The energy per unit area absorbed by a material during fracture under a single high-speed impact load.
Impact strength is measured by Charpy (horizontal beam, notch centred, struck from behind) or Izod (vertical cantilever, struck at top) tests. A pendulum hammer breaks the specimen; energy absorbed = mgh₁ − mgh₂. Results in kJ/m² or J/m. The notch introduces a stress concentration that triggers brittle failure even in otherwise ductile materials, making impact strength notch-geometry-dependent.
Impact strength is critical for enclosures, protective cases, tool handles, and any part subjected to accidental drop or impact. ABS has historically been the preferred FDM material for impact-critical applications; PETG offers a better balance of impact and ease of printing. TPU absorbs very high impact energy due to its elastomeric nature. Adding carbon fibre to a matrix increases stiffness but usually reduces impact strength.
Charpy and Izod values are not interchangeable. For FDM parts, impact strength is highly anisotropic: notch orientation relative to layer direction dominates the result. Reported impact values are almost always for 100% infill, solid specimens. Low temperatures dramatically reduce impact strength of most thermoplastics. ABS becomes notably brittle below −10°C.
Related terms: Toughness, Brittleness, Ductility
| Field | mechanics, engineering |
|---|---|
| Also called | Charpy Impact, Izod Impact, Notched Impact Strength |
Engineer, author of The Big Book of 3D Printing and additive manufacturing expert