Abstract
In order to investigate the applicability of a creep damage evaluation method based on damage mechanics, creep tests on the specimens from five kinds of Cr-Mo-V steel differing in impurity content were carried out at 550°C-21kgf/mm2 and 575°C-16kgf/mm2. The results obtained are as follows:
(1) When calculation was carried out on the basis of the generalized damage equations derived from the Kachanov-Rabotonov equations, the calculated results corresponded relatively well to the experimental results for both the creep curve and creep damage parameters.
(2) The generalized damage equations in (1) are widely applicable to the damage evaluation of actual components under intergranular fracture conditions.
(3) Among the creep damage parameters, the A parameter value corresponded best to the calculated results of ω in comparison with the other two parameters, i.e. the cavity number and fraction of area. Therefore, the A parameter value is the suitable quantitative parameter for cavities in arranging them with t/tr.
(4) Consequently the equation to estimate the creep life fraction from the A parameter value is given by:
t/tr=1-(1-A)η+1 and: η+1=nλ/(λ-1) where n and λ are material constants and A is the A parameter value.
Furthermore, in consideration of dependence on material composition, λ is denoted by:
λ=10(1-Y)where Y is the creep ductility parameter, defined as the Y-factor.
On the basis of the above equations, a creep damage evaluation method to estimate the creep life fraction from the A parameter value is proposed.
