Brittle-to-ductile transition during rock cutting by chisel pick under deep-sea confining pressure

• Failure mode transition characteristics of rock cutting under deep-sea confining pressure of 0-12 MPa were investigated. • Three failure modes and two critical cutting depths for rock cutting under deep-sea confining pressure were established. • FDEM-CEL numerical method was developed for rock-breaking in deep-sea confining environment. • Critical cutting depth and multi-tooth spacing arrangement for rock-breaking equipment applications were discussed. The advancement of deep-sea mineral extraction necessitates a comprehensive understanding of rock failure mode transitions under high confining pressures to optimize mining efficiency. This investigation systematically examines ductile-to-brittle failure transitions during rock cutting across a range of confining pressures, with particular emphasis on elucidating the relationship between critical transition cutting depth and confining pressure. Further investigation examines chip formation and crack propagation across different failure scenarios through a coupled finite discrete element-Euler method. The findings indicate that rock cutting is characterized by three distinct failure modes: ductile failure, ductile-brittle failure, and brittle failure. Each mode corresponds to the formation of specific chip morphologies—fine powder, flake-like chips, and chunk-like chips, respectively. Additionally, these modes align with three piecewise functions ( S E ∝ d 0 , S E ∝ d − 0.6 and S E ∝ d − 1.1 ) and distinct failure zones (the crushed zone, the plastic flow zone and the main failure zone). Notably, the critical transition cutting depth increases approximately linearly with confining pressure. As confining pressure rises, crack propagation diminishes, ultimately becoming confined to the region directly in front of the cutting tip. This study provides valuable insights into the development of low-disturbance and efficient mechanical rock-breaking techniques for deep-sea mining.