Fatigue Life Calculator

• •Use the Fatigue Life Calculator when solving homework or exam problems that require quick numerical verification of your hand calculations — instant feedback helps identify arithmetic errors before they propagate.
• •Use it during the early design phase to rapidly iterate on parameters and narrow down feasible configurations before committing time to detailed finite element simulations or full design packages.
• •Use it when reviewing a colleague's calculation or checking a vendor's data sheet for plausibility — a quick sanity check can prevent costly downstream errors.
• •Use it to generate reference data for a technical report or presentation without manual computation, ensuring consistent, reproducible numbers throughout the document.
• •Use it in the field when a quick estimate is needed and a full engineering software package is not available.

The Fatigue Life Calculator is a precision engineering calculation tool designed for students, engineers, and technical professionals. Calculate factor of safety using Goodman, Soderberg, and Gerber criteria with modified endurance limit correction factors All calculations are performed using established engineering formulas from the relevant scientific literature and standards. Inputs support both metric (SI) and imperial unit systems, with unit conversion handled automatically — simply select your preferred unit from the dropdown next to each field. Results are computed instantly in the browser without sending data to a server, ensuring both speed and privacy. This calculator is intended as a supplementary tool for learning and design exploration; always verify results against authoritative references for safety-critical applications.

Fatigue life prediction estimates how many load cycles a component can withstand before crack initiation and growth cause failure. For constant-amplitude loading with mean stress σ_m and alternating stress σ_a, the three common failure criteria are: Goodman: σ_a/S_e + σ_m/S_u = 1/FS (most common); Soderberg: σ_a/S_e + σ_m/S_y = 1/FS (very conservative); Gerber: σ_a/S_e + (σ_m/S_u)² = 1/FS (parabolic, better match to test data). Here S_e is the endurance limit (stress below which infinite fatigue life is achieved, typically 0.5·S_u for steel and non-existent for aluminum which has no true endurance limit), S_y is yield strength, S_u is ultimate strength, and FS is the fatigue safety factor. For variable amplitude loading, Miner's rule sums damage fractions: Σ(n_i/N_i) = 1 at failure, where n_i is cycles at stress level i and N_i is the cycles to failure at that stress level. This linear damage accumulation works reasonably for random loading but has known limitations for very different stress sequences. S-N curves (stress vs cycles-to-failure) are determined experimentally for each material and geometry. Factors affecting fatigue life: surface finish (polished < machined < rough), size (smaller specimens are stronger), load type (axial < rotating bending), and notches (Kf reduces fatigue strength by the notch factor).

• •Rotating shaft fatigue analysis: shafts with bending loads experience alternating stress as they rotate, requiring fatigue-based sizing.
• •Pressure vessel fatigue: vessels with fluctuating internal pressure (pump discharge, reactor cycles) are designed for specific cycle count requirements.
• •Bridge structure fatigue: steel bridge members under traffic loading accumulate damage over decades. Maximum stress range and cycle count set design life.
• •Aircraft structure fatigue: wing bending, pressurization cycling, and gust loads all contribute to fatigue accumulation in commercial aircraft.
• •Connecting rod and crankshaft: IC engine components experience millions of load cycles per year at substantial stress levels.