Issue 41

V.Shlyannikov et alii, Frattura ed Integrità Strutturale, 41 (2017) 285-292; DOI: 10.3221/IGF-ESIS.41.38 290 shown contours of damage zones around the crack tip at  =50Mpa and creep time t / t T = 45.7 for material different properties defined by the value of constant  =  t /  c . Contours in Fig.4 demonstrated process of the crack tip damage accumulation as a function of creep time. Figure 2 : Von Mises equivalent stress angular distributions for different solids states. Figure 3 : Contours of damage around crack tip at  =50Mpa and creep time t/t T =45.7. Figure 4 : Contours of damage around crack tip as a function of creep holding time. The important factor in the present study is the influence of state of stress on the damage process. To this end a plane strain analysis of a plate containing an internal crack of relative length a/w =0.01 which is loaded by remote tension was also carried out. In Fig.5 the numerical results for the maximum size of creep damage zone behavior are shown as a function of creep time. It follows from these data, in essence, maximum damage size is sensitive to the maximum principal stress or to the hydrostatic stress through effective stress function formulation by Eqs.(5,6). An increase in hydrostatic stress with  < 1, then increases the damage zone leading to failure at lower strains and lower times. As in the case of the dimensionless stress angular distributions   ij (Fig.2), the main effect of damage parameter  or material properties  on the dimensionless displacement rate components  i u arises through the normalizing factor in the form of creep I n -integral (Eqs.17-19). Figure 6,a represents variation of the I n -integral distributions through the creep stage for different values of the governing parameter  for material behavior constitutive equation. It should be noted that the values for creep I n -integral do not coincide with those of the HRR elastic-plastic field HRR n I = 5.024 at the same hardening exponent n = 5. Furthermore, in the frame of creeping solids formulation, I n -integral distributions as a function of creep time for undamaged and defective materials are different and these distinctions increase with increasing of the holding time. It is obvious that in creeping solids the behavior of the governing parameter of crack-tip field with elapsed time beyond t/t T > 1 is very sensitive to the material constant  =  t /  c variation.