Crack-tip constraint in mode II deformation

Studies of cracked specimens loaded in mode I have shown that the stresses near the crack tip depend significantly on the level of constraint. The stresses can be determined near the crack tip using the HRR solution, but only for high constraint specimens. For other levels of constraint, O'Dowd and Shih's Q parameter may be used to adjust the stresses derived from the HRR solution. Only limited research has been carried out to study the effect of constraint in mode II. In this paper a mode II boundary layer formulation is used to study the effect of far field elastic stresses on the size and shape of the plastic zone around the crack tip and on the stresses inside the plastic zone. It is shown that in mode II, both positive and negative values of remote T-stress influence the tangential stress along the direction of maximum tangential stress. In the spirit of O'Dowd and Shih, a dimensionless parameter Q(II) is introduced to quantify the constraint for mode II specimens failing by brittle fracture. The relation between Q(II) and T/sigma(0) is determined for different values of the strain hardening coefficient n. To investigate the range of validity of the Q - T diagram for real specimens, the constraint parameter Q(II) is calculated directly from finite element analysis for three mode II specimens and compared with the evaluation using the Q - T diagram.