Poisson's ratio of =0.32. The loading fixtures of the three specimens were also presumed to be of aluminum alloy 7075-T6 for the purpose of comparison. The effects of stiffness of the loading fixture on the proposed specimen was analysed separately. The three specimens were analysed for pre-crack lengths, af varying from 0.5 mm to 10 mm and corresponding values of ½KI/KII½ and KII are shown plotted against pre-crack length for the three specimen in Figure 2(a) and 2(b) respectively. Generally, the value of ½KI/KII½ was lower while KII was higher for the proposed specimen suggesting that it is the most compact specimen and at the same time experiences the least influence from a normal stress ahead of the crack tip. Furthermore, an optimal precrack length of approximately 3 mm is suggested in Figure 2(a) for the configuration of the proposed specimens at which the value of ½KI/KII½ would be zero. This is not apparent in the case of the other two specimens. Also a pre-crack length of 3 mm would be appropriate from the point of view of Figure 2(b) as there would be no significant increase in the value of KII with pre-crack length from then on. Hence, based on the foregoing considerations, it would appear that the proposed specimen would be the most suitable for mode II fracture testing. Figure 2: Analytical Results. Investigation of Grooving and Loading Fixtures As indicated in the foregoing discussion, the application of a groove to the faces of the proposed specimen would be a necessary feature of mode II fracture testing. Hence, the influence of grooving on the two characteristic parameters ½KI/KII½ and KII has been examined. In the analyses, the groove depth was varied such that the ratio of ligament thickness after and before grooving (t/T) ranged from 0.2 to 1. The results have been plotted in Figures 2(c) and 2(d). In Figure 2(c), it is apparent that grooving did not significantly influence the value of ½KI/KII½ while on the other hand, as shown in Figure 2(d), KII increased with depth of grooving, which, from the standpoint of compactness, would be advantageous. In both instances, the optimum pre-crack length of 3 mm was maintained. The influence of the stiffness of the loading fixture was also examined, where the relative stiffness of loading fixture and the proposed specimen was specified as: 0 2 4 6 8 10 af (mm) -6 -5 -4 -3 -2 -1 0 1 KI /KII (%) Proposed Richard Banks-Sills 0 2 4 6 8 10 af (mm) 0.0 0.5 1.0 1.5 2.0 2.5 KII ' 0 2 4 6 8 10 af (mm) -0.3 -0.2 -0.1 0.0 0.1 0.2 0.3 KI /KII (%) t/T = 0.2 t/T = 0.4 t/T = 0.6 t/T = 0.8 t/T = 1.0 0 2 4 6 8 10 af (mm) 0 1 2 3 4 5 6 KII ' 0 2 4 6 8 10 af (mm) -0.3 -0.2 -0.1 0.0 0.1 0.2 0.3 KI /KII (%) D = 1 D = 2 D = 4 D = 8 D = 14.58 0 2 4 6 8 10 af (mm) 0.0 0.5 1.0 1.5 2.0 2.5 KII ' (a) (b) (c) (d) (e) (f)
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