Issue34

Yu.G. Matvienko et alii, Frattura ed Integrità Strutturale, 34 (2015) 255-260; DOI: 10.3221/IGF-ESIS.34.27 256 constant term of the series of Williams has been expressed by the parameter T and it is incorporated into the basic criterion equation. To demonstrate the validity of the proposed MATS criterion, this criterion is directly applied to experiments reported in the literature for the mixed mode I/II crack growth behavior. M AXIMUM AVERAGE TANGENTIAL STRESS (MATS) CRITERION he tangential crack-tip stress under mixed mode I/II loading can be characterized by the singular (the first order term) and the nonsingular term (the T-stress) in polar coordinate following to Williams [7] 2 2 1 3 cos cos sin sin 2 2 2 2 I II K K T r                 (1) Here, r and  are the crack tip coordinates, I K and II K are mode I and mode II stress intensity factor, respectively. The maximum average tangential stress (MATS) criterion is assumed to be applicable and can be expressed mathematically as follows [8] 0       , 2 2 0       . (2) This criterion states that a crack grows when the maximum average tangential stress   in the fracture process zone ahead of the crack tip reaches its critical value and the crack growth direction coincides with the direction of the maximum average tangential stress along a constant radius around the crack tip. Combining Eq. (1) with Eq. (2), the MATS criterion leads to predicting the direction of fracture angle 0  [8]   - - 0 0 0 0 8 sin 3cos 1 2 cos sin 0 3 2 I II T K K d              (3) 0,0 0,2 0,4 0,6 0,8 0 10 20 30 40 50 60 MATS Criterion Experimental Results [9] Direction of Fracture Angle,  o 0 M e Figure 1 : The predicted and experimental directions of fracture angle for the mixed mode I/II crack growth behavior of Guiting limestone. V ALIDATION OF THE MATS CRITERION o validate the proposed MATS criterion, Eq. (3) is directly applied to the experimental results [9] for the mixed mode I/II crack growth behavior of Guiting limestone. Different combinations of modes I and II are characterized by a mixity parameter e M T T