MODELLING THE RESIDUAL BREAKING FORCE CURVE OF DIFFERENT ROPE TYPES IN CBOS-TEST
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Summary
Fibre ropes and steel wire ropes continue to be the focus of various development projects. Fibre ropes are also increasingly being used in applications such as cranes and lifts, where steel wire ropes were previously the only option. In these applications, the relevant standards for tensile members (regardless of whether steel wire or fibre rope) specify residual load-bearing capacities at the end of the service life. A common limit is a residual breaking force of 80 % of the minimum breaking force as a defined limit value, e.g. according to DIN EN ISO 8100-1:2024 or ISO/TS 23624:2021. This also corresponds to the residual load-bearing capacities/safety levels of the terminations according to DIN EN ISO 13411-1 to 7. The service life of running ropes is usually specified in terms of rope bends. This immediately raises the question of how the residual load capacity decreases with increasing number of bending cycles. During operation, this determines the current safety factor until the discard criterion specified in the standard is reached. The loss of load-bearing capacity as a result of wear and material fatigue due to continuous bending manifests itself differently in different rope types/designs and rope materials. In order to be able to describe these different characteristics over time, a corresponding mathematical model is being developed. Each rope is a redundant tensile member and has a number of parallel load-bearing substructure elements (e.g. wires, strands, yarns, threads, Figure 1). Discrete modelling does not appear to be effective given the large number of individual elements, especially for fibre ropes. Instead, the residual breaking force is modelled statistically across the rope cross-section. The suitability of the model is demonstrated using various historical and current data, and possible applications of the model are highlighted.
Author(s): C. Müller, M. Helbig, A. Kretschmer
