This drop became less steep as the annealing time increased, which indicates that relatively brittle fracture might have occurred in AR specimens and relatively ductile fracture in AN24 and AN120.
It is observed that E of AN24 is approximately three times as large as that of AR.
A clear hackle fracture could not be seen in AN24 and AN120.
The area over which the rough features are present in AN120 is found to be smaller than the corresponding area in AN24. This reduction in area may be a reason for the small decrease in [E.sub.p] when the specimens are subjected to annealing beyond [t.sub.a] = 24 hrs.
The optical microscopic picture of one such section cut from the interior zone of AN24 is shown in Fig.
Under low magnification, the fracture surface at the interior zone of AN24 shows a number of dimple patterns, as shown in Fig.
11 shows the evidence of such a fibrous structure on the fracture surface of AN24. These fibrils behave like miniature tensile specimens undergoing micro-necking arid sustain more strain, resulting in higher fracture energy.