Impact-Sliding Composite Wear Properties of Shield Cutter Ring Material

The wear of disk cutters has greatly effects on the working efficiency of tunnel boring machines. The cutters are mainly suffered by impact-sliding composite wear. By using the self-developed impact-sliding wear test device, the wear properties of the cutter ring base material (H13 die steel) under different structural stiffness were studied to simulate the variation of the relative stiffness between cutter and rock. The contact angle was fixed at 45°. The contact pressure between the flat sample and counter-part was within the range of hundreds megapascals, which was on the same order of magnitude as the real load on the disk cutters. The micro-morphology, wear volume and wear depth of the material samples after the tests were analyzed by the optical microscope, scanning electron microscope and white light interferometer, and then the wear mechanism was revealed. The results indicated that, with the increase of structural stiffness, the sliding distance of the Si₃N₄ ball along the H13 steel sample decreased, the pressure load and the action time increased, also the contact time in the sliding zone increased, resulting in that the most damaged area of the flat samples tended to move along the sliding direction. In the impact region, the larger structural stiffness increased the von Mises stress and the contact pressure on the micro-convex body of the interface, which made the base material be removed quickly. Therefore, the wear volume and the maximum wear depth of the flat sample increased, and the major wear form of the impact region was ploughing and the wear mechanism was abrasive wear. In the sliding region, the sample surface bore relatively small stress under the condition of low structural stiffness, so the wear was mild and no obvious increase of the wear volume and maximum wear depth in each region with the increase of loading cycles. Accordingly, the contact state, friction coefficient and load value were almost unchanged during the test. As the structural stiffness increased, both the wear scratch width of the flat sample and the wear area of the Si₃N₄ ball increased, and the contact area increased continuously, implying the contact surface became more compatible. In addition, the contact time of the grinding pair in the sliding region increased when the structural stiffness became larger. Therefore, with the increase of loading cycles, the wear of the sample surface became more severe, and the main damage area moved from the front side to the back side of the sliding region, and the most serious wear area appeared in the back of the sliding region. The number of wear debris between the interface kept growing and a cutting effect was induced to the sample surface, thus the ploughing phenomenon appeared in the sliding zone. At this point, the stress values in the sliding region were large enough to cut off the abrasive debris adhering to the surface of the flat sample, leading to the delamination in the sliding region. Correspondingly, the wear mechanism changed from abrasive wear to a mixture of abrasive wear and adhesive wear. In summary, the impact-sliding composite wear microcosmic working state of the interface of the disk cutter was reproduced, and the microscopic wear mechanism of H13 steel was thoroughly investigated. It would be helpful to a better understanding of the interaction between the cutter and the rock with different degrees of contact stiffness, offering a guidance for the structural design of the cutterhead under the composite stratum, and provide a new research method for the evaluation of wear properties for cutter materials.