MICRO-CRACK GROWTH AND LIFE PREDICTION OF A 1CRMOV STEEL UNDER AXIAL-TORSIONAL LOW-CYCLE FATIGUE AT 550-DEGREES-C

Micro-crack behaviour under axial and torsional loading at 550 degrees C was observed by replica techniques. Cracking behaviour and micro-damage observations were correlated using several parameters that are based on equivalent strain parameters. From the observations, micro-cracking of the oxide films at the crack tip in the strain localized regions seems to be a dominant micromechanism of fatigue crack growth. The maximum principal strain has been identified as an important parameter in multiaxial fatigue at high temperature. A good correlation was obtained between the principal strain range and the crack growth rate. Finally, a life prediction method was proposed based on maximum crack length.