What is stress concentration factor Kt?

Kt is the ratio of maximum local stress to nominal stress at a geometric discontinuity. Kt = σ_max / σ_nom. It depends only on geometry, not material. A circular hole in a wide plate under tension has Kt ≈ 3.0.

What causes stress concentrations?

Any abrupt change in geometry: holes, notches, fillets, keyways, threads, grooves, changes in cross-section. The stress flow lines crowd together at these features, increasing local stress.

How does Kt affect fatigue life?

Stress concentrations dramatically reduce fatigue life because fatigue cracks initiate at the point of highest stress. The fatigue notch factor Kf ≤ Kt accounts for material sensitivity: Kf = 1 + q(Kt-1), where q is the notch sensitivity factor.

How can stress concentrations be reduced?

Use generous fillet radii, avoid sharp corners, use gradual transitions, add relief grooves near shoulders, polish surfaces at critical points, and use shot peening to introduce beneficial compressive residual stress.

What is Peterson's Stress Concentration Factors?

Peterson's is the definitive reference book containing charts and equations for Kt values for hundreds of geometric configurations. It provides Kt as a function of geometric ratios (r/d, D/d, etc.) for tension, bending, and torsion loading.

Free Engineering Tool

Stress Concentration Factor Calculator

Look up Kt for common geometries — hole in plate, shoulder fillet, U-notch — using simplified Peterson’s chart data.

Peterson’s ChartsKt Lookup#173

Results

Stress Concentration Factor Kt

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Max Local Stress σ_max

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Geometry Ratio

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Stress Concentration Factor

Typical Kt Values

Geometry	Kt Range
Central hole in wide plate	~3.0 (small d/W)
Shoulder fillet (D/d=2, r/d=0.1)	~1.8–2.5
U-notch	~1.5–3.5
Circumferential groove	~1.5–3.0

⚠️ Note: These are approximate values from simplified curve-fit equations. For precise values, consult Peterson’s Stress Concentration Factors or perform FEA. Kt is for elastic analysis only.

Stress Concentration Factor Kt Calculator | Vibromera

Published by Nikolai Shelkovenko on February 15, 2026 March 5, 2026

Results

Stress Concentration Factor

Typical Kt Values