Wear of WR-CVT Discontinuous Contact Wire Rope Based on ARCHARD Wear Model

As the core component of a new type of continuously variable transmission WR-CVT (Wire rope continuously variable transmission), the performance of wire rope directly affects the service life. Wire rope of WR-CVT has two geometric characteristics: straight and bent. In the bending section, there is a tiny gap between the metal blocks, and the contact between the wire rope and the metal blocks is not continuous. With the action of tension, stress concentration would occur on the contact surface of steel wire, which would further aggravate the wear of wire rope. Aiming at the problem that wire rope of WR-CVT is easy to wear under discontinuous contact condition, the influence of wear on contact parameters such as contact compressive stress and slip amplitude was studied based on finite element method, and the wear mechanism was revealed by experiments. Specifically, taking 6×7+IWS wire rope as the research object, the geometric model of the wire rope with the transmission ratio of 0.483 under the minimum working radius (35 mm) of the driving pulley was established based on Frenet-Serret frame method. The neutral axis algorithm sweeping mesh generation technology was used to divide the wire rope grid. Secondly, the Archard wear model was modified. Based on the Archard wear model and the grid adaptive technology, the Umeshmotion subroutine suitable for wire rope of WR-CVT discontinuous contact wear was written in FORTRAN language. 0~7 000 wear cycles of wire rope of WR-CVT under axial load were simulated. Finally, the wire rope of WR-CVT wear test was carried out on the self-made wear test rig. In order to distinguish the contact part between steel wire and metal block, the non-contact part between non-jointed wire rope and pulley was dyed. JP-008 ultrasonic cleaning machine was used to clean the wear debris of the wire rope after the test, and Gemini360 scanning electron microscope was used to observe the wear marks of the side strand and side wire rope contacting the pulley after the test. The results showed that the contact area between wires increased and the contact compressive stress decreased in different degrees after wear. The larger contact range made the contact pressure spread to more positions, and then the value of the concentrated position of contact compressive stress decreased. The maximum wear depth was about 0.053 2 mm at the discontinuous contact between the steel wire and the edge of the metal block. The contact compressive stress was 2 276 MPa before wearing, and decreases to 145 MPa after wearing, with a decrease of 93.6%. The removal of material alleviated the stress concentration level at the contact edge. With the wear progressing, the slip amplitude and wear depth at the discontinuous contact were increasing, but the increasing range was decreasing. The point stress concentration area appeared at 1 000 wear cycles, and the line stress concentration area appeared at 3 000 wear cycles, which indicated that the contact area between steel wire and metal block gradually changed from point contact to line contact. When the wear cycles reached 5 000 cycles, the stress concentration area moved along the axial direction of the steel wire, the wear surface of the steel wire was gradually rugged, and at the same time, the steel wire was slightly twisted, and then a new stress concentration point appeared. Finally, when the wear cycles reached 7 000 cycles, the contact stress was minimum and the contact form changed into face contact. The experimental results showed that there were obvious flat wear marks on the steel wire surface, obvious furrows and abrasions on the contact surface along the sliding direction, and the widths and lengths of furrows were different. There were pits caused by particle shedding, and wear debris, as the third body, had furrow effect on the matrix. The contact surface was uneven where the wear was serious, and the shear failure made the contact surface material extrude and deform, which formed uneven appearance. As a result, it had plastic deformation, delamination and microcracks. Some contact surfaces had strong shaping deformation, a small amount of furrows, spalling pits formed by material spalling and tiny wear debris. Therefore, the wear mechanism of wire rope of WR-CVT under discontinuous contact was mainly abrasive wear, adhesive wear and fatigue wear.