The quantified buffer between a design's predicted capability and its requirement limit, expressed as margin of safety MS = (FoS – 1) or as a percentage of capacity remaining.
MS = (allowable / applied) − 1. MS > 0 = passing; MS = 0 = exactly at limit; MS < 0 = failing. Design margins account for: material variability, load uncertainty, manufacturing imprecision, environmental factors, and model error. Aerospace typically requires MS ≥ 0 at limit load and MS ≥ 0 at ultimate load.
For FDM printed structural parts, apply additional uncertainty factor of 1.5–2× beyond standard FoS to account for anisotropy, layer adhesion variability, and unknown print quality. Document margin assumptions. Margin is not a license to over-design: excessive margin wastes material and adds weight.
Margins computed from isotropic material data are non-conservative for FDM. Always verify margin with test data from the actual print process. Consuming margin to correct a design error is a red flag: address the root cause.
Related terms: Factor of Safety, Stress Concentration, Tolerance
| Field | engineering |
|---|---|
| Also called | margin of safety, MS, design reserve |
| Source | EDi Brain: rules-core |
Engineer, author of The Big Book of 3D Printing and additive manufacturing expert