DIN 743 Shaft Fatigue Calculator — Load Capacity of Shafts and Axles
DIN 743 — Calculation of load capacity of shafts and axles
DIN 743 is the German standard for calculating the load-carrying capacity of rotating shafts and non-rotating axles. It defines the method for determining the fatigue safety factor under combined alternating and mean bending and torsional stresses, accounting for the material endurance limit, the notch effect (fatigue stress-concentration factor Kf), the size influence factor, and the surface factor. DIN 743:2012 is the current edition, structured in four parts, and is the standard cited in German and European drivetrain and machinery design.
MechanixCalc runs the DIN 743 fatigue check — alongside a von Mises static yield check, bending deflection (Roark), and first critical (whirling) speed (Rankine–Dunkerley / FEM) — directly in your browser for multi-segment stepped shafts. The full worked method, with safety factors at each section, is exported in a shareable PDF engineering report.
Calculators that implement DIN 743
What DIN 743 covers
- Fatigue safety factor under cyclic bending and torsion with Goodman mean-stress correction (DIN 743-1)
- Notch effects — fatigue stress-concentration factor Kf for shoulder fillets, keyways, grooves and threads (DIN 743-2)
- Material fatigue properties: endurance limit, ultimate strength, size and surface influence factors (DIN 743-3)
- Static safety factor against yielding under combined bending and torsional stress (von Mises criterion) (DIN 743-1)
- Multi-segment stepped shafts — critical-section identification across the full shaft geometry
- Assessment of both load-controlled (R = -1) and mean-stress-shifted (R ≠ -1) fatigue conditions
Parts of the standard
- DIN 743-1Calculation procedure
- DIN 743-2Theoretical stress concentration factors and fatigue notch factors
- DIN 743-3Material properties
- DIN 743-4Calculation of equivalent mean and amplitude stresses, supplementary rules
Governing formulas
σ_a / S_e + σ_m / S_u = 1 / SF_fatwhere σ_a = local alternating stress amplitude (bending or von-Mises equivalent), including Kf; σ_m = local mean stress; S_e = corrected component endurance limit (material limit reduced by Kf, size factor K_d and surface factor K_R); S_u = ultimate tensile strength; SF_fat = fatigue safety factor
σ_vM = √( (σ_b + σ_ax)² + 3·τ² ) ; SF_stat = S_y / σ_vMwhere σ_b = bending stress at the critical section; σ_ax = axial direct stress (F_ax / A); τ = torsional shear stress; S_y = material yield strength; SF_stat = static safety factor against yielding
n_c = 945.81 · √(1 / δ) [rpm, with δ in mm]where n_c = first lateral critical speed (rpm); δ = maximum static bending deflection under self-weight and attached masses (mm). The constant 945.81 = (60 / 2π) · √9810, for g = 9810 mm/s². A healthy design keeps the operating speed at least 20–25 % away from n_c.
Frequently asked questions
What is DIN 743 used for?
DIN 743 is used to verify that a rotating shaft or non-rotating axle has adequate fatigue strength under combined cyclic bending and torsional loading. It calculates the fatigue safety factor — accounting for notch effects (Kf), the size influence factor and the surface factor — so the designer knows how much margin exists against a fatigue crack initiating at a stress-raising feature such as a shoulder fillet, keyway or groove.
What is the difference between DIN 743 and the Goodman criterion?
DIN 743 uses the Goodman mean-stress line as its core fatigue relationship, but adds a structured framework on top: it defines how to compute the component endurance limit S_e from the material limit by applying Kf (fatigue notch factor from DIN 743-2), the size factor K_d and the surface factor K_R (from DIN 743-3). The Goodman line itself is then applied to the locally corrected S_e, so a notched shaft is never assigned the smooth-specimen endurance limit.
How does DIN 743 handle stress concentration at keyways and shoulder fillets?
Part 2 (DIN 743-2) provides theoretical stress-concentration factors Kt and the fatigue notch factor Kf for the common features: shoulder fillets (as a function of D/d and r/d), keyways, circlip grooves and threads. Kf is applied to the alternating-stress component before the Goodman check, so the fatigue safety factor correctly reflects the weakening effect of each notch. MechanixCalc applies Kf from the Peterson/Pilkey chart look-up for each feature type you enter.
What safety factor does DIN 743 recommend?
DIN 743-1 does not mandate a single universal value; the required minimum depends on the application, load-data uncertainty and consequence of failure. Typical industry practice for power-transmission shafts is SF ≥ 1.5 for fatigue and SF ≥ 1.2 for static yield, with higher margins (≥ 2.0 fatigue) where load data are uncertain or failure is safety-critical. The MechanixCalc shaft calculator flags warning and fail states at its own configurable thresholds and shows the raw margin so you can apply your own requirement.
Is the DIN 743 shaft calculator free?
You can use it during a free 30-minute preview with no sign-up, and a free 14-day account trial unlocks every calculator with no credit card. The branded PDF report and saved calculations are part of a paid plan.
Related standards
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