The initial crack propagation angle was calculated using MTS and minimum SED criterion and compared with the angle measured from the specimen. A good match was observed between the calculated crack propagation directions (45.8 ) and the measured crack propagation direction (45 ). A mode mixity of 0.58 was obtained using Eq. 18.5. Using the SIF obtained experimentally just prior to initiation of Epoxy crack, the criticality of crack tip stress state was checked for crack initiation in the Epoxy layer by using MTS and minimum SED criteria. It was observed that the equivalent mode I SIF, calculated using MTS and SED criterion (0.54 0.03MPa√m), is close to the mode-I fracture toughness of Epoxy. Similar results were also obtained for s ¼8mm. a b z y x Fig. 18.7 Fracture surface of failed specimen (s ¼6mm) Fig. 18.6 Stress intensity factor as a function of load inAFPB 0 0.4 0.8 1.2 1.6 01234567891011 Z (mm) X (mm) PMMA Epoxy b b a a Fig. 18.8 Profile of the crack surface 152 A.J. Jacob et al.
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