Creep-Fatigue Damage Rule Based on Strain Range Partitioning Concept and Its Application to 316LC Steel
Miyahara Mitsuo; Tokimasa Katsuyuki
Abstract:The creep-fatigue life prediction model previously proposed for evaluating Mod.9Cr-1Mo steel under variable strainings was applied to 316LC steel. In the proposed model the small crack growth curves in a smooth specimen are predicted in accordance with the applied straining conditions by using the material parameters and they are used as the damage accumulation curves. The feature of this model is its potential to evaluate the material damage and the residual life under arbitrary variable creep-fatigue strainings. For examining whether or not it is possible to determine the material parameters for 316LC steel based on the same creep-fatigue life prediction model as for Mod.9Cr-1Mo steel, creep-fatigue tests, crack growth tests, and high-low (HL) and low-high (LH) type two-step variable straining tests were conducted with PP(fast-fast) and CP(slow-fast) type strain waveforms at 700 degree and 800 degree. It was suggested that the crack initiation life cannot be negligible not only in PP type low strain ranges but also in CP type low strain ranges whereas it is negligible in CP type low strain ranges for Mod.9Cr-1Mo steel, and the model was partly modified to describe the initial crack growth behavior of 316LC steel. The remaining life in HL and LH tests was well predicted by the modified proposed model. Key Words:creep-fatigue, material damage, small crack, remaining life prediction, 316LC steel