Notch impact toughness (Dutch “kerfslagwaarde”) indicates how much energy is needed to break a standardised, notched metal test piece in a single blow at a given temperature. It is a measure of a metal’s toughness: the higher the value, the tougher the material and the more it deforms before it breaks. It is measured in joules (J) using the Charpy notch impact test.
How it works
- A test piece with a triangular or U-shaped notch is struck by a heavy pendulum hammer
- The energy the hammer loses in breaking the piece is the notch impact value
- Temperature is crucial: steel becomes more brittle in the cold and the value drops sharply
Application
- Material selection for structures — a low value points to brittle fracture without warning, dangerous under dynamic or low-temperature loading
- Steel designation — in S355J2, the “J2” means at least 27 joules at −20 °C; “J0” at 0 °C, “JR” at +20 °C
- Bridges, lifting gear and cold applications — where toughness at low temperature matters
| J2 | At least 27 joules at −20 °C |
|---|---|
| J0 | Tested at 0 °C |
| JR | Tested at +20 °C |
Points to note
- For outdoor structures and frost, choose a steel grade with sufficient toughness at low temperature (e.g. J2)
- The value applies per temperature; always state the test temperature
- Notch impact toughness and tensile strength are different properties; a strong steel can still be brittle
Related terms
- Steel
- Reinforcing steel
- Bending strength
- Compressive strength
- Eurocode
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