Fracture Toughness Calculator
Fracture toughness & stress intensity factor calculator for steel — K_Ic, critical crack length, safe stress, ASTM E399 check. Free tool.
Fracture Toughness & Crack Integrity Calculator (K₁ / Kc)
Determine the mode-I stress intensity factor (K), critical crack length, safe design stress, or ASTM E399 plane-strain validity for a cracked steel component — with real steel-grade presets, unit switching, and a live substituted-formula view.
1. Choose what you want to solve for
Material & units
Loads typical yield strength & Kc into the fields below — every value stays fully editable.
Crack geometry
Y auto-fills a typical value for the selected geometry; override it any time.
Center crack, length 2a, in a wide plate under remote tension σ.
Inputs
MPa·√m
Plane-strain fracture toughness from test data or material spec.
MPa
Nominal tensile stress remote from the crack, perpendicular to it.
mm
Half-length for a center (through) crack; full depth for an edge/surface crack.
Auto-set from the crack geometry above; adjust if you have a handbook-specific value.
MPa
mm
mm
kN
Result
—
Enter your inputs to see a live result.
Formula used (with your numbers)
$$ K_I = Y \cdot \sigma \sqrt{\pi a} $$
Base LEFM relation, rearranged automatically for the selected mode.
ASTM E399 plane-strain validity
B, a ≥ 2.5·(KIc/σy)² must hold for KIc to be a valid material property (not just a provisional KQ).
Accuracy note: this tool implements standard linear-elastic fracture mechanics (LEFM) relations for quick design checks and education. Results depend entirely on the accuracy of your input KIc, σy, and geometry factor Y — always verify against certified material data and a qualified engineer's review before use in a safety-critical design.
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Typical KIc reference values
Representative plane-strain fracture toughness for common structural & machine steels at room temperature. Use as a sanity check only — always confirm with a certified mill or test report for design work.
| Material | σy (MPa) | Typical KIc (MPa·√m) | Typical KIc (ksi·√in) |
|---|---|---|---|
| ASTM A36 | 250 | 90–120 | 82–109 |
| ASTM A992 | 345 | 80–110 | 73–100 |
| ASTM A572 Gr.50 | 345 | 85–115 | 77–105 |
| AISI 4140 (Q&T) | 655–895 | 60–90 | 55–82 |
| AISI 4340 (Q&T) | 860–1240 | 50–90 | 45–82 |
| AISI 4130 (normalized) | 460 | 80–110 | 73–100 |
| Stainless 304 (ann.) | 215 | >200 (fully ductile, often EPFM) | >182 |
| Stainless 316 (ann.) | 205 | >200 (fully ductile, often EPFM) | >182 |
Continue your structural integrity check
This calculator covers linear-elastic fracture mechanics. For the rest of the design chain, see related SteelSolver tools:
