Failure index and safety factor

After loads and restraints are fully specified, click the Simulation step on the Workflow bar and then Run Simulation (Tutorial: your first simulation). When the solve finishes the results are loaded and contour plots are shown; use the controls in the left-hand panel to switch between stresses, displacements and failure index.

Failure index (FI) is a scalar field computed from the local stress state and fiber orientation. In the results view it is shown as a contour. The Safety card reports Max FI, the highest FI in the loaded results — the same field used for the color plot.

FI < 1 — below the failure limit at that location
FI = 1 — at the failure limit
FI > 1 — above the failure limit

NoviPath marks Near limit when Max FI > 0.8, and Exceeds limit when Max FI > 1.

Safety factor is the inverse of Max FI (SF = 1 / Max FI). Example: Max FI = 0.5 → SF = 2.0.

What the failure index does and does not tell you

The failure index is computed from the local stress state and the local fiber orientation, so it is a property of the whole simulation setup rather than of the material alone.

Failure index is specific to that part geometry, orientation, material, tip, toolpath parameters, and loads and restraints. Changing any of those inputs changes the simulation and therefore the estimated failure index.

If the structure can experience two or more distinct loading conditions, run a simulation for each condition (or a justified combination) to obtain an actionable failure index.

The failure load reported on the Safety card is obtained by scaling the applied loads by 1 / Max FI (Failure load). It therefore assumes linear elasticity and that the full load set scales proportionally; it is an estimate from the linear solution, not a nonlinear failure prediction.

Failure index and safety factor

What the failure index is, the thresholds on the Safety card, how the safety factor is derived, and what the index does not tell you.