Engineering tool · ISO 281 duty cycle

Adjusted & Variable-duty Life

Reduce a multi-speed, multi-load duty cycle to an equivalent load and estimate basic and modified rating life.

Lnmh / Peq

Variable operating conditions

Calculate by duty fraction

Duty shares are normalized automatically. Include short high-load periods because they consume fatigue life disproportionately.

RESULT / 03

Duty-weighted load and speed

Lnmh adjusted operating life—includes entered reliability and aISO factors

Basic L10h life—90% reliability basis

Equivalent load Peq—revolution weighted

Equivalent speed neq—time weighted

Combined life factor—a1 × aISO

Lnmh = a1 · aISO · 10⁶/(60n) · (C/Peq)^p

Enter valid data to calculate.

Calculation method

The equivalent load is weighted by both speed and duty share so each block contributes in proportion to its revolutions.

01 / EQUIVALENT LOADPeq = [Σ(Pᵢᵖ nᵢ Uᵢ) / Σ(nᵢ Uᵢ)]¹⁄ᵖ

Heavy-load blocks receive the correct fatigue weighting.

02 / MODIFIED LIFELnm = a1 · aISO · L10

a1 accounts for reliability; aISO must reflect validated lubrication, contamination and fatigue-limit inputs.

03 / LIMITPeak and shock loads still require separate checks

Also verify static safety, minimum load, speed, temperature and mounting limits.