PSI - Issue 18

Abdeljalil Jikal et al. / Procedia Structural Integrity 18 (2019) 731–741 Abdeljalil JIKAL et al./ Structural Integrity Procedia 00 (2019) 000–000

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homogeneous loss of wire cross-section and a reduction of the strength at cable failure. In addition, they reduce deformation at wire failure and promote fatigue-crack. Both types of corrosion can cause wire rope failures by exceeding the admissible stress, the failures being of a ductile nature Périer et al (2009). A significant factor in the lifespan of a cable is its fatigue life. Cable failure phenomena are due to fatigue rather than a load exceeding the ultimate strength of the cable. Due to the construction of a cable, the different wires are subjected to tensile, contact, frictional and torsional bending loads [3]. These phenomena occur due to increasing in the number of broken wires until the wire rope becomes completely broken. Many numerical and experimental research studies were conducted to characterize and predict the mechanical behaviour of the cables. For instance, the reliability of wire rope damaged by fatigue at different percentages of its wires was studied by Meksem et al (2011). Tijani et al (2017) discussed the effect of the combined degradation modes of accelerated corrosion and wires breaking on the mechanical properties of a wire rope. Furthermore, Molnár et al (217) conducted research on a rope sample and wire samples to examine the process of degradation of the mechanical properties of ropes in the corrosive environment. In addition, Meknassi et al (2015) were interested in the corrosion of the wires extracted of a wire rope. Therefore, the aim of this work is to study the influence of corrosion on the mechanical behavior of the outer layer strand of a steel wire rope during service period. Besides, the strand damage evolution is monitored as a function of the immersion time in sulfuric solution for different lengths of time. Based on an experimental study carried out on virgin and other corroded samples and the damage models, we determine the different stages of damage as well as the critical life fraction that can lead to sudden failure of the wire rope. New concepts based on the limit force formulas such as Faupel et al (1953), this formula led to two ways of damage modeling of strand of a wire rope: • A theoretical model based on the Faupel formula applying a corrective coefficient  ; • An adaptive model using the force formulation ( ) F  as a function of the life fraction and the critical life fraction and assuming that the applied force corresponds to the calculated force ( ) F  corresponding to the last experimental life fraction. This modeling is considering the theoretical calculations of the strand's failure force, for different level of corrosion, by either the Faupel or ( ) F  formulas. Therefore, we consider the failure force of a strand as the ultimate rupture force, maximum force, while the other forces, related to the damaged strands, are considered as residuals for theoretical and adaptive damage models. These methods are verified and compared with the static damage model calculated through the tensile test in order to assess their accuracy. The strand studied in this paper was extracted from the outer layer of a 19*7 steel wire rope, with (1*7 + 6*7 + 12*7) non-rotating constructions of 10 mm diameter. The rope sample was prepared according to ISO 6892 1984 Aegerter et al (2009), which deals with tensile tests at ambient temperature of metallic materials. The rope specimen was previously cut to a length of 300 mm, of which 200 mm according to the international standard and 100 mm for the fixing element, then unwrapped to obtain the strands. This operation was performed with particular care to avoid damage of specimens. A length of 200 mm was taken as the tests length for all strand samples. The study of Wang et al (2014) on the influence of corrosive environments demonstrated the harmfulness of acid solution on wire ropes. The corrosion damage to the specimens was achieved by immersing a well-defined number of strands constituting the sample in a 30% concentration of 2 4 H SO sulphuric acid solution for different times, under ambient conditions, in order to damage the central part of the strands, followed by measurements of the loss of cross-section as a function of the immersion time. 2.2. Tensile tests on specimens The tensile tests were conducted on virgin and other specimens damaged by corrosion at different levels. They were realized in monotonous tensile according to the NF EN 10002-1 standard with imposed displacement corresponding to a strain rate of 1.5 mm/min Tijani et al (2017), on a Zwick Roell tensile machine with a capacity of 10 kN as 2. Material and method 2.1. Sample preparation