The effect of constraint on ductile fracture initiation from a notch tip under mode I and mixed mode (involving modes I and II) loading is investigated. To this end, mixed mode fracture experiments are performed with Compact Tension Shear (or CTS) specimen of a ductile 2014-O aluminium alloy. The con- straint effects are investigated by considering specimens with two crack length to width ratios. The effect of crack tip constraint on the relationship between the critical value of the J-integral at fracture initiation (Jc) and M_p is examined. Further, the micromechanics of mixed mode ductile fracture initiation is investigated by performing fractographic studies and metallographic examination of the mid-plane region of the speci- men near the notch tip.
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