Charpy Impact Testing Sub-Size Specimens to ASTM E23, A370 and ISO 148-1

ASTM E23 and ISO 148-1 define test methods for Charpy impact testing of notched-bar metallic specimens. ASTM A370 also includes Charpy impact test method requirements but focuses only on steel products. All three standards provide details for properly measuring the energy absorbed by the notched specimen when impacted by a swinging pendulum. A typical Charpy test requires the notched metal specimen to rest on supports at each end (in a horizontal fashion) while coming in contact with vertical anvils adjacent to the supports. The specimen is then struck opposite the anvils at its centerline by a striker that is attached to a swinging pendulum (hammer). The illustration image found above shows a common specimen arrangement for Charpy impact testing.

Challenge

In order to measure the toughness of a material using a Charpy impact test, it is necessary to prepare specimens from the material or product of interest. In some cases, size limitations of the product needing tested will not allow for standard size specimens to be prepared. In other cases, a standard size specimen may produce an impact energy that is greater than 80% of the available testing machine capacity, thus violating the standards. In either scenario, it becomes necessary to test sub-size specimens.

These smaller specimens require supports that raise the specimen higher in order to keep it centered with the striker and anvils. It is also necessary to make sure these smaller specimens produce impact energies that are above the lowest verifiable reading of the pendulum impact testing system being used.

Instron Solution

Standard and sub-size Charpy specimens can be tested on either an SI or MPX Series Pendulum Impact test system. Both models accommodate optional support blocks for standard and reduced width specimens.  Refer to the following part numbers.

• W-3594 for 2.5 mm x 10 mm
• W-3595 for 5 mm x 10 mm
• W-3596 for 7.5 mm and 10 mm
• W-3585 for 10 mm x 10 mm (standard size)
• Supports for other sub-sized thicknesses can also be supplied

Use of Fracta impact software with an integrated angular encoder on either the SI Series or MPX Series provides the best solution when really low impact energies are required. The MPX Series uses a high resolution encoder allowing for an extremely low verified energy reading on even the largest machine capacities.