الفهرس 
IntroductionOnly 14 pages are availabe for public view
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Abstract
Due to vastly increased use of nodular iron, it is important that meaningful design data be obtained for this materail, that is data which will enable the desiger to predict fail-safe behavior.
Many tests have been carried out (ASTM) to measure the critical stress intensity factor, KIC, in metallic and non-metallic materials. Nearly all of those tests have strict requirements for specimen size and teseing procedure.
Nowadays, the double torsion test appears to be more universally applicable than ASTM Tests.
Its principal attributes are that it requires only a very simple specimen configuration then, eliminating the need for expensive and time consuming specimen machining operations. Also the calculation of KIC is independent of crack length, therefore the only parameters reqired to be measured are the specimen dimensions and critical load for crack propagation.
The preset study is a further contribution to study the following points:-
1)The effect of austempering time on fracture toughness and other mechanical properties such as ultimate strength, percentage elongation and hardness of ductile iron.
2)The effect of thickness between side grooves and specimen dimensions on stress intensity factor (KQ).
3)The effect of shape of crack front profile of different type of ductile irons.
4)The effect of casting thickness and matrix strucure on mechanical properties and fracture toughness.
Test results showed that, as the austempering time increases, the strese intensity factor (KQ), ultimate tensile strength (UTS) and elongation percentage increases while hardness decreases.
Furthermore, the conditional fracture toughness increases with increases the thickness between side grooves, (tc), Then decreases until it reaches a constant value independent of any further increase in TC.
It was, also found that the crack front is curved and extends further anong the tensile surface than the compressive surface, and that the crack front profiles of all types of ductile iron have the same general trend.
Beside, it was found that the casting thickness has slight effect on mechanical properties within the studied range.