Impact Testing 3

[diretz]

What if the effect of the dimensions of a test specimen to the impact energy during impact testing?
I mean: If the thickness is decreased two times, will the impact energy also be decreased two times?
Has anybody any idea about this?

 

[gdodd]

Sounds like a good subject for a post graduate thesis!!

 

[diretz]

Well this problem seem to be quite easy but:
I'm facing a situation having to do with this. My sense says that dimensions and impact resistance are not proportional but when I searched to find relevant articles to support this attitude (ASME, etc), I found nothing.
I' appreciate anyone who can give me a clue.
Thanks

 

[diamondjim]

This is basically just a shear stress
and I do not see why the equation
Ss = F/A does not apply. So from the
equation, if the A (area) doubles,
the Force would be doubled to shear
the part.

 

[arunmrao]

If you decrease the thickness of the test specimen,how will you accomodate the U notch or V notch.These are standardized and cannot be altered. But the question of reducing or increasing thickness of the plates or test specimen is well and the effect on impact properties is well presented in any fracture mechanics text book.

 

[mikemkc]

Sir,

There is a nonlinear relationship that is dependent on strain hardening coefficient of the specific material. I would be glad to offer some guidance with regard to literature sources if you can provide more detail.

Mike

 

[Viktor]

The effect of specimen thickness in impact test is very well know. I would like to refer you to a student textbook G.E.Dieter, Mechanical Metallurgy, Third Ed., 1986, Page 356, Section 11-5 K1c Plane Stain Toughness Testing, Fig. 11-76 Effect of specimen thickness on the stress and mode of fracture. I can provide many more sources if you need.

Regards
Viktor

 

[diretz]

Dear Victor,
Thank you very much for your advice.
Can you please send me a copy of this paper?

Regards
Dimitris

 

[diretz]

Supplement to the previous one: My e-mail address is diretz@hotmail.com
Redards
Dimitris

 

[Viktor]

Dear Dimitris
This is a book and so I cannot send it via e-mail.
Regards
Viktor

http://viktorastakhov.tripod.com

 

[jmagee]

If you guys really want to know, I have a friend that does this type of testing for a living. He is the QC Manager for a manufacturing company that is certified under ISO-9000 and NCA-3800 for the nukes as well as MIL-I-45208 for the government. I will be glad to give you his number so you can get it straight from the horses mouth.

 

[brad]

arunmrao's post above is on target. For a fairly straightforward set of assumptions, a fracture mechanics approach may be able to elicit the same answer.

Another thought--somebody please help me on this term if I am wrong. I recall that this is known as the "Theory of Verisimilitude" (but I could be wrong on the term). This is commonly used in fluids and structures testing. Essentially, if one can qualify the dependency of terms for specific function, then one can appropriately scale terms as the model scales. This is commonly taught in an undergrad fluids course.

If you could describe the behavior using a basic functional relationship, you could apply this and arrive at the equivalent energy. However, this may not work for your specific problem.

What are the dimensions of the specimen, and are there notches, etc? Also, is the material brittle or ductile? If it is ductile, it would definitely be hard to characterize the effect on the energy due to this change.

Brad

 

[diretz]

The dimensions of the specimen will be:
length: nominal
width: 5 (V notch width: 5mm) mm
thickness: 10mm
Thanks

 

[Hush]

For what its worth API 6A provides the following adjustments for sub-size specimens:
10 mm x 7.5 mm 0.833
10 mm x 5 mm 0.667
10 mm x 2.5 mm 0.333