Quick3D Impact strength: Izod vs Charpy, notched vs unnotched
Impact strength shows how well a material survives a sudden blow. Learn the difference between Izod and Charpy, and notched and unnotched.
What it means in practice
Impact strength is the energy a material absorbs when it is struck hard and fast. It separates materials that shrug off a knock from those that shatter. Strength and stiffness alone cannot tell you this.
Key takeaways
- Impact strength is the energy a material absorbs when struck hard and fast.
- Charpy and Izod load the bar differently; their numbers cannot be converted.
- Only compare matching tests: notched with notched, same units.
- Use the numbers to rank materials, then test your own part.
It matters for:
- Handheld devices and housings that may be dropped.
- Protective covers, guards and bumpers.
- Tool holders, clips and latches that get knocked about.
- Any part used in the cold, where plastics turn more brittle.
How it’s measured
A heavy pendulum swings down and breaks a small bar. The energy it loses in doing so is the energy the bar absorbed.
Izod vs Charpy
Charpy
(ISO 179): the bar lies flat across two supports and is hit in the middle, from the side opposite the notch.
Izod
(ISO 180, ASTM D256): the bar is clamped upright at one end, like a post, and hit near the top on the notched face.
The two set-ups load the bar differently, so their numbers cannot be converted into each other.
Notched vs unnotched
- Notched: a small V-notch is cut into the bar first. It acts like a crack or sharp internal corner. It tells you how the material copes once a flaw exists.
- Unnotched: a plain bar. Values are much higher, and many tough plastics simply do not break (often shown as “NB”).
Units
- ISO results are in kJ/m²: energy divided by the cross-section behind the notch.
- ASTM Izod results are in J/m: energy divided by the bar’s width.
Watch out
Different units mean different maths. Never compare a kJ/m² value with a J/m value directly.
How to read and compare it
- Match the test exactly: Charpy with Charpy, notched with notched, same units. Our hub stores Charpy values separately for notched and unnotched bars for this reason.
- Notch quality. A machined notch and a notch printed into the bar give different results. Good sheets say which.
- Orientation. Printed bars hit across their layers can split along a layer line. See print orientation: XY vs Z.
- Temperature. Most values are at room temperature. Many plastics lose much of their toughness below freezing.
- Moisture. Nylons are noticeably tougher when conditioned than when bone dry.
- Not a drop test. Real parts have corners, holes and thin walls. Use the number to rank materials, then test your own part.
Range in our catalog
Notched Charpy
- All materials: 0.6–115 kJ/m² (median 6.7 kJ/m², 144 materials)
- Filaments: 1.6–115 kJ/m² (median 8 kJ/m², 98 materials)
- Resins: 0.6–44 kJ/m² (median 1.54 kJ/m², 20 materials)
- Engineering materials: 0.9–53 kJ/m² (median 7.4 kJ/m², 81 materials)
- PLA 172.4–38.9
- PETG 92.6–11.6
- PC 53–21.28
- ABS 106.1–38.6
- PA12 410.2–16
- PEEK 77–30
- PEI 44–11
Bar = lowest to highest, dot = median. 56 materials, live from our database.
Unnotched Charpy
- All materials: 11–224.8 kJ/m² (median 38 kJ/m², 69 materials)
- Filaments: 11–224.8 kJ/m² (median 35 kJ/m², 57 materials)
Highest and lowest in our catalog
Toughest, notched Charpy
| Material | Polymer | Charpy impact strength, notched |
|---|---|---|
| Ultrafuse TPU 64D | TPU | 115 kJ/m² |
| Kexcelled THE K8 TPU 64D | TPU | 62–66 kJ/m² |
| Fiberlogy PC ABS | PC/ABS | 53 kJ/m² |
| Formfutura ReForm rPP GF30 UV Pellets | PP | 44 kJ/m² |
| Formlabs PU Rigid 650 Resin | Polyurethane | 44 kJ/m² |
Most brittle, notched Charpy
| Material | Polymer | Charpy impact strength, notched |
|---|---|---|
| Ultracur3D RG 1100 | Photopolymer | 0.6 kJ/m² |
| Ultracur3D RG 35 | Photopolymer | 0.6 kJ/m² |
| Ultracur3D EPD 2006 | Photopolymer | 0.7 kJ/m² |
| Ultracur3D RG 9400 B FR | Photopolymer | 0.9 kJ/m² |
| Ultracur3D RG 3280 | Photopolymer | 0.98 kJ/m² |
Toughest, unnotched Charpy
| Material | Polymer | Charpy impact strength, unnotched |
|---|---|---|
| Ultrafuse PPSU | PPSU | 224.8 kJ/m² |
| Ultrasint PA11 Black | PA11 | 193 kJ/m² |
| LEHVOSS LUVOCOM 3F PEEK 9581 | PEEK | 185 kJ/m² |
| Ultrasint PA11 | PA11 | 184 kJ/m² |
| Formlabs Tough 1000 Resin | Photopolymer | 180 kJ/m² |
Related properties
- Elongation at break — a rough guide to ductility.
- Tensile strength — toughness needs strength as well as stretch.
- Young’s modulus — very stiff materials are often less tough.
- Glass transition temperature — explains why some plastics turn brittle in the cold.