Issue 41

V.Shlyannikov et alii, Frattura ed Integrità Strutturale, 41 (2017) 291-298; DOI: 10.3221/IGF-ESIS.41.39 291 Figure 5 : Crack tip damage zone maximum size as a function of creep time. Figure 6 : I n -factor (a) and (b) creep stress intensity factor behavior as a function of creep time. Finally Fig.6,b represents the corresponding numerical results for creep stress intensity factor behavior as a function of creep time according to Eq.(15). The curve concerns to the undamaged material for the steady state of secondary creep solution is also shown in this figure. The creep damage rate dependence of creep stress intensity factor arises from the time dependence of the I n -integral. Again it is clear that the effect of damage evolution appears at the extensive creep condition behind of the small-scale state when the transition time t/t T > 1. It should be note that as recommended by corresponding ASTM standards, the description of the crack growth rate under creep and creep-fatigue conditions should be given in the terms of C(t) or C* -integral. However, this parameter a-priory may not take into account the effect of the accumulation and growth of damage. Unlike the definition for the elastic stress intensity factor and C -parameters, the creep stress intensity factor approach gives the possibility to obtain the crack growth rate as a function of creep damage. To this end, it was necessary to calculate the I n -integral distribution for each crack front position corresponds to a certain combination crack length and creep time and as consequence accumulated creep damage. Recall that in the present study all calculations carried out for the stationary crack under steady state secondary creep conditions. Going back to the crack growth interpretation it should be noted that the effect of the creep damage accumulation on the creep crack growth rate may be scaled through the corresponding value of the creep stress intensity factor. In addition, an inherent property of the creep SIF is their dependence on the multi-axial state of stress through the equation for the damage function (13). Under certain circumstances, this numerical solution may also have application to creeping solids which undergo damaging near the crack tip. Thus, the creep SIF may by identified as damage sensitive high temperature fracture parameter for correlating crack growth under multi-axial stress of state conditions.