Reaction uncertainty
Support stiffness and shaft deflection can redistribute bearing load.
Engineering
Bearing Sensitivity Calculator
Quantify how load increase and rating reduction change basic bearing L10 life, life retention, and loss.
BEARING LIFE SENSITIVITY
Show why a modest load increase can remove most of the life estimate
Basic life varies with a power of C/P. The calculator preserves the base case, applies explicit adverse changes, and reports the remaining share of base life.
Base L10 life (million rev)-
Adverse L10 life (million rev)-
Life retained-
Life lost-
Larger isolated life effect-
ENGINEERING DECISION VIEW
See nonlinear life loss from a changed C/P ratio
Use the output to prioritize evidence; do not publish the adverse value as adjusted service life without the complete method.
| Case | Rating C | Load P | C/P | L10 (million rev) | Meaning |
|---|
LIVE CALCULATION PROCESS
Formula, substitution, and reconciliation
L10,base=(C/P)^p; L10,adverse=[C(1-reduction)/P(1+increase)]^p
The page changes rating and load explicitly and recalculates the nonlinear life equation. The rating reduction is a transparent scenario, not a replacement for prescribed modified-life factors.
HOW TO USE
Stress-test one life assumption
- Enter reviewed base C, P, and exponent.
- Choose a load increase from a specific uncertainty or duty change.
- Enter rating reduction only for an explicit comparison.
- Compare cases, then replace scenarios with the proper final life model.
- Archive the reaction or duty evidence behind the load change and the exact basis of any rating scenario; neither percentage is a formal life-modification factor.
SUBJECT FUNDAMENTALS
Why life is highly load-sensitive
- C/P ratio
- Core dynamic rating-to-load ratio.
- Power-law response
- Life changes with the ratio raised to p.
- Load sensitivity
- Change in equivalent load after reaction or duty revision.
- Rating sensitivity
- Explicit change in C for a comparison.
- Life retention
- Adverse life divided by base life.
- Scenario
- Deterministic comparison, not probability.
CALCULATION METHOD
Recalculate both cases instead of scaling life linearly
L10,base=(C/P)^p; L10,adverse=[C(1-reduction)/P(1+increase)]^p
The page changes rating and load explicitly and recalculates the nonlinear life equation. The rating reduction is a transparent scenario, not a replacement for prescribed modified-life factors.
DEFAULT CASE AUDIT TRAIL
Symbols, units, substitution, and independent check
| Symbol | Meaning | Unit |
|---|---|---|
| C | Base dynamic rating | kN |
| P | Base equivalent dynamic load | kN |
| p | Life exponent | dimensionless |
| Delta P | Adverse load increase | % |
| Delta C | Adverse rating reduction | % |
| L10 | Basic rating life | million revolutions |
Default values
- C = 90 kN, P = 30 kN, and p = 3.
- Delta P = +15% and Delta C = -5%.
Unit conversion
- Adverse load multiplier = 1.15 and adverse rating multiplier = 0.95.
- All C/P ratios are dimensionless; resulting basic lives are in million revolutions.
Numerical substitution
- Base life = (90 / 30)^3 = 27.000 million revolutions.
- Adverse load = 30 x 1.15 = 34.5 kN; adverse rating = 90 x 0.95 = 85.5 kN.
- Combined adverse life = (85.5 / 34.5)^3 = about 15.22 million revolutions.
- Life retained = adverse/base x 100 = about 56.4%; life lost is about 43.6%.
Named intermediate results
- Load-only life is about 17.75 million revolutions, a loss of about 34.3%.
- Rating-only life is about 23.15 million revolutions, a loss of about 14.3%.
- The load increase has the larger isolated life effect in the default scenario.
Independent check:The combined retention also equals [(0.95)/(1.15)]^3 x 100, independent of the absolute base C and P values; this reproduces the adverse/base life ratio.
DEEPER ANALYSIS
Where adverse inputs should come from
Duty evidence
Higher P should come from a load-duration record or documented event.
Rating provenance
C belongs to an exact bearing; application modifiers follow prescribed methods.
WORKED DECISION CASES
Two sensitivity decisions
Reaction redistribution
A 15% P increase removes much more than 15% of basic life, prompting arrangement review.
Substitute bearing
A lower-C substitute is compared transparently before technical approval.
Bearing sensitivity terminology
- Base case
- Reviewed reference rating and load.
- Adverse case
- Declared changed rating and load.
- Life retention
- Percent of base life remaining.
- Life loss
- Percent reduction from base.
- Damage equivalence
- Conversion of variable duty into fatigue effect.
- Derating
- Documented reduction under a defined method.
EVIDENCE AND DATA LINEAGE
Retain both cases and why inputs changed
Keep bearing identity, C source, base P, exponent, duty, reaction model, change rationale, substitute data, units, and both unrounded results.
LIMITS AND EXCLUSIONS
What deterministic sensitivity excludes
- No uncertainty distribution, adjusted life, reliability, contamination, lubrication, variable duty, static safety, speed, fit, or thermal analysis is included.
- Rating reduction is not an ISO or manufacturer factor.
- The same basic-life equation is assumed for both cases.
RELIABLE SOURCES
References for the method and its boundaries
FREQUENTLY ASKED QUESTIONS
Questions about life sensitivity
Why is loss larger than load increase?
Because life follows a power law, not linear subtraction.
Can reduction represent contamination?
Not in the formal method; use prescribed factors.
Can reduction be zero?
Yes, to isolate load sensitivity.
Can load increase exceed 100%?
Yes when documented, though the same model must remain applicable.
Is the larger percentage the governing cause?
No; inspect power-law effects and physical evidence.
Is adverse life the new required life?
No; it remains a scenario until formally adopted.
RELATED CALCULATORS
Continue the engineering review
Bearing Safety Factor Calculator
Return to the selected bearing and compare basic life with the static C0/P0 gate.
Bearing Efficiency Calculator
Keep frictional heat sensitivity separate from rating-life sensitivity.
IMPORTANT NOTE
Use sensitivity to target evidence, not invent a rating
Final life needs validated loads, exact ratings, duty, reliability, lubrication, contamination, temperature, and arrangement conditions.