Creep damage evaluation via uniaxial miniature testing for multiaxially stressed Mod.9Cr–1Mo steel components

In this study, creep damage in a biaxially creep-damaged Mod.9Cr–1Mo component has been examined via uniaxial miniature creep testing. Using cruciform specimens, biaxial tension creep tests were conducted at principal stress ratios (λ) of λ=0.0 and 1.0 at 923 K. The principal stress ratio is the ratio of the y-directional principal stress (σy) to the x-directional principal stress (σx) in a cruciform specimen (λ=σy/σx). The equi-biaxial creep test was interrupted at a half lifetime, and two miniature specimens were machined from the damaged cruciform specimen in the x- and y-direction. The applicability of the linear cumulative creep damage rule was assessed using the results of the miniature lifetimes. The linear cumulative creep damage rule gave an unconservative estimate to the remaining life of a biaxially damaged cruciform specimen. Using the hyperbolic constitutive relationship, the unconservative estimate according to the damage accumulation was explained.