Development of a novel approach to correlate small punch fatigue with uniaxial ratcheting fatigue

•Cyclic behaviour of SS 316LN and P91 steels is studied through small punch fatigue (SPF) and uniaxial ratcheting.•The effect of loading parameters on fatigue life for SPF and uniaxial ratcheting is analyzed.•Three different fatigue life prediction models are compared to derive correlation between SPF and uniaxial ratcheting.•A new deformation rate based damage parameter is proposed and a novel SPF - ratcheting correlation is established.•Crack surface morphology of failed SPF and ratcheting samples is reported. The miniaturization of fatigue specimens has seen significant advancements, realized either by scaling down conventional specimens while preserving their geometry or by experimenting with novel specimen shapes and loading configurations. In this study, the small punch test (SPT) technique, which is well-established for estimating tensile, creep, and ductile-to-brittle transition temperature (DBTT), is employed to predict the cyclic deformation behaviour of SS 316LN and modified 9Cr-1Mo (P91) steels. The small punch fatigue (SPF) experiments demonstrated continuous displacement accumulation, similar to strain accumulation in ratcheting. The study evaluates the influence of various load parameters, such as amplitude and mean load, on SPF outcomes and compares these to the effects of stress amplitude and mean stress on ratcheting results. The differences in deformation behaviour between ratcheting and small punch fatigue and the effect of biaxiality in SP configuration life is analysed. Finally, to establish a correlation between SPF and ratcheting results, the three life prediction models (Gerber, Goodman, and Smith-Watson-Topper) are examined and a new correlation is proposed by introducing a novel damage parameter.