DEAR ALL
WHAT IS DIFF BETWEN CHARPY TEST AND CTOD TESTING?
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DEAR ALL
WHAT IS DIFF BETWEN CHARPY TEST AND CTOD TESTING?
The reply below is incorrect: CTOD is not related to cyclic stresses. Both Charpy and CTOD measure fracture toughness. However Charpy is empirical whereas CTOD is a method of measuring material toughness such that the results can be used in fracture mechanics calculations to determine the criticality of material flaws of a known size in that material and corresponding microstructure. CTOD has its notch sharpened by fatigue cracking, but that is to give a very start initiator for the test only. The specimen should be the full thickness of the component to which the test relates, and the test temperature should be the minimum design temperature.
CTOD testing is inherently more complex and is much more expensive that Charpy testing and requires laboratories which are rather more specialised than those which can perform Charpy.
Alan Denney
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I fully understand, Meisam. The results of the test are used in fracture mechanics analysis to determine the critical defect size for fracture. If the service loading includes cyclic stresses then these are taken into account in that analysis. The defect has to be ‘grown’ using the ‘Paris law’ and that grown defect has to be less than that critical defect size for fracture.
Alan D
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