Issue 30

Yu.G. Matvienko, Frattura ed Integrità Strutturale, 30 (2014) 311-316; DOI: 10.3221/IGF-ESIS.30.38 315 1 2 zz zz zz T               (12) The determination of xx T and zz T is similar to the procedure for the stress intensity factor including extrapolation to the point r =0. The effect of thickness and loading mode mixity To study the effect of thickness and loading mode mixity of the specimen on zz T -stress, the compressive load is adjusted so that the xx T -stress is remained approximately constant at variation of the specimen thickness ( B = 10; 20; 040 and 80 mm) at constant crack length (for the corresponding values of mixity parameter M e ). To reflect mixed mode loading conditions, an effective stress intensity factor K eff is introduced into consideration as follows 2 2 eff I II K K K   (13) The results of calculation of the effective stress intensity factor and the zz T -stress in the middle plane of the crack front ( s =0) for different mixed mode loading conditions and thickness of the specimen are summarized in Fig. 3. The increase of the specimen thickness is 8 times greatly reduces the zz T -stress (up to 75% at M e =0,25), whereas the value of xx T is virtually unchanged [8]. Thus, magnitudes of the zz T -stress have significant correlation with thickness of the specimen and allows taking into account the level of the out-of-constraint which should be included into assessment of the fracture toughness of full-scale structures. Figure 3 : The effect of thickness and loading mode mixity on the effective stress intensity factor and out-of-plane constraint in the middle plane of the crack front. C ONCLUSIONS he theoretical analysis of the joint influence of the nonsingular components of the T -stresses ( xx T and zz T ) on the plastic zone around the crack tip of mode I is carried out with attraction of asymptotic formulas, which take into account triaxiality of the stress state at the crack tip, and the von Mises yield criterion. The size of the plastic zone around the crack tip at the middle plane of the CT specimen decreases with the increase of specimen thickness. It is confirmed that the plastic zone is affected by the zz T -stress, i.e. there is strong effect of out-of-plane constraint on crack tip plastic zones. T