Effect of Biomimetic Erosive Medium on the Rolling Friction and Wear Behavior of TBM Cutter/Marble

The cutters of tunnel boring machines (TBMs) suffer severe wear and low rock-breaking efficiency when encountering hard rocks including marbles and granites that have high hardness and abrasiveness. Recently, the studies have revealed a few biomimetic erosive media for degrading the mechanical properties of rocks, but little work has been completed on the effect of the media on the rock-breaking performance and wear behavior of TBM cutters. Therefore, the work aims to investigate the rolling friction and wear behavior of TBM cutter/marble under different normal loads in a biomimetic erosive medium, and elucidate the effect of the biomimetic erosive medium on marble surface damage and cutter wear, to provide valuable insights for the chemically assisted improvement of TBM rock-breaking efficiency. In this study, flat samples were natural marbles of 270 mm in diameter and 15 mm in thickness, and ring-shaped counterparts were reduced-scale TBM disc-cutters that were made in H13 steel with an outside diameter of 15 mm and an edge width of 0.8 mm. A mixed solution of EDTA-2Na, phytic acid and KOH developed by the inspiration of bio-erosion in nature was used as biomimetic erosive medium (EP) and deionized water as control medium. The corrosiveness of EP was characterized with marble and cutter samples. A self-made rock-breaking test rig was employed to conduct the rolling friction and wear tests of the cutter/marble pair in the deionized water and EP and three normal loads of 45, 75 and 105 N were used. Surface hardness of samples was measured with a micro-hardness tester. The wear morphologies and profiles were characterized by a laser confocal scanning microscope, a scanning electron microscope and a three-dimensional optical microscope. All tests were conducted at 20 ℃. The bionic erosion medium EP was not obviously corrosive to the cutters but induced secondary cracks and corrosion pores on the surface of marble sample, and the surface hardness of marble was reduced by about 20.6% after 1 min immersion in the EP. Under the given rolling friction contact condition, the EP promoted the breakage and material removal on the marble surfaces and reduced the wear of cutters. When the applied normal loads were 45, 75 and 105 N, respectively, the wear volume of marble in the EP increased by 25.3%, 9.3% and 17.5% and the specific energy of cutter decreased by 28.3%, 11.4% and 20.0%, respectively, compared with those in the deionized water. The surface damage of marble samples was characterized by the grinding and exfoliation of mineral particles and the resulting slight material removal at 45 N, obvious material removal and development of dense cores at 75 N, and significant cracking and material removal at 105 N. In sum, due to no obvious metal corrosion but the potential to weaken rock surface mechanical properties, the biomimetic erosive medium (EP) can facilitate the breakage and material removal on marble surface under rolling friction contact condition and reduce the wear and specific rock-breaking energy of cutters. The facilitation effect of EP on the rock-breaking performance of cutters is affected by the damage patterns of rock surface. The damage of marble surface is dominated by the exfoliation of mineral particles and the development of dense cores under low normal loads, and the EP only acts on the rock surface, leading to a limited contribution. At high normal loads, cracks and fractures are produced on the rock surface to enable the penetration of EP inwards, thereby facilitating the material removal of marble surface and improving the rock-breaking efficiency of cutters. © 2024 Chongqing Wujiu Periodicals Press. All rights reserved.