What is Charpy Testing and what ASTM standards require it?
Charpy testing, or impact testing was developed in 1905 by Georges Charpy in order to determine the amount of energy absorbed by a material during fracture. It was noticed that as the temperature drops, the tensile and yield of steel increases, but the ductility drops, leading to brittle and sometimes catastrophic failures.
A standard Charpy test is performed by machining a 10mm x 10mm x 55mm test piece with a notch cut at the intended fracture point. The test sample is then brought down to the specified temperature, typically in a liquid medium. The sample is placed into the fixture, and a pendulum is set to swing and break the sample at the grooved notch. The testing machine calculates the amount of energy absorbed by the sample by measuring how high the pendulum swings after fracture. The lower the swing, the more energy was absorbed. One charpy test is actually three separate tests, with the reported result being the average of the three.
Below are some commonly tested fastener grades, and their respective charpy requirements.
| Grade | Foot-Lbs (Ave-min) | Temperature |
|---|---|---|
| F1554 grade 55 | 15 | +40F |
| F1554 grade 105 | 15 | -20F or +40F |
| A320 grade L7 | 20 | -150F |
| A320 gradeL43 | 20 | -150F |
ASTM F1554 supplemental requirement S4 is tested at +40F for use with either Grade 55 or Grade 105 and -20F for use with Grade 105 only.
Portland Bolt inventories charpy tested steel round bar in F1554 grades 55 and 105 and A320 grade L7. Special charpy testing can be performed on request.
While it is a supplementary requirement…Is charpy testing grade 105 actually necessary?
I want to make sure I’m buying the proper product.
@Garry- If the bolt is going to be in a cold weather situation, charpy testing is a good safeguard to make sure the bolt will not get too brittle. However as to whether it is necessary, that would be up to the design engineer.
Can you perform a charpy impact test on galvanised products. Or does it affect the results?
@David- In the limited amount of pre-galv and post-galv charpy testing we have performed we have not noticed a significant difference one way of the other.
Is it possible to impact test an ASTM A325, Type-1 bolt [size 5/8″ or 3/4″] at a temperature of -20°C expecting a minimum absorbed energy of 27J?
@Hamid- In our limited experience charpy testing A325 bolts, we have not found them to fare well in low temperature testing. If the bolt is large enough, we can manufacture it from different raw material and have better luck, but the off the shelf product does not typically pass.
Is it possible to impact test an ASTM A394 bolt at a temperature of -30 ° C expecting a minimum absorbed energy of 27J?
@Manuel- Anything can be tested, but we don’t have any experience charpy testing A394 bolts, so we don’t have any feel for whether or not the bolt would pass that or any charpy.
Hi Can we make charpy test to stud bolts ASTMA 193-B8 CL.2, 3/4-10 X 7″
@Rosy- Yes, we could have that stud charpy tested as long as we were provided with the test parameters.
Dear Sir,
Can we achieve impact properties in nut material of Gr.4 @ -101 deg. C
ASTM A 320 specification mentions in the foot note that ” it is generally difficult to meet impact properties for Gr.L7 @-101 Deg. C hence Gr.L43 may be preferred “. In this case if client has specified to use Gr.4 nuts with Gr.L7 studs and both have to be impact tested @-101 Deg.C, is Gr.4 nut material capable of meeting impact properties @-101 Deg.C ( Latest ASTM A 194 have now discontinued Gr.4 nuts).
Please advise.
@Bharat- Typically speaking, before grade 4 was discontinued, we were able to find nuts off the shelf that had the -101C charpy (4L). Now that grade 4 is no longer a current grade, we do not know how available they will be. We have not been asked to supply a grade 4 nut in quite some time.
If the A320 L7 studs are impact tested at -150F, should the 7L or 4L nuts be impacted at the same temperature? Or is there a different temperature to be adhered to?
@Ebenezer- Typically the 4L or 7L nuts are also charpy tested at -150F.
In respect to the the common requirements listed, why is the temperature +40 for F1554 Grade 55 and -20 for F1554 Grade 105?
The idea is to ensure the material will not have a brittle failure in cold temperatures, correct?
Is there something else that comes into play that will ensure the grade 55 anchor will continue to behave in a ductile fashion at negative temperatures (even though it is my understanding grade 55 will not typically absorb 15 ft-lbs of energy at -20)?
@Dan- We think that the +40F and -20F for grade 55 and 105 respectively were chosen because they were the lowest temperatures that were consistently achievable. You could certainly retest at a lower temperature and see if the material would pass at the lower requirement, but besides that we are not aware of any other way to assure that the steel would remain ductile.
Hi, what’s the smallest specimen for grade A320 L7M? I have studbolt size 9/16″ . However, it still have threaded after machining so can we machine to size 5mm x 10mm x 50mm?
Thanks
@Fairuz- ASTM A320 allows charpy sample pieces of 10mm x 10mm and sub-size pieces of 10mm x 7.5mm. If you want to test a 5mm x 10mm piece, you would need to get a variance from your customer since that would be outside the parameters of the standard.
How can we do charpy V notch test for small studs
@Rajmohan- A normal charpy test piece is 10mm x 10mm x 50mm. There are allowances for undersized test pieces for situations where the host material is not large enough. However, you will need to contact your testing lab to see what their specific capabilities are.
Dear Sir,
Can we do Impact test for the Heavy Hex Nut ASTM A194 Gr.7 ? or only do for Stud A320 L7
Please kindly advise.
Thank you very much
@Ha- Normally, both the stud and the nut are charpy tested. However, the nut in its finished condition may be too small for a charpy test sample, so typically the test is done during manufactuing using a larger test piece from the same steel.
The structural steel project where I am assigned now involves big diameter bolts (M42, M48, up to M72) manufactured per BS EN 14399 which refers to EN ISO 898-1, ISO-148, and EN 10045-1 for the conduct of Charpy Impact tests. In all these references, there is no mention about the number of test specimens for the tests, which usually involves 3 specimens.
Is it okay to carry out the impact test using only one test specimen?
@Noeto- The normal charpy test procedure is to test three specimens and take the average of those. That said, we are not familiar with the specifics of the standards you reference, so we cannot be certain.
Are nuts able to be Charpy Tested or is it just done on threaded stud products?
@Nick- Charpy tests can be run on nuts if the nuts are large enough to machine a charpy coupon out of. Normally the nuts need to be larger than 1-1/2″ in order to be able to yield a test coupon. Otherwise, if you know you need a charpy at the time of manufacture, the nut manufacturer can hold out a test piece to run the charpy on.