DEFORMATION-BASED LIFETIME PREDICTION FOR ROPES UNDER CBOS LOADING
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Summary
The existing lifetime prediction methods of running ropes do not consider differences in material properties, which can lead to incorrect prediction. This article presents the development of a strain-based prediction approach, which enables significantly increased prediction accuracy. Cyclic Bending Over Sheave (CBOS) tests are reported. Experimental comparisons show a direct correlation between the deformation applied per bending cycle, the rope-specific deformation capacity and the lifetime actually achieved. By taking a holistic view of the rope deformation curve – i.e. the relationship between stress and strain until breakage – each load can be assigned a load-dependent and rope-specific deformation. With knowledge of the loads acting during operation, the deformation occurring per bending cycle on the rope can be determined using the stress-strain curve and set in relation to the rope-specific total deformation capacity. This forms the basis for a strain-based approach to predicting the lifetime of running ropes. By using strain as a predictive parameter for lifetime, it is possible to define effective safety against fatigue. Furthermore, by considering the rope-specific deformation curve, the transition from fatigue to violent failure, known as the Donandt point, can be explained and deduced. The results indicate that the quasi-static tensile test is sufficient as a quick test for predicting the lifetime of nominally identical ropes of different qualities.
Author: W. Frick
Key words: CBOS, fatigue, lifetime prediction, stress safety, strain safety, deformation behaviour, strain-based prediction
