Creep damage analysis of mod.9Cr-1Mo steel welds considering void mechanics modeling

Type IV creep crack initiation and propagation in mod.9Cr-1Mo steel welds

“…Distribution of creep void density changes as time progresses, reflecting the re-distribution of stress through the thickness. Predicted crack initiation and rupture time by creep damage analysis were 4825 h and 5100h, within a factor of 2 on life when compared with the experimental rupture life of 2775.2h [15]. Case 2 is a circumferentially welded tube subject to internal pressure and axial load at 650℃.…”

“…The creep constitutive law of the FGHAZ is given in eq. ( 1), showing secondary and tertiary creep due to strain __________________ __________________________________________________ softening and damage; the creep law for the base metal and weld metal are the same Blackburn type equation, showing primary and secondary creep [15]. During creep, stress re-distribution in the welded joints occurs due to the progress of creep strain and damage.…”

“…Since void nucleation and damage models for the FGHAZ have been reported in a previous paper [14,15], only an outline is given here. A creep constitutive law of the FGHAZ was formulated based on the model of Perrin-Hayhurst [17] as shown in eq.…”

“…Creep void density distributions in the large-uniaxial cross welds was predicted with the help of stress distributions determined from FE creep analyses, and final rupture life was also predicted using a damage mechanics concept. Honda et al [14,15] developed a damage simulation method combining continuum damage mechanics and a void nucleation model (void mechanics model) proposed by Gonzalez and Cocks [16] in which a grain-size cavity formed by failure of all its facets under a multiaxial stress state is regarded as a void. The merit of this method is to be able to predict both creep void density and rupture life of welded structures at the same time.…”

“…The merit of this method is to be able to predict both creep void density and rupture life of welded structures at the same time. From a damage-mechanics point of view, the mechanism of Type IV creep failure within the FGHAZ is composed of two stages [14,15]: a stage of increasing creep void density with a size comparable to the FGHAZ grain size (5μm); and a strain softening stage in the last part of creep life.…”