Charpy Impact Test - Reporting 2

[Guest102023]

I have long questioned the practice (very common in my experience) of reporting average results for lateral expansion and % shear, in addition to an average result for absorbed energy. I am dubious as to the physical significance of these 'averages', and wish to settle the question for myself. My feeling is that lab techs may have not have thought it through - they calculate and report these figures just because they do it for absorbed energy.

ASTM A370 gives no guidance (it doesn't mention average for any Charpy outcome in fact). ASME Section VIII-D1 mentions average lateral expansion only in the event a retest is required.

Any thoughts on this?

 

[TVP]

brimstoner,

ASTM E 23 is the standard test method for notched bar (Charpy) impact testing of metallic materials. Here is an excerpt from section 10 on reporting:

10.2 For commercial acceptance testing, report the following information (for each specimen tested):
10.2.1 Specimen type (and size if not the full-size specimen),
10.2.2 Test temperature,
10.2.3 Absorbed energy, and
10.2.4 Any other contractual requirements.
10.3 For other than commercial acceptance testing the following information is often reported in addition to the information in 10.2:
10.3.1 Lateral expansion,
10.3.2 Unbroken specimens,
10.3.3 Fracture appearance (% shear, See Note A6.1),
10.3.4 Specimen orientation, and
10.3.5 Specimen location.
NOTE 7—A recommended format for computerization of notched bar impact test data is available in Practice E 1313.

 

[redpicker]

I think you are basically correct, brimstoner.

The average absorbed energy is reported because most specification requirements for CVN testing have both an average and minimum value requirement on the absorbed energy. Both get reported to indicate conformance (or, non-conformance) to the requirements. I don't recall ever seeing anything but a minimum value requirement for lateral expansion or fracture appearance; most often these measurements are requested for information-only. However, it only takes a single 3rd party surveillance inspector to ask for these averages to be shown on the report to result in a specific lab including this information on all reports (lcd theory).

rp