Load-Capacity Interference and the Bathtub Curve

E. E. Lewis, Hsin Chieh Chen

Research output: Contribution to journalArticlepeer-review

27 Scopus citations


Load-capacity (stress-strength) interference theory is used to derive a heuristic failure rate for an item subjected to repetitive loading which is Poisson distributed in time. Numerical calculations are performed using Gaussian distributions in load & capacity. Infant mortality, constant failure rate (poisson failures), and aging are shown to be associated with capacity variability, load variability, and capacity deterioration, respectively. Bathtub-shaped failure rate curves are obtained when all three failure types are present. Changes in load or capacity distribution parameters often strongly affect the quantitative behavior of the failure-rate curves, but they do not affect the qualitative behavior of the bathtub curve. Neither is it likely that the qualitative behavior will be affected by the use of non-Gaussian distributions. The numerical results, however, indicate that infant mortality and wear-out failures interact strongly with load variability. Thus bathtub curves arising from this model cannot be represented as simple superpositions of independent contributions from the three failure types. Only if the three failure types arise from independent failure mechanisms or in different components is it legitimate simply to sum the failure rate contributions.

Original languageEnglish (US)
Pages (from-to)470-475
Number of pages6
JournalIEEE Transactions on Reliability
Issue number3
StatePublished - Sep 1994


  • Failure rate
  • aging
  • bathtub curve
  • infant mortality
  • interference theory
  • load-capacity interference
  • stress-strength interference

ASJC Scopus subject areas

  • Safety, Risk, Reliability and Quality
  • Electrical and Electronic Engineering


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