Abstract
The aim of this work is to show nucleation and development of creep voids under multi-axial stresses. Type-IV creep damage has been a troublesome problem formed in a fine-grained heat effected zone (HAZ), and it resulted in the degradation of the creep strength of structural components. The stress condition in the fine grained HAZ is usually under multi-axial stress state because the HAZ is bound by the base and the weld metals. In this study, some interrupted creep tests were performed employing circumferentially notched bar specimens of pure aluminum to examine the relation between nucleation/development of creep voids and multi-axial stress field. Distributions of creep voids were measured and counted the number and the damage ratio after segmentalizing metallographs. The photographs were divided by some types of grid lines at counting these damage, and evaluated by a similar A-parameter method. Experimental results showed that creep voids were formed in notch root inclined from the loading axis by about 45 degrees. Elastic creep FE analyses were performed to calculate the change of triaxial factor A in the notch root during creep. The triaxial factor A and the distribution of voids were almost the same trend in the distribution of voids.
