13th International Conference on Fracture June 16–21, 2013, Beijing, China 3 * ( )q da C C d , (2) where , C and q denote the time, creep crack growth coefficient and exponent, respectively. Provided C* has the unit of Nmm-1h-1, C and q for tests of compact tension (CT) specimens of 316 stainless steel at 600ºC [15] are also shown in Table 2. Table 2. Material properties of the 316 stainless steel tested at 600ºC. E (MPa) A (MPa-nh-1) n C q f (%) 148000 0.3 1.47×10-29 10.147 2.774×10-2 0.958 27 2.3 Creep-damage model The continuum damage mechanics model can trace its roots to Kachanov and Rabotnov’s work [16, 17]. Since then there have been many attempts to develop an appropriate model [5, 18-20]. Recently, the authors presented a creep-damage model to simulate creep fracture, which is capable of characterizing the full creep curve and can reasonably reflect the influence of stress state on creep deformation and damage. More detailed description and validation of the proposed creep-damage model can be found in Refs. [21, 22]. The proposed model is as follows: 1 2 2 1 1 3 1 2 n c n ij e ij e A s , (3) and * c f , (4) where A and n are material constants. c ij , ij s , e and 1 are the creep strain tensor, deviatoric stress tensor, equivalent stress and maximum principle stress, respectively. , c and * f denote the damage variable, creep strain rate and multi-axial creep failure strain, respectively. is a stress-independent function reflecting material behavior, having the form 2 3 4 2 3 4 2 3 3 3 2 1 1 9 1 108 1 n n n n n n n n n n , (5) where the micro-crack damage parameter, , depends primarily on the number of micro-cracks per unit volume and their average diameter. Suppose the damage variable is given as the reduction of the effective area in the cell, we can obtain 3/2 2( 1) 1 3/ n n . (6)
RkJQdWJsaXNoZXIy MjM0NDE=