Issue 41

V.Shlyannikov et alii, Frattura ed Integrità Strutturale, 41 (2017) 291-298; DOI: 10.3221/IGF-ESIS.41.39 287  plane strain                                      2 2 1 1 1 1 1 1 mp f D (10)                                2 2 1 1 1 1 mp f D (11) Figure 1 : Rupture loci computed from multi-axial stress functions. By writing     0 i i where  0 is uniaxial rupture stress, the magnitudes of the biaxial stresses can be determined for different values of the governing material parameter  . In Fig.1, the results of calculations are shown for plane stress and plane strain conditions using Eqs.(8-11). For constant rupture time the particular forms (8-11) of general relationships (5,6), show a marked sensitivity to stress biaxiality and material constant  . It would clear therefore that in order to obtain material constants that govern the behavior of general stress function in the form of Eqs.(5,6) two sets of standard tests should be conducted: first set to determine the uniaxial tensile rupture characteristics, a second set carried out under uniaxial compression. The tests carried out under uniaxial compression, as it shown in Fig.1, are the most sensitive in their response to the material behavior under multi-axial stress conditions. C REEP DAMAGE FUNCTION et  denote the measure of damage with  = 0 denoting the undamaged state and  = 1 the fully damaged state. An equation describing the evolution of damage under a multi-axial stress state has been proposed by Hayhurst [1]                     1 2 1 1 mp A J J (12) Similarly, we introduce a function for rate of accumulation of creep damage as follows                   1 m f D C (13) L