Determination of the critical depths of indentations for local rolling contact fatigue initiation

•Local rolling contact fatigue (LRCF) is reproduced by scaled twin-disc tests.•Critical indentations over which LRCF initiates are found for test discs.•Influence of indenter geometry on plastic strain of indentations is analyzed.•Transferrable critical plastic strain for LRCF initiation is obtained.•Size-dependent critical depths are proposed for indentations in practice.