extracted from a 19 * 7 non-rotating steel wire rope. The static damage enables to monitor the evolution of residual stresses of damaged samples with different corrosion levels. Based on the ultimate residual stress and the endurance limit of the virgin strand, the influence of corrosion on the strand‘s endurance limit was studied by plotting the S-N curves according to the unified theory. The obtained results enabled to assess the mechanical behavior of the strand in a corrosive environment under static stress and to predict the number of cycles at which the strand will break. This procedure makes it possible to anticipate the service life of this structure under corrosive conditions. It also helps to establish a solid maintenance system that ensures a safe and reliable working environment.