A material's resistance to localised surface deformation or indentation under a standardised load.
Hardness is measured by standardised indentation tests. Common scales: Vickers (HV, diamond pyramid), Rockwell (HRC/HRB), Brinell (HBW, steel ball), Shore A/D (polymers and elastomers). For metals, UTS ≈ 3.3 × HV (MPa). Hardness correlates with wear resistance but not directly with fracture toughness.
Shore D is reported for rigid thermoplastics (PLA ~80D); Shore A for flexibles (TPU 85A-98A). Harder materials resist scratching but tend to be more brittle. Abrasive filaments (CF, GF, metal-fill) require hardened or ruby nozzles: hardness mismatch drives rapid nozzle wear.
Hardness says little about bulk structural strength. A brittle ceramic can be very hard yet fracture at low tensile load. Shore A and Shore D scales are not directly comparable to HV or HRC. FDM part hardness varies with infill density: low infill parts feel soft even if the material is nominally hard.
Related terms: Toughness, Tensile Strength, Ductility
| Field | mechanics, engineering |
|---|---|
| Also called | Shore Hardness, Vickers Hardness, Rockwell Hardness |
Engineer, author of The Big Book of 3D Printing and additive manufacturing expert