FW: [MW:23164] CTOD AND CHARPY TEST

Hi Meisam & Alan,

 

A little bit of clarification on the subject.

 

Chary impact test draws a demarcation between ductility and brittleness.While CTOD tell the fracture toughness .Off course from the basics of metallurgy, both higher Charpy values  and greater CTOD   are the measure of higher ductility and toughness.The reverse ( brittleness) is shown when the values are quite low.

 

Charpy  impact is the common screening method of materials for ductility and brittleness , in the most cost effective way.. Thus most of the design codes, such as BPV codes and Piping codes recommends this testing.While CTOD is mandatory for offshore construction in addition to Charpy. Higher CTOD in addition to Charpy is always  a measure of good toughness  thus avoiding catastrophic failures.

 

I would think the attached links will clear the doubts quite well.

 

Thanks.

 

 

Pradip Goswami, P.Eng,IWE

Welding & Metallurgical Engineer/Specialist

Ontario, Canada

pgoswami@quickclic.net

pradip.goswami@gmail.com

 

http://www.twi-global.com/technical-knowledge/job-knowledge/ctod-testing-076/

http://www.twi-global.com/technical-knowledge/faqs/material-faqs/faq-what-is-charpy-testing/

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From: materials-welding@googlegroups.com [mailto:materials-welding@googlegroups.com] On Behalf Of meisam shokri arfaei
Sent: Friday, April 24, 2015 11:48 AM
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

 

Tel.: +98 21 66282127

Fax: +98 21 66282779

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ISA-ISTS - Metallurgy Lab. Manager

ASNT NDT Level III

International Welding Engineer

Tel.: +98 21 66282127

Fax: +98 21 66282779

Mob.:+98 912 1394023

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