Issue 52

A.V. Tumanov et alii, Frattura ed Integrità Strutturale, 52 (2020) 299-309; DOI: 10.3221/IGF-ESIS.52.23 303 1 0 3 0 (1 ) 1 m m e C D t m         (16) Based on the fact that the damage parameter is equal to one at failure 1   the fracture time at the known stress level can be calculated directly: 1 ( 1) cr m e t m D    (17) C REEP CRACK GROWTH RATE or elastic-nonlinear-viscous material behavior, the stress, strain and displacement rate fields can be use in order to account for a creep stress intensity factor cr K , which is amplitude of singularity. For extensive creep conditions the relation between the C -integral and creep stress intensity factor is introduced by the authors [19] in the form: 1 * 1 1 cr n cr ref cr C K BI L          (18) 1 * cos 1 sin cos cr n cr e cr r r rr r rr r n C Br d n u u u u r d r r                                                                   (19) where ref  - is reference stress, cr K is amplitude of singularity in the form of creep stress intensity factor, C* is the C - integral, i u  are displacement rate angular functions, ij  are stress components. It should be noted that the cr I - integral values are determined similar to p I and can be determined directly from the finite element analysis by distribution of the displacement rate functions, i u  , and dimensionless angular stress functions, ij   , [9]. More detail in determining the cr I - integral for different creeping cracked body geometries are given by Refs. [12, 19-22]. For a static crack in the outer region of the small-scale creep zone, the elastic crack-tip fi eld still dominates. In this case, the expression of C -integral has a simple form [5]: 2 2 1 (1 ) ( ) ( 1) cr cr K C t E n t     (20) The elastic stress intensity factor for a compact tension specimen is [23]: 1 1 F K Y b w  (21) where F - is applied load, 1 Y - is geometry correction function: 2 3 4 1 3/2 (2 / ) (0.886 4.64 / 13.31 14.72 5.6 (1 / ) a w a a a Y a w w w w a w                          (22) F