The behavior of cutting discs for mechanized tunneling under cyclic loading conditions

• Published in: Tunnelling and underground space technology 2023-07, Vol.137, p.105151, Article 105151
• Main Authors: Brackmann, Lukas, Röttger, Arne, Treppmann, Michelle, Weber, Sebastian
• Format: Article
• Language: English
• Subjects: Crack growth; Disc cutter; Fatigue behavior; Mechanized tunneling; Wear
• ISSN: 0886-7798; 1878-4364
• DOI: 10.1016/j.tust.2023.105151

•Micromechanisms of damages imposed on cutting discs by cyclic loads were investigated.•Cyclic loading causes fatigue cracks and spalling of chips due to plastic deformation.•The strength of the employed steel determines the resistance against these damages.•Currently employed hot work tool steels dont exploit the full strength potential.•Ledeburitic cold work tool steels offer improved strength by including hard phases. In the case of a heterogenous ground condition, tunneling tools are exposed to cyclic loading. The cyclic loads can exceed the materials' permanent load-bearing capacity, which is associated with fatigue crack growth. Subsequently, the coalescence of fatigue cracks can cause spalling of material from the tool surface, leading to the deterioration of their functionality. The problem of fatigue damage on tunneling tools has lately been recognized. However, the underlying micromechanism of subcritical crack growth and the counteraction of fatigue by advanced material concepts still require fundamental research. In this work, miniaturized cutting discs made of different tool steels are subjected to a laboratory scale fatigue test and subsequently analyzed concerning fatigue damages and the material response to cyclic loading. The hot work tool steel X40CrMoV5-1, widely used for cutting discs in industrial practice, showed fatigue crack growth and significant plastic deformation of the cutting edge under cyclic loading, leading to chip formation and spalling at the cutting edge. An improvement was found by using X153CrMoV12 ledeburitic cold work tool steel, which offers a higher strength due to the coarse chromium carbides distributed in the microstructure. Due to their high young modulus, the carbides can inhibit the plastic deformation of the softer metal matrix at the cutting edge, thus increasing the edge retention and suppressing chip formation.