The tendency of a material to fracture with little or no plastic deformation before failure.
Brittle materials fracture at or near the elastic limit with %EL < 2-3%. Fracture occurs by rapid crack propagation along cleavage planes or grain boundaries without significant energy absorption. Brittle fracture is stress-controlled; surface cracks are catastrophic stress concentrators. Glass, ceramics, and many composites are inherently brittle; PLA is brittle relative to most engineering thermoplastics.
Brittleness determines design strategy: avoid stress concentrations (sharp corners, notches), use generous fillets, and do not rely on energy absorption during impact. For FDM parts, brittleness is amplified in the Z-direction due to poor interlayer fusion. Post-processing such as annealing can reduce brittleness in semi-crystalline polymers like PLA by increasing crystallinity.
A brittle material can have very high UTS and hardness yet fail catastrophically at low loads due to surface flaws. Dynamic (impact) loads are far more dangerous for brittle materials than static ones. Colder operating temperatures increase brittleness in most polymers: PLA parts used outdoors in winter can fail unexpectedly.
Related terms: Ductility, Toughness, Elongation at Break, Tensile Strength
| Field | mechanics, engineering |
|---|---|
| Also called | Brittle Fracture |
Engineer, author of The Big Book of 3D Printing and additive manufacturing expert