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
From: materials-welding@googlegroups.com [mailto:materials-welding@googlegroups.com] On Behalf Of meisam shokri arfaei
Sent: 24 April 2015 17:48
To: materials-welding@googlegroups.com
Subject: Re: [MW:23161] CTOD AND CHARPY TEST
Dear Alan,
I think there is a misunderstanding about my reply. I didn't say that the test is based on cyclically loading of the specimen.
Also this is true that the mechanism of inducing the crack is by fatigue loading type and this will continued by the three point bending for studying the behavior of the material under loading.
But after the test we use the results to calculate the critical defect/crack size and in most cases this parameter uses in cyclically loading conditions (this was my viewpoint).
Also the results may use in FFS evaluations or it may use just for characterization of a material (whether metallic or non-metallic).
Regards
On Fri, Apr 24, 2015 at 11:46 AM, Alan Denney <alan@denney1.freeserve.co.uk> wrote:
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
From: materials-welding@googlegroups.com [mailto:materials-welding@googlegroups.com] On Behalf Of meisam shokri arfaei
Sent: 23 April 2015 16:36
To: materials-welding@googlegroups.com
Subject: Re: [MW:23150] CTOD AND CHARPY TEST
Charpy test is type of test to measure the resistance of a material to shock type stresses whether in room or minus temperatures.
CTOD (Crack Tip Opening Displacement) is for measuring the resistance of material to cyclic type of stresses whether in room or minus temperatures.
So the main difference is the type of load which used during the test. So the specimens preparation and test procedures are different.
Regards
On Thu, Apr 23, 2015 at 12:42 PM, S.Mohammed <mohd52100@gmail.com> wrote:
DEAR ALL
WHAT IS DIFF BETWEN CHARPY TEST AND CTOD TESTING?
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M. Shokri Arfaei
ISA-ISTS - Metallurgy Lab. Manager
ASNT NDT Level III
International Welding Engineer
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