How to Measure Impact Strength? ASTM D256 Izod vs. Charpy Explained

Impact strength: Impact strength is defined as the ability of material to absorb applied energy. Unit: J/m.

Resilience: It is defined as the ratio of energy given up on recovery from deformation to the energy required to produce the deformation. Area under stress-strain curve upto yield point gives the resilience of the material.

Notch sensitivity: The ratio of impact strength of un-notched specimen to the notched specimen of same material is called notch sensitivity.

Test Method:

ASTM D 256 (Izod) & (Charpy), ISO 180 (Izod)

The impact test methods are as following:

• Pendulum impact tests
• Izod impact test
• Charpy impact test
• Chip impact test
• Tensile impact test
• High-rate tension test
• Falling weight impact test
• Drop weight (top) impact test
• Dart Impact test
• Instrumented impact tests
• High- rate impact testers.
• High speed ball impact tester
• High speed plunger impact tester
• Miscellaneous impact test

IZOD IMPACT TEST:

Specimen Dimension: 63.5 x12.7 x 3.2 with notch angle 45^o and notch depth 2.54mm.

Test Procedure:

• The test specimen is clamped in a position so that the notched end of the specimen is facing the striking edge of the pendulum.
• Check for properly positioned the test specimen.
• The pendulum hammer is released, allowed to strike the specimen and swing through.
• If the specimen does not break, more weights are attached to hammer and the test is repeated until failure is observed.
•  The impacts values are read directly in in- lbs are ft- lbs from the scale.

CHARPY IMPACT TEST:

Specimen Dimension: 63.5 x12.7 x 3.2 with notch angle 45^o and notch depth 2.54mm.

Test Procedure:

• This test is conducted in a very similar manner to the Izod impact test.
•  The only difference is the positioning of the specimen.
• In this test the specimen is mounted horizontally and supported at both ends. Only the specimens that break completely are considered acceptable.
• The Charpy impact strength is calculated by dividing the indicator reading by the thickness of the specimen.
• The results are reported in ft-lbs/in. of notch for notched specimen and ft-lbs /in. for unnotched specimens.

Difference between Izod and Charpy Impact Test

Summary : The toughness of a material—its capacity to absorb energy during fracture under abrupt impact loading is assessed by the Izod and Charpy impact tests.They aid in figuring out a material’s resistance to fracture propagation and ductile-to-brittle transition temperature (DBTT).