Neodymium magnets are the strongest magnets in the world — and some of the most fragile. They do not bend or stretch; they chip, crack and snap. Anyone who has let two magnets snap together knows the sound of a broken corner. Here is why that happens, and how to keep your magnets in one piece.
Hard and strong, but brittle
Think of a sintered NdFeB magnet as a very hard ceramic rather than a metal. It resists scratching, and it is strong when you squeeze it. But it has almost no ability to bend — engineers call this brittleness. A steel part flexes before it fails; a magnet gives no warning at all. One moment it is fine, the next there is a crack running through it.
Where the trouble starts
- Knocks and drops. Edges and corners are the weakest spots — a small hit can knock a chunk off.
- Magnets hitting each other. They can slam together hard enough to crack each other. Always separate them with a spacer.
- Machining. Magnets can be cut and ground, but only with coolant and slow feeds — heat and vibration cause cracks. Most buyers order finished sizes instead.
- Mounting. Use adhesive or a snug pocket that spreads the load. Never rest a magnet on a sharp edge.
Typical behaviour at a glance
| Property | Behaviour |
|---|---|
| Hardness | High — resists scratching |
| Squeeze (compression) | Strong — the safest loading |
| Bending and pulling | Weak — avoid in design |
| Impact | Poor — chips easily |
Designing around it
Good designs keep magnets in compression and away from impacts: chamfered edges, a protective pocket, and cushioning against vibration. If the application is genuinely rough — things banging together — consider bonded NdFeB, which is far tougher and can be molded into complex shapes, at the cost of some magnetic strength.
Read on: physical properties → · dimensions and tolerances →