Q: How is the equivalent dynamic bearing load P calculated?

The equivalent dynamic load P combines radial load Fr and axial load Fa: P = X·Fr + Y·Fa, where X and Y are load factors from the bearing catalog. For pure radial loading, P = Fr. For variable loads, the equivalent load is P_eq = (Σ(Pᵢ^p·nᵢ·tᵢ) / Σ(nᵢ·tᵢ))^(1/p). FEA results from tools like Abaqus or LS-DYNA can provide more accurate load distributions for the P calculation.

Question 1

What is L10 bearing life?

Accepted Answer

L10 life is the life that 90% of a group of identical bearings will reach or exceed before the first evidence of fatigue failure (flaking). Per ISO 281, L10 = (C/P)^p million revolutions, where p=3 for ball bearings and p=10/3 for roller bearings. For example, a ball bearing with C=20 kN and P=5 kN gives L10 = 4³ = 64 million revolutions.

Question 2

What is the difference between L10 and modified life Lnm?

Accepted Answer

L10 life assumes 90% reliability and standard lubrication conditions. Modified life Lnm accounts for the reliability factor a₁ and the ISO lubrication/contamination factor a_ISO: Lnm = a₁ × a_ISO × L10. For 95% reliability, a₁ = 0.62; for 99%, a₁ = 0.21. Clean, well-lubricated conditions can push a_ISO up to 4, while heavy contamination reduces it below 0.1.

Question 3

What is a good C/P ratio for bearing selection?

Accepted Answer

The C/P ratio (basic dynamic load rating to equivalent load) is a key bearing selection criterion. A C/P ≥ 3 (L10 ≥ 27 million revolutions) is generally recommended for industrial applications. For high-reliability applications, C/P ≥ 5 is preferred. A C/P < 2 indicates excessive load with high risk of premature fatigue failure, requiring re-selection of the bearing.

Question 4

How is the equivalent dynamic bearing load P calculated?

Accepted Answer

The equivalent dynamic load P combines radial load Fr and axial load Fa: P = X·Fr + Y·Fa, where X and Y are load factors from the bearing catalog. For pure radial loading, P = Fr. For variable loads, the equivalent load is P_eq = (Σ(Pᵢ^p·nᵢ·tᵢ) / Σ(nᵢ·tᵢ))^(1/p). FEA results from tools like Abaqus or LS-DYNA can provide more accurate load distributions for the P calculation.

Rolling Bearing Life Calculator (L10)

Theory (ISO 281)