Coupled influence of pore defects on the failure site for high-speed railway gearbox material

•A coupling factor considering the effective volume and diameter, f, is proposed to describe the competitive effect.•Fatigue specimens mostly fail at the pore with the largest f.•Fatigue crack propagation rates exhibit a linear relationship with the coupling factor, when it exceeds 2.•The geometry features of pores, as well as the orientations of ellipsoid pores are insignificant compared with pore size and pore location.