ABSTRACT
This chapter introduces the integrated creep-fatigue theory (ICFT), but first reviews the current constitutive modeling and life prediction theories. The ICFT constitutive law and life evolution equation are derived from two principles: i) physical deformation decomposition including all deformation mechanisms, and ii) holistic damage accumulation process consisting of nucleation and propagation of surface/subsurface fatigue cracks in coalescence with internally distributed damage promoted by creep and intergranular embrittlement. The ICFT overcomes the shortcomings of the existing theories and models. The unified constitutive theory does not delineate mechanism strain (it only evaluate the lump-sum viscoplastic strain) and therefore does not correlate with physical deformation and damage. The continuum damage mechanics uses a parametric damage concept, which does not differentiate the physical nature and type of damage, i.e. intragranular or intergranular. It will be shown in later chapters how ICFT works out for all deformation phenomena including creep, low-cycle fatigue and thermomechanical fatigue.
