Development of a combined tension-bending fatigue testing device for FAST cable-driven steel wire ropes

The feed cabin of the Five-hundred-meter Aperture Spherical radio Telescope (FAST) achieves large-scale spatial movement under the traction of six cable-driven steel wire ropes, which form the core load-bearing structure of the feed support system. One end of each rope is connected to the feed cabin, whereas the other end runs sequentially over tower-top and tower-bottom pulleys and is finally wound around and anchored to the winch drum. During astronomical observations, the spatial position of the feed cabin must be frequently adjusted to track different celestial targets. Consequently, FAST cable-driven steel wire ropes are continuously subjected to alternating tensile loads and repeated bending deformations as they pass through pulley groups, thereby experiencing combined tensile–bending fatigue throughout their service lives. The combined tension–bending fatigue life of these wire ropes directly determines the operational safety of the entire feed support system. A comprehensive investigation of domestic test conditions for steel wire rope fatigue reveals that no specialized testing device currently meets the requirements for combined tension–bending fatigue testing of FAST cable-driven steel wire ropes. While most existing test platforms can only conduct independent tensile and simple fatigue tests, they cannot simultaneously apply stable tensile and cyclic bending loads to test specimens. This complicates the reproduction of the actual combined stress state of FAST cable-driven steel wire ropes in service and restricts the accurate evaluation of their fatigue performance. To accurately assess the combined tension–bending fatigue life of FAST cable-driven steel wire ropes, the authors developed a dedicated testing device.

First, the actual service conditions of the wire ropes were comprehensively analyzed to obtain key operational parameters of the ropes, including the tensile load variation range, bending cycle characteristics, and matching pulley dimensions. These parameters provided a solid basis for subsequent design schemes. Second, based on the acquired operational parameters, the design indices of the testing device were defined, covering load capacity, test frequency, and pulley dimensions. On this basis, an overall design scheme for a fully hydraulically driven combined tension–bending fatigue testing device for steel wire ropes was proposed, and the device adopted the structural form of "horizontal integral frame–dual-wheel-train bending loading mechanism–hydraulic linear cylinder tension loading system." Third, targeted calculations and analyses were performed on core device components, specifically the driving torque of the hydraulic oscillating cylinder, the service life of bearings and linear guide rails, and the force conditions of pulley assemblies, to verify the design rationality and safety. Finally, load commissioning of the testing device was conducted using actual FAST cable-driven steel wire ropes as test specimens.

The commissioning results show that the testing device operates smoothly under preset working conditions. It fully meets the requirements for combined tension–bending fatigue testing of FAST cable-driven steel wire ropes, faithfully reproducing their actual service conditions. All performance indices meet the predetermined design requirements, and the device satisfies the conditions for formal fatigue testing.

Once operational, this testing device will enable researchers to reveal the fatigue failure mechanism and life evolution laws of FAST cable-driven steel wire ropes through systematic experiments, providing key data support for the operational safety assessment of FAST. Additionally, the device will provide essential support for domestic steel wire rope performance testing and quality evaluation, promoting the high-quality development of the industry nationwide.