What is an S-N curve?

An S-N curve (Wöhler curve) plots stress amplitude (S) versus number of cycles to failure (N) on a log-log scale. It characterizes a material's fatigue behavior and is used to predict fatigue life under cyclic loading.

What is the Basquin equation?

The Basquin equation σa = a·N^b (or equivalently N = (σa/a)^(1/b)) describes the S-N curve in the high-cycle fatigue regime. Constants 'a' and 'b' are determined from material testing. Typical b values range from -0.05 to -0.12.

What is the endurance limit?

The endurance limit (Se) is the stress amplitude below which a material can theoretically withstand infinite cycles without failure. Steel and titanium typically exhibit an endurance limit at ~10⁶-10⁷ cycles, roughly 40-50% of UTS. Aluminum and copper do not have a true endurance limit.

What factors affect fatigue life?

Surface finish, stress concentration (notches, holes), mean stress, temperature, environment (corrosion), loading type (bending vs axial vs torsion), residual stresses, and material microstructure all significantly affect fatigue life.

How accurate is the S-N approach?

The S-N approach is widely used for high-cycle fatigue (>10⁴ cycles) and provides reasonable estimates. However, scatter in fatigue data is large — life predictions typically have a factor of 2-3 uncertainty. For critical applications, use probabilistic approaches and testing.

मुक्त अभियांत्रिकी साधन

थकवा आयुष्य कॅल्क्युलेटर

S-N वक्र पद्धत आणि Basquin समीकरण वापरून अपयशापर्यंतच्या चक्रांची संख्या अंदाजित करा. ताण आम्प्लिट्यूड, पदार्थ स्थिरांक आणि endurance limit प्रविष्ट करा.

S-N वक्रBasquin समीकरण#170

Results

अपयशापर्यंतची चक्रसंख्या N

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Basquin घातांक b

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Basquin गुणांक a (σ’f)

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मूल्यांकन

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S–N वक्र (Wöhler आरेख)

Basquin समीकरण (उच्च-चक्र थकवा)

स्थिरांक a (थकवा सामर्थ्य गुणांक) आणि b (थकवा सामर्थ्य घातांक) हे S-N वक्रावरील दोन ज्ञात बिंदूंमधून व्युत्पन्न केले जातात: (N=1000, σ≈0.9·UTS) आणि (Ne, Se).

⚠️ Note: जर σ_a ≤ Se असेल, तर घटकाचे आयुष्य अनंत असते (endurance limit च्या खाली). हा कॅल्क्युलेटर सरलीकृत Basquin पद्धत वापरतो आणि mean stress (Goodman/Gerber) किंवा surface finish corrections विचारात घेत नाही.

Fatigue Life Calculator | S-N Curve | Basquin Equation | Free Online Tool

Published by Nikolai Shelkovenko on फेब्रुवारी 15, 2026 फेब्रुवारी 15, 2026

Results

Basquin समीकरण (उच्च-चक्र थकवा)

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