Shaft Analysis Calculator — Fatigue, Deflection & Critical Speed (DIN 743)

At every section the tool combines the bending and torsional stresses into the von Mises equivalent stress and reports the yield safety factor against the segment material's yield strength — the headline static check. The DIN 743 fatigue check below then governs the endurance of the same geometry under cyclic load.

DIN 743 evaluates fatigue at every notch by comparing the local alternating and mean stresses against the component fatigue limit, which is the material endurance limit reduced by the notch effect (Kf), the size factor and the surface factor. MechanixCalc folds the fatigue stress-concentration factor Kf into the alternating component before applying the mean-stress line, so a notched shaft is never shown infinite life on its nominal stress alone.

The first lateral critical speed is found from the static bending deflection of the shaft under its own and attached masses (the Rankine–Dunkerley method). When the rotational speed approaches this value the shaft whirls, so a healthy design keeps the operating speed well below — or deliberately above — it.

Bending deflection and slope are integrated along the stepped geometry from the second moment of area of each segment (Roark). Torsional shear stress follows from the transmitted torque and the polar section modulus, with the angle of twist from the shear modulus and the segment lengths.