Micro mechanics based on vacancy diffusion coupled with damage mechanics related to creep deformation and prediction of creep fracture life

Abstract

In situ observations of crack growth and damage progression were conducted under creep conditions for P92 and titanium aluminides inter-metallic compound. A proposed analysis of stress induced particle diffusion was applied to stress induced vacancy diffusion. Results obtained from this analysis were successfully correlated with the experimental behaviour of macroscopic damage progression and a theoretical characteristic of creep deformation was derived. It was found to be in good agreement with experimental characteristics of creep deformation. Furthermore, the experimental characteristics of creep damage progression which concern voids and micro crack formations at grain boundary were found to be well correlated with those of deformation. From these results, correlation between vacancy diffusion in nano-scale, creep damage in mezzo-scale and creep deformation in macro-scale were successfully realized.

A review of a time-dependent fracture life law (or model) based on a proposed multi-scale analysis

“…The first category closely concerns fracture mechanics [15][16][17][18][19][20]. The second category closely concerns macro-scale damage mechanics [21][22][23] and the nucleation theory of voids caused by vacancy diffusion [24][25][26][27], whereas the third category relates to vacancy diffusion and the adopted method of analysis of stress induced vacancy diffusion [28]. The adopted basic equation is that of potential driven particle diffusion which was validated by many authors [29][30][31].…”

“…A void is originated by nucleation mechanisms and it grows and links with other voids, which results in micro grain boundary cracks. Previous work has shown that the mechanical treatment of the damage function, ω, is different depending on the scale of each observed damage [28]. Furthermore, based on the application of experimental results obtained in laboratories to the case of actual engineering structures, the effect of local multi-axial stress on creep deformation and crack growth is involved in structural geometries of engineering structures.…”

“…Some of the authors have developed in-situ observational equipment for damage originating in specimens under high temperature creep and fatigue conditions and have observed damage formation at the scale of voids and grain boundary micro cracks [28,36,37]. The system for in-situ observation of creep damage was designed and developed to enable automatic real-time observational experiments with CCD microscope [28,36].…”

“…The system for in-situ observation of creep damage was designed and developed to enable automatic real-time observational experiments with CCD microscope [28,36]. Using this equipment, in-situ observation of creep damage progression was conducted.…”

“…The damage region around a notch tip was identified as a dark region that of a micro crack that originated along grain boundaries as shown in Fig. 3(a)-(c) [28,36,37]. Damage is initiated by micro cracking along a grain boundary that consists of voids at grain boundaries as shown in Fig.…”